BLM LIBRARY

88016798

T/N 338
Filing Code 66ll

' • . * , Date Issued October 1979

TECHNICAL yOJE7 ah 11 .»

U.S. DEPARTMENT OF THE (HTr^^^gg^y(+OF LAND MANAGEMENT

HABITAT MANAGEMENT GUIDES

for
BIRDS OF PREY

by MAYO CALL

Additional copies of Technical Notes are available from DSC, Federal Center Building 50, Denver, Colo., 80225

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HABITAT MANAGEMENT GUIDES FOR BIRDS OF PREY

by

Mayo W. Call

Avian Biologist

Denver Service Center

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TABLE OF CONTENTS

Page

LIST OF FIGURES iv

PHOTO CREDITS vi

HABITAT MANAGEMENT FOR RAPTORS 1

Habitat Nesting, Roosting, and Feeding Surveys 3

Habitat Management Considerations in Mineral Exploration,

Mining Operations, and Associated Activities 3

Potential Conflicts 4

Management Recommendations 4

Habitat Management Considerations in Forestry Operations . 5

Northern Spotted Owl 6

Other Owls 7

The Accipiters — Goshawk, Cooper's hawk, and Sharp-
Shinned Hawk 8

Management Recommendations for Accipiters 8

Bald Eagle 9

Recommended Restrictions within the Primary Zone ... 10

Recommended Restrictions within the Secondary Zone . . 10

Osprey 11

Habitat Management Considerations in Livestock Grazing

Operations 12

Habitat Management Considerations in Vegetation Manipulation

Projects 15

Maintentance of Existing Raptor Habitats 16

Nesting Habitats 16

Roosting Habitats 18

Protection of Crucial Habitats 20

Management of Prey Base 21

Acquisition of Crucial Raptor Habitats 22

Management of Historical Raptor Eyries 23

li

Table of Contents

Page

Restrictions on Human Use of Raptor Nesting/Roosting Areas. 24

Shooting Prohibitions 24

Restrictions on Rock Climbing 26

Restrictions on Recreation Uses 26

Restrictions on Low-flying Aircraft 28

Discretion in Raptor Surveys and Research Activities . 28

HABITAT DEVELOPMENT FOR RAPTORS 30

Artificial Nesting Structures 30

Construction of Artificial Nesting Structures 31

Cliff-Nesting Species 31

Tree-Nesting Species 38

Cavity-Nesting Species 55

Species Nesting Underground 57

Use of Man-made Objects for Nesting Sites 57

PUBLIC I & E PROGRAMS 63

LAW ENFORCEMENT 64

LITERATURE CITED 65

ADDITIONAL REFERENCES 7Q

Figure Number

LIST OF FIGURES

Page

1. Artist's concept of artificial cavity that could be
constructed for golden eagles, red-tailed hawks, or

prairie falcons 33

2. Typical natural nesting sites of kestrels, old flicker

nesting cavities, or holes in dirt banks or cliffs 34

3. Great horned owls (left) and barn owls (right) often

use cavities for nesting 34

4. Nesting cavities of prairie falcons showing variety in

types of cavities used and locations on cliffs 35

5. Nesting ledge of natural golden eagle eyrie, showing

normal placement on cliff 36

6. Typical nests of golden eagles showing nest size for

these birds 36

7. Typical tree nesting sites of ferruginous hawks 40

8. Types of artificial nest structures that have been used to

try to attract ferruginous hawks to nest 41

9. Artificial nest structure occupied by ferruginous hawks near
Boise, Idaho 42

10. Artificial nest structure occupied by ravens near

Boise, Idaho 42

11. Wire basket nest construction for ferruginous hawks. Chicken
wire is being securely tied to branches with heavy wire . . 44

12. Branches and other material are placed in chicken wire

basket as base for nest 44

13. Completed "artificial" nest as it looked immediately after
construction 45

14. Artificial wire basket nest utilized by ferruginous hawks

the same year it was constructed 45

15. Additional examples of artificial nests constructed for
ferruginous hawks in northern Colorado 46

IV

List of Figures Page

16. Fenced and unfenced trees containing raptor nests.

Unfenced trees are almost dead because of cattle abuse ... 47

17. Very large active ferruginous hawk nest in very small
tree. Building a support under nest might preserve nest

for many years; otherwise it will soon topple 47

18. Artificial nesting burrow constructed for burrowing owls

by Curtis Orde, Pawnee National Grasslands, Colorado .... 49

19. Young great horned owlets on reconstructed ferruginous hawk
nest that had been used for several previous seasons by

hawks 49

20. Golden eagle nest in northern Colorado which was recon-
structed and provided with stable base to assure more
permanent nest 50

21. Artificial nesting platform used by golden eagles in
northern Colorado, Pawnee National Grasslands. To date,

use of such structures by golden eagles has been rare ... 50

22. Two tripod-type nest structures built for bald eagles in
Arizona 52

23. Bald eagle incubating on artificial nest shown in Figure 22,
right-hand photo 52

24. Oregon biologist "topping" a dead snag to provide nest

base for ospreys 54

25. Young ospreys on artificial nest structure in Oregon .... 54

26. Section of aspen containing flicker nest cavity was placed
on author's house in early winter 1979. Pair of kestrels
utilized cavity as nesting site and fledged 3 young

in 1979 56

27. Kestrel boxes placed in good locations to attract nesting
birds 56

28. Use of various man-made structures for nesting by raptors. . 59

29. Eagle nest platform layout and assembly (Nelson, 1978) ... 61

30. Close-up view of nesting structure designed by Nelson

(1978) for eagles and other raptors 62

31. Nesting structure for eagles and other raptors in place

on steel transmission tower in Idaho 62

v

PHOTO CREDITS

Brown, Lonnie : Fig. 1 (drawing)

Call, Mayo W. : Figs. 2 (both), 3 (both), 4 (all), 5 (both), 6 (both)
7 (all), 8 (lower right), 11, 12, 13, 14, 15 (all), 16 (both),
17, 19, 20, 26, 27 (all), 28 (upper left & right, lower left).

Canutt, Rod: Fig. 24

Gilmer, David: Fig. 28 (left center & lower right)

Grubb, Teryl: Figs. 22 (both), 23

Howard, Richard: Figs. 8 (upper right & left, lower left), 9, 10

Knight, Richard: Fig. 28 (center, right)

Nelson, Morlan: Figs. 29, 30, 31

Orde, Curtis: Figs. 18 (both), 21 (both)

U. S. Forest Service: Fig. 25

VI

HABITAT MANAGEMENT FOR RAPTORS

Habitat management for raptors may mean either: (1) the manipulation
of uses and activities in an area so that birds of prey will be either
benefitted or at least not seriously adversely affected, or (2) the
physical change or development of the habitat such that it is more
suited to the needs of one or more species, e.g., creating artificial
nest sites or platforms where no suitable ones are present.

In raptor management we are primarily concerned with the perpetuation of
each species (or selected species) in the face of many kinds of con-
flicting land uses. It should be immediately obvious that we cannot
protect all birds and their required habitats wherever they are found.
The development of natural resources to meet essential human needs
precludes this possibility. In view of this "fact of life," biologists
should determine through surveys where the most important areas are for
each species and then provide these areas with the most protection from
human molestation possible. Frequently, slight modifications to proposed
land uses can be made to provide the birds sufficient freedom from
molestation to fulfill their life requirements.

First, we need to have a basic understanding of (1) habitat requirements
and food habits, and (2) bird behavior. We cannot expect to manage
habitat to meet the needs of selected components of the fauna unless we
understand the needs of the selected species. Further, we must under-
stand that we cannot maximize habitat equally for all species that use
the area. For example, permitting (or initiating) land use practices
that will change vegetation from grass to shrub species will be adverse
to kestrels and beneficial to accipiters.

The goal in land management may not necessarily be to maximize numbers
of all raptors but rather may simply be to maintain the diversity of the
wild populations that can be sustained in the existing habitats. While
we are becoming more involved in constructing artificial nesting sites
for a variety of species of raptors in order to sustain their numbers,
we must also be aware that some members of the conservation community
are "turned off" by such artificial nesting habitats. To them, the goal
of maximizing numbers is secondary to keeping the birds in as natural
and wild a condition as possible. Most of us would agree that the
sight of golden eagles (Aquila chrysaetos) nesting atop an artificial
tower does not compare with the esthetic value of the same birds on a
cliffside eyrie. Many factors need to be considered in determining
management goals for raptors, and these will logically vary in different
management units.

Many land managers and some biologists are not aware that some species
of raptors are quite susceptible to nest abandonment during certain
stages in the nesting cycle. This is especially true during nest
building, egg-laying, and incubation. For example, one pair each of
ferruginous hawks (Buteo regalis) , red-tailed hawks (Buteo jamaicensis) ,
and Swainson's hawks (Buteo swainsoni) are believed by the author to
have abandoned their nests after only one human visit to the nest. This
ooourred when the clutches were only partially complete (2 ferruginous
hawk eggs3 2 red-tailed hawk eggs} and 1 Swainson's hawk egg). It is
not known whether any further human disturbance occurred at the nest
sites prior to the next visit by the author, but at the next visits all
three nests were abandoned.

While some individual birds will tolerate greater amounts of disturbance
than others, it has been demonstrated that a caged ferruginous hawk
incurred a three fold increase in its heart rate at the sight of an
approaching human (Busch et al., 1978 and unpub. M.S. thesis). Under
field conditions a raptor's heart rate may increase substantially before
the bird actually flushes from its nest. While this is not adequately
documented, some unknown degree of fear or stress will cause some birds
to abandon their nests permanently if disturbed when eggs are present.
After the young hatch, the parents still incur stress but apparently
have greater attachment to the young and will abandon less readily. The
fact that some species are susceptible to nest abandonment does not
mean that we should not conduct essential research or surveys on them,
but simply means that we need to exercise greater caution in so doing.

The degree of susceptibility of raptors to nest abandonment seems to
vary with the site on which they nest, which influences the normal
nearness of approach. For example, cliff nesters appear to be less
disturbed by someone at the base of the cliff than birds of prey that
watch someone walk directly up to their ground nest. Birds seem to
sense that their nest has been compromised when humans actually climb to
it or approach sufficiently close to look into it. Nearness of approach
to the nest then is one of the important factors to be considered in
conducting nesting surveys. The nearness of approach to nests,
frequency of molestation or visits, adaptability to disturbance of
individuals (or pairs) , and behavior variances among the species are all
subjects of concern both to inventory specialists and to land managers.
Lack of knowledge on such subjects requires that resource managers be
somewhat conservative in activities permitted near nesting areas of
sensitive, threatened, and endangered raptors. Less concern need be
exercised for raptors that have become habituated to nesting or feeding
near human habitations. This would include such species as kestrels
(Falco sparverius) , great horned owls (Bubo virginianus) , and Swainson's
hawks. (Note photo of kestrel nest on author's house, Figure 26.)

In many cases, personnel involved in mineral exploration/development or
other types of land development activities conduct their operations
seemingly oblivious to the presence of much of the wildlife around them,
including nesting raptors. Some of this seeming lack of awareness may
be caused by the need to be attentive to the particular job at hand, but
never-the-less, such persons engaged in resource "development" activities
often fail to note large nests on cliffs or nearby trees or to under-
stand the significance of "whitewash" along the edges of cavities and
ledges. Much of the subsequent disturbance that occurs probably results
from ignorance of the birds' presence, rather than from intentional
harrassment. By having good inventories of sites used by nesting
raptors (or roosting or feeding sites) , resource managers can direct
personnel engaged in authorized field activities away from important
nesting areas, or else caution them concerning consequences, both
biological and legal, that may occur if the birds are unduly disturbed
during the nesting period.

This paper is intended to be only a beginning point for developing a
knowledge of compatible activities between man and the birds of prey.
Many other sources of raptor management recommendations are available
(see Literature Cited). These should be reviewed and suggested methods
tried that seem to be applicable to your specific area of concern. The
following pages include management and/or development methods that have
benefitted raptors in the areas in which they were used.

Habitat Nesting, Roosting, and Feeding Surveys

BLM Technical Note 316, Nesting Habitats and Surveying Techniques for
Common Western Raptors, provides some techniques for surveying nesting
habitats of common western raptors. However, the biologist must be
aware that many species are quite adaptable; i.e., they will use a
variety of nesting sites in different regions, they will utilize the
prey that is available, and their behavior patterns may vary depending
on the type of habitat they occupy, their familiarity with man, or for
other reasons.

After the biologist has obtained a basic knowledge of the species'
nesting and feeding requirements, he will then be able to consider means
for enhancing raptor habitats as a resource management objective.

Habitat Management Considerations in Mineral Exploration, Mining
Operations, and Associated Activities

Many activities associated with mining exploration and/or development
may either disrupt nesting or directly destroy nesting sites of various
species of birds of prey. Operations conducted in winter may also cause
bald eagles or other raptors to abandon historical roosts or force them
away from important feeding areas.

Potential Conflicts — Primary problems associated with mining
activities during the nesting season include: (1) disturbance of birds
of prey during the nesting phase with possible abandonment of nests,
(2) sufficient disturbance of adults to cause missed feedings of young
with subsequent mortality of young, (3) complete abandonment of terri-
tory because of excessive human disturbance, (4) complete destruction of
the nest and site in conjunction with the mining operation, (5) destruc-
tion of primary feeding areas, (6) influx of personnel into the mining
area with adverse impacts from their recreational use of surrounding
areas, (7) frequent indifference of mining personnel to protected
wildlife and their habitat, (8) inflexibility of mining rehabilitation
policies to permit highwalls or other potential raptor nesting habitat
to be retained after completion of the mining operation, and (9) excessive
road construction or other land disturbance in immediate vicinity of
mining operation.

Conflicts that may occur during the winter in areas being utilized for
wintering by birds of prey include: (1) mining operations conducted
sufficiently close to roosting areas so that the birds are frequently
disturbed and may abandon current or traditional roost sites,
(2) prevention of use of important bald eagle feeding areas, such as
along rivers or around the edges of lakes/reservoirs because of nearby
mining activities, and (3) construction of mining/processing facilities
in important feeding or roosting areas, including construction of
processing plants, pipelines, roads, power lines, etc., and (4) actual
destruction of important roosting or feeding habitat in the mining
operation.

Management Recommendations — The following recommendations will help
alleviate some of the adverse impacts created by mining activities and
associated operations.

1. Conduct as complete an inventory as time and money permit on
raptor nesting, roosting, and feeding areas. This is necessary if
potentially adverse impacts of mining operations are to be adequately
assessed.

2. Request that mining company officials confer with BLM land
managers before commencing any field operations. This will permit BLM
land managers to be aware of the geographic locations and types of
activities planned, and they can then relate these to potential impacts.

3. Request mining supervisors to instruct their employees
concerning the species of birds of prey that will likely be found in
their area of operation and try not to molest them in their operational
conduct. Advise them to avoid, when possible, destruction of raptor
nests or noisy or lengthy operations in the vicinity of such nests.

Make mining personnel aware of the legal implications of disturbing or
molesting either bald {Haliaeetus leuaooephalus) or golden eagles
(Aquila ohrysaetos) or their nests. Both are fully protected under the
Bald Eagle Protection Act, and the bald eagle is protected under the
Endangered Species Act. Advise that a permit from the U.S. Fish and
Wildlife Service is required if nests or nesting activities are to be
disrupted in any way, including molestation of the birds themselves.
Assure that mining personnel are also aware of the other species
protected under the Endangered Species Act.

4. Mining operations, either exploratory or developmental, should
not be conducted within roughly -5 to 1 mile from active nests of eagles,
peregrine (Faloo peregrinus) and prairie falcons (Falao mexiaanus) , and
some of the soaring hawks. Distance will vary according to species of
raptor, terrain, amount of screening vegetation, and type of mining
activity. Professional judgment must be exercised to provide some
reasonable protection to the birds.

5. Advise enforcement personnel of the U.S. Fish and Wildlife
Service and State wildlife agencies of legally protected birds or nests
that may be adversely disturbed during planned mining operations.

6. Where winter bald eagle roosts are involved, place stipulations
in construction proposals (pipeline, roads, etc.) to permit the birds
some undisturbed use of the roosts at crucial times. For example, for
pipeline construction, do not permit work until approximately 0900 hours
in the mornings (by which time the birds have frequently left their
roosts) or after such time in the afternoons that the birds will have at
least one hour of daylight in which to return to the roosts for the
night. While many eagles will continue to use the roosts as loafing
sites during the day, some freedom from disturbing activities during
early and late periods of the day will create less stress on them.

Habitat Management Considerations in Forestry Operations

A wide variety of raptors, ranging from bald eagles to pygmy owls, use
forest habitats for nesting. The real factors influencing nest place-
ment, roosting sites, and feeding areas may not be precisely known, but
general characteristics of nesting habitat for each species have been
described by various workers. In this section, discussion will be
centered on key habitat management principles for species of high
interest.

In order to manage a forested habitat for any species of raptor, we need
to know as much as possible about the following parameters :

1. Distribution of raptors throughout the area.

2. Interspecific competition and/or tolerance.

5

3. Description of most commonly used nesting site.

a. Kinds of trees used for nesting.

b. Size of trees and most common location of nest in tree.

c. Density of trees at nest site and in surrounding area.

d. Use of secondary canopies or understory trees.

e. Approximate territory size in a given forest type.

f. Use of alternate nest sites.

g. General tolerance of the species to various forestry
activities.

h. Importance of snags or large mature trees for roosting,

perching, sunning, plucking, nesting, etc.
i. Distribution and relative abundance of prey species,
j. Water requirements.

4. Availabilty of suitable, alternate nesting locations.

5. Probability of recycling, or re-nesting, if the first nesting
attempt fails.

When information on several of the above parameters is lacking, it is
always advisable to be conservative in the types of activities to be
authorized in the proximity of active nesting sites. The amount of
disturbance tolerated by most raptors is much less during egg-laying and
incubation than after the young hatch. Permitted activities may vary
depending on the nesting phase of the particular species.

Specific Habitat Considerations

Northern Spotted Owl (Strix ocoidentalis oaurina) — The northern
spotted owl is almost completely habitat specific to old growth forest
in Oregon, Washington, and northern California. Management area para-
meters prepared by BLM, Forest Service, and Oregon State University are
as follows (based on existing knowledge in October 1977, and subject to
change as new research is forthcoming) :

Territory Size — Minimum size should be 1,200 contiguous acres
per pair (i.e., one home range).

Habitat Description — Each pair should have a core area of at
least 300 acres of old growth forest. If 300 acres of old growth does
not exist, then maintain all remaining old growth and enough of the
oldest contiguous or closely adjacent second growth to total 300 acres.
The remainder of the habitat should be managed to provide at least
50 percent of the acreage in stands of 30+-year-old forests. Old
growth forest must be at least 200 years old and contain an average of
eight to ten old growth overstory trees (minimum of four) per acre, with
a developed understory greater than 30 years of age.

Number of Pairs — The management area should encompass the home
ranges of a minimum of three pairs, with six pairs ideal. Single pair
enclaves are acceptable in peripheral situations, such as in eastern
Oregon, or where remnant habitat exists.

Proximity of Pairs — Core areas for each pair should be
separated by approximately one mile, center to center.

Distribution throughout Known Range — As a goal, management
areas of three or more pairs should be eight miles, not to exceed
12 miles, apart. Single bird management areas should be five miles, not
to exceed eight miles, apart.

Northern spotted owls freqently roost in summer in close proximity to
small streams or springs that apparently cool the lower levels of the
forest habitat. Such moist areas should be given special consideration
in spotted owl habitat management plans.

Other Owls — The large variety of owls other than spotted owls that
nest in forested areas makes it difficult to manage large areas of
forest for any specific species, since they have varied requirements.
Pygmy owls (Glaucidium gnoma) , saw-whet owls (Aegolius acadious) ,
flammulated owls (Otus flammeolus) , screech owls (Otus asio) , and elf
owls (Miovathene whitneyi) are all small species that nest in various
kinds of habitats within forests or in scattered clumps of trees. Only
general rules should be applied for management of the group as a whole.

One thing all small owls have in common is their nesting site, which is
almost always some type of woodpecker or flicker hole or other cavity in
a tree, cactus, or similar type of vegetation. Since they all nest in
some type of cavity, the big emphasis should be on snag retention and
management in all forestry programs. Publications by the Pacific
Northwest Forest and Range Experiment Station at La Grande, Oregon,
discuss differences in cavity requirements and utilization by various
kinds of birds. It is likely that the various species of small owls
also have unique preferences for specific locations or kinds of cavities,
A general program of snag retention would be advised until more specific
nesting habitat requirements are available.

Several species of larger owls, including the long-eared {Asio otus),
great horned {Bubo virginianus) , great gray (Strix nebulosa) , and
barred (Strix varia) , will be found nesting in other raptors' nests,
either in dense or mixed forest stands. They will also utilize large
cavities in trees, such as those which occur during decay or from wind
breakage, so the importance of retaining old, decadent trees or snags
may also be important for the larger owls. Since large owls do not
construct any kind of stick nest themselves, the preservation of as many
stick nests of other large birds as possible should be another manage-
ment objective.

The Accipiters — Goshawk (Aceipitev gentilis) , Cooper's Hawk
(Ace-ipiter oooperii) , and Sharp-Shinned Hawk (Aoeipiter striatus) —
Various researchers have described subtle differences in nesting habitat
requirements for each of the three accipiters (Shuster, 1979, in press;
Reynolds et al. , 1978; Jones, 1979). Differences in primary nesting
habitats are also apparent in different regions of the continent. Over
much of Alaska, goshawks nest predominantly in deciduous trees, while
from Canada south most of them nest in coniferous trees. Structure and
size differences between the two tree types are obvious. Some of the
more common differences in nesting sites between the three species are
as follows:

Goshawk — These birds commonly nest on benches or basins
surrounded by much steeper slopes. In Oregon, goshawk nests were in
stands of conifers, ranging from those with closed mature canopies and
few shade-tolerant understory trees, to stands with more open mature
canopies and many understory trees, effectively producing multi-layered
canopies that began a few meters above the ground and rose to above
60 meters. In Colorado most nests were in the older mature trees of a
stand and were more often on gentle slopes than on steep slopes.

Cooper's Hawk — These hawks are generally considered to be
lower elevation birds than the goshawks. They commonly nest in trees,
both coniferous and deciduous, along the bottoms of draws and other
stream sources. It is not uncommon to find their nests in the mountain
brush zone of mountain slopes.

Sharp- Shinned Hawk — This species frequently nests in relatively
dense stands of second-growth conifers, or in dense stands of mountain
brush or hardwoods.

Reynolds et al. (1978) stated that the principal differences in vegetation
structure among the three species were associated with successional age
of the stands: sharp-shinned hawks nested in A0-to-60-year-old, even-
aged conifer stands; Cooper's hawks in 50-to-80-year-old, even-aged
conifers with somewhat larger and more widely spaced trees, and goshawks
in 100- to- 150-year-old conifer stands. While this research was
accomplished in the Northwest, general differences in successional
stages of trees as nesting sites seem to apply throughout the West.
With regard to vegetation density, goshawks seem to nest most commonly
in the least dense vegetation, while sharp-shinned hawks nest in the
most dense areas.

Management Recommendations for Accipiters — According to Reynolds
(in press) and Shuster (1979, in press) and based on nest site require-
ments, the following management measures are recommended:

1. Inventory nest sites using criteria for most common nesting
habitats.

8

2. Request all resource staff specialists to report any nests
located during routine work.

3. Leave an undisturbed area around Aooipiter nests such that the
area includes much of the stand upslope from the nest, all plucking and
roost sites, and at least some portion of the stream or spring (if one
is close by the nest site). The shape of the leave area will be deter-
mined by the topography and shape of the stand of trees at the individual
nest sites.

4. Nests should not be isolated by any silvicultural treatment,
such as clearcutting, commercial thinning, etc.

5. Nests discovered during logging activities should be protected
from further disturbance within 3/10 mile (0.5 km) of the nest. This
is especially important during early stages of nesting, generally from
March thru May.

6. Snags and fallen and arched trees should be preserved in
forest stands to serve as perches and plucking sites.

7. In timber management, try to develop diversity in both tree age
and forest density. Even-aged stands are poor nesting habitat for
goshawks and are less than ideal for the other two species.

Bald Eagle {Haliaeetus leuoooephalus) — Bald eagles and ospreys
(Pandion haliaetus) commonly nest in trees bordering streams or lakes.
Osprey nests are most frequently constructed in the tops of dead trees,
but bald eagles may nest either in the tops of dead or living trees or
on strong supporting branches below the canopy.

General guidelines for habitat management for bald eagles are presented
in the publication by Region 5, U.S. Forest Service, entitled Bald Eagle
Habitat Management Guidelines and in the guidelines prepared by the U.S.
Fish and Wildlife Service for the Pacific Northwest entitled Bald Eagle
Management Guidelines: Oregon-Washington. Both sets of guidelines
refer to management of primary and secondary management zones. The
primary zone is the most critical area immediately around the nest. The
secondary zone is the additional buffer area immediately adjacent to the
primary zone. Areas recommended for protection in either zone apply to
both active and alternate nests, since alternate nests may be used in
different years. The same guidelines would apply equally to golden
eagles that are found nesting in forested areas.

As defined by the Fish and Wildlife Service, the protected area of the
primary zone should include all area within 300 feet (5 chains) of the
nest, except under unusual circumstances where a particular pair of
eagles is known to be tolerant of closer human activity. The size of
the protected area should be adjusted by the actual use of the area
around the nest tree to include frequently used perch trees. Where
isolated groups of trees are likely to blow down, the primary zone

should not be less than 20 acres, and the opinion of a qualified
forester should be obtained in order to take measures to minimize that
likelihood.

Recommended Restrictions within the Primary Zone — The following
human activities are likely to cause disturbance to eagles and, there-
fore, should not occur within the primary nesting zone at any time'.

1. Major land uses such as logging, the development of new
commercial and industrial sites, the building of new homes, roads and
other construction, and mining of any kind.

2. Use of chemicals toxic to eagles. These include DDT, other
persistent organochlorine pesticides, PCB, mercury, and lead.

In addition, certain human activities are likely to disturb eagles
during the critical period of nesting, which is defined as the time
between the arrival of adults at the nest site and three weeks after the
fledging of any young. This period will vary in different geographic
locations depending on elevation and other factors which influence the
birds' nesting chronology. In most locations the critical period will
probably be between February 1 and August 1. Eagles are most vulnerable
to disturbance during the first 12 weeks of the critical period.
Therefore, during the critical period there should be no human entry
into the primary nesting zone, and there should be no permited low-level
aircraft operations.

Additional management recommendations for public lands (and waters) may
include: (1) closing land and water access to the nest, (2) posting the
boundary of the area, if necessary, to reduce travel near the nest
(without specifying the presence of an eagle nest), (3) prohibiting
recreational activity entirely or seasonally, and (4) permitting only
the necessary research and management activities near or at the nest
site.

Additional management recommendations for private lands and waters may
include: (1) working with the landowner to encourage him to voluntarily
protect the primary zone around the nest, (2) acquire or encourage
another agency or conservation organization to acquire the area in fee,
by easement, or by exchange.

Recommended Restrictions within the Secondary Zone — Certain human
activities of a permanent nature are likely to disturb eagles and/or
potentially cause nest desertion and should not, therefore, occur within
the secondary zone at any time. Such activities include development of
new commercial and industrial sites, building of new homes, building of
new roads and trails that may increase access to the nest, and use of
chemicals toxic to eagles.

10

Certain human activities have time-limited effects that may be adverse
to nesting birds. Because of this, human entry into the secondary zone
should be avoided during the critical nesting period. Examples include
disturbance from logging, selective cutting, and other forestry activities;
mining; low-level aircraft operations; use of firearms; camping; and
picnicking. Occasional and limited human intrusion such as hiking, bird
watching, and fishing should not be disturbing in most cases. Land
modifications, such as permanent campgrounds, boat launching facilities,
gravel pits, roads, etc., would encourage excessive use and should not
be permitted in the secondary zone.

If a pair of eagles chooses to establish a new nest in an area already
receiving human use, the human activities occurring at that time can
continue, except the use of toxic chemicals. Any expanded human activity
should be avoided.

Additional management recommendations for the secondary zone would
include those stated for the 'primary zone. Special caution must be
exercised during the two weeks prior to anticipated fledging of the
young eagles. If disturbed by humans during this period, the young
birds may attempt to fly prematurely, possibly damaging wing feathers,
bones, or causing internal injuries. Also, the birds may not be able
to regain flight again if they end up on the ground.

In addition to the recommendations for active nest sites provided
by the U.S. Fish and Wildlife Service (1977), they also suggest
the following actions for potential nest sites:

1. In potential or traditional eagle nesting habitat where no nest
now exists, for every 320 acres less than H mile from a river, lake
larger than 40 acres, or tidewater, leave four to six overmature trees
in the stand with an open view of and clear flight path to the water in
an area free of human disturbance. These should be the largest trees in
the stand and preferably have dead or broken tops. In addition, four

to six mature trees (80-year-old) should be left to provide nesting
sites over the long-term period (50 to 100 years).

2. Since eagles have been known to reoccupy a nest unused for
several years, do not remove old nest trees, even though they have
been seemingly abandoned. Trees in the surrounding zone should
also be protected until the nest is destroyed by the elements.

Osprey (Pandion haliaetus) — Human activities can significantly
influence productivity, especially in colonial nesting areas where
disturbance could adversely affect several breeding pairs of ospreys
simultaneously (Zarn, 1974). Therefore, for ospreys Kahl (1971, 1972)
recommends implementing the following protective measures whenever
possible:

11

1. Permit no human activity within 200 m (650 ft) of any active
osprey nest and restrict all vehicular traffic to roads not having
portions lying within 200 m (650 ft) of any active nest, from April 1 to
September 15.

2. Close nesting areas to hunting or shooting between April 1 and
September 30. Hunting may be permited after September 30, as most
ospreys have migrated south by then.

3. Prohibit tree or snag cutting by private individuals in close
proximity to lakes, reservoirs, and streams.

4. Permit no overnight camping in or near osprey nesting areas
from April 1 to September 15.

5. Construct no developments excepting osprey habitat improvements,
Walking trails and public observation points for viewing ospreys (if
desired) should be placed so as not to disturb the birds or their
activities.

6. Enforce all regulations protecting ospreys.

Habitat Management Considerations in Livestock Grazing Operations

The primary effect on raptors of livestock grazing is an indirect
influence produced by changes in the vegetation composition, density,
and structure. Such changes in the vegetation produce concurrent
changes in the composition and populations of the fauna (small mammals,
birds, reptiles, and amphibians) that utilize the grazed (or browsed)
habitat.

As browse ranges gradually change to grass, or vice-versa, the fauna
will be favored whose habitat needs are best met by the new habitat
conditions. For example, prairie dogs (Cynomys spp.) do not do well in
dense stands of sagebrush; conversely, Brewer's sparrows (Spizella
breweri) are largely habitat-oriented towards sagebrush and are seldom
found in grassland habitats. Through this ecological mechanism, live-
stock grazing indirectly causes changes in the prey base available to
raptors using the area. The species of raptors will be most favored
whose food needs will be met by the fauna residing in the local habitats.
Golden eagles and ferruginous hawks do best where the habitats favor the
production either of rabbits (Lepus and Sylvilagus spp.), prairie dogs
{Cynomys spp.), or ground squirrels (Citellus and Ammospermophilus spp.),

Changes in the density and structure of brush habitats are frequently
beneficial to raptors. Lower vegetation with lesser density tends to
make small rodents and lagomorphs more available, or vulnerable, for
capture by foraging raptors. Moderate to heavy livestock grazing of
sagebrush for several consecutive years in winter reduces the vigor of

12

the brush, causing the death of many of the plants and helps to open up
the area. Moderate to heavy grazing of grassland areas also removes
much rodent cover and may be especially beneficial to birds of prey
during the nesting season. Thus, cover manipulation provides one
opportunity for improving predation success by raptors.

Improved predation success for raptors as the result of reduced cover
for their prey may be partially offset by possible prey reduction on
overgrazed ranges or ranges in poor condition. Craighead and Craighead
(1956) stated that ranges in good condition provide a greater abundance
of prey than ranges in poor condition. They also stated that golden
eagle numbers would probably decline in areas of poor range condition.
According to Anderson (1972), there is a definite reduction of density
and diversity of both rodents and birds with heavy livestock grazing.
While relatively high populations of lagomorphs and certain rodents are
sometimes observed in heavily grazed areas, it is probably more a
function of irregular cyclic fluctuations or favorable conditions over
short periods than it is a result of overgrazing.

Golden eagles and some other raptors occasionally prey on sage grouse
(Centroeercus urophasianus) and blue grouse (Dendragapus obsaurus) .
Habitat desirability for sage grouse declines as the sagebrush under-
story of grasses and forbs decreases, or as sagebrush height increases
beyond about 15 inches. Grassland ranges that are gradually converting
to sagebrush would be improving for sage grouse until the percent of
sagebrush in the composition exceeds approximately 30 percent. Continu-
ation of high grazing use in most low and middle elevation areas would
cause a gradual decline in the grass and forb species, making the habitat
less suitable for grouse.

Goshawks feed quite heavily on blue and ruffed grouse (Bonasa umbellus)
in some parts of the country (Eng and Bullion, 1962). Production of
these grouse is partly dependent on the quality of their nesting and
brooding habitat. In the West, wet meadows and/or stream bottoms are of
paramount importance to grouse for brooding their young. These areas
are among the most heavily grazed by cattle, making them less suitable
for grouse. Green plant parts, seeds, and berries are needed by adult
grouse, while the young utilize large quantities of insects associated
with these areas, as well as green grass and other plant parts. Grouse
use these areas for raising their young at the same time that cattle may
be using them in the spring months.

Trampling of wet meadows increases erosion and generally decreases their
quality as grouse brooding habitat. If the meadows are in good condition,
they are also utilized by many kinds of small mammals, birds, and reptiles,
all of which may provide additional prey for resident raptors. Ruffed
grouse are more frequently found in dense vegetation along stream bottoms
or on hillsides covered with mountain brush. Grazing practices that
deplete grasses and/or forbs in such areas will be detrimental to this
species just as for the blue and sage grouse.

13

On high desert ranges, short grass prairies, or other vegetation
associations that contain very few trees, cattle often create an
additional adverse impact. As described by Olendorff and Stoddart
(1974), the death of the few available nesting trees is often hastened
by cattle that seek shade from them or use them as rubbing posts. The
vegetation and soil at the base of the trees become trampled; wind blows
the loose soil away; and the exposed roots eventually die. Combined
with the rubbing of the tree bark, the trees finally die. A high
percentage of the trees on the Pawnee National Grasslands of northern
Colorado, whether planted by early homesteaders or growing naturally
along intermittent water courses, have been used by a wide variety of
birds of prey for nesting for several decades. Birds like the ferru-
ginous hawk will continue to use the trees for nesting until they finally
topple. Where trees are very scarce in such areas, they should be
fenced to prevent damage by livestock. They are not that important as
livestock shade but may be highly important as raptor nest sites. The
need to preserve the available nests in such trees was discussed by
Olendorff and Stoddart (1974), and the techniques are presented in a
later section of this publication. In areas where ferruginous or other
hawks most commonly use trees as nesting sites, the preservation of such
trees is especially important. Ferruginous hawks most often construct
tree nests throughout Colorado and in southern Idaho, for example, while
they nest predominantly on the ground or on rocky outcrops in southern
Wyoming .

It is unlikely that actual trampling of ground nests by livestock is of
any consequence. Nests of marsh hawks (Circus oyaneus) and short-eared
owls (Asio flammeus) are sufficiently scattered so that there is very
little likelihood of a chance encounter of a nest by either sheep or
cattle. There is little information available relative to the behavior
of ground-nesting raptors when approached closely by either cattle or
sheep. Patterson (1952) reported that sage grouse sometimes abandoned
their nests during the early stages of incubation if disturbed frequently
by foraging sheep but seldom abandoned their nests during the late
stages of incubation. During his intensive sage grouse study, he recorded
no instances of sheep destroying eggs by actually stepping on them.
However, in a few instances, the sheep caused the birds to flush and
simultaneously to flip eggs out of their nests with loss of the eggs,
and sometimes, nest abandonment. Whether marsh hawks and/or short-eared
owls are more tenacious while on their nests and their reactions to
livestock are not known.

In most areas of the West and Southwest, riparian zones are heavily
grazed by domestic livestock. One effect of this grazing has been the
destruction of sapling cottonwoods (Poplar spp.), aspen (Populus
tremuloides) , and other tree species that are the primary nesting sites
of numerous species of raptors. Especially in the Southwest, the
critical nesting tree, the cottonwood, for several peripheral buteos
[black (Buteogallus anthracinus) , zone-tailed (Buteo albonotatus) , and

14

gray hawks (Buteo nitidus)~] is not replacing itself in many areas
(Snyder and Snyder, 1975; Glinski, 1978, personal commun. ) . Cotton-
woods and other trees of the riparian zone in many regions are replacing
themselves only in areas that are not grazed by cattle. Grazing
management systems established by land managing agencies must take this
problem into consideration if species of raptors in these areas of
critical tree shortage are to be maintained.

Habitat Management Considerations in Vegetation Manipulation Projects

Several investigators on the nesting ecology of the ferruginous hawk in
northern Utah and southern Idaho have mentioned the potential vulnerability
of these birds to revegetation projects and other land use alterations
(Murphy, 1978; Piatt, 1971; Howard, 1975; Woffinden, 1975). Ferruginous
hawks used Utah juniper (Juniperus osteosperma) for nesting in 95 percent
and 66 percent of the nest sites in the studies by Howard and Woffinden,
respectively. Woffinden (1975) also pointed out that nest trees are not
randomly selected, but lone or peripheral trees are preferred. Murphy
(1978) reiterated that the nests, therefore, are not randomly distributed
throughout the intermontane valleys but instead occur in clumps around
the periphery of the valleys. Because of this fact, Murphy (1978)
recommended that wherever range rejuvenation projects involve the
destruction of juniper stands, individual trees or a thin screen of
trees be left standing near valley margins.

While the removal of nesting trees may be adverse to certain species of
raptors whose behavioral instincts impel them to nest in trees, this is
not the only significant impact caused by vegetation conversion projects.
Conversion of brushlands to grass to benefit cattle will alter both the
species of prey present in the area and their populations. It is
especially disrupting to production of both jackrabbits and cottontails
that survive best in mixtures of brush and grassland types. Such
changes are probably most adverse to ferruginous and red-tailed hawks
and golden eagles. Swainson's hawks normally use a wider variety of
grassland prey, including a variety of small bird species and their
young and a mixture of the larger insect species, such as grasshoppers.
By knowing the specific prey requirements of the various raptors,
particular species of raptors may be either benefitted or adversely
impacted by different kinds of vegetation conversion projects. Those
species of raptors whose local, regional, or national populations are
known to be declining should be given highest management priority.

Where possible, areas of brushland habitat should be retained in
scattered patches within the planned vegetation treatment area. This
will help maintain the prey species that many of the nesting raptors
depend on in that particular area. While little control of private land
vegetation changes can be exercised by Federal or State officials, there
are some areas where exchange of use is a common practice and where some
control can be accomplished. Exchange of use occurs where boundaries

15

between public and private ranges are not fenced and the livestock
operator is licensed to use the entire area during a given season (s)
with the total amount of forage to be used agreed upon by the private
landowner and the public land administrator. In such areas the landowner
may agree to certain stipulations in use of his private land (for the
benefit of raptors or other wildlife) in exchange for the specified use
of the public lands.

Maintenance of Existing Raptor Habitats

Nesting Habitats — Insofar as is feasible in the face of resource
developments to meet increasing human needs, existing nesting sites or
eyries should be protected and maintained in their present condition.
Raptors nest where they do because of innate behavioral instincts that
guide them in their selection of nest sites. Some species are extremely
specific in their selection of nesting sites, while others appear to be
very adaptable. Management priorities should be directed towards those
species that are most habitat or site specific in their selection of
nest sites. For example, cliff-nesting species such as peregrine falcons
need greater protection of traditional nesting eyries than do kestrels.
Eagle nesting sites are more critical than those of ferruginous hawks
(since ferruginous hawks nest in a much wider variety of sites) .

Many species of raptors maintain alternate nesting sites which are used
at the birds' discretion on an irregular basis. Alternate nests are
usually in the same kind of site as the currently active nest and are
often clustered in a relatively small area, commonly less than a mile in
diameter. Distance between alternate golden eagle nests may be a little
farther, while ferruginous hawk nests may be grouped along a rocky
outcropping just a few hundred yards apart or less. Distance between
alternate nest sites depends largely on the availability of suitable
nesting substrates in the particular area. For example, the distance
between nest sites of tree-nesting golden eagles in areas where trees
are scarce will depend on the nearness of suitable trees. In an area of
western Wyoming, four active golden eagle nests lie generally in a line
in scattered cottonwood trees that have developed along a foothill
canal. The nests are approximately one to three miles apart, and no
alternate nests are presently known. Most of the other cottonwood trees
in the area do not have adequate branches for supporting the large nest
of an eagle. All four nests are on private land. The destruction of
these trees by the private landowners for any reason would probably mean
the elimination of the pair (or pairs) of eagles from the area. Interest-
ingly, one of the pairs of eagles nests in a group of cottonwoods that
lie within a pasture where sheep lambing occurs each spring. No evidence
of eagle predation on the sheep has been reported, and it is unlikely
that the landowner is unaware of the presence of the birds in their
conspicuous nest.

16

The preservation of alternate nest sites is just as important as the
preservation of the currently active nests, since they will be used
intermittently over the years.

In considering the need to maintain existing raptor nesting sites, we
must consider what would be lost if the sites were eliminated. Cliff
sites are in limited supply throughout many parts of the West and are
essential for nesting by many species of raptors, such as peregrine
falcons, prairie falcons, and most golden eagles. The loss of cliffs
generally means an irreplaceable loss of key nesting habitat, since
cliffs cannot be economically reconstructed. A substitute for cliffs
being used by some cliff-nesting raptors is the high walls produced by
surface mining of coal and some of the hard rock minerals. The use of
such high walls for nesting by golden eagles, prairie falcons, and great
horned owls has been documented. Unfortunately, State and Federal laws
on mining reclamation do not permit permanent retention of high walls
because of safety and pollution hazards, erosion problems, and general
loss of land production. But, in many situations, high walls would
serve as substitutes for natural cliffs that had been destroyed or
they provide nesting sites for cliff-nesting raptors where no natural
cliffs had existed before. In such situations a new type of habitat
could be developed that had not existed before and could be of greater
importance than returning the land to its original topography and
production. Inflexible laws and regulations could prevent land managers
from producing wildlife habitat that is actually more valuable than the
habitat that was destroyed by the mining (or other) activity.

The loss of tree nesting sites may be a serious temporary or short-term
impact but, given time, trees can be replaced if desired. In the
absence of trees, nesting platforms are acceptable to some birds of
prey. Power lines are also being used as nesting sites by golden
eagles, red- tailed hawks, ferruginous hawks, great horned owls, Swainson's
hawks, and ravens (Corvus aorax) where natural, elevated nesting sites
are not available. In general, however, trees that contain nests should
be retained whenever possible because of their proven value as nesting
sites. We can never be sure that artificial nesting platforms will be
utilized by the desired species.

Specific nest sites of ground-nesting species are not as crucial as tree
and cliff sites, because there is generally a greater abundance of
potentially suitable sites. Marsh hawk, short-eared owl, and ferru-
ginous hawk nests have been found in a wide variety of ground habitats
throughout the West. Also, ground-nesting species do not normally use
the same nesting site on subsequent years (except for ground-nesting,
ferruginous hawks that sometimes use the same ground nest for several
years). The author does not believe that most populations of ground-
nesting raptors will be seriously affected if occasional nests are
destroyed by land development activities. This may be subject to
differing opinions, but in many areas ground-nesting opportunities are
almost unlimited.

17

Protection of snags for cavity-nesting species is very important. In
the past, snags have been largely eliminated during timber harvesting
operations with a concurrent loss of nesting sites for a variety of bird
species, including a multitude of passerines, woodpeckers, and owls.
Saw-whet, screech, elf, pygmy, flammulated, barred, spotted, hawk
(Sumt-a ulula) , and great horned owls will all utilize cavities in trees
for nesting. The small owls normally use holes made by woodpeckers
or flickers (Colaptes spp.), while larger owls may nest in cavities
created by broken tops or branches or in decaying cavities in the tree.
Loss of snags over wide areas during timber harvesting operations may
cause significant reductions in populations of birds depending on
cavities in trees for nesting sites. Every effort should be made to
retain as many snags as possible during timber harvesting operations.

Dead trees are commonly taken by woodcutters when they are readily
accessible or close to roads. In such areas land managers may want to
place signs on selected trees to indicate they are important for wild-
life and are not to be cut. Studies by Thomas et al. (1979) are a good
reference for the numbers of snags required by different species of
birds.

Roosting Habitats — Communal roosting behavior is encountered in a
wide variety of habitat situations and undoubtedly confers some survival
advantage upon the participants (Murphy, 1978). Such roosts are probably
selected because they offer special advantages to the birds, such as
proximity to feeding areas; protection from wind, snow, rain, cold, etc.;
favorable exposure to sun; favorable updrafts to the site; isolation;
or for other reasons. Removal of such roosts or creation of disturbance
sufficiently near the roosts to cause their abandonment may cause an
additonal stress on the birds that could affect their survival. Agencies
having land management responsibilities should locate, map, and provide
the appropriate management classification to protect them from incompatible
uses.

Roost trees are usually large enough to provide safety from any predatory
threat from the ground (U.S. Forest Service, 1977). They are typically
the largest trees in the stand; the crown near the top or the middle
portion of the tree must be open and have stout lateral limbs with
reasonable access for the large birds.

Many large bald eagle winter roosts are known throughout the United
States, and many smaller ones are scattered in between. Because biologists
are uncertain as to potential effects produced by the destruction of
such roosts, it is considered advisable to protect all roosts to the
greatest possible extent. Any bald eagle roost containing more than
five birds should be given complete protection. While it may be argued
that a few scattered bald eagles along a river bottom or elsewhere may
have unlimited sites at which to roost, we should not overlook the
possibility that subtle factors of exposure, tree height, limb size and

18

structure, or other factors may be important in their selection. Legal
requirements of both the Bald Eagle Protection Act and the Endangered
Species Act suggest that maximum protection be provided both nests and
roosts (or any other identified crucial areas).

Disturbing activities, such as pipeline construction, oil and gas
drilling operations, etc., should be permitted only during seasons when
the eagles have migrated out of the area and have not returned to either
nest (in northern latitudes), to spend the winter (in more southern
latitudes), or during times of the day that will be least disturbing to
eagle activities.

Biologists should try to recognize signs of eagle reactions to human
presence and disturbance. Bald eagles exhibit great variation in
response to human activities depending on the type, frequency, and
duration of the activity; types of modifications being made in the
physical environment; time in the birds' reproductive cycle; and
individual bird's tolerance to disturbance. Eagles seem to tolerate a
degree of human presence, but there is a threshold level beyond which
they will leave the area, perhaps being forced into less desirable
habitat.

There is some indication that snowmobile activity may be adversely
affecting both the nesting and roosting of bald eagles in some areas
(U.S. Forest Service, 1977). Eagles have abandoned territories after a
long period of occupancy where the levels of activity to which they were
accustomed were gradually increased. Such abandonment may take several
years before it occurs, possibly indicating a gradual increase in stress
level as human activity increases. Human disturbances may be both
quantitative and cumulative. A conservative assumption would be that
bald eagles need some degree of isolation from disturbing activities in
order to carry out their essential life functions at critical times.
The extent of this need for both spatial and psychological isolation
varies from case to case and should not be generalized.

Many winter roosts are in western valleys located on private lands; in
such cases it may not be practical to purchase tracts of land to convert
them into bald eagle sanctuaries as has been done by private conservation
organizations in some parts of the country. However, agency personnel
and others interested in the welfare of eagles can often form effective
liaisons with landowners and develop in them a cooperative attitude and
proprietary interest in maintaining the roost area in a manner that will
minimize disturbance. Interestingly, bald eagles may choose to roost in
large trees bordering small towns and farms in some locations, even
though mountain roosting sites are within easy flight range. At Vernon,
Utah, bald eagles have roosted in winter near human habitations for
several years. By their own choice _, these birds roost very near disturbing
activites (dogs barking, boys shouting, vehicular traffic) that most
eagle biologists would consider untenable for the birds. Such tolerance
for humans by individual birds is similar to that of some eagles that

19

have nested close to human dwellings in Washington State (Grubb, 1978,
personal commun.). However, we must not try to apply this behavior to
the speoies as a who1es because the bulk of the population is known to
be more sensitive to human intrusions.

Protection of Crucial Habitats — Several species of raptors have
significant traditional use areas for nesting, roosting, or feeding to
which the species are largely tied for their survival. California condors
(Gymnogyps oalifornianus) are. surviving only in selected parts of
California; peregrine falcons of the interior West are now nesting in a
very limited number of active eyries; major numbers of bald eagles
migrate southward from Canada to spend their winters in various size
groups in selected areas; black, zone- tailed, and gray hawks are somewhat
limited in their nesting distribution to specific canyons and river
bottoms in Arizona, with only a few scattered pairs of black and zone-
tailed hawks found in adjacent states (the United States only); Mississippi
kites (Ictinia mississippiensis) are found nesting only in certain river
bottoms of Colorado and Arizona in these two states. Many other examples
could be given of restricted use areas of specific species.

These very limited use areas in several states may be classified as
crucial areas. They may be of great importance to the survival of the
species within a state or for the species as a whole. In either situation
they should be provided maximum protection. This is in contrast to
raptors that are relatively common and that may nest irregularly and in
a wide variety of habitats over vast acreages. A review of the literature
will reveal the primary distribution of the different species and their
primary nesting and wintering areas. From this information the biologist
can determine areas that should be surveyed to verify their presence and
to delineate the important habitat areas under various management
jurisdictions.

The more habitat specific a species is, the more vulnerable the species
is to changes or loss in their special habitats. Since ospreys are
completely tied to fish-bearing bodies of water, they are much more
adversely affected by changes in these specific sites than are red-
tailed hawks that utilize habitats varying from dense tropical rain
forests of Puerto Rico to western deserts to Alaskan taiga. The degree
to which a raptorial species is tied to a specific habitat type and the
extent of that habitat type will determine the urgency for providing the
special considerations to that species in land use decisions. Very
limited habitats occupied by raptors should be classified and protected
as critical habitats. On-the-ground judgment must be exercised by the
biologist to determine how much area within the specific habitat type
should be protected against conflicting uses. Such determinations will
be influenced by distribution, numbers, and availability of the required
prey base; location of required habitat components (for nesting,
roosting, etc.), and the influence of various human activities on the
behavior of the birds. If knowledge is lacking, be conservative in the
birds ' favor. You can always decrease the size of protected areas if
forthcoming data shows greater tolerances to disturbances than originally
thought.

20

It is important not to advertise site specific nesting or roosting
areas. While specific locations may need to be revealed to selected
land managers and planners, general knowledge of nesting sites of
endangered or threatened species frequently encourages their visitation
by photographers, nature lovers, and others whose very presence may
cause nesting failure or abandonment of choice roosting sites. It is
natural for birdwatchers to desire to view unusual or rare species,
but ardour sometimes needs to be tempered with wisdom.

Management of Prey Bases — Many of the small mammal species utilized
as prey by various raptors are known to be irregularly cyclic in their
population fluctuations. Populations often change because of intrinsic
factors that have little relationship to their habitat. A frequent
cause of small mammal population declines is density related stress
which occurs because of frequent encounters with members of their own
species. Rabbits are also known to be more or less regularly cyclic,
and the raptors which prey on them may either fail to nest or have poor
production during the years when the rabbits are at a low point in their
population cycles. Little can be done to manipulate rodent or rabbit
cycles.

The most productive management of prey, as with all wildlife } comes from
management of the habitat so as to produce the desired fauna. The term
"desired" is somewhat philosophical, since each group or species of
animal usually has its own devoted advocates. However, certain raptors,
such as bald and golden eagles, peregrine falcons, ospreys or other
species which have either State or Federal protected status, will have
priority in land management programs. Management of prey bases for such
priority species might include maintenance of wetlands for shorebird and
waterfowl production for utilization by peregrines; perpetuation of
prairie dog colonies through suitable grazing practices as a prey
source for golden eagles, prairie falcons, and ferruginous hawks; and
maintenance of suitable habitat conditions in rivers, lakes, or reservoirs
for fish production for bald eagles and ospreys. Range management
practices that produce or maintain ranges in good condition will provide
a greater abundance and variety of prey for a multitude of raptorial
species. We must be especially careful about the use of pesticides or
rodenticides distributed to destroy rodents, rabbits, or other fauna
that may be crucial to the survival of the raptors present.

A further consideration is that larger species of raptors normally
utilize larger forms of prey. Average size of prey utilized by various
raptors include: golden eagle — 1,825 g; ferruginous hawk — 1,394 g;
red-tailed hawk — 1,386 g; and Swainson's hawk — 905 g (Smith and Murphy,
1973; Olendorff and Stoddart, 1973). Therefore, the prey species that
should have priority in management programs will depend somewhat on the
raptor species selected for primary management efforts. Also correlated
with this is the statement by Lack (1966) that "the large prey on which
large raptors depend are in general much sparser than the small prey on
which small raptors depend...."

21

The widespread poisoning of prairie dogs during the last two decades in
southern New Mexico is believed to have been responsible for the dis-
appearance of ferruginous hawks in the area (Hubbard, personal commun.).
Reasons for the decline in birds could have been indirect poisoning or
simply a reduction in their primary prey.

In flat prairie or desert country where natural, elevated observation or
feeding perches are very scarce, artificial perches may be erected for
use by raptors. Artificial structures such as power poles receive high
use by eagles and other raptors, especially when they are located near
good prey populations. It is questionable whether such perches are
really significant in the overall survival of the birds. However, they
are undoubtedly a real convenience to the birds and would permit them to
expend less energy in searching for prey than if they were forced to
remain aloft in order to sight potential prey. In one study in Utah by
the U.S. Forest Service, artificial perches were erected in mountain
meadows to test their use by raptors and to determine any possible
benefits they might offer through their use by raptors in controlling
pocket gopher populations. It was concluded that, while there was
significant reduction of pocket gophers near the hunting perches, the
total impact of raptor predation on the gopher population was not clear
and required further study.

The development of reliable methods of assessing prey species habitat or
populations is a necessary prerequisite to raptor population manipulation
(Fyfe and Armbruster, 1977). One technique for assessing prey populations
has been simply to carry out population surveys of prey species in
association with current and previous nest sites, thereby permitting
comparison of the relative abundance of prey species. Another approach
has been an -evaluation of habitat use by prey species or, in the Canadian
prairie region, to assess the influence of land use practices on prey
abundance and on raptor population density and productivity (Owens and
Myers, 1973; Hodson, 1975).

Acquisition of Crucial Raptor Habitats

Preservation of sufficient habitat in undegraded condition is a critical
necessity for a number of species of raptors having specific habitat
requirements (Snyder and Snyder, 1975). While there are many areas of
public lands that are highly important to raptors and -may be managed for
their preservation at the discretion of the administering agency, there
are many other crucial areas that are under private ownership. Indivi-
dual owners may or may not have empathy for the birds of prey or other
fauna on their lands. For long-term effectiveness in providing protec-
tion to declining raptor populations or for the peripheral species of
the Southwest, it would be advantageous to either (1) bring the required
land acreages into public ownership by Federal purchase or land exchange,
(2) transfer ownership to private conservation organizations through
direct purchase, (3) acquire ownership through purchase by the state

22

wildlife agency, or (4) enter into a cooperative agreement with the
private landowner to provide adequate undisturbed habitat to assure
the perpetuation of the selected raptors.

Where large tracts of land in private ownership have significant raptor
use, it is entirely possible that private organizations will achieve
greater success than government agencies in persuading business or
industry representatives to adopt management procedures designed to
protect the resident raptors (Murphy, 1978) . Many raptor species do not
seem to be flexible in changing their habitat preferences in the face of
intensive real estate developments or other land uses. For such species,
only the preservation of relatively undisturbed or unmodified tracts of
land will provide a degree of assurance that those species will be
maintained as viable populations. Examples of human encroachment into
raptor habitats are: urban sprawl in the Phoenix area (causing displace-
ment of Harris' hawks (Parabuteo uni-cinctus) ; construction of summer
homes, ranch homes etc., at the bases of cliffs throughout the West,
producing unacceptable disturbance to golden eagles, prairie falcons,
and other species that may have nested in the cliffs for generations; or
development of oil and gas or coal mining facilities in good nesting
canyons with the subsequent elimination of large nesting raptors that
will not tolerate the noise and human activities. As emphasized in
previous sections, priorities in raptor management should be to
(1) identify through surveys the most important habitats for each
raptor species, (2) identify the management objectives for each species,
and (3) develop the procedures necessary to accomplish the objectives.
Since we must assume that present and future human demands for natural
resources will preclude the preservation of all existing raptor use
areas, we must first identify the most important habitats and then
direct our energies to preserving the habitats having greatest signi-
ficance in the preservation of the species. Secondary efforts may be
provided to mitigate impacts on areas of lesser importance.

Management of Historical Raptor Eyries

Resource managers are aware of many historical eyries (some active and
some not) of several species. An example of histovioal eyries are those
of peregrine falcons along the Wasatch Front in Utah that are no longer
active but which were used for decades prior to the decline of the birds
during the DDT era. Specific sites are selected by raptors for nesting
because of some special characteristics of those sites that fill
specific needs of the birds. Most birds act as if they were programmed
to behave within certain limitations, whether it be for nesting,
feeding, or in meeting other physiological or psychological needs. Nest
site selection is the expression of one of these innate behavioral
patterns. The fact that a specific kind of site and location is selected
is good indication that the site meets the birds' requirements. Some-
times in the first nesting attempt, young birds will select sites that
seem to be somewhat marginal based on the usual pattern for the species.
This may be because the more desirable sites are already occupied by

23

established pairs, or the process may be partially a learning experience
for new nesters. In any case, the protection and maintenance of inhabited
or utilized sites must be given much higher consideration than setting
aside areas for use by raptors based on human judgments of desirability,
especially where such areas may not have demonstrated much active raptor
use in past years.

Investigations are presently underway by the U.S. Fish and Wildlife
Service to determine the feasibility of relocating golden eagle nests.
This is being accomplished under the direction of the Denver Research
Center to determine if golden eagle nests removed from proposed coal
mining sites and re-situated on adjacent cliffs will be accepted and
used by the displaced birds. In the author's opinion, if a golden eagle
nest is destroyed (after the nesting period) by a coal mining operation
or other land use, and there are other undisturbed and suitable nesting
sites within the pair's territory, they will quite likely move to such
sites in subsequent years and construct a new nest. Actually, most
golden eagles have alternate nests already constructed within their
territories and will simply switch to one of these alternates in sub-
sequent years if their current, active nest is destroyed. The success
in acceptance of translocated nests should be tested, but the actual
need for such actions may remain questionable.

Complete protection of nests and adjacent areas (variable, depending on
situation) of threatened or endangered species should be provided.
Because of the very real possibility of creating further declines in
endangered species' numbers by trying to accommodate a variety of land
uses in proximity to the nest site, only those uses that are known to be
acceptable to the birds, such as livestock grazing, should be authorized.
Testing of behavioral responses to various disturbances should be
restricted to species with healthy populations. For example, research
on golden eagles is acceptable because the population seems to be doing
well throughout most of the West (author's opinion).

Restrictions on Human Use of Raptor Nesting/Roosting Areas

Shooting Prohibitions — In general, the impact of shooting appears
to increase with the size of the raptor, probably because of the con-
spicuousness of large raptors (Snyder and Snyder, 1975, from Brown,
1974). Glue (1971) stated that diurnal raptors seem to suffer more loss
than nocturnal ones. Despite legal protection in most states and total
Federal protection, shooting of raptors still continues. This is
indicated by the fact that most band returns for diurnal raptors are
reported as shot. Studies by Henny and Wight (1970) indicate that red-
tailed hawks and Cooper's hawks both suffered considerable mortality
from shooting. Mortality from this cause was estimated to be from 12 to
24 percent for these two species during the period from 1946 to 1957.
The estimated shooting mortality was sufficiently high to make Henny and
Wight (1970) believe that the population decline in Cooper's hawks
reported by Bent (1937) in the early part of this century was largely

24

by shooting. Shor (1970) estimated that over half the first-year
peregrines wintering on the Texas coast end up shot. Scientific
collecting probably caused an overwhelming stress on populations of the
California condor around the turn of the century, causing a possible
irreversible trend in their population.

Most raptors are highly vulnerable to shooting when perched on power
poles, and there is evidence to indicate that large numbers are still
being killed for "sport" throughout the West. Several additional
citations are given by Snyder and Snyder (1975) to substantiate this.

Because raptors are frequently shot by persons seeking unusual targets,
it may be necessary to close some public land areas to firearms. This
has already been initiated in the Snake River Birds of Prey Natural Area
in Idaho during the nesting season and in the Aravaipa Canyon Primitive
area in Arizona, two areas of BLM administration. Present disregard for
laws protecting raptors from shooting suggest that more stringent laws
would accomplish very little unless greatly expanded enforcement and
education were implemented simultaneously (Snyder and Snyder, 1975).
Complete protection of raptors from shooting verges on the impossible
because of vast acreages of public lands and the large areas of respons-
ibility for each enforcement agent. However, firearms closure does
reduce the use of firearms in such areas and should be considered for
any raptor concentration areas or in areas where peripheral, endangered,
threatened, or seriously declining populations occur.

A variety of factors cause mortality in raptors, so it is usually
difficult to determine what percent of the total mortality is caused by
shooting. However, studies such as those by Ellis et al. (1969)
indicate that in some situations shooting of birds of prey is very high.
In a year and a half study, Ellis et al. found an average of 3.14 dead
raptors per mile along a 12.1-mile road paralleling a power line in
Utah. The dead birds were primarily golden eagles but also included
bald eagles, buteos, and other species. They believed that most of this
mortality had been caused by shooting and emphasized the high vulner-
ability of raptors on utility poles that parallel roads. The number of
dead birds found was highest in fall and winter, at which time the
greatest amount of sport hunting for rabbits occurs. It is likely that
many of the raptors were shot as additional targets by rabbit hunters
who had no empathy for the birds. The number of dead raptors found that
may have been attributed to electrocution by the power lines was not
documented, but most mortality was be'l'ieved to have occurred from
shooting.

Land management considerations that might reduce the amount of shooting
of raptors on power poles would include the following: (1) siting power
lines away from highways and other roads, (2) prohibiting road construc-
tion adjacent to power lines, (3) shifting to underground power cables
where feasible, and (4) increasing public education programs to
enlighten the public on the esthetic, scientific, ecologic, and
economic values of birds of prey.

25

Restrictions on Rock Climbing — Mountain (or rock) climbing has
become a popular sport throughout many parts of the country, particularly
in the West. Unfortunately, many of the better cliffs for climbing are
also some of the better nesting sites for golden eagles, peregrine and
prairie falcons, red- tailed hawks, or other raptors. Most climbers are
interested primarily in the challenge of the climb (or descent) and
have no intention of causing any problems with nesting birds. Others
will recognize the presence of the nest of an eagle or other large raptor
and will climb into the nest just because of the increased attraction
it offers during the climb (or descent).

Military units of various kinds include rock climbing training for
selected personnel. High cliffs are their specialty and many instances
are known where descents were made during the course of a day or for
several days in the vicinity of eagle and falcon eyries. The timing of
such training and of individaul activities may be critical to the birds.
In general, rock climbing at cliffs containing nests should not be
allowed at the time when the birds are on eggs and should be permitted
no closer than \ mile to nests containing young. Such activities
normally involve various amounts of shouting or other noise which will
be sufficiently disturbing to the birds to keep them away from their
nests if the activity occurs close by. The young birds may miss impor-
tant feedings or may be subjected to intolerable heat or cold in the
absence of brooding.

Cliffs containing several nests of various species of raptors or of the
same species should be closed to rock climbing during the nesting
season, generally from February 1 through August 1. This is especially
true for any cliffs containing eyries of bald eagles (in Arizona) ,
peregrine falcons, or California condors. A single nest of any of the
endangered species will justify cliff closure to any human activities.

Restrictions on Recreation Uses — Unfortunately, many areas preferred
by humans for recreation are areas that coincide with raptor preferences
for nesting sites. This is especially true of riparian zones, since
water-based recreation sites are at a premium, especially throughout
much of the Southwest, and they are becoming more popular each year.
Consequently, people congregate at such areas in spring and early summer
at the time when black hawks, zone- tailed hawks, gray hawks, and other
raptors are laying eggs and beginning to incubate. This is the worst
possible time for disturbance to the birds, and many of them fail to
bring off a brood because of frequent disturbances near their nest
sites. Dr. Jay Schnell (1979) of Klondike, Arizona, has been studying
the ecology of the black hawks in Aravaipa Canyon in Arizona for several
years and has observed the abandonment and/or disruption of nesting
activities on several occasions. Re-nesting attempts also frequently
fail due to hikers, backpackers, and campers using this highly scenic
area. BLM has recently placed restrictions on human use in the canyon
to preclude some of this disturbance during critical periods. Increasing

26

numbers of recreation sites are being developed along river canyons of
the West to accommodate the increasing numbers of vacationers. Each new
development creates some additional stress on the wild creatures of the
area. While some forms of wildlife can adapt to human activities, many
cannot.

Throughout the West and Southwest, canyons containing running water
serve as cool camping and picnicking areas. Such canyons may also
provide the best cliffs or trees for raptor nesting in the entire area,
and conflicts between humans and birds are inevitable.

Many benefits to the raptors could be achieved if trails, campgrounds,
interpretive sites, rest areas, etc., were sited in areas that had no
special attraction to the birds for nesting, roosting, or feeding. The
other possibility is to restrict human activities in such areas until
after mid-summer. This would permit the birds to complete their nesting
activities without undue disturbance from humans and their accompanying
pets and vehicles.

Off-road vehicles continue to create concern over their effects on
wildlife. Occasional and irregular ORV traffic appears to have less
effect on terrestrial mammals and reptiles than on raptors. Many bird
biologists believe that the nesting period is the most crucial time in
the birds' annual cycle. This is a time when the birds are already
under considerable physiological stress and often cannot stand the
stresses created by recreating humans. While human activities in winter
may create many kinds of disturbances, the birds at this time are not
tied to specific geographical areas and can move to other areas with
little apparent stress. While snowmobiling, skiing, pipeline construction,
and other activities may cause the birds to change locations, it does
not usually cause any significant mortality. The reader may cite
instances where habitat needs, other than for nesting, may be crucial in
the life cycle of raptors, but the nesting period continues to be the
most cruoial for most species as far as annual needs are concerned. It
is likely that problems will continue to worsen unless land managers
recognize the threat of off-road vehicles to certain forms of wildlife
and take the necessary steps to protect the more sensitive species from
disturbances at the most critical periods of their life cycles. This
can best be done by restricting certain forms of human activities during
the critical nesting periods for the species concerned. Such protection
may also be needed in selected roosting and feeding sites. It should be
reiterated that speoies behavior in the face of human disturbances is
the most important consideration in deciding which land use activities
may be tolerated and those which cannot.

Where deemed appropriate for the protection of threatened or sensitive
species, landowners may be approached and their assistance solicited in
preventing disturbance to nesting raptors on their private lands.
Indeed, protection provided by the closure of private lands to public
use is almost as good as established sanctuaries in some parts of the

27

West. Development of empathy for raptors by landowners Is very important
for species such as the gray hawk that nest mostly (if not entirely) on
private lands in southern Arizona.

Restrictions on Low-Flying Aircraft — White and Sherrod (1973)
indicated in their paper for Alaska that gyrfalcons (Falco rusticolis) ,
peregrine falcons, and rough-legged hawks are generally not greatly
affected by low-flying helicopters or fixed-wing aircraft. However, the
amount of disturbance will be governed partly by the amount of hovering
time over the nest or the number of close passes made by the aircraft.
White and Sherrod mentioned that falcons and eagles will sometimes
attack aircraft that are hovering or flying close to their nest. This
can be dangerous to both the birds and the aircraft occupants if they
should come together in an inappropriate manner.

In his years of aerial surveys the author does not know of any nests of
eagles, falcons, or buteos that were abandoned because of his aerial
survey activities, but his flying was done mostly with fixed-wing air-
craft of the Cessna 172, 180, and 182 types. The usual precautions must
be taken when using aircraft as when doing surveys from the ground,
i.e., (1) do not keep the adults away from the nests any longer than
absolutely necessary to accomplish the research or survey; and (2) do
not hover over nests during periods of cold, heat, or moisture when the
young birds would be unduly exposed to the elements.

Discretion in Raptor Surveys and Research Activities — Conservation
groups and private individuals sometimes accuse raptor researchers of
causing the mortality of young birds during the course of their investi-
gations. It must be acknowledged that some mortality is caused usually
because of inexperience with raptors by new researchers, but sometimes
even by experienced personnel due to unusual circumstances or extreme
sensitivity of the adults. Because of the amount of knowledge now
available on raptor behavior and essential precautions to be exercised
in the conduct of raptor investigations, there is probably much less
mortality of eggs or young caused now than there was 15 to 20 years ago.

whenever new personnel are sent into the field to conduct surveys or
research, they should be thoroughly apprised of the precautions that
need to be taken. These are thoroughly discussed in Fyfe and Olendorff
(1976) and in Call (1978). Those who are engaged in the business of
preserving the nation's birds of prey and who periodically conduct
various kinds of research to obtain needed management information
should be those who will be the most careful in their conduct while in
close proximity to the nests they are studying. Needless mortality
should be avoided to the maximum extent possible. Most persons become
biologists because they enjoy observing or handling wild animals, but
this enthusiasm must always be tempered by wisdom and caution if handling
birds or even closely approaching the nest. It may cause the death of
the very animals we are seeking to preserve. Before anyone undertakes
research or surveys on selected species, they should become thoroughly
knowledgeable on the behavioral characteristics of those species.

28

Raptor surveys are being conducted throughout the West (and throughout
the nation) in order to obtain needed information for land use deci-
sions. Sometimes more than one agency becomes involved in collecting
information on birds of prey in contiguous or even the same areas.
Double or triple disturbance of the birds is sometimes caused by these
overlapping survey activities. All survey and researah activities
should be coordinated with all agencies or groups that may be interested
in the same species in the same area. If the state wildlife agency is
planning to conduct a survey of raptors in a specific area; BLM, USFS ,
or other agencies may cooperate but should not duplicate the work. By
combining money, manpower, and expertise, a more efficient job can be
accomplished, and usually a larger area surveyed. Do not be afraid to
take the initiative in coordinating work between conservation agencies or
private conservation groups. It will pay off in the long run!

29

HABITAT DEVELOPMENT FOR RAPTORS

Biologists recognize that there has been a progressive loss of suitable
habitat for many species of raptors. In view of this we should keep in
mind the statement by Snyder and Snyder (1975): "No species (of raptor)
oan survive in the wild without adequate acreages of habitat to which it
is adapted, and thus safeguarding habitat is the primary necessity in
preventing the loss of species and in maintaining the numbers of raptors
at desirable levels." The maintenance of suitable natural habitat for
the various wildlife species must be our primary objective. While
artificial habitats such as artificial nesting platforms can serve to
supplement nesting sites for populations in areas where natural nesting
substrates are very limited, they should not be considered as a panacea
to our habitat management problems. Artificial structures should be
used with discretion after management objectives for the area have been
established and should be made to look as natural as possible. They
are frequently useful in maintaining raptor populations in areas where
natural nest sites are being gradually destroyed or made unacceptable by
nearby activities of man or in building populations where all other life
requirements are available except suitable nesting sites. But... first
consideration should be to maintain as nearly a natural environment as
possible.

In areas where raptor populations are gradually increasing, some birds
may be forced to nest in substandard sites. In such situations, either
the eggs or young may be in jeopardy from numerous mortality agents
throughout the nesting period; thus, artificial nesting structures in
good sites may increase chances for survival.

Artificial Nesting Structures

There are many examples of successes in the use of artificial nesting
structures. Raptor biologists all across the country are trying various
modifications of proven designs and achieving varying degrees of success.
This paper will present only a few representative examples.

Hamerstrom et al. (1973) demonstrated that kestrels could be substantially
increased by the construction and placement of nest boxes in areas where
lack of suitable nesting sites was the primary population limiting
factor. The Susanville, California, District of the Bureau of Land
Management has had a similar response from kestrels from the placement
of 100 nesting boxes in juniper trees. Good results were also obtained
by Woyda and Martin (1977) in Cache Valley, Utah. Fyfe (1979, personal
commun. ) has had excellent success in acceptance of artificial cavities
by prairie falcons in Canada and in acceptance of artificial nest
structures by ferruginous hawks. Anderson (1979, personal commun.) has
had excellent success in acceptance of both modified and completely
artificial nest structures by ferruginous hawks in Colorado, and Howard
(personal commun.) has had similar experiences in Idaho. Two of three

30

artificial nest structures initiated by the author in 1979 on the
Pawnee National Grasslands in Colorado were utilized the same year by
ferruginous hawks. Postupalsky and Stackpole (1974) increased a popu-
lation of ospreys at a reservoir site in Michigan through provision of
artificial nesting platforms. Artificial nest sites for ospreys have
also been tried with some success in California (Garber et al. , 1974),
Oregon (Neitro, 1978, personal commun.), and on Chesapeake Bay (Reese,
1970). Artificial nest structures for everglade kites (Rostrhamus
sociabilis) in Florida also apparently have proved to be of value (Sykes
and Chandler, 1974).

Owls do not construct their own nests and the use of any suitable nests
by the various owl species is well known. Virtually any type of arti-
ficial nesting structure is acceptable to great horned owls, and other
species, including great gray owls, will also use them. One design for
artificial nests for great horned owls has been published by Bohm (1977).

Attracting bald eagles to artificial nesting structures is apparently
not so easy, but both Postupalsky (1977) and Grubb (1979, personal
commun.) have had bald eagles accept and lay eggs and/or raise young on
artificial nest structures. Bald eagles accepted an artificial nest
constructed by Dunstan and Borth (1970) and laid two eggs but were
unsuccessful in fledging any young. Following are some examples of
designs that have been successfully used in attracting various species
of raptors to artificial nesting sites.

Construction of Artificial Nesting Structures

Descriptions of methods that may be used to attract raptors to artificial
nest sites will be discussed under the following headings: (1) cliff-
nesting species, (2) tree-nesting species, (3) cavity-nesting species,
and (4) species nesting underground. Several species nest in a variety
of locations and no attempt will be made to include all possibilities .

Cliff-Nesting Species — Birds of prey that normally nest in cavities
or on ledges of cliffs include the golden eagle, peregrine falcon, prairie
falcon, kestrel, gyrfalcon, red-tailed hawk, California condor, great
horned owl, barn owl (Tyto alba), bald eagle (in Alaska and sometimes in
Arizona), turkey vulture (Cathartes avira) , zone-tailed hawk, and osprey.

Creation of cavities or ledges in cliffs, especially in the lower
portions of mountain ranges, is a good method for creating additional
nesting sites for a variety of species. In this context the author also
includes high dirt or clay banks. While golden eagles and other raptors
may be found nesting anywhere from the top to the bottom of a cliff,
they seem to prefer to nest from about one-half to about four-fifths of
the way to the top. A good rule to follow would be to construct the
cavity at least one-half of the way to the top, with an assortment of

31

different cavities being constructed, if time and manpower permit. The
size of the cavity or ledge needed will vary with the species of raptor,
and a general rule would be to construct the cavity to permit adequate
room for the birds to exercise their wings without excessive contact
with either the sides or top of the cavity.

It is not uncommon in the wild to see two of the young birds exercising
their wings at the same time, with occasional precarious positioning of
one or both birds near the edge of the nest. The author has film of a
young golden eagle that apparently lost its balance while exercising its
wings, fell over the edge, and remained attached to the nest with only
one foot. Fortunately, the bird was capable of flapping its wings and
pulling itself back onto the nest.

Nest cavities or ledges for golden eagles should be at least 6 feet
long, 4 feet deep, and 4 to 6 feet high (Fig. 1,5). Large amounts of
nesting material are used by eagles and cavities tend to become filled
with debris over the years. Cavities sometimes become so filled with
sticks, etc., that the birds can no longer use them. Cleaning out part
of the nesting material will prolong the useful life of the eyrie.

The primary idea in cavity or ledge construction is to build it so that
the young can have free movement, the adults can land without difficulty,
and there will be some degree of permanence to the site.

For the larger falcons, a cavity approximately the length of the wing-
spread should be satisfactory (Fig. 4). While many biologists have
observed successful fledging of young falcons from relatively small
cavities, these are probably not optimal sites. There tends to be a lot
of trampling of each other and sibling face-swatting during exercising
in small cavities.

Considerable work has been done by Fyfe and Arbruster (1975) in con-
structing cavities for prairie falcons in cliffs that had few or no
suitable natural holes. Cliffs were selected on the basis of several
criteria including: (a) site location in relation to suitable habitat
for prey species; (b) freedom from excessive human activity; (c) a
minimum cliff face height of 7 m (22 ft) ; (d) a relatively permanent or
solid substrate of clay, conglomerate or sandstone; and (e) freedom from
excessive erosion, such as serious undercutting and slumping along river
channels.

In sites meeting these criteria, cavities were then built having minimum
dimensions of 30 cm (12 in) deep x 60 cm (24 in) long x 30 cm (12 in)
high. Several digging methods were tried, including the use of dynamite,
but digging by hand with a small shovel generally proved more efficient.
Of interest is the fact that some of these cavities or ledges have been
used by Canada geese.

32

— «N-

Figure 1. Artist's concept of artificial cavity that could be constructed
for golden eagles, red- tailed hawks, or prairie falcons. For golden
eagles, cavity or ledge should be approximately 6' long x 6' high (if a
cavity) x 4' deep. Prairie falcon cavities should be about 24" long x
12" high x 16" deep.

33

Figure 2. Typical natural nesting sites of kestrels: old flicker
nesting cavities, or holes in dirt banks or cliffs.

Figure 3. Great horned owls (left) and barn owls (right) often
use natural cavities for nesting.

34

Figure 4. Nesting cavities of prairie falcons showing variety in types
of cavities used and locations on cliffs.

35

Figure 5. Nesting ledges of natural golden eagle eyries showing normal
placement on cliffs.

*r 0* 1

• • **^j!I

iamb im

•373

:<-'<^

^8

3tvK v *

J^-:

jjr**

Figure 6. Typical nests of golden eagles showing nest size for these
birds.

36

Initial success was encouraging. In 1970, of five nest holes or ledges
dug along cliff faces, four were occupied by pairs of prairie falcons
and the fifth by a lone male prairie falcon. In 1971, of 12 holes or
ledges, eight were used by either falcons or by Canada geese. Since
then, the Canadian Wildlife Service field crews and Saskatchewan Fal-
conry Association members have made over 200 nesting holes, and there is
occupancy data for about one-fourth of the sites. Since they were
dealing primarily with sedimentary materials, there was considerable
difficulty with cliff instability, and many of the artificial nest sites
eroded or slumped away.

Kestrels use a wide variety of natural cavities for nesting, from flicker
holes to eroded holes in trees and dirt banks (Fig. 2). They very
commonly nest in cliffs in small potholes or cavities. In areas of the
West containing cliffs, there are probably adequate holes to take care of
their population's nesting needs and, in such places, no construction is
recommended. In areas where kestrels are dependent on cavities in trees,
erection of nest boxes may increase the population, as described below.

Red-tailed hawks may nest on practically any projecting ledge on a
cliff. If cliffs not having suitable nesting ledges are near good
rodent populations, it may be desirable to construct two or three
ledges for any of the raptors, including red-tails, that might (and
probably will) use them. If cottonwoods or other tall trees or even
pinyon or juniper are present in the vicinity of the cliffs, there is
probably little justification for constructing cliff sites, since they
will nest in trees just as readily (if suitable nest branches are
available) .

California condor numbers have declined greatly in the past half century,
and it is probable that adequate nesting cavities are available for the
remaining populations.

Turkey vultures will nest not only in cliff cavities but also under
fallen trees, on the ground under trees or bushes, or between boulders.
It is not necessary to construct cliff-nesting sites for these birds
since potential sites are not limited.

Great horned owls have virtually unlimited nesting sites, since they
nest early and have the choice of other raptor nests in their area.
They will also nest in many types of cavities in dirt banks, cliffs,
broken trees, etc. While artificial nest structures would be accepted
by great horned owls, you should give careful consideration to the
number of these birds you wish to manage in any given area. They are
mortal enemies of prairie and peregrine falcons and sometimes take young
of these species from their eyries at night. Inadvertent flushing of
great horned owls in daytime may cause their death if large falcons are
nearby, as falcons almost always "stoop" on the owls when they are
flushed in daytime. Despite their large size, great horned owls seem

37

to be doing very well in most areas of the country because of their
secretiveness and nocturnal habits. Cavities or ledges constructed for
any other species may be used by these owls.

Barn owls nest in cliffs in some regions but also nest in old buildings,
processing plants, silos, barns, etc. They are occasionally found
roosting or nesting in natural cavities in dirt or shale banks in the
Southwest. Where other natural cavities are not available, digging
holes in dirt banks may increase the number of these birds nesting in
the locality. Holes should be dug at least 6 feet above the ground. In
a study by Brian Millsap (1978, personal commun.), 22 nests located in
the Fort Collins, Colorado, area were all in clay or dirt banks (Fig. 3).
Millsap constructed large boxes in 1977 and hung them from high dirt
banks in an effort to attract the barn owls to nest in them, but no
nesting use has been made of them to date (1979). However, one or two
were being used for roosting. In northern Utah where barn owls often
use silos for nesting, platforms are being constructed in the upper
portions of the silos and are being used for nesting (Wagner, personal
commun. ) .

Bald eagles nesting on cliffs and ledges along coastlines, in Arizona,
or in other western states probably have adequate potential nesting
sites for reasonable numbers of birds to occupy. Other factors would
probably limit nesting density before nesting sites. No situations are
presently known by the author that would justify construction of nesting
sites for bald eagles in cliffs of the West or Alaska.

Ospreys sometimes nest on seastacks, rocky pinnacles, or projecting
structures on cliffs. Since they readily accept elevated nesting
structures in trees or on poles, the development of cliff-nesting sites
is not recommended. Design of platforms in trees is discussed later.

Because of the limited number of zone-tailed hawks nesting on cliffs in
the Southwest, no special site construction is recommended. Most zone-
tailed hawks nest in trees.

Tree-Nesting Species — Raptors that commonly nest either in trees,
high bushes, saguaro cacti, or other high vegetation include bald and
golden eagles, all buteos (and other soaring hawks) except the rough-
legged hawk in Alaska, all accipiters, merlins (Falco columbavius) ,
ospreys, Audubon's caracara (Polybarus oheriway) , owls (great horned,
great gray, long-eared, barred, spotted, and boreal [Aegolius fwnereus~\) ,
Mississippi and swallow-tailed kites (Elanoides fovfioatus), and very
rarely, turkey vultures (in the tops of dead trees if cavities are
available) (Bent, 1937). Raptors that nest in cavities will be considered
in the next section.

In future years students of raptors will undoubtedly try to attract each
of the various tree-nesting raptors to one kind of artificial nest site
or another. It has already been pointed out that all of the larger owls
will accept the nests that are constructed by almost any of the other

38

birds of prey, providing they are large enough to provide room for their
young (and sometimes when they are not!). For this paper, examples
illustrate some types of nesting structures or platforms that have
worked in one area or another. The author is unaware of any artificial
nesting structures that have been used by merlins, Mississippi or swallow-
tailed kites, caracaras, vultures, or any of the accipiters.

The most common tree-nesting species that have utilized artificial
nesting structures are ferruginous hawks, red- tailed hawks, golden
eagles, bald eagles, ospreys, and great horned owls.

Typical tree-nesting sites of ferruginous hawks are shown in Figure 7,
and Figure 8 illustrates the variety of artificial structures that have
been tried for ferruginous hawks. Bill Anderson of La Junta, Colorado,
while working with Gerald Craig of the Colorado Division of Wildlife,
probably has had more experience in attracting ferruginous hawks to
artificial nest structures than anyone else in the United States. They
plan to publish on their results in the near future.

More often than not, ferruginous hawk nests are less than 15 feet above
the ground, often in dead or dying trees. Throughout much of the West,
ferruginous hawks nest in juniper trees with the nest being only about
8 to 10 feet above the ground. These birds will continue to use these
nests even if the trees die. In Colorado, some nests in dying trees
become so heavy that they break their supporting branches and the site
is no longer usable. Bill Anderson (1979, personal commun.) is pre-
serving many such nesting sites by either removing the nest, building
a supporting structure and then replacing the nest, or by simply building
a support under the existing nest. He also "tops" some of these nests
to reduce total weight.

Some researchers have tried to attract ferruginous hawks by simply
installing some type of pole with a nesting platform at the top, without
constructing any semblance of a nest on the platform. My observations
and experience indicate that the birds are best attracted to an arti-
ficial structure by creating a man-made (ferruginous hawk) nest within
the structure. (Even the proper amounts of dried cow manure are properly
inserted around the structure!) Sagebrush and other dried sticks can be
used for the basic structure, with dried grass, weeds, or leaves being
used for the nest cup. Examples of artificial nest structures placed by
Richard Howard, U.S. Fish and Wildlife Service, Boise, Idaho, are shown
in Figures 9 and 10. Note the sun shades. At least one of his structures
has been used by ravens which will nest on a wide variety of man-made
structures, either intended or not intended for nesting. Ferruginous
hawks seem to accept nest structures very well that are in the range of
8 to 15 feet from the ground. Howard (1979, personal commun.) emphasizes
the need to wire some of the major branches into the wire basket to
prevent the wind from blowing the nest off. He also recommends that all
artificial structures be placed at least % mile from any road to reduce
potential vandalism.

39

Figure 7. Typical tree nesting sites of ferruginous hawks,

40

Figure 8. Types of artificial nest structures that have been used
to try to attract ferruginous hawks to nest.

41

Figure 9. Artificial nest structure occupied by ferruginous hawks
near Boise, Idaho.

Figure 10. Artificial nest structure occupied by ravens near

Boise, Idaho.

42

Figures 11 through 14 show a sequence of photos taken by the author
during the construction of three wire basket nest sites on the Pawnee
National Grasslands during late February and early March of 1979.
Ferruginous hawks had used two of these trees for nesting in years past,
but the nests had not been active for two years and the original nests
had blown down.

Chicken wire mesh was slung between two or three heavy branches and
securely tied to them with heavy wire. Wire was also woven through the
meshes and then tied to the branches to support the open ends. Wooden
debris and heavy branches were used to form a solid bottom to the structure,
with additional branches worked into the structure until a semblance of
a nest was created. A hollow center portion was formed of smaller
branches, leaves, debris, and dried cow manure to provide a nesting cup.
The photos in Figure 15 show the finished products. It was found that
upon acceptance of such nests ferruginous hawks added very little except
some inner lining materials for the nest cup. As usual, however,
additional materials were added throughout the nesting period.

On prairies and other shrub-grassland areas where trees are very scarce,
the trees are at a premium as nesting sites for raptors. Where nests
occur in such trees, it may be advisable to fence livestock away from
the tree or group of trees in order to prolong the life of the site.
Otherwise, cattle tend to "shade up" under these scattered trees, rubbing
the bark and trampling dirt away from the roots until the trees eventually
die (Fig. 16; also see Olendorff and Stoddart, 1973).

Ferruginous hawks frequently use the same nest for several years. Many
of these nests are in dead trees or on dead branches that will not last
long without supplemental support (see Fig. 17). If the tree is fairly
solid, the nest may be given greater longevity by providing nest supports
only. In some cases, however, the entire tree may need to be braced if
the nest is to be saved.

In Alberta, Fyfe (1975) reported that a major limiting factor for some
of the buteos appeared to be the lack of trees or elevated areas for
stick nests. The ferruginous hawk and some of the other buteos regularly
used remnants of old stick nests of crows, magpies, or other buteos as a
base upon which to build their nests. Fyfe (1975) first constructed and
erected artificial tree nests in 1971 in five areas where old sites had
been destroyed. Four of these were occupied in 1972. Since then (by
1975) 37 baskets have been erected, of which 22 were erected in former
raptor territories and 15 in grassland areas judged to have adequate
prey but with no previous record of occupancy. Of the 37 baskets, a
total of 16 had been occupied by 1975, indicating the effectiveness of
this technique. The majority of the occupancy was in former territories,
indicating that these should receive first priority for artificial nest
structures.

43

Figure 11. Wire basket nest construction for ferruginous hawks,
Chicken wire is being securely tied to branches with heavy wire.

Figure 12. Branches and other material are being placed in chicken
wire basket as base for nest.

44

Figure 13. Completed "artificial" nest as it looked immediately
after construction.

Figure 14. Artificial wire basket nest being utilized by ferruginous
hawks the same year it was constructed.

45

Figure 15. Additional examples of artificial nests constructed for
ferruginous hawks in northern Colorado.

46

Figure 16. Fenced and unfenced trees containing raptor nests.
Unfenced trees are almost dead because of cattle abuse.

Figure 17. Very large active ferruginous hawk nest in very small
tree. Building a support under nest might preserve nest for many years
otherwise it will soon topple.

47

Figure 19 shows a great horned owl nest which was a reconstructed
ferruginous hawk nest (Anderson, 1979, personal commun.). Bill Anderson
reconstructed the nest to make it more permanent for ferruginous hawks,
but it was taken over by great horned owls in 1979. The author observed
three ferruginous hawk nests that were taken over by great horned owls
during the early spring of 1979.

Great horned owls will utilize old stick nests in a wide variety of
settings, sometimes even in low, dead trees having no foliage cover.
Bohm (1977) had good acceptance of artificial nest structures by great
horned owls in central Minnesota. The nests were made of 1 m x 1 m
pieces of 2.5 cm mesh chicken wire. A 1 m x 1 m piece was formed into
a shallow cone by cutting from its center to one of the corners and
then overlapping the edges. The completed cone measured approximately
75 cm (top diameter) by approximately 45 cm (depth) ; its shape was
secured by bending the sharp wire ends around the wire that they
overlapped. The cone was then lined with tar paper and provided with
a drainage hole at the base before nest material was added. Bohm
(1977) felt that unlined nests were much more susceptible to weathering.
His artificial nests consisted of twigs, leaves, and branches, with the
finer material near the top where the eggs would be laid. Larger
branches were interwoven with each other and the chicken wire as tightly
as possible to provide a solid nest structure. Once the entire nest was
complete, it was then tied to a rope, pulled up into a tree, and
secured in a suitable crotch with wire and/or large staples. Red-tailed
hawks tend to nest near the tops of trees, but great horned owls will
nest at practically any elevation above the ground. Nests that are
constructed primarily for the larger owls should be in place by early
January since most owls will begin establishing their nesting
territories very early in the year.

Long-eared owls and great gray owls will also accept artificial nest
structures (Nero, 1977). In the bogs of southeastern Manitoba, Nero
(1977) had placed more than 60 artificial nest structures in trees,
mostly tamaracks, by 1977. Nest heights varied from 15 to 40 feet
above the ground and they were widely accepted by great gray owls.
He employed a wire-mesh screen for the nest base, placing it in trees
having suitable crotch arrangement to support the structure. Ideal
trees consisted of deformed tamaracks having crowns of upright limbs
that formed cradles in which the nests could be constructed.

Golden eagle nests in trees become bulky and very heavy over a period
of years and often break the branches that support them. Some raptor
biologists have removed such nests, constructed solid bases of wood
or wire mesh, and then placed the nests back on the structures. Where
feasible, this kind of work may increase the useful life of eagle
nests by many years. Figure 20 illustrates a golden eagle nest in
northern Colorado where Gerald Craig and Bill Anderson constructed a

48

-^^fc*'4 ^ '"'■ - - v

;.*. .,

JBLf /

Figure 18. Artificial nesting burrow constructed for burrowing
owls by Curtis Orde, Pawnee National Grasslands, Colorado.

Figure 19. Young great horned owlets on reconstructed ferruginous
hawk nest that had been used for several previous seasons by hawks.

49

Figure 20. Golden eagle nest in northern Colorado which was
reconstructed and provided with stable base to assure more permanent
nest.

I *■ H

*•■****.

v~< ^p

//■-:••• ■*■■■«-.*■

Figure 21. Artificial nesting platform used by golden eagles
in northern Colorado, Pawnee National Grasslands. To date, use of
such structures by golden eagles has been rare.

50

solid base and the eagles continued to use the nest. Figure 21 shows
an artificial nesting platform on the Pawnee National Grasslands of
northern Colorado that successfully fledged one eaglet in 1979. The
eaglet was still on the nest on August 5, which might indicate a
re-nesting of this pair. Use by golden eagles of artificial nesting
structures such as this one is fairly rare.

Some workers have had success inducing bald eagles to use reconstructed
nests or artificial nesting structures (Postupalsky , 1977; Grubb, 1978,
personal commun. ; Dunstan and Borth, 1970). Figures 22 and 23 show the
structures built by Terry Grubb in Arizona, with the adult bald eagle
on eggs on one of the artificial nests. It sometimes requires several
years for bald eagles to accept and use nest platforms (Postupalsky,
1977), but Grubb (1978, personal commun.), in cooperation with personnel
from the U.S. Fish and Wildlife Service, succeeded in attracting bald
eagles to nest on a tripod structure the first spring it was in place.
In the case of Postupalsky (1977) and Dunstan and Borth (1970), bald
eagle nests fell from decadent trees and were reconstructed by these
workers in nearby healthy trees. In the case of Grubb (1978, personal
commun.), the eagles built a nest in a flimsy snag which blew down.
He and his associates then decided to construct a strong tripod-shaped
affair which would be permanent. They reconstructed the nest in the
top portion of the structure and it was accepted by the eagles the first
year thereafter. Two eggs were laid but, unfortunately, no young were
successfully fledged.

Artificial nests for bald eagles should be placed in either historical
or active nesting territories if one expects to attract nesting eagles
to the structures.

Many persons have worked on maintenance or improvement of habitat for
ospreys. Lehenbauer (1966) and others recognized that "Two habitat
factors are of prime importance: (1) numerous snag nesting sites and
(2) an abundant fish food supply. Any wide-scale alteration to either
of these factors would significantly affect the welfare of the osprey."
Land managers usually recognize that protection of existing nest sites
and food supply are essential elements in management programs if ospreys
are to be maintained in an area. Obviously, these goals have to be
coordinated with other planned uses of the area.

If ospreys have habitually used an area, it probably has an adequate
food source. However, fish populations in the area should be checked
to determine species, status, and trends. Maintaining adequate fish
sources will be essential to maintaining the osprey population and
should be coordinated closely with the state wildlife agency.

51

Figure 22. Two tripod-type nest structures built for bald eagles
in Arizona.

Figure 23. Bald eagle incubating eggs on artificial nest shown in
Figure 22, right-hand photo.

52

Maintenance of osprey nesting sites is the second most important
consideration. Areas having adequate fish supplies but lacking nesting
sites or where present nesting snags are falling might benefit through
the construction of artificial nesting platforms (Zarn, 1974) .
Artificial nesting platforms should offer an elevated, unrestricted
view and access to a food supply. Platforms intended to replace a
deteriorated nest snag should be placed reasonably close to the snag.
Additional nest sites may be developed in suitable areas where none
are available.

Several workers have constructed nesting platforms that have been
accepted by ospreys (Postupalsky and Stackpole, 1974; Reese, 1970;
Bent, 1961; Kahl, 1971, 1972; Johnson and Melquist, 1973; Roberts,
1969, 1970). Their general recommendation is that the optimum size
and location of nesting platforms need to be determined through
experimentation and analysis of active nest sites within the area.
Means for preserving natural snags may vary between areas because of
differences in size of snags, height of trees, proximity to water,
degree of decay of the snags, or other factors.

New reservoirs in mountainous or other tree-lined areas often inundate
shoreline trees that eventually drown and die. The resultant snags
may provide ideal nesting sites for ospreys, but these too begin rotting
at the waterline and fall down or blow down over a period of years. In
some high-use nesting sites, such as Craine Prairie Reservoir in Oregon,
the management plan proposes methods for prolonging the usable life of
the snags by installing guy wires, tripod braces, and telephone pole
stubs (Roberts, 1969). As substitutes for natural snags, they have
suggested the construction of nest platforms atop treated timbers or
aluminum poles. The possibility of creating snags by girdling or
poisoning dominant trees in adjacent green buffer strips was also
considered. Artificial nesting structures would then be constructed in
the tops of these snags if necessary for nest support. Removing tops
from suitable living or dead trees increases their attractiveness to
ospreys (Kahl, 1972). Figure 24 shows how dead trees are "topped" to
provide bases for osprey nests, and Figure 25 shows young ospreys on
an artificial nesting platform.

Construction of artificial nesting platforms for ospreys (or other
raptors) in areas that are not within the known traditional nesting
range of the birds has been considered by some biologists. If the
structures are placed near the boundaries of known nesting ranges,
they may offer the possibility of extending osprey (or other raptor)
nesting ranges if food supplies are adequate but natural nesting sites
are not available. For example, ospreys nest in Mexico and in various
parts of the western United States. Portions of the lower Colorado
River, while appearing suitable except for the absence of nesting sites,
apparently have not been used in recent times. Construction of nesting
platforms in such areas may invite passing ospreys to stop for the
nesting season.

53

Figure 24. Oregon biologist "topping" a dead snag to provide
nest base for ospreys.

Figure 25. Young ospreys on artificial nest structure in Oregon,

54

Cavity-Nesting Species — Several species of raptors utilize cavities
for nesting in trees, dirt banks, cliffs, or buildings. Many species
that use such sites have already been discussed as cliff-nesting species
and will only be discussed here in relationship to their use of
artificial nesting boxes. The small owls normally use flicker or
woodpecker holes in trees, saguaro cacti, or other treelike vegetation.
Included are the screech, saw-whet, elf, pygmy, ferruginous, flammulated,
and boreal owls. Larger owls that sometimes use cavities for nesting
include the great horned, barred, spotted, hawk, and barn owls (Fig. 3).

All of the falcons could conceivably be attracted to artificial nesting
cavities (boxes or barrels of one kind or another) . Olendorf f and
Stoddart (1974) discussed the possibility of using wooden barrels hung
over the sides of cliffs, on power poles, or in trees to attract nesting
prairie falcons. To my knowledge, no one has successfully accomplished
this yet. Fyfe (personal commun.) has tried to attract prairie pigeon
hawks to nest boxes in Canada but has had no positive results yet.
Because of recent declines in numbers of peregrine falcons, it is
unlikely that their populations are limited by nesting sites and it
would seem unfeasible to attempt to attract them to nest in boxes on
cliffs.

Kestrels are reasonably easy to attract to nest boxes of appropriate
size. Numerous workers throughout the United States and Canada have
constructed large numbers of kestrel boxes and achieved a high degree
of occupancy (Henney, 1979, personal commun. ; Hamerstrom, Hamerstrom
and Hart, 1973; Woyda, 1977; U.S. Bureau of Land Management, 1978,
personal commun. ) Nest boxes for kestrels should be placed in
reasonably open areas, such as openings in forests, along prairie or
desert fences, on the borders of towns and ranches, etc. (Fig. 27).
The author was successful in attracting a nesting pair to an aspen
birdhouse placed on his home in Littleton, Colorado, where there is an
open field on one side of the house (Fig. 26). The section of aspen was
an old flicker nest. Such a cavity is the type normally used by kestrels
in the wild, and the results were probably typical. Five kestrels
hatched and survived for about one week, but only three of the five
ultimately fledged. I suspect the other two either suffocated or
received too little food to survive. Their remains were not found. As
with most other raptor species, the last one or two birds that hatch
have a tough time competing.

Most researchers construct kestrel boxes approximately 20 to 24 inches
high and about 10 inches square, with a 3-to-4-inch hole about 3/4 of
the way up from the floor. This is much larger than a natural flicker
cavity and provides additional space for the young. In the wild, many
kestrels use natural cavities in trees that provide them with
additional room for the young. Lack of suitable nesting cavities seems
to be limiting the kestrel population in some areas. In such areas the

55

Figure 26. Section of aspen containing flicker nest cavity was
placed on author's house in early winter 1979. Pair of kestrels
utilized cavity as nesting site and fledged three young in 1979.

I/flBvr MF\^f ~*1

v^gga

vs IT

1.3

J&lM—-lJ#40i

ith •$>'%&

■WuP^

^r-

Figure 27.
nesting birds.

Kestrel boxes placed in good locations to attract

56

reason for this should be identified before a lot of work is expended
on constructing and placing nest boxes across the countyside. Also, the
decline may be caused by something other than lack of nesting cavities.

Screech owls also utilize nest boxes placed in woodlots or clumps of
trees. While they do not accept the boxes as readily as kestrels, some
workers have had good success in their use (Henney, 1979, personal
commun.). Saw-whet owls will also sometimes use them, with pygmy owls
apparently less receptive of artificial boxes. More research needs to
be conducted on the acceptability of nest boxes by other small owls.

Species Nesting Underground — The only species of raptor that truly
nests underground in open prairies or deserts is the burrowing owl. It
normally utilizes old prairie dog, rabbit, or other rodent burrows but
will accept artificial burrows. Landry (1977) had considerable success
in their use at the Seal Beach Naval Weapons Station in Orange County,
California. Other workers are presently testing their use (Orde, 1979,
personal commun.) (Fig. 18). Several pairs of burrowing owls may live
in the same prairie dog colony. Sometimes such colonies are completely
destroyed by poisoning, plowing, or building homes on the land where
the colony existed.

The status of the burrowing owl throughout much of the West is still
uncertain. Therefore, protection of known nesting areas should be
provided until trends in their populations are better known. Areas in
which artificial nesting structures are placed should be free of any
high vegetation, either grass or shrubs, so they can be found by the
owls. Prairie dogs will sometimes fill up the openings with dirt, so
they should be checked frequently during the spring to be sure they are
serviceable.

Use of Man-Made Objects for Nesting Sites

A wide variety of raptors are sufficiently adaptable to be able to use
various man-made structures as nesting sites. Some of them are as
follows:

Golden eagle — observation platforms, railroad abutments, steel
and wooden power poles, and abandoned quarries.

Osprey — steel and wooden power poles, offshore duck blinds,
channel markers, and pilings.

Peregrine falcon — abandoned shooting platforms and shallow

willow baskets placed in trees in Germany, stone ledges, and
concrete buildings.

Prairie falcon — stone sheepherder monuments.

57

Gyrfalcon — gold dredges and other mining structures.

Kestrel — building eaves, flicker holes in walls, and nesting
boxes.

Ferruginous hawk — metal-roofed building in deserts, top of stone
chimneys, steel and wooden power poles, windmills, water
control structures at reservoirs, upper platforms of pumping
stations, haystacks, sheepherder monuments, and uranium spoil
piles.

Red- tailed hawk — steel and wooden power poles.

Swainson's hawk — steel and wooden power pole structures and
windmills.

Turkey and black vultures — inside abandoned buildings.

Common raven — in bridge structures, windmills, pumping stations,
steel and wooden power poles.

Great horned owl — in abandoned buildings (attics), silos, in old
nests on steel and wooden power poles, abandoned quarries, and
abandoned mine buildings.

Screech, saw-whet, and pygmy owls — bird boxes.

Barn owl — silos, barns, abandoned buildings, water towers,
abandoned mining shafts, church steeples, old wells, and
concrete plants.

The use of such man-made structures, not intended as bird nesting
sites, is generally widespread with regard to species and geography
(Fig. 28). A high percentage of ferruginous hawks reported by Gilmer
and Wiehe (1977) were nesting either on steel transmission line towers
or on haystacks in North Dakota, but these are relatively uncommon
nesting sites for the West as a whole. While more that 90% of the
ferruginous hawks in southern Wyoming probably nest on the ground or on
rocky outcroppings, pinnacles, or boulders, from two to three nests each
year are located on wooden power poles.

Nelson (1978) began testing the use of artificial nesting platforms
for golden eagles in 1975. Noting that several species of birds,
including golden eagles, ospreys, red-tailed hawks, ferruginous hawks,
and ravens, were using steel and wooden transmission line towers for
nesting, he reasoned that Well-constructed nesting platforms on the
towers would provide the needed nesting sites and also create less
chance for power outages that could occur from nesting materials. His

58

K. ■

pt » P\jj, v^y

^^Mlid

•' *"'% ^f-<^ 2^r^2SSBP'**^tt

■

Figure 28.
raptors.

Use of various man-made structures for nesting by
59

preferred design is as shown in Figure 29 and is shown in place in
Figures 30 and 31. Working with the Bonneville Power Administration
and the Idaho Power Company, he erected six platforms prior to the 1977
nesting season on lines with voltages up to 720,000. All platforms
were between 75 feet and 175 feet above the ground. Of the six
installed nesting platforms, five nesting attempts were made. Three
were successful (for a red-tailed hawk, golden eagle, and osprey) ,
while two were unsuccessful (for an osprey and a bald eagle). The
platforms were placed on power poles in habitat types that would be
acceptable to the species involved.

Nelson (1978) emphasized the importance of shade and protection from
the wind in exposed sites. In hot desert areas, young golden eagles,
red- tailed hawks, and prairie falcons may die from overheating if
shade is not available for at least the head and shoulders. Shelter
from the wind also appears to be beneficial to eagles and red-tailed
hawks, but ferruginous hawks and ospreys seem to have no requirement
for protection from either the sun or the wind.

Use of man-made structures for nesting seems to occur most where
natural nesting sites are scarce. The use of these kinds of
structures implies that artificial nesting structures will be most
acceptable where normal nesting substrates are scarce or unavailable,
such as in deserts, grasslands, tundra, or low shrub areas. There is
little reason for erecting artificial nesting structures where normal
nesting sites are -plentiful.

60

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Figure 29. Eagle nest platform layout and assembly (from
Nelson, 1978).

61

Figure 30. Close-up view of nesting structure designed by
Nelson (1978) for eagles and other raptors.

Figure 31. Nesting structure for eagles and other raptors
in place on steel transmission tower in Idaho.

62

PUBLIC AND I & E PROGRAMS

Until recent years, man has tended to view raptors mainly as predators
of game and livestock. Even game law enforcement agents tended to
consider birds of prey more as enemies of game species, such as ducks,
grouse, doves, etc., than as favored species in their own right. One
law enforcement official for the Wyoming Game and Fish Commission that
the author talked to 20 years ago had "personally killed more than 40
golden eagles" in that single year. His reasoning was that eagles
"kill ducks, grouse, and other game birds." The slaughter of golden
eagles in the early 1970s by livestockmen in Wyoming, Texas, and other
states is well known.

During the last decade or two there has been a growing interest in
raptors by Nature enthusiasts, biologists, enforcement agents, and
conservationists. Those wishing to use birds of prey for falconry
have also grown in numbers. Persons interested in raptors recognize
a multitude of values of these birds, including scientific, ecologic,
economic, and esthetic. Several TV programs have beautifully
illustrated different species and helped to create additional public
interest.

Efforts to inform the public of the many values of raptors must
continue if general preservation goals for these species are to be
realized. There will always be unthinking, uncaring individuals in
our society who will continue to destroy that which is beautiful to
others. But there are many other thousands whose hearts are waiting
to be tuned in to conservation philosophies and whose inner beings
will ultimately thrill to the sights and sounds of Nature. These
are the ones that may be reached by continuing public education
programs.

63

LAW ENFORCEMENT

The new migratory bird treaty between the United States and Mexico,
signed in 1972, placed all birds of prey under Federal jurisdiction
and protection. In addition, most states have specific laws
protecting all or most birds of prey. Laws, however, are only as
good as enforcement capability of those laws which can never be
total or complete. Irresponsible trappers and hunters will continue
to rise from upcoming generations; activities will take them into
isolated areas that may be separated greatly both in time and
distance from the nearest wildlife enforcement agents. While law
enforcement and violators' apprehension play a vital role in preventing
more widespread shooting and general irresponsibility towards wildlife,
the greatest rewards will come from increasing emphasis on public
education. Conservationists across the country have been assisting in
providing lectures and training to children in public schools, both
thru good visual programs and by bringing live raptors into the
classroom. Building empathy in our youth now will hopefully create
less need for enforcement in the future.

64

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Christensen, R.C. 1972. Raptor predation on pocket gopher

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Eng, R.L., and G.W. Gullion, 1962. The predation of goshawks upon
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65

Fyfe, R.W. , and H.I. Armbruster. 1977. Raptor research and management
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Fyfe, R.W., and R.R. Olendorff. 1976. Minimizing the dangers of
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Hamerstrom, F. , F.N. Hamerstrom, and J. Hart. 1973. Nest boxes:

an effective management tool for kestrels. J. Wildl. Manage.,
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66

1972. Osprey management on the Lassen National Forest

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67

Reese, J.G. 1970. Reproduction in a Chesapeake Bay osprey
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Roberts, H.B. 1969. Management plan for the Crane Prairie Reservoir
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the Eastern Great Basin of Utah: Brigham Young University Science
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the use of rotor-winged aircraft in raptor surveys: Raptor Research
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Woffinden, N.D. 1975. Ecology of the ferruginous hawk (Buteo regalis)
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68

Woyda, A.L., and J. A. Martin. 1977. The nesting biology of the

American kestrel in Cache Valley, Utah (Abs.): Raptor Research
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Zarn, M. 1974. Osprey. Habitat management series for unique or
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69

ADDITIONAL REFERENCES
(Personal Communications)

Anderson, William. 1979. La Junta Junior College, La Junta, Colorado.

Fyfe, Richard, 1979. Western and Northern Region, Canadian Wildlife
Service, 10025 Jasper Ave., Edmonton, Alberta, Canada.

Glinski, Richard. 1978. Arizona State University, Biology Dept.,
Tempe, Arizona.

Grubb, Teryl. 1979. Rocky Mountain Forest and Range Experiment Station,
U.S. Forest Service, Tempe, Arizona.

Henney, Charles J. 1979. Pacific Northwest Field Station, U.S. Fish
and Wildlife Service, 480 SW Airport Road, Corvallis, Oregon
97330.

Howard, Richard. 1979. U.S. Fish and Wildlife Service, Boise, Idaho.

Hubbard, John. 1979. New Mexico Dept. of Fish and Game, Sante Fe,
New Mexico.

Miilsap, Brian. 1978. Phoenix District Office, U.S. Bureau of Land
Management, Phoenix, Arizona.

Neitro, William. 1978. Oregon State Office, U.S. Bureau of Land
Management, Portland, Oregon.

Orde, Curtis. 1979. District Biologist, U.S. Forest Service, Greeley,
Colorado .

Schnell, Jay. 1978. Klondyke, Arizona. Works in Aravaipa Canyon.

U.S. Bureau of Land Management. 1978. Susanville District, California.

Wagner, Phil. 1978. Utah Division of Wildlife Resources, Salt Lake
City, Utah.

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