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POCKET GOPHERS AND REFORESTATION
IN THE PACIFIC NORTHWEST:
A Problem Analysis

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Sup nt°

JUM 1 91973.

UNITED STATES DEPARTMENT OF THE INTERIOR

FISH AND WILDLIFE SERVICE

BUREAU OF SPORT FISHERIES AND WILDLIFE

Special Scientific Report-Wildlife No. 155

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402

UNITED STATES DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
Bureau of Sport Fisheries and Wildlife

POCKET GOPHERS AND REFORESTATION IN THE PACIFIC NORTHWEST:

A PROBLEM ANALYSIS

By
Victor G. Barnes, Jr,

Special Scientific Report — Wildlife No
Washington, D. C. ' 1973

155

CONTENTS

page

ABSTRACT iv

THE PROBLEM 1

Types of damage 1

Significance of damage

Economics 3

BIOLOGY 4

Taxonomy and distribution 4

General habits 4

Reproduction 5

Populations 6

Food habits 6

Animal associations 6

Population regulators 7

DAMAGE CONTROL METHODS 7

Basic approaches 7

Control of damage on forest lands 8

RESEARCH NEEDS 10

Control research 10

Ecological research 12

Behavioral research 13

Damage appraisal 13

REFERENCES 14

in

ABSTRACT

Pocket gophers (Thomomys spp . ) have an important effect on
reforestation in the Pacific Northwest through damage to conifer
reproduction. Damage is most serious east of the Cascade Range in
Washington and Oregon (Canutt, 1969a; Crouch, 1969) and northeastern
California (Packham, 1969). Damage also has been reported in northern
Idaho (Kuck, 1969) . The purpose of this report is to review pocket
gopher problems in the Northwest, summarize present knowledge of gopher
biology, outline current control methods, and suggest future research
needs .

IV

THE PROBLEM

Pocket gopher damage to forest crops was reported as early as 1940
(Moore, 1940), but there were few reports (Moore, 1943; Dingle, 1956;
Tevis, 1956; Oregon Department of Forestry, 1961; Hermann and Thomas,
1963) until recent years, when damage by pocket gophers acquired top
priority as a reforestation problem. This increased importance is the
result of intensified management and recognition that gophers are
responsible for some damage previously attributed to porcupines
(Erethizon dorsatum) (Moore, 1940; Crouch, 1969) . Although most damage
to date has been on ponderosa pine (Pinus ponderosa) plantations, a
growing interest in lodgepole pine (P. contorta) management will
undoubtedly focus more attention on gophers in that forest type.

The pocket gopher-reforestation problem is analogous to many other
forest-wildlife situations. The animals are widely distributed in
timber stands, but primarily concentrated in mesic sites such as river
banks, spring areas, meadows, and other breaks in the forest canopy
where ground vegetation provides ample forage. Openings created by
harvest or wildfire, and the successional vegetation that follows,
improve gopher habitat. Although quantitative data are lacking, it
appears that substantial gopher populations can become established on
these areas in 2 to 3 years. Since the current trend is to plant or
seed soon after the forest has been opened, gopher densities often are
high when seedlings are young and most vulnerable. On some areas it
has been noted that establishment of brush is accompanied by a
reduction in forb and grass cover and in pocket gopher density.
However, this natural or successional process is slow, and tree stocks
often are severely depleted before brush becomes a dominant factor.

Types of damage

The two most common forms of tree damage by gophers are root
pruning and a combination of stem girdling and clipping. Stems of
small seedlings (basal diameters of 1/2 inch or less) are cut into two
or more sections. Seedlings are frequently clipped at or near ground
level and the roots or the stems are taken. Gophers also remove entire
seedlings and leave only burrows or plugged holes as evidence. Root
pruning and girdling of small seedlings occur year-round but are most
frequent in winter.

Root pruning on larger seedlings and saplings also occurs year-
round. The seasonal frequency has not been determined, primarily
because damage generally does not become evident until long after the
trees have been injured. In addition, some trees probably incur damage
over a period of several years. Root-pruned trees are detected when
they begin to tilt or change color.

Clipping and girdling on larger trees occurs primarily under snow
cover. Logically, this damage is more prevalent in areas where heavy
snowpacks persist.. Girdling is often complete, leaving white stalks
that are easily spotted in spring. Extensive winter girdling has been
observed on the Dugout Lake burn west of Sisters, Ore., and the
Johns-Manville clearcuts near the east border of Crater Lake National
Park. Girdling at heights above 7 feet has been observed on lodgepole
pine at the Dugout Lake burn.

Other types of tree damage caused by gophers include root exposure
by burrowing (Tevis, 1956) and burying of seedlings by winter casts or
mounds (Kuck, 1969). It seems likely that root exposure would most
often occur in conjunction with root gnawing and girdling. Only very
small seedlings, probably resulting from natural or artificial seedfall,
would be damaged by casts or mounds. This latter type of damage might
be offset by the favorable seedbeds created by gopher soil disturbances
(Tevis, 1956; Larrison, 1942). Root exposure and burying usually are
of minor importance in comparison with other types of damage.

An indirect effect of pocket gophers on ponderosa pine was
reported by Moore (1943) . He concluded that lack of natural
reproduction in forest openings of the Ochoco National Forest was due
to seed foraging by white- footed deer mice (Peromyscus spp.) using
gopher burrows as shelter. He felt that mice were less efficient in
collecting seed on areas where gophers had been removed.

Significance of damage

Factors relating to pocket gophers and tree damage are not well
understood, although it is known that severity of damage varies
considerably with habitat type, weather conditions, and gopher
population fluctuations. Dingle (1956) reported losses of 12 percent
in 1 year and 30 percent in 2 or 3 years on ponderosa pine plantations
in eastern Washington. Hermann and Thomas (1963) recorded substantial
gopher losses in ponderosa pine over a 10-year period on an Oregon
plantation. More recent investigations by G.L. Crouch (USFS Pacific
Northwest Forest and Range Experiment Station, personal communication)
and ourselves on Cave Mountain burn in south-central Oregon have
indicated that annual seedling mortality on plantations in the
ponderosa pine zone might vary from 5 to 50 percent. Our studies at
Dugout Lake burn, at about 5,000-feet elevation in a lodgepole-ponderosa
pine transition zone, indicate the damage potential in heavy snowfall
areas. In 1 year, gophers destroyed 67 percent of the planted ponderosa
pine seedlings on two 20-acre study units, and approximately 92 percent
of that mortality occurred between October and June.

The only available published data on lodgepole pine damage were
obtained from a regeneration study in western Colorado. Ronco (1967)
found that gophers killed from about 3 to 30 percent of the lodgepole
pine seedlings on his plots each winter. Summer mortality averaged
near 1 percent. In the same study, gopher-caused mortality to
Engelmann spruce (Picea engelmannii) seedlings varied from zero to
about 25 percent over winter and averaged less than 1 percent during
summer. A later study by Ronco (1970) revealed that gophers caused
from 4 to 54 percent annual mortality of spruce seedlings during a
5-year period.

Economics

The importance of gopher damage in the Northwest generally has
been expressed in terms of geographic distribution or an arbitrary
ranking among other types of wildlife damage. The lack of sufficient
damage information from throughout the region precludes a true economic
analysis. However, there are records for some plantations that roughly
indicate the economic impact of pocket gophers on forest land.

The history of Cave Mountain burn illustrates the reforestation
losses that can occur on gopher-occupied habitat. A wildfire in 1959
was followed by ponderosa pine plantings in 1961, 1962, and 1963; by
1965 the 1,500- acre plantation was considered a failure. Pocket
gophers were judged to be the single greatest loss factor, although
weather, disease, domestic livestock, and other wildlife certainly were
responsible for substantial losses. Since 1965, gopher control
(baiting) has been largely unsuccessful. Economic losses to date
include approximately $200,000 in planting costs plus an annual $9,000
loss of estimated growth potential (450 thousand board feet per year)
(Canutt, 1970).

Noteworthy losses can also occur on smaller plantations. For
example, the 170-acre Dugout Lake burn was first planted in 1964, and
by 1968 the stocking had been virtually eliminated. Gophers are
believed to have been a major cauae of the failure, and our current
studies support that conclusion. The lost investment of the first
planting totaled $15,000 (planting plus animal damage control). The
burn was replanted in 1969, and success to date has been marginal
because of weather factors and animal damage. The total cost of the
second planting has reached about $14,000; this includes about $2,000
for one animal repellent treatment to prevent deer browsing and roughly
$3,500 for two baiting operations to control gophers (D. Rowe, Sisters
Ranger District, personal communication).

BIOLOGY

Control of animal damage is most effective when based on sound
ecological principles. As Canutt (1970) pointed out, there is a need
for basic ecologic information relevant to gophers and forest
management. Control work on forest land currently is based on pocket
gopher research related to range and agricultural problems. Continued
development and improvement of control methods will depend on research
directly applicable to reforestation problems. This section is
included to expose some of the factors and problems of gopher control
and to provide a foundation for future research specific to the forest
damage problem.

The following is a general summary of the biology of the genus
Thomomys , and reference to specific populations is not intended. The
genus is remarkably adaptable, as indicated by its wide geographical
and ecological distribution; certain characteristics will differ
importantly even between local populations. This inherent variability
of gopher populations is a major problem in management of the animal
(Crouch, 1942).

Taxonomy and distribution

Ingles (1965) lists six species of Thomomys occurring in
Washington, Oregon, and California. The northern and mazama pocket
gophers (T. talpoides and T_. mazama) are widely distributed from the
Canadian border to northeastern California and are probably the two
species most common in the presently recognized damage areas. They are
virtually indistinguishable by external characteristics. The Botta
gopher (T_. bottae) is found throughout almost all of California and
extends into southwestern Oregon. The mountain pocket gopher (J_.
monticola) in east-central California and the Townsend gopher (T.
townsendii) in northeast California and southeast Oregon have more
limited distribution. The large Camas pocket gopher (J_. bulbivorus)
is confined to the Willamette Valley in Oregon and is of little concern
to foresters.

General habits

Gophers occupy burrow systems that provide shelter and access to
forage. The systems consist of runways 4 to 18 inches below the ground
surface. Side tunnels off the main runways are used as exits from the
system and for deposition of soil, debris, excess food, and feces.
Larger chambers are used for nest sites and food storage. Moore and
Reid (1951) found that burrow systems may contain more than one nest

cavity, and reported nests down to 5 feet below the surface. The
burrow system is a closely regulated microenvironment, and the gopher
will generally plug any openings in the system within 48 hours — often
within 24 hours. This plugging trait of gophers can be used to
evaluate the success of control operations (Miller, 1953; Richens,
1967; Barnes, Martin, and Tietjen, 1970).

The typical horseshoe-shaped mounds pushed up by gophers are the
result of soil excavated as they extend and repair their burrow systems.
Mound-building is most common in late summer and fall when young-of-
the-year are establishing burrow complexes and older animals are
enlarging systems in preparation for winter. It is during this period
that the above-ground signs of activity can be counted to estimate
gopher abundance (Richens, 1965; Reid, Hansen, and Ward, 1966). A
more difficult sign to detect is the small circle of disturbed soil at
the ground surface, commonly known as an earth plug. These plugs are
usually formed where gophers have emerged to forage and plugged the
hole upon re-entry. In spring and early summer, plugs may be the only
soil indicators of gopher activity.

In winter, gophers extend their systems into the snow, apparently
to facilitate their search for food. Later, excess soil is pushed into
these snow burrows to create the ribbonlike "winter casts" that become
evident as the snow melts. Since these casts indicate winter activity,
they also pinpoint areas where damage can be expected. Winter casts
should not be confused with the surface ridges created by moles
(Talpidae) .

Gophers are solitary animals except during the breeding season and
when females are rearing young. During most of the year, each system
serves as both the territory and the home range of an individual gopher.
After the young have dispersed and established their own burrow systems,
territories are thought to remain stable and mutually exclusive until
the following spring breeding season (Hansen and Miller, 1959). Both
Tryon (1947) and Ingles (1965:206-211) reported that gophers vigorously
defend their territories against others of their own kind.

Reproduction

The time and length of the breeding season of Thomomys apparently
is quite variable throughout its range. Miller (1946) summarized a
number of reports on breeding data in the Northwest and concluded that
the breeding season is limited to the spring months in the northern
portions and at higher elevations, but might extend from fall through
spring in southern localities. Continuing, he stated that the number
of litters per year can vary from one to three. Although Wight (1930)

and Horn (1923) documented two litters per year in eastern Oregon,
single litters probably are most common east of the Cascade summit
(Scheffer, 1931). The number of young per litter can range from 2 to
12 (Ingles, 1965; Colorado Cooperative Pocket Gopher Project Technical
Committee, 1960) ; average litter sizes generally range from 3 to 7
(Miller, 1946; Tryon, 1947; Moore and Reid, 1951; Hansen, 1960). The
gestation period is reported as approximately 19 days (Schramm, 1961;
Ingles, 1965).

Populations

Pocket gopher populations are dynamic and, according to Aldous
(1957), exhibit random fluctuations. Rapid natural die-offs have been
reported by Howard (1961) and Hansen (1962). In Colorado, Reid, Hansen,
and Ward (1966) found gopher densities ranging from 3 to 34 per acre,
and in Utah, Richens (1965) reported from 12.5 to 39.3 animals per acre
under varying degrees of control. The annual turnover in gopher
populations is high; juveniles (1 year old or less) may account for
more than 75 percent of the population at peak levels of the year
(Tryon, 1947; Hansen, 1960).

Food habits

A number of studies have investigated the food habits of Thomomys
on rangelands, including those reported by Aldous (1951), Moore and
Reid (1951), Ward and Keith (1962), Hansen and Ward (1966), and Tietjen
et al. (1967). In summary, there is a general preference for forbs
over grasses. Consumption of woody plants generally occurs when more
preferred species are unavailable. Above-ground parts of plants are
taken with greatest frequency in spring and summer, while below-ground
portions become more important during winter. Keith, Hansen, and Ward
(1959) demonstrated that gopher feeding habits will change when
vegetative composition is altered. However, as Tietjen et al. (1967)
pointed out, a marginal diet reduces the ability of gophers to survive,
and reduced populations are a likely result.

Animal associations

A variety of animals may occupy active or abandoned gopher burrows
and must be considered when control is anticipated. Some of the most
common associates of gophers are deer mice, pocket mice (Perognathus
spp.), kangaroo rats (Dipodomys spp.), voles (Microtus spp.), ground
squirrels (Citellus spp.), and weasels (Mustela spp.). In addition,
numerous reptiles and amphibians have been observed or captured in
gopher runways (Howard and Childs, 1959; Vaughn, 1961; Hansen and Ward,
1966).

Population regulators

Several natural factors reduce pocket gopher numbers, although it
appears that very few significantly affect ultimate population levels.
Howard and Childs (1959) suggested that territoriality might have an
influence, but felt that it was subordinate to food and cover. The
effect of parasitism also has been considered insignificant (Tryon,
1947). Predation is another factor to consider. The major predators
include weasels, coyotes (Canis latrans) , bobcats (Lynx rufus) , badgers
(Taxidae taxus) , great horned owls (Bubo virginianus) , great grey owls
(Strix robulosa) , barn owls (Tyto alba) , hawks (Buteo spp.), and snakes
(Tryon, 1947; Moore and Reid, 1951; Howard and Childs, 1959; Hansen and
Ward, 1966). Dispersing juveniles probably are the most vulnerable to
predation, since they have no established burrow systems and sometimes
travel above ground (Howard and Childs, 1959). Tryon (1947) believed
that gophers were as easily preyed upon as other rodent species, but
felt the overall effect of predation on populations was small. Hansen
and Ward (1966) concurred, adding that the effect of predation was to
slow the rate of increase rather than prevent a population peak.

Weather and vegetation probably have the greatest effect on
population levels. Hansen and Ward (1966) believed that the depth and
water content of snow affected the survival of young and thus exerted
an influence on population density. They indicated that the quantity
and quality of forage, as affected by characteristics of the growing
season (length, temperatures, moisture) were also important. Moore and
Reid (1951) reported that a rise in the water table could cause
significant mortality.

DAMAGE CONTROL METHODS

Basic approaches

Direct control of damaging animals is the most widely used
approach to alleviate gopher damage, and trapping and poisoning are the
techniques most often employed. Other methods that have been used
include flooding, fumigation, shooting (Crouch, 1942), and exclosures
and caging (Dixon, 1922; Keith, 1961). In addition, reproductive
inhibitors (Hippiy, 1969) and repellents (D.E. Howell, Oklahoma State
University, personal communication) appear promising but need further
investigation. The introduction of disease also has been suggested,
but Scheffer (1931) and Crouch (1942) were pessimistic of the idea.

Indirect or ecological control involves habitat modification,
usually to make the target area less suitable for gopher occupation.
On range and agricultural lands this can be accomplished with

herbicides or crop rotation (Colorado Cooperative Pocket Gopher Project
Technical Committee, 1960). Application of 2,4-D herbicide in Colorado
reduced gopher populations by 80 to 90 percent, and repopulation of
treated areas has in general been slow. Success was attributed to
decreased forb production (Keith, Hansen, and Ward, 1959; Hansen and
Ward, 1966; Tietjen et al., 1967).

Other possibilities of habitat manipulation that have been
advanced include the introduction of plant species or buffer foods that
would divert feeding from the valued crop. Storer (1945) suggested
that gophers could be controlled by destroying their burrows.

Control of damage on forest lands

Trapping. — Trapping has been used on forest lands to a limited

extent. It is extremely slow and time consuming and is practical only

on small areas or as a supplement to other forms of damage control.
Consequently, there appear to be few forest situations where trapping

would be feasible. Several types of traps are available, although the

Macabee kill-trap probably is the most popular (Crouch, 1942; Colorado

Cooperative Pocket Gopher Project Technical Committee, 1960).

Hand-baiting, mechanical bait dispenser. — Baiting by hand is a
much faster operation than trapping and is safe and effective when done
properly. The technique requires three steps: (1) location of a
runway by probing or excavation; (2) placement of the toxic bait in the
burrow by hand, spoon, or other appropriate means; and (3) covering of
the exposed burrow. Specific procedures and types of bait for this
technique are well documented (Crouch, 1942; Moore and Reid, 1951; U.S.
Fish and Wildlife Service, 1952; Colorado Cooperative Pocket Gopher
Project Technical Committee, 1960). Hand-baiting has been used on
forest plantations, but its effectiveness has not been evaluated.
Canutt (1970) cited a report from the Umatilla National Forest in
northeastern Oregon that estimated the cost of hand-baiting at less
than $6 per acre. He equated this figure with the cost of treating
approximately 5 acres of densely populated agricultural land.

An improvement over hand-baiting is the mechanical bait dispenser —
it is faster and just as efficient (Hansen, 1956) . This device allows
an operator to locate (probe) a runway and deposit bait in the same
operation. With this device Canutt (19 70) was able to dispense bait at
the rate of 1 acre per hour.

Hand-baiting or the bait dispenser may be useful for control on
small acreages or with isolated populations, or to maintain control and
prevent invasion. However, use of the techniques on large plantations

might be impractical. There are indications that efficiency decreases
rapidly on areas exceeding 5 acres (H.P. Tietjen, Denver Wildlife
Research Center, personal communication) .

Burrow-builder . — The introduction of the burrow-builder in the
late 1950's was an important development in pocket gopher control. In
principle, the burrow-builder creates an artificial burrow, by means of
a subsurface torpedo, and in the same operation places bait in the
burrow. Prototypes were developed almost simultaneously in Colorado
(Ward and Hansen, 1960) and California (Kepner et al., 1961).
Subsequent reports have detailed construction methods, modifications,
and evaluation techniques for use in agricultural areas (Colorado
Cooperative Pocket Gopher Project Technical Committee, 1960; Sargeant
and Peterson, 1964; Marsh and Cummings, 1968). A reinforced model,
called the forest-land burrow-builder, was developed for use in more
rugged forest terrain (Canutt, 1969b) and has been successfully used to
apply toxic oat baits to reduce gopher populations on forest
plantations (Packham, 1969; Barnes, Martin, and Tietjen, 1970).

The efficiency of the burrow-builder depends on a number of
variables, including topography, soil texture, soil moisture, and
obstructions. Accordingly, Canutt (1970) estimated that the machine
could be used to treat from 2.5 to 6 acres per hour. He reported cost
estimates of $2.65 and $7.35 per acre for two projects on the Winema
National Forest. Packham (1969) estimated that approximately 28 acres
could be treated per day at a cost of about $6 per acre.

Analysis of baiting. — Many benefits have been derived from pocket
gopher baiting programs, and the technique is the most common in use
today. However, baiting has limitations that should be recognized.
First, treatment must be done expertly to assure effectiveness, since
mortality of less than 75 percent generally is no greater than would
occur naturally. Second, even effective baiting provides only temporary
relief. This is an important concept, since tree protection may be
necessary for 10 years or more. Complete reduction rarely, if ever,
occurs, and offspring of survivors will quickly repopulate unoccupied
systems. In many areas, invasion from uncontrolled populations can
also be expected (Storer, 1945). Not only will an abundance of
unoccupied systems likely increase survival of dispersing young, but
reduced population densities might temporarily stimulate reproduction.
Studies by Moore and Reid (1951), Richens (1965), and Julander, Low,
and Morris (1969) have demonstrated that persistent baiting is
necessary on rangeland to maintain control. This same problem has
become apparent on forest lands, where we have noted reinvasion 3 to 4
months after treatment.

An equally important consideration is that the pesticides and
baits currently in use are not necessarily specific to gophers, and
nontarget wildlife may be in jeopardy of poisoning. Secondary hazards
to predator species appear to be lessened by the tendency of gophers to
die underground (Ward et al., 1967), but could still be a problem in
some areas.

Use of the burrow-builder on forest lands introduces additional
factors not encountered with hand-baiting. Initial site preparation
often is desirable or even necessary to make pathways for the machine.
The additional cost probably is not important considering the machine's
efficiency, but the resulting soil disturbance can promote forb
development and increase the potential for gopher repopulation. In
addition, the artificial burrows may persist a year or more, and the
possibility that they expedite reinvasion should not be discounted.
One of the most critical factors governing the use of the burrow-
builder is soil moisture. In dry climates, where most gopher-
reforestation problems occur, use of the machine is restricted to
periods in spring and fall. Moisture requirements can usually be met
in spring, but reinvasion will necessitate fall treatment in most
cases. Fall moisture is unpredictable and at higher elevations may
first appear in sufficient quantity as snow. The necessity of last-
minute scheduling places an added burden on management.

Operational use of the burrow-builder on forest land is a recent
development; the significance of these factors and the effectiveness of
long-term burrow-builder treatment are unknown. Nevertheless, burrow-
builder treatment, where usable, currently is the best technique for
reducing tree damage by pocket gophers.

RESEARCH- NEEDS

The need for continued pocket gopher research on timber-producing
lands is apparent. The following outline identifies important research
problems and is intended to serve as a guide to interested researchers
for cooperative and complementary efforts.

Control research

A. Burrow-builder evaluation. — Since the burrow-builder presently
is the most practical method for baiting gophers, it is essential that
the technique be evaluated on a long-term operational basis.

B. Control mortality factors. — Although methods exist for
estimating population reduction, specific effects of baiting — where
mortality occurs, how long before mortality occurs, and how long bait

10

is available and effective — are not known. Answers to these questions
could suggest ways to improve baiting effectiveness and also indicate
potential secondary hazards and other sources of nontarget mortality.

C. Habitat manipulation. — Probably the greatest potential for
effective, long-lasting control is through habitat manipulation.
Forage appears to be one of the most critical factors determining
population levels, and high priority should be given to the development
of safe and efficient methods of limiting production of essential
gopher foods. The effects of herbicides, brush, introduced plant
species, and forest management practices need thorough investigation.

D. Repopulation. — Population recovery on treated areas has two
sources — reproduction by survivors and invasion from adjacent areas.
The impact of the former is dependent on control efficiency, further
stressing the need to investigate control success and related factors.
The invasion problem is particularly difficult, since it usually
originates from populations on land that is not accessible to machine
baiting or is not managed for timber production. Invasion on small
plantations (less than 50 acres) probably can be countered only by
periodic treatment. Buffer strips might effectively restrict invasion
on large plantations, but more data are needed on distances and other
factors relating to the time it takes gophers to invade unoccupied
habitat. Our studies so far suggest a minimum distance of about 1,000
feet per year for moderate to high gopher populations .

E. Evaluation of new animal damage control agents . — Various
agencies continue testing potential damage control agents that may
prove to be more effective, more specific, or safer to man and
nontarget wildlife. Agencies or companies concerned with pocket gopher
damage should be prepared to participate in the evaluation of new
control agents that warrant field testing.

F. Evaluation of hand-baiting. — There are areas that are too
extensive for trapping and too rocky or inaccessible for the burrow-
builder where baiting by hand or with a bait dispenser is probably the
only practical means of control. Studies should be conducted to
evaluate the technique and develop procedures for maximum efficiency.

G. Winter baiting. — In 1970, we conducted a preliminary study of
winter bait acceptance. Results were negative, but winter baiting
remains a possibility and should receive further study.

H. Repellents . — Repellents have been used successfully to protect
buried cable (Tigner and Landstrom, 1968) and fruit trees (D.E. Howell,
Oklahoma State University, personal communication) from gopher damage

11

and have potential for tree protection on forest land. Studies are
needed to determine the reaction of gophers to various repellents and
also the effects of repellents on tree survival and growth.

I. Secondary hazards, nontarget mortality. — There is increasing
demand for control programs that are specific to the target animals.
Studies are needed to determine the direct and indirect toxicity of
both traditional and experimental toxicants to predators and other
animal associates of gophers.

J. Foam or grease carriers, grooming inhibitors, long- lasting ,
baits ♦ — Toxic foam or grease placed in artificial burrows might provide
more lasting control than bait. Development of a bait that resists
breakdown has also been suggested. Another idea has been the inclusion
of wetting agents or tacky substances in the soil or burrows to inhibit
grooming and cause gophers to avoid certain areas, abandon their
systems, or become less able to survive. The feasibility of these
ideas should be investigated in the laboratory.

K. Mechanical barriers. — Although enclosing trees in individual
cages or area exclosures probably would not be economical in most
forest situations, net tubing or repellent-coated tubing might be
practical. Net tubing has shown promise as a means of reducing
seedling damage by black-tailed deer (Odocoileus hemionus) and snowshoe
hare (Lepus americanus) (Campbell, 1969).

L. Reproductive inhibitors. — The development of effective methods
for controlling reproduction is complex. Major difficulties with
gophers would be the long breeding season, variation in onset and
cessation of breeding (latitude and altitude factors) , and breeding
under snow cover. However, a specific and effective reproductive
inhibitor might be more acceptable to the public than poison bait.

Ecological research

A. Population. — Population density, sex and age composition in
various habitats, the relationship of population density to tree
damage, and the response of populations to land management are
important data needed. They would indicate habitat requirements and
limiting factors, be useful for evaluating control, and be valuable
for predicting future problem areas.

B. Food habits. — Knowledge of the preferred and essential foods
of pocket gophers in lodgepole and ponderosa pine habitats is
especially important in the development of habitat control methods.
There is currently no quantitative information available on the feeding
habits of gophers as they relate to reforestation.

12

C. Seasonal activity, movements. — The effectiveness of control is
dependent on many factors, such as timing, application rate, spacing,
size of treatment area, and size of buffer strips. These factors
cannot be given rational consideration without knowledge of the
seasonal movement and activity patterns of adult and juvenile animals.

D. Reproduction. — Data on breeding season, litter size, and
number of litters per year have utility for evaluating long-range
effects of control, especially where the control methods alter the
habitat. This information also is needed for development of
reproductive inhibitors.

Behavioral research

Studies of food-handling and grooming behavior, factors of food
selection, and the effects of temperature and moisture on feeding
behavior could reveal important relationships not detectable under
field conditions. In addition, knowledge of the response of individual
animals to introduced substances will be necessary in evaluating
several techniques that have been proposed (toxic foam, tacky
substances) .

Damage appraisal

The existence of a pocket gopher-reforestation problem is evident,
but quantitative data on gopher damage in different habitats are
lacking. Detailed damage surveys are needed throughout the Northwest.
Although research agencies have been responsible for gathering most of
the damage information now available, the opportunity for collection of
information at the local management level should be considered.

13

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14

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15

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16

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17

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18

As the Nation's principal conservation agency, the Department
of the Interior has basic responsibilities for water, fish, wildlife,
mineral, land, park, and recreational resources. Indian and Ter-
ritorial affairs are other major concerns of this department of
natural resources.

The Department works to assure the wisest choice in managing
all our resources so that each shall make its full contribution to
a better United States now and in the future.

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FfSH AND WILDLIFE SERVICE

BUREAU OF SPORT FISHERIES AND WILDLIFE

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