RAPTOR RESEARCH Raptor Research Foundation, Inc. Provo, Utah, U.5.A. Fall 1981 RAPTOR RESEARCH Volume 15, Number 3, Pages 65-96 CONTENTS SCIENTIFIC PAPERS Leslie Brown— Some Memories 65 Captive Propagation of Bald Eagles at Patuxent Wildlife Research Center and Introductions into the Wild, 1976-80— Stanley N. Wiemeyer 68 Artificial Burrows Provide New Insight into Burrowing Owl Nesting Biology— Charles J. Henny and Lawrence J. Blus 82 Harrier Nest-Site Vegetation— Frances Hamerstrom and Mark Kopeny 86 Have the Eggs of the Orange-breasted Falcon ( Falco deiroleucus ) Been Described?— Douglas A. Boyce, Jr., and Lloyd F. Kiff 89 Merlins as Nest Predators— L. Henry Kermott 94 BOOK REVIEW 95 ANNOUNCEMENTS .96 RAPTOR RESEARCH Published Quarterly by the Raptor Research Foundation, Inc. Editor Dr. Clayton M. White, Dept, of Zoology, 161 WIDB, Brigham Young University, Provo, Utah 84602 Editorial Assistant Elise V. Schmidt, 136 WIDB, Brigham Young University, Provo, Utah 84602 Editorial Staff Dr. Frederick N. Hamerstrom, Jr. (Principal Referee) Dr. Byron E. Harrell (Editor of Special Publications) The Raptor Research Foundation, Inc., welcomes original articles and short notes concerning both diurnal and nocturnal birds of prey. Send all papers and notes for publication and all books for review to the Editor. Most longer articles (20 or more typeset pages) will be considered for publication in Raptor Re- search Reports, a special series for lengthy and significant contributions contain- ing new knowledge about birds or new interpretations of existing knowledge (e.g., review articles). However, authors who pay page costs (currently $36.00 per page) will expedite publication of their papers, including lengthy articles, by ensuring their inclusion in the earliest possible issue of Raptor Research. Such papers will be in addition to the usual, planned size of Raptor Research whenever feasible. SUGGESTIONS TO CONTRIBUTORS: Submit all manuscripts in duplicate, typewritten, double spaced (all parts), on one side of 8V2 X 11 inch paper, with at least 1 inch margins all around. Drawings should be done in India ink and lettered by lettering guide or the equivalent, if possible. Photographs should be on glossy paper. Avoid footnotes. Provide an abstract for all papers more than four double-spaced typed pages in length, not to exceed 5 percent of the total length of the paper. Keep tables at a minimum, and do not duplicate material in either the text or graphs. For advice concerning format refer to the Council of Biological Editors’ Style Manual for Biological Journals or to previous issues of Raptor Research. Proofs will be sent to senior authors only. Major changes in proofs will be charged to the authors. Reprints should be ordered when proofs are returned. 1981 MEMBERSHIP: (If paid prior to 15 February of each year) $11— U.S. student $13— U.S. regular and foreign student $13 and $15 after 15 February. LESLIE BROWN-SOME MEMORIES 1 Leslie Brown, who was felled by a heart attack at his home near Nairobi in early Au- gust, had become the world’s best known expert on birds of prey. How does one write an obituary on such a remarkable man? We could give an inventory of his achieve- ments, but these are well-known to all of us and they are well summarized in the cita- tion accompanying the award of the medal of the British Ornithologists’ Union in 1970 (see Ibis, 112: 427-428). Not that he rested on his laurels after that, and the last ten years of his life were some of his most productive, despite ill health. Leslie published half a dozen books on birds of prey and more are to come. He had underway, in joint authorship, books on the Golden Eagle and on the owls of Europe. More technical aspects were dealt with in numerous papers in periodicals. I (D.A.) prize most highly Leslie’s first raptor book, titled simply Eagles (1955) based on research at his beloved Eagle Hill, where about a dozen species bred, not to mention Peregrines. Nor was Brown’s work confined to raptors. He did basic research on, for example, the Lesser Flamingo ( Mystery of the Flamingoes, 1959), even learning to pilot a plane so he could locate and map its colonies on the sulfurous flats of Lake Natron, where he was once mired and nearly lost his life. He wrote the volume on Africa in the Continent We Live On series, perhaps the best of the lot, and even found time for a book on coral reef fishes as observed near his hide-away on the Kenya coast. How did Leslie Brown, who, after all, was a busy colonial officer in the agricultural service into middle age, accomplish so much? Partly by an unremitting capacity for toil; partly because his mind, while without the superficial flashes of brilliance, was yet so or- ganized and retentive that he could write page after page of manuscript ready for the printer almost without revision. Physically Brown was a big strapping Scotchman with hair inclined to the reddish and with a bristly beard— the sort of figure one might have found at the prow of a Vik- ing warship. And indeed he was a bit of a rebel. His early experiences in poaching salmon and duck on Scottish estates were hair raising. Leslie often drew a small figure of a cobra with raised hood next to his signature on a letter; the message, just as with the rattlesnake in colonial America, was “don’t tread on me.” In financial matters, however, he was a typical conservative Scot. I (P.S.) learned a great deal about Leslie in Scotland. He was an accomplished poacher, but he only poached because it added spice to the chase. I wonder how many can kill a cock pheasant in flight with a catapult? He loved his food and was very knowledgeable about wines. He had the gift of tongues and in later years I remember his impatience with me when I could not read a paper in Spanish on the Booted Eagle— “Why don’t you learn it? I did.” He loved classical music. His general knowledge ex- ceeded that of any man I know. As a raconteur he had no peer. How I wish I had space to repeat some of his hilarious stories. Perhaps his greatest ability was to commit his thoughts directly to paper in clear readable prose. It was as if he carried the whole plan of a book in his head. Few people can produce a first draft that requires almost no alter- ation. He could. Leslie suffered from more than his share of physical afflictions: terrible asthma, two operations for skin cancer, and cardiac attacks. All this did not seem to slow him down— if anything the reverse— but it did make him a trifle irritable at times. He dismissed art- ists, no matter how talented, who did not deliver as many plates as they promised as 65 Raptor Research 15(3):65-67 66 RAPTOR RESEARCH Vol. 15, No. 3 “hopeless dilettantes.” Nor did he make any concessions as to food and drink. He once told me that if I (D.A.) ate a “decent breakfast” I wouldn’t start glancing at the clock about 11:30 to see if it was lunch time. For Leslie a “decent” breakfast was perhaps 3 eggs, a large helping of ham, 3 or 4 slices of toast heavily spread with sweet butter and jam, all washed down with an ample amount of coffee, by preference laced with heavy cream. Leslie Brown also found time to do consulting work for UNESCO and other agencies, especially in Ethiopia. I (D.A.) conclude with his final experience in that country some 6 or 7 years ago, which gives a little further insight into Brown’s character. He was mak- ing an aerial ecological survey in the company of 4 or 6 Swedes, those most tireless of international do-gooders, when, as Leslie put it, “The bloody incompetent fool of a pi- lot” became disoriented and flew off into Somalia, then, and perhaps still, at war with Ethiopia. When nearly out of fuel they saw a tiny airstrip with a village and put down. Arrest came immediately and it was about 5 weeks before the party was released. The others in the group literally worried themselves sick but Leslie, who as the only English- man was in the greatest danger, strode up to their captors and in effect said: “If you’re going to shoot me, get it over with, if not give me some pencils and paper.” He bluffed them into doing so, and by the time they were released had written the entire text of a charming little book, recently published, each chapter of which relates to an unusual ex- perience Leslie had with one species or another of animal— ranging from the chim- panzee to the huge whale-shark which one day swam around and beneath his tiny boat as he drifted off the Kenya coast. In his last year Leslie was a very sick man, but he continued to drive himself relent- lessly. He died just before his book on the African Fish Eagle appeared and he was pre- paring a major work on the birds of Africa. At the end it was almost as if he had the words of Dylan Thomas in mind: “Do not go gentle into that good night. Rage, rage against the dying of the light.” Leslie Brown— truly we shall not gaze upon his like again. Fall 1981 Leslie Brown 67 'Editor’s note. This memorial is the combined work of Dean Amadon and Peter Steyn. The photos were sup- plied by Walter R. Spofford. I have taken excerpts from Steyn ’s article, published in Bokmakerie 32:86, 1980 with permission of Steyn and the Editor of Bokmakerie. We are grateful to these men for their knowledge of and camaraderie with Leslie and their shared experiences. CAPTIVE PROPAGATION OF BALD EAGLES AT PATUXENT WILDLIFE RESEARCH CENTER AND INTRODUCTIONS INTO THE WILD, 1976-80 by Stanley N. Wiemeyer U.S. Fish and Wildlife Service Patuxent Wildlife Research Center Laurel, Maryland 20811 Abstract One to 5 pairs of the Bald Eagle ( Haliaeetus leucocephalus ) were in the captive prop- agation project at Patuxent Wildlife Research Center during 1976-80. Four pairs pro- duced viable eggs or young by natural mating in one or more years. Pairs laid second clutches 9 of 11 times when their first clutches were collected within 8 days of clutch completion. Sixty-nine percent of fertile artificially incubated eggs hatched; 93% of fer- tile parent-incubated eggs hatched. Eleven eaglets from artificially incubated eggs were hand reared. Age of birds at the time they were acquired from the wild was not a factor in their reproductive success. Ten hand-reared and 2 parent-reared young were fostered to adult Bald Eagles at ac- tive wild nests; 11 were accepted and survived. Eleven parent-reared young were pro- vided to hacking projects. Egg transplants to wild nests were conducted, but dis- continued because of poor success. Double clutching of captive pairs has not resulted in substantially increased numbers of eaglets. Additional research is needed in artificial in- cubation, artificial insemination, and nutrition and care of hand-reared eaglets. Introduction Bald Eagles have been maintained in captivity, primarily in zoos, for many years but few attempts have been made to propagate them. The lack of interest in breeding this species in captivity probably relates to its infrequent use in falconry. Most captive prop- agation attempts before 1973 were summarized by Hancock (1973). Other successful propagation attempts have also been reported (Anonymous 1969, Wellenkamp 1973, Johnson and Gayden 1975, Maestrelli and Wiemeyer 1975, Minnemann 1976). These breeding attempts resulted in the production of less than 30 eaglets, most of which were produced at the Buffalo Zoo between 1910-16 (Annonymous 1909, Hancock 1973) and by a pair held by an individual in Toledo, Ohio in the 1880’s (Hulce 1886, 1887). The first successful captive breeding of Bald Eagles at Patuxent Wildlife Research Center, Laurel, Maryland was in 1973 when one pair produced two eaglets (Maestrelli and Wiemeyer 1975). This pair produced three young from a single clutch in 1974 and four young from two clutches in 1975, two by hand rearing and two by parent rearing (Wiemeyer, unpublished). The pair (male from Alaska; female from Alabama) was sepa- rated following the 1975 breeding season; new mates were of more similar geographic origin. Limited information on the reproductive behavior of this pair and one additional pair, both of which were present in 1973, was reported by Gerrard et al. (1979). The purposes of this paper are to present information on procedures used and results obtained in propagating Bald Eagles at the Center, and in introducing eggs and eaglets into the wild for the years 1976-80. The primary purpose of this project was to pro- 68 Raptor Research 15(3):68-82 Fall 1981 Wiemeyer — Propagation of Bald Eagles 69 duce eggs and eaglets for supplementing production in depressed wild populations and for reintroduction attempts where Bald Eagles have been extirpated. This breeding proj- ect was funded by the Environmental Contaminants Evaluation Program of the U.S. Fish and Wildlife Service. It was transferred to the Endangered Wildlife Research Pro- gram in October 1980. Source of Birds and Age at Acquisition The eagles were acquired from a number of sources (Table 1). Some individuals were obtained through zoos; their histories were often incomplete. Others that had been taken from the wild following sickness or injury were obtained from law enforcement authorities. All birds were capable of flying about in the breeding pens without difficulty. Table 1. Source and age of Bald Eagles in the breeding project. Original Age When Age When Date State of Acquired Paired Pair Paired Sex 4 Acquisition From Wild b (years) b A 17 Feb. 1976 M Florida Immature 6 + F Alabama ca. 3 years 14 B 28 Feb. 1977 M Alaska large nestling 11 F Wisconsin large nestling 11 C 28 Feb. 1977 M Maine Immature 0 6 + F Minnesota < 1 6 D 20 Oct. 1977 M Florida Nestling? 6 F Florida Nestling or Immature 14 E 23 Jan. 1979 M Alaska < 3 12 + F Michigan Adult 13 + a M = male, F = female. b Some ages based on the time when adult plumage was first obtained in captivity, assuming that it is nor- mally acquired at 4 years. c Originally acquired November 1970. Released in Maryland in January 1973. Found shot and reacquired in Delaware in April 1975. The age of some birds of prey at the time they are taken from the wild has been an important consideration in determining the probability that they will successfully breed in captivity. Falcons taken as large nestlings and raised with congeners have been pro- ductive breeders in captivity, whereas those taken as independent immatures or as adults have done poorly (Cade et al. 1977). Eagles in this project that were obtained as large nestlings, immature independent birds, and as adults have bred successfully. In an- other study, two Bald Eagles taken from the wild as adults laid eggs, incubated and hatched them, but lost both eaglets within 17 days of hatching (Barger 1963). Sex Determination and Pairing Most birds in the breeding project were sexed on the basis of past reproductive per- formance or by laparotomy. The male of pair E was sexed by cloacal examination. The method of sexing eagles with plasma steroid hormones previously used (Dieter 1973) was found to be unreliable. A male and female of similar geographic origin were placed together to form each breeding pair and hereafter are referred to by letter (Table 1). When most pairs were formed alternate choices for mates were unavailable. The male was placed in the breed- 70 RAPTOR RESEARCH Vol. 15, No. 3 ing pen for several days to several weeks in advance of the female. This seemed to lessen early aggression initiated by the female. On 7 December 1979 pair D was separated and removed from the pen. The male pro- duced by pair A in 1976 was introduced into the pen on that date. The female was re- turned to the pen on 12 December. The male was rejected by the female and he was re- moved on 25 January 1980. Her original mate was returned on 28 January. Facilities and Maintenance The pen design (11 X 22 X 5.5 m high) used by our breeding pairs has been de- scribed (Maestrelli and Wiemeyer 1975). Four adjoining pens of this unit were used in one or more of the years 1976-78. A new row of eight adjoining pens of the same design was constructed in 1978 in an area of the Center isolated from human disturbance. The exterior of the pens was cov- ered with 2.5 X 5 cm mesh welded wire and the interior partitions were of 2.5 X 2.5 cm mesh welded wire. Placement of the nest platform, perches, shelter and feeding blocks was the same as in the older pens. A 3.7 X 3.7 m area of corrugated aluminum roofing was placed on the roof of each pen over the nest area. Wood sides, 34 cm high, were added to the nest platforms to help retain nest material. Nests were then filled with sticks, cattails, straw, and pine bark mulch. Sticks and straw were placed on the ground of each pen for the adults to add to the nests. Fresh nesting material was placed in the nests each year. Grass and forbs covered the ground of the pens. Both nesting materials provided to the birds and naturally oc- curring materials were added to the nests by the birds. Woody vegetation and vines in the pens were controlled with herbicides and by mowing. In 1979 and 1980 the new pens 1, 2, 3, 5 and 7 were occupied by Bald Eagle pairs. Pens 4 and 6 were occupied by single 4-year-old Bald Eagles and pen 8 was occupied by two immature Andean Condors ( Vultur gryphus ) in 1979. In 1980, pen 4 was empty and pens 6 and 8 were occupied by immature Andean Condors. Eagles were fed 6 days a week during the non-breeding season and daily during the breeding season. The birds were fed through small wire feeding doors adjacent to each feeding block. The diet consisted of laboratory rats, fish (mostly brackish and saltwater varieties), and 3- to 5-week old chickens. Fish and rats were usually fed three times each week. When chickens were available (primarily before and during the breeding seasons) they were fed one or two times a week in place of other items. Hamsters were occasion- ally substituted for rats and Coturnix quail for chickens. Rodents and fowl were obtained alive, killed with C0 2 and frozen. Fresh fish were obtained and then frozen. Food was thawed as needed. One or more items were placed on each of the two feeding blocks in each pen to avoid conflicts over single items. Leftover food items within reach of feed- ing doors were removed daily. Items out of reach of feeding doors were removed less frequently. Most birds were very defensive during the breeding season, discouraging en- try into the pens for removal of leftover items. A few birds made entry difficult through- out the year. Water was provided in a stainless steel pan. Pans were placed just inside the door of each pen to facilitate removal for cleaning. Pans were cleaned and refilled once or twice a week as needed. The birds frequently bathed in the pans, especially following cleaning. Drinking was observed very infrequently. There was no electrical service to the new pens, therefore the pans were unheated. Water was periodically provided in winter, but rapidly froze during cold weather. Fall 1981 Wiemeyer — Propagation of Bald Eagles 71 The birds were observed with a 30x spotting scope from an elevated blind approx- imately 120 m from the older pens and 67 m from the newer pens. Observations were not conducted on a regular basis and periods seldom exceeded one hour, except in 1980. A mirror over each nest facilitated observations of nest contents from a point immedi- ately in front of each pen. The mirrors were placed so that birds were unlikely to see their reflection. A few birds were observed looking at the mirrors and one bird was seen to briefly attack one mirror on two occasions. Copulation Most copulations that were observed occurred from 6 days before to 3 days following the laying of the first egg of the first clutch. The earliest copulation that was observed occurred 37 days before the laying of the first egg of a first clutch. Three pairs were seen copulating following collection of a first clutch. Most instances occurred before or during the laying of a second clutch. For example, in 1978, copulation by pair B was ob- served three times (3.2 h of observations) 1 day before the laying of the first egg of the second clutch and once on the day of laying, but before the egg was laid. Copulation by this pair Was also observed 4 days following the collection of the second clutch in 1979, after it failed to hatch. Pairs C and E were each seen copulating three or more times fol- lowing the collection of their first clutches in 1980; neither laid a second clutch. Cop- ulation normally occurred at one of the nest perches; pairs A and E were observed cop- ulating on the ground on several occasions. Artificial Insemination In 1980, semen collections were made from three males that were not paired. A modi- fied massage technique described by Gee and Temple (1978) was used. Males were net- ted and then restrained in a standing position with their feet on a log perch. One assist- ant held the legs of the bird and a second held the wings against its body; both assistants faced the rear of the bird. The operator then stroked the bird and manipulated the cloaca. Occasionally ejaculation occurred. Semen was collected from the ventral lip of the cloaca on the lip of a plugged glass funnel or with a propipette attached to a small pipette. The process from stimulation by the operator to collection of the semen was usually accomplished in less than 30 seconds. On 14 March 1980 semen was collected from the male produced by pair A in 1976 and from a crippled southern male. The semen was pooled. The female of pair D was netted, restrained, and the semen deposited into her cloaca, within an hour of collection. Insemination into the oviduct would have been better than into the cloaca, but she was difficult to restrain. She laid the first egg of a second clutch of two eggs (see below) on 21 March. Both eggs failed to hatch and appeared infertile when examined. Repeated inseminations would have been preferable, but were not conducted because of the risk of excessive disturbance to breeding birds in nearby pens during capture of the female. Laying, Incubation and Hatching Dates of laying of the first egg of the first clutch for each pair are given in Table 2. The initiation of laying may have been delayed in some cases by late dates of pair for- mation (Table 1) or late return of pairs to their pens following repairs and rebuilding of nests (early to mid-February in 1976-78). The initiation of egg laying by the female of pair C in 1977 and 1978 also may have been delayed as the result of reproductive activi- ties of pairs in adjacent pens. 72 RAPTOR RESEARCH Vol. 15, No. 3 The time of day of egg laying was noted on two occasions; both occurred between 1530 and 1640. Eggs were laid at a minimum of 2 day intervals. Incubation nearly al- ways began with the laying of the first egg. Many pairs did not stop incubating in the presence of caretakers, making it impossible to determine laying dates of subsequent eggs. The female of pair B laid the first egg of a fertile two egg clutch only 16 days fol- lowing pair formation in 1977. Table 2. Dates of laying of the first egg of the first clutch for females of captive Bald Eagle pairs.® Pair Year 1976 1977 1978 1979 1980 A 23 March 14 March 6 March 2 March 28 February B (22 March) b 16 March 27 February 20 February 3 March C (6 March) 17 April 4 April 12 February 2 February D 27 January 29 January 15 February E (20 March) 26 March 21 February a Initiation of egg laying was delayed by dates of pairing and pen maintenance in some years (see text). Some dates approximate. b Dates in parentheses are for years when the females were not paired. First clutches were collected for artificial incubation (Table 3) from 3 pairs in 1978 and 4 pairs each in 1979 and 1980, approximately 5 to 8 days following clutch com- pletion. Each pair laid a second clutch with two exceptions in 1980 (Table 3). Both members of each pair were normally caught and restrained before the collection of their eggs to prevent attacks upon collectors. Eggs to be artificially incubated were left with the pairs for several days of natural incubation following clutch completion because this has been found to increase the hatchability of wild birds’ eggs that were to be artificially incubated (Cade et at 1977). If collection of first clutch eggs is delayed too long the pairs may not relay. No second clutch was laid by pair A in 1977 following collection of the first clutch about 13 to 16 days following clutch completion. The inter-clutch inter- val (time from collection of the first clutch to laying of the first egg of second clutch) ranged from 18 to 23 days. This interval was similar to the interval between pairing and laying of two pairs (16 days for pair B in 1977 and 18 days for pair D in 1980). Eggs to be artificially incubated were placed in Petersime Model 5 incubators at 37.6° C dry bulb and 30° C wet bulb (about 56% relative humidity), and turned auto- matically every 2 h. (Use of brand names does not imply endorsement by the Federal government.) Eggs were placed on their sides in trays used for duck eggs as modified to hold eagle eggs. It might have been better to place them large end up, but space restric- tions between trays prevented this. No eggs were available to experiment with various temperatures and humidities of artificial incubation, therefore those used may not be optimal. Eggs were placed in the hatching compartment of the incubator when they pipped, and the relative humidity was increased to about 70%, although a higher humidity might have been preferable. Eggs were placed on their sides with pips uppermost. Hatching occurred from 24 to 48 h after pipping. Some eaglets were very carefully helped from the shell if they appeared to not be making any appreciable progress 30 h after pipping. One eaglet in 1979 pipped and hatched, with help, from the apex end of Fall 1981 Wiemeyer — Propagation of Bald Eagles 73 the egg. The eaglet had an external yolk sac (see below). Eaglets were heard vocalizing within the shell at least 12 h before pipping on several occasions. Twenty-one fertile Bald Eagle eggs were artificially incubated in 1978-80 (Table 3). Three of them were transplanted to nests in the wild and one was given to another cap- tive pair. One egg from pair B in 1980 was buried in the nest lining and was cold when collected. Eleven of 16 remaining eggs (69%) hatched. For the years 1976-80, 34 Bald Eagle eggs were parent incubated (Table 3). Fertility of parent-incubated eggs was determined by examining their contents after they failed to hatch. Small embryos may have gone undetected. The fertility of three eggs that were transplanted to wild nests was not determined. Fifteen of the remaining 31 eggs were fertile and 14 hatched (93%). The only fertile parent-incubated egg that failed to hatch was not incubated to full term by pair C in 1979, possibly because of interference by a wild adult Bald Eagle at the pens at about the time incubation ceased (Table 3). For those parent-incubated clutches containing at least one fertile egg, 74% of the eggs laid hatched. All pairs incubated their eggs; both members of each pair participated Table 3. Reproduction by pairs of captive Bald Eagles. Pair Year Clutch No. Eggs Young Raised* 5 Laid a Fertile Hatch A 1976 1 3(P) 1 1 1(P) 1977 l c 3(P) d (1) — — 1978 l c 3(A) 3 - — 2 2(P) 2 2 2(P) 1979 1 3(A) 3 3 3(H) 2 2(P) 2 2 2(P) 1980 1 3(P) 2 2 2(P) B 1977 1 2(P) 2 2 2(P) 1978 1 3(A) 3 e 1 1(H) 2 2(P) 2 2 2(P) 1979 1 2(A) 2 2 2(H) 2 2(P) 0 0 0 1980 1 2(A) 2 1 1(H) 2 2(P) 1 1 1(P) C 1977 1 2(P) 0 0 0 1978 1 2(P) 2 2 2(P) 1979 1 3(A) 3 3 3(H) 2 1(P) 1 0 0 1980 1 3(A) 3 0 0 D 1978 1 2(A/ 0 0 0 2 2(P) 0 0 0 1979 1 2(A) 0 0 0 2 2(P) 0 0 0 1980 1 3(A) 0 0 0 2 2(P) 0 0 0 E 1979 1 2(P) 0 0 0 1980 1 2(A) 2 1 1(H) a P = Parent-incubated; A = artificially incubated. b P = Parent-reared; H = hand-reared. c Eggs transplanted into wild nests. d Eggs not candled; one hatched in wild nest. e One egg given to pair D after their eggs failed to hatch; they failed to hatch this egg. f One broken. 74 RAPTOR RESEARCH Vol. 15, No. 3 (Gerrard et al. 1979). Both sexes have brood patches. The incubating pairs were quite defensive of humans and of eagles in adjoining pens that approached the partitions. The major cause of infertility appeared to be lack of copulation. One pair (D) pro- duced six clutches of infertile eggs. The first clutch produced by each of two pairs (C and E) in the first year they were paired (1977 and 1979) were also infertile. In each case copulation was not observed before or during laying of the first clutch. The above factors accounted for 74% of all infertile eggs produced. Additional pairs were not seen copulating before or during the laying of their first clutches (A in 1976, B in 1977 and 1980, C in 1978 and 1980), but each produced one or more fertile eggs in these clutches. Average clutch size was 2.5 eggs in first clutches and 1.9 eggs in second clutches. One female (A) consistently laid three eggs in each of five first clutches. Bacteriological cultures were attempted from four fertile eggs that failed to hatch un- der artificial incubation in 1980. All cultures using as many as six media were negative, including tests for Salmonella. Two of these eggs were cultured for adenoviruses; these attempts were negative. Eaglet Care One case of an unretracted yolk-sac was observed in 1979. The sac was ligated at the sphincter; an antibiotic salve was applied to the umbilicus area and the sac was allowed to drop off. It might be preferable to cut the sac off immediately following ligation. The eaglet survived. The eaglets were removed from the hatcher after they had dried. They were then placed in a thermostatically controlled forced air incubator-brooder and the temper- ature was initially maintained at about 36°C and the relative humidity at about 50%. The temperature was gradually lowered about 0.5 °C per day. In 1979 and 1980, when the eaglets were about 1 week old, they were moved to a larger thermostatically con- trolled brooder. There was no control of humidity in these, however a room humidifier was used to help maintain humidity. When the eaglets were about 3 weeks old and were able to thermoregulate at room temperature, they were placed in large boxes and main- tained at room temperature (about 22°C). Correct temperature was determined by ob- servation of the eaglets’ behavior. They panted when too hot, chittered and shivered when too cold, and slept quietly when comfortable. The eaglets were kept in low boxes within the brooders and later inside the large boxes in the room. The inner boxes restricted the movement of the eaglets so that they could not readily come in contact with their feces. Inner boxes, which were slightly larger than the eaglets, were lined with absorbent paper backed with plastic, and with fumigated straw. The birds were kept in depressions in the straw when small, to prevent spraddling of their legs. Brooder liners, boxes and bedding material were changed as needed. Eaglets were raised with their siblings in 1979, usually within the same inner box. If one became excessively aggressive they were kept in separate inner boxes, but in sight of one another. The eaglets were first fed within 24 h of hatching. They were given small pieces of food with blunt forceps. In 1979 and 1980, the diet consisted of one-half to two-thirds fowl (Coturnix quail, chickens, or ducks) and the remainder fish. The muscle, heart, and liver of fowl and scaled and filleted fish were used. Fish liver was occasionally in- corporated into the diet. The items were cut into pieces appropriate to the size of the eaglets. The diet was supplemented with Polyvisol (liquid infant vitamins) at 1-2 drops per 10 g of food. After the eaglets were a few days old, calcium carbonate was added to Fall 1981 Wiemeyer — Propagation of Bald Eagles 75 make up 1 to 1.5% of the diet. Vionate (a vitamin-mineral supplement) was gradually in- corporated into the diet when the eaglets were about 1 week old and constituted less than 1% of the diet. When the eaglets were about 3 weeks old the fish were no longer scaled. The food was wet with water before feeding to help the eaglets in swallowing it and to insure that they did not become dehydrated. Food types were mixed at each feeding. Eaglet weights were recorded daily. The amount and types of food were re- corded at each feeding. These records were useful in monitoring the health of the birds. Some eaglets began to avoid hand feeding when 5 to 6 weeks old, especially if they were frequently handled. The eaglets were fed about every 3 h during daylight for the first few days. The fre- quency of feeding declined to four or five feedings per day at 3 weeks of age. The birds were often fed until gorged in 1979. This was avoided in 1980 by visual inspection and palpation of the esophageal area, as excess food may spoil in the digestive tract and re- sult in poisoning (Cade et al. 1977). Feedings in 1980 were normally given on empty or near empty crops. One eaglet from pair C in 1979 developed a 90° lateral rotation of the tibia. The cause was unknown. All efforts to correct the rotation failed and the eaglet was euthanized. The hand-reared eaglet from pair E in 1980 developed crooked toes on both feet that curled laterally when about 8 days old. After several initial unsuccessful attempts to straighten the toes, we taped a piece of heavy cardboard the size of the eaglet’s foot to the end of a tongue depressor cut to the length and width of the eaglet’s tarsus. The eag- let’s tarsi were wrapped with cotton and the above devices taped around each tarsus. The toes were placed inside short slit-open pieces of plastic tubing, the interior diame- ters of which were about the same size as the respective toes. The tubing was aligned on the cardboard so that the toes were straight and then taped to the cardboard. The de- vices were changed every 1-2 days and adjustments to the components made in re- sponse to the growth of the eaglet. The toes were virtually straightened when the eaglet was 25 days old, 1 day before it was sent to New York. When the eaglet was examined 3 weeks later it appeared normal; the toes were still straight, but the middle toe of one foot seemed weak (P. E. Nye, pers. comm.). The cause of the original abnormality is unknown. The parent eagles with young were provided extra food items so that sufficient food was always present for them to feed their young. Food was often provided to them twice a day so that a fresh item was available more frequently. When the eaglets were less than 1 week old a saliva-like fluid was seen dripping from the tip of the upper man- dible of the adult feeding the young, thereby providing extra moisture and possibly di- gestive enzymes to the young with the pieces of food. This has also been observed for the White-tailed Sea Eagle ( Haliaeetus albicilla ) (Fentzloff 1978). A female Golden Eagle ( Aquila chrysaetos ) fed pieces of food to a small chick that she had partially swal- lowed (Hamerstrom 1970). The adult females provided the great majority of food to the eaglets in comparison to the males. The parent eagles successfully reared all of the young hatched by them to 3 to 9 weeks of age at which time the eaglets were needed for transplant to wild nests or for hacking. Egg Transplants Eggs to be transplanted to wild nests, including eggs that were collected during trans- plant operations and during some eaglet introductions, were placed in an oversized at- 76 RAPTOR RESEARCH Vol. 15, No. 3 tache case (45 X 32 X 17 cm). The case was lined with styrofoam. Eggs were placed in depressions cut in the styrofoam. The temperature in the case was maintained with hot water in two hot water bottles that laid on a sheet of styrofoam separating them from the eggs. Holes in the styrofoam sheet allowed passage of heated air. The sheet pre- vented contact between the eggs and the killing temperature of the hot water bottles. Temperature in the case near the eggs was monitored with a dial thermometer that was inserted through a small hole in the case near the handle with the dial on the exterior. The temperature was maintained within a range of 32-37 °C for up to 4 h, providing the case was not opened, without changing the water in the bottles. Cases of similar design have been used to transport bird eggs of several species (Erickson 1981). Captive-produced Bald Eagle eggs were transplanted into active nests in the Chesa- peake Bay region in both 1977 and 1978 (Table 4). The recipient nests had histories of reproductive failure for several years or high levels of contaminants in eggs produced in the previous year. Three eggs from pair A were used in transplants each year. The eggs transplanted in 1977 had been incubated by the captive pair for 2 to 3 weeks when col- lected; it was not known if all eggs were fertile or viable. Those transplanted in 1978 were in the fourth week of incubation, 3 weeks of which were under artificial in- cubation; all were fertile and appeared viable. Only one introduced egg was known to hatch; the eaglet survived and fledged (Table 4). Four of five of the remaining eggs failed to hatch, presumably because of nest aban- donment (Mason Neck 1978) and chilling of the eggs from delays in the resumption of incubation by the wild birds. The cause of failure to hatch of the fifth egg (Mason Neck 1977) was unknown. Four of the six wild-produced eggs removed from nests during egg transplant oper- ations were non-viable. One hatched under artificial incubation, but the eaglet died. The remaining egg was thought to have been non-viable because of a floating air cell (probably caused by a handling mishap), but appeared viable when opened. Table 4. Transplants of captive-produced Bald Eagle eggs into wild nests. Recipient Wild-produced Eggs Hatched in Site Present Removed Introduced Wild Nests 1977 Mason Neck, VA 1 l a 2 1 Holly Forks, VA 2 2 b 1 0 1978 Mason Neck, VA 1 l c 2 0 Bombay Hook, DL 3 2 a 1 0 a Eggs non-viable; failed to hatch under artificial incubation. All contained high levels of environmental contaminants. b One non-viable egg cracked and one viable egg probably damaged (floating air cell) as a result of a handling mishap at the nest. c Egg hatched under artificial incubation. Eaglet died of chronic bronchio-pneumonia when 33 days old. It also had secondary osteomalacia, possibly as a result of changes made in its diet in an effort to keep it eating during its long (18 day) illness. Fall 1981 Wiemeyer — Propagation of Bald Eagles 77 Eaglet Introductions into Wild Nests Ten hand-reared and two parent-reared captive-produced eaglets were fostered to wild adults in active nests, usually with long histories of reproductive failure, when they were 2.5 to 6 weeks old during the years 1978-80 (Table 5), Eaglets younger than 2.5 weeks may not be able to thermoregulate for extended periods while awaiting care by wild adults, and thus may become excessively chilled. Hand-reared eaglets in excess of 6 weeks may not have enough time to overcome imprinting on humans before fledging Table 5. Fostering of captive-produced Bald Eaglets to adults at wild nests 1978-80. Recipient Site Nest Contents c on t en t s Captive Young Eggs Young Removed* Introduced 13 Fledged Captive Source Pair Disposition of Nest Contents Removed Bonum Cr., VA 0 1 1Y 1978 2(P) 2 A Eaglet moved to Jones Pond, VA nest; placed alongside young of similar size. Both fledged. Hemlock L., NY 1 0 IE 1(H) 1 B Egg non-viable. Dahlgren, VA 0 1 1Y 1979 2(H) 2 A Eaglet moved to Chantilly, VA nest; placed alongside young of similar size. Both fledged. Coles Neck, VA 0 l c 0 1(H) 1 A - Hemlock L„ NY 0 0 - 2(H) d - B - Pymatuning L., PA (2) 0 (2E) 1(H) 1 B Goose eggs had been placed in the nest to maintain incubation; discarded. Brandy Pond, ME 2 0 2E 1(H) O' 5 B One egg non-viable. The other was thought to have been non-viable when candled, but appeared to have been viable when opened later. Swan Is., ME 2 0 2E 1(H) 1 C Both eggs hatched under artificial incubation. One eaglet died. The other eaglet was hand- reared and placed in a nest near Steuben, ME alongside a wild- produced young of similar size. Both fledged. (Cont. on next page) 78 RAPTOR RESEARCH Vol. 15, No. 3 Machias, ME Ottawa, OH Table 5 (cont.) 1 0 IE 1(H) 1 0 l c 0 1980 1(H) 1 C Egg hatched under artificial incubation. Eaglet hand-reared and placed in nest near Passadumkeag, ME alongside a young of similar size. Both fledged. B - Hemlock L., NY (1) 0 (IE) 1(H) E Dummy egg in nest removed. a Y = young; E = egg. b P = parent-reared; H = hand-reared. c Eaglet left in nest with introduced young; both fledged. d Eaglets not accepted by wild pair. The pair had been seen in incubation posture in the nest, but the nest was found to be empty when eaglets were introduced. The eaglets were later removed and introduced into nests elsewhere. e Eaglet killed by wild adult. from wild nests. Three kinds of nests were used: those with eggs (including goose eggs and dummy eggs placed in empty nests to maintain incubation), with wild-produced young of similar size (which were left in the nest), and in place of wild-produced young of different size, which were in turn moved to other wild nests with young of their size. Eaglets were transported in cardboard cartons or wood crates (that were lined with clean straw as bedding material) by auto, single engine government aircraft and com- mercial aircraft. Eleven of 12 fostered eaglets were accepted by wild adult eagles, and were either seen in advanced stages of development in nests or were known to have fledged. All wild-produced eaglets in manipulated nests were also seen in advanced stages of development and presumably fledged. Captive-produced White-tailed Sea Eagles have also been fostered to wild adults (Fentzloff 1978). One 5-week-old eaglet introduced into a nest at Brandy Pond, Maine (Table 5) was killed by a wild adult eagle. It had been introduced into the nest in place of two eggs and was standing in the nest when the wild adult returned and landed on a limb about 2.5 m from the nest 10 minutes after the climbing crew left the tree. The eaglet spread and flapped its wings. The adult immediately left the limb, flew off, circled, came back to the nest in a stoop with outstretched talons and killed the eaglet, knocking it out of the nest (R. B. Owen, Jr., pers. comm.). The adult presumably mistook the eaglet for a predator or intruding eagle. A second hand-reared eaglet of similar age, even though hungry, refused food from its caretakers before being placed in the Machias, Maine nest (Table 5). It begged for food from a wild adult upon the adult’s arrival at the nest, even though it had never before seen an adult eagle. Eaglet introductions in the Maine nests in 1979 (Table 5) were all conducted in terri- tories with long histories of reproductive failure. Three of five eggs removed from the three nests hatched under artificial incubation. Two eaglets survived hand rearing; the third, very small at hatching, died. The two surviving eaglets were introduced into Maine nests alongside wild-produced young of similar size. All were seen in advanced stages of development and presumably fledged. Fall 1981 Wiemeyer — Propagation of Bald Eagles 79 Captive-Produced Young Sent to Hacking Projects Eleven captive-produced parent-reared young 7 to 9 weeks old were provided to hacking projects between 1977-80 (Table 6). Seven young were provided to New York and were hacked successfully to the wild at Montezuma National Wildlife Refuge (P. Nye, pers. comm.) where Bald Eagle hacking procedures were first developed by Mil- bum (1979). Four young were provided to the Georgia Department of Natural Re- sources; they were hacked successfully to the wild at Sapelo Island, Georgia (R. Odum, pers. comm.). Hacking has also been used in the reintroduction of White-tailed Sea Eagles in Scotland (Love and Ball 1979). Table 6. Captive-produced Bald Eagles provided to hacking projects. Hacking Year Project 1977 1978 1979 1980 New York 2(B)“ 4(B,C) _ 1(B) Georgia - - 2(A) 2(A) “Source pairs given in parentheses. Discussion and Conclusions Considerable progress has been made in the captive propagation of Bald Eagles in the last 10 years. Current knowledge and effort have made possible the production of mod- est numbers of eaglets for reintroduction attempts and supplementing production of de- pressed populations. Information and experience gained during these years has been helpful in assessing the value and potential of various techniques. Bald Eagle egg transplants should not be considered as a productive method of sup- plementing the production of depressed populations. Major problems encountered in the use of this technique in this study were the outright abandonment of introduced eggs and excessive delays in the resumption of incubation following transplants. These prob- lems were also encountered in transplants of wild-produced Bald Eagle eggs from the Great Lakes states to Maine in 1974-76 (F. Gramlich, C. Madsen and P. Nickerson, pers. comms.). These problems might have been lessened in a few isolated cases in these studies by reductions in time spent at recipient nests by egg introduction teams. The strong desire to determine if and when a wild pair returns to its nest following an egg transplant may be counter-productive in some cases. An observer even at a distant ob- servation site might cause a delay in the resumption of incubation, resulting in chilling of eggs and death of embryos. Perhaps efforts to obtain such information should be abandoned. An aerial check of the nest 1 h following an egg transplant could provide in- formation on acceptance or abandonment of eggs. Even with these modifications egg transplants should be considered only when other techniques cannot be used. The place- ment of goose eggs or dummy eggs in nests shortly following the loss of wild-produced eggs or in the nest of a pseudo-incubating non-laying pair can hold pairs on their nests until eaglets become available for introductions, as occurred in Pennsylvania in 1979 and New York in 1980. Double clutching of captive pairs at this Center has not resulted in substantially in- creased numbers of eaglets. If all 16 fertile eggs that were artificially incubated to ter- mination (see above) had been left with the parents (no double clutching) and all had hatched and eaglets survived (similar to actual success for parent-incubated fertile eggs), the production would have been the same as that actually observed from these pairs 80 RAPTOR RESEARCH Vol. 15, No. 3 with double clutching. Modest improvements in hatchability of artificially incubated eggs and consistent laying of and production from second clutches are needed before double clutching will result in increased production. The time and expense of hand rear- ing first clutch young must be balanced with the need for increased production, with the manager making appropriate decisions with regard to available resources and the value placed on the birds. Double clutching could be reserved for unpaired females that are to be artificially inseminated or individual pairs that fail to incubate their own eggs or rear their own young. It could also prove beneficial with specific pairs that con- sistently produce viable first clutch eggs and young from second clutches, especially if modest improvements in hatchability of artificially incubated eggs are realized. Knowledge of proper nutrition and care of hand-reared young has not been perfected, as suggested by the occasional appearance of skeletal abnormalities. No abnormalities of these types have been seen in parent-reared eaglets. Eaglets should not be hand-reared for more than 5 weeks because of problems in the acceptance of food from caretakers. If eaglets must be hand-reared for longer periods they should be allowed to pick up pieces of food on their own. Hand-reared young should not be used in hacking projects because they most likely will become imprinted on humans. Very little work has been done with artificial insemination of bald eagles. Artificial insemination techniques with Golden Eagles were previously described (Hamerstrom 1970, Grier 1973). The technique should prove valuable when working with females that are imprinted on humans and with unpaired egg-laying females. Forced semen col- lections did not prove to be difficult in very limited attempts. Methods of preserving eagle semen for later use could be explored. Modest to major contributions to Bald Eagle production have resulted from the fos- tering and hacking of captive-produced eaglets into the wild. In New York, 7 of 22 Bald Eagles successfully hacked to the wild in the years 1976-80 were produced at this Cen- ter, whereas fostering of eaglets into a wild nest accounted for all and one-half of the to- tal production from wild nests in the state in 1978 and 1980 (P. Nye, pers. comm.). In Georgia, no young were produced by wild eagles during 1979 and 1980 when four cap- tive-produced eaglets were hacked to the wild (R. Odum, pers. comm.). The fostering of one eaglet in Ohio in 1980 accounted for 25% of the total production of Bald Eagles for the state (D. Case, pers. comm.). In Pennsylvania in 1979, the fostering of one eaglet ac- counted for all of the production in the state (M. Puglisi, pers. comm.). Fostering of cap- tive-produced young in Virginia in 1978 and 1979 accounted for 10 and 13% of the total eaglet production (Dittrick and Clark 1978, Pramstaller and Clark 1979) whereas in Maine in 1979 it accounted for only 5% of total eaglet production (F. Gramlich, pers. comm,). The ultimate success of any captive breeding program with release of progeny occurs when released birds successfully reproduce in the wild. Two wild-produced bald eagles that were hacked to the wild in New York in 1976 paired and produced young in 1980 (P. Nye, pers. comm.). The earliest that this could occur for this program would be in 1981 when those young released in 1977 could first reach sexual maturity, assuming sur- vival. Larger numbers of released young should first become sexually mature in 1982 and 1983. It may be difficult to locate released birds at maturity because only those re- leased at hacking projects carried adequate color markers for individual identification. There are few breeding birds in the hacking areas (New York and Georgia) thereby making easier the detection of new breeding pairs. Fall 1981 Wiemeyer — Propagation of Bald Eagle; 81 Acknowledgments I thank Keith W. Babcock, John T. Cockey, Kathryn A. Dale, Timothy N. Hall, Dan- iel C. Huffman, James M. Speicher, Joseph H. Snyder, John A. Stegeman, and Michael J. Weber for care of birds in the breeding colony and for assistance in hand-rearing eag- lets. Members of the Chesapeake Bay Bald Eagle Banding Project of the Raptor Infor- mation Center, National Wildlife Federation provided tree climbing expertise for egg transplants and eaglet introductions in Virginia, Delaware, and Pennsylvania. The fol- lowing individuals assisted with egg transplants and young introductions, provided back- ground information on recipient nests, and provided data on the outcome of these activ- ities and hacking attempts in their respective areas; Mitchell A. Byrd and personnel at Mason Neck National Wildlife Refuge in Virginia; Peter E. Nye in New York; Francis J. Gramlich, Ray B. Owen, Jr. and Charles S. Todd in Maine; Ron Odum in Georgia; Denis S. Case in Ohio; Michael J. Puglisi in Pennsylvania; and Don R. Perkuchin at Bombay Hook National Wildlife Refuge in Delaware. Barbara K. and Charles S. Todd hand reared an eaglet in Maine. James W. Grier provided advice and discussions on hand rearing eaglets. George F. Gee provided information on the sex of several captive birds as the result of cloacal examinations, collected semen from several captive males, and artificially inseminated a captive female. James W. Carpenter conducted laparotomies on several birds and he and J. Christian Franson provided medical care and advice on nutrition. I thank George F. Gee, James W. Grier, Charles J. Henny and Vivian M. Mendenhall for reviews of the manuscript. Literature Cited Anonymous. 1909. Wild birds bred in captivity in the Eastern United States. Zoological Society Bull. 36:580-583. Anonymous. 1969. American Bald Eagle. Z oonooz 42:13. Barger, B. A. 1963. Bald Eagles hatched in captivity. Passenger Pigeon 25:24-25. Cade, T. J., J. D. Weaver, J. B. Platt and W. A. Burnham. 1977. The propagation of large falcons in captivity. Raptor Research 11:28-48. Dieter, M. P. 1973. Sex determination of eagles, owls, and herons by analyzing plasma steroid hormones. U.S. Bureau of Sport Fisheries and Wildlife. Special Scientific Report— Wildlife No. 167. Washington, D.C. Dittrick, B., and W. S. Clark. 1978. Chesapeake Bay Bald Eagle banding project report 1978. National Wildlife Federation, Raptor Information Center, Washington, D.C. Erickson, R. C. 1981. Transport case for incubated eggs. Wildl. See. Bull. 9(l):57-60. Fentzloff, C. 1978. The breeding and release of the White-tailed Sea Eagle (Haliaeetus albicilla) as performed by the Deutsche Greifenwarte Burg Guttenberg. Pages 97-103 in T. G. Geer, ed., Bird of Prey Management Techniques. British Falconers Club. Gee, G. F., and S. A. Temple. 1978. Artificial insemination for breeding non-domestic birds. Symp. Zod. Soc. Land. 43:51-72. Gerrard, P. N., S. N. Wiemeyer and J. M. Gerrard. 1979. Some observations on the be- havior of captive Bald Eagles before and during incubation. Raptor Research 13:57-64. Grier, J. W. 1973. Techniques and results of artificial insemination with Golden Eagles. Raptor Research 7(1): 1-12. Hamerstrom, F. 1970. An eagle to the sky. Iowa State University Press, Ames. 142 pp. 82 RAPTOR RESEARCH Vol. 15, No. 3 Hancock, D. 1973. Captive propagation of Raid Eagles Haliaeetus leucocephalus— a re- view. International Zoo Yearbook 13:244-249. Hulce, H. 1886. Eagles breeding in captivity. Forest and Stream 27:327. Hulce, H. 1887. Eagles breeding in captivity. Forest and Stream 28:392. Johnson, M. J,, and R. Gayden. 1975. Breeding the Bald Eagle Haliaeetus leucocephalus at the National Zoological Park, Washington. International Zoo Yearbook 15:98-100. Love, J. A., and M. E. Ball. 1979. White-tailed Sea Eagle Haliaeetus albicilla reintro- duction to the Isle of Rhum, Scotland, 1975-1977. Biol Conserv. 16:23-30. Maestrelli, f. R., and S. N. Wiemeyer. 1975. Breeding Bald Eagles in captivity. Wilson Bull. 87:45-53. Milburn, E. H. 1979. An evaluation of the hacking technique for establishing Bald Eagles ( Haliaeetus leucocephalus ). Master of Science Thesis, Cornell University. 184 pp. Minnemann, D. 1976. Aufzucht eines Weisskopfseeadlers ( Haliaeetus leucocephalus ) durch ein Adlerbussardpaar (Buteo rufinus). Zod. Garten 46:54-65. Pramstaller, M. E., and W. S. Clark. 1979. Chesapeake Bay Bald Eagle banding project report 1979. National Wildlife Federation, Raptor Information Center, Washing- ton, D.C. Wellenkamp, J. 1973. A first— in baby bald eaglets. Southern Living 8:36-38. ARTIFICIAL BURROWS PROVIDE NEW INSIGHT INTO BURROWING OWL NESTING BIOLOGY by Charles J. Henny and Lawrence J. Blus Patuxent Wildlife Research Center 480 SW Airport Road Corvallis, Oregon 97330 Introduction The breeding biology of Burrowing Owls (Athene cunicularia) is poorly understood, primarily because of the difficulty of studying an underground nesting species. Before the use of artificial burrows (Collins and Landry 1977), few attempts were made to in- tensively study Burrowing Owl nesting because of the nest destruction problem. Twenty artificial burrows, similar to those used by Collins and Landry (1977), were installed in eastern Oregon (Umatilla and Morrow counties) in the spring and summer of 1979; how- ever, sandy soil and wind erosion resulted in only 12 burrows being relocated in 1980. In 1979 and 1980, we made observations on four nesting attempts by Burrowing Owls us- ing these burrows. Our objective was to collect additional information on the breeding biology of this species. The points made in this paper all come under the basic heading “know the species” which is essential before attempting to develop a census procedure, or even a method for evaluating productivity of a species. Results The observations recorded during this study are presented separately for each burrow, although the food habits information is pooled. Raptor Research 15(3):82-85 Fall 1981 Henny and Blus — Artificial Burrows 83 Burrow No. 1 (1979) An artificial nest was placed in a burrow being excavated on 4 April 1979. The site was rechecked on 11 April and contained an owl incubating 10 eggs of which 1 was col- lected for pesticide analysis. Thus, the Burrowing Owl laid 10 eggs in no more than 8 days; it seems unlikely that a second female contributed eggs to the clutch as additional adults were not observed near the burrow. On 9 May eight young (about 1-2 days old) were in the nest; this suggested an incubation period of about 27-28 days. Seven young were banded in the box on 22 May (Fig. 1). On 6 June (young about 1 month old) two of the banded young were in the nest box in which the eggs were laid, and four of the banded young were in another box about 45 m away. Prey was found in both boxes. Burrow No. 1 (1980) The burrow discussed above was first checked on 19 March 1980; two adults were flushed from the burrow. It contained no eggs. On 7 April six cold eggs were present and one was collected for pesticide analysis. No prey was found in the box with eggs, but prey was found in the box 45 m away. On 26 April 11 eggs were in the nest. On 15 May at least six young were in the nest, but some were also in the tunnel. On 22 May no owlets (about 10 days old) were in the box where the eggs were laid, nor were they in the adjacent box. Other natural burrows were known to be in the vicinity. However, on 27 May 10 young were in the nest in which the eggs were laid; these were banded. On 6 August one adult and at least five young were seen nearby. Burrow No. 2 (1980) This burrow was first checked on 8 April 1980. An adult flew from the nest, but its mate remained inside. One cold egg was also in the nest. On 14 May the nest was re- visited and contained 10 eggs, most of which were pipped, and one had hatched. If the 10 eggs were laid in 8 to 10 days, the incubation period for the clutch was 28 to 30 days. Revisits on 2 and 9 June revealed no young in the box, although they could have moved to a natural burrow nearby; an adult was seen in the vicinity on one visit. Burrow No. 3 (1980) On 14 May 1980 an adult was near the entrance, and the female was inside in- cubating eight eggs of which one was collected. On 2 June seven young, about a week to 10 days old, were in the nest, and they were all banded on 9 June. Prey species found in the burrows during the nesting season included the following: Ord kangaroo rat ( Dipodomys ordi) (13), deer mouse ( Peromyscus maniculatus ) (5), vole (probably Microtus sp.) (3), northern pocket gopher ( Thomomys talpoides) (2), Great Ba- sin pocket mouse ( Perognathus parvus ) (2), young mountain cottontail ( Sylvilagus nut- talli) (1), young black-tailed jackrabbit (. Lepus californicus ) (1), house mouse ( Mus mus- culus) (1), and young Ring-necked Pheasant ( Phasianus colchicus ) (1). Numerous authors, using pellet studies, have noted the importance of insects in the diet of Burrowing Owls (e.g., Maser et al. 1971). We also found pellets in mid-August that contained mostly in- sect remains. Insects, however, would be less likely to be found in burrows because they probably are eaten immediately. Discussion and Conclusions Egg laying occurred from early through late April. The clutches were large (12, 10, 10, 8) with the latest clutch initiated being the smallest. Burrowing Owls appear to pro- 84 RAPTOR RESEARCH Vol. 15 No. 3 duce the largest clutches of any North American raptor. Murray (1976) gathered clutch size data of various owls from museums and egg collections and found that the mean size of 439 Burrowing Owl clutches was 6.48 (range 1-11). Eggs in a nest from this study were laid at a rate of more than one per day (assuming two females were not in- volved), which is in contrast to reports for most owls (see review, Welty 1962) and a Burrowing Owl in captivity (Howell 1964). Incubation lasted about 4 weeks (27-28 days and 28-30 days) at two nests in this study, which agreed with Zarn (1974), but differed from Bendire’s (1892) statement of about 3 weeks. Bendire stated that incubation did not appear to begin until a clutch was nearly completed; that agrees with the findings of this study— a cold, incomplete clutch of six eggs was recorded, and a nearly synchronous hatching of eggs occurred in another clutch. In contrast, Thomsen (1971) assumed that incubation began with the laying of the first egg, based on size of young at first emergence. Although 1 egg was collected from each clutch, 10, 7, and 7 young reached about 2 weeks of age in 3 nests; however, some attrition appeared to occur over the next 2 weeks. Owlets only 10 days old were known to move among nest burrows, thus making productivity studies difficult. Further, banded young from one nest were found in two different burrows at the same time, making casual counts of young in front of burrows a somewhat tenuous method of obtaining productivity (a minimum count only). Even with artificial burrows, we were uncertain about the outcome of Nest No. 2. The young may have moved to natural burrows. From the literature, the number of young pro- duced per pair is varied, but in some studies it was much lower than the average clutch size. Estimates of attrition of young from the egg stage to fledging may be highly inflat- ed if measurements are not corrected for the movement of young to adjacent burrows. Following pair formation, Thomsen (1971) reported that some pairs were seen at only one burrow, while others were seen at more than one burrow before choosing one as a nest site. In the present study, even during the egg laying period, some adults used at least two burrows and brought prey to each. The phenomenon even tends to complicate the counting of active nesting pairs— a task originally thought to be relatively straight- forward. These cautions are important because the recent concern for Burrowing Owls may result in a number of future studies. Detailed studies of Burrowing Owls are much more difficult than we, and probably most workers, anticipated. Acknowledgments Biological technicians assisting in this study included Robert Sheehy, Gregory Green, Bruce Forman, and Kevin Hansen. The artificial burrows were constructed by YACC people at the William L. Finley National Wildlife Refuge, Corvallis, Oregon. The man- uscript was improved by the comments of Chris Maser and Eugene H. Dustman. Literature Cited Bendire, C. E. 1892. Life histories of North American birds. U.S. National Museum, Spe- cial Bull. No. 1. Collins, C. T. and R. E. Landry. 1977. Artificial nest burrows for Burrowing Owls. N. Am. Bird Bander 2:151-154. Howell, T. R. 1964. Notes on incubation and nesting temperatures and behavior of cap- tive owls. Wilson Bull 76:28-36. Fall 1981 Henny and Blus — Artificial Burrows 85 Maser, C., E. W. Hammer, and S. H. Anderson. 1971. Food habits of the Burrowing Owl in central Oregon. Northwest Sci. 45:19-26. Murray, G. A. 1976. Geographic variation in the clutch sizes of seven owl species. Auk 93:602-613. Thomsen, L. 1971. Behavior and ecology of Burrowing Owls on the Oakland Municipal Airport. Condor 73:177-192. Welty, J. C. 1962. The life of birds. W. B. Saunders, Co., Philadelphia. Zarn, M. 1974. Burrowing Owl Speotyto cunicularia hypugaea. Habitat Management Series for Unique or Endangered Species. Report No. 11, Bur. Land Manage., Denver. Figure 1. Seven young (14-15 davs old) in Burrow # 1 on 22 May 1979. HARRIER NEST-SITE VEGETATION by Frances Hamerstrom Rt 1, Box 448 Plainfield, Wisconsin 54966 and Mark Kopeny 717 E. Thomas St. Arlington Heights, Illinois 60004 The Northern Harrier ( Circus cyaneus hudsonius) is highly adaptive as a nester. It uti- lizes essentially all niches used by the three European harriers (C. c. cyaneus, C. aerugi- nosus, and C. pygargus) with the exception of the rather recent adaptation by C. c. cyaneus to forest nesting in Scotland (Watson 1977). The Northern Harrier has adjusted to significant changes in available vegetation for nest sites on the Buena Vista Marsh, Central Wisconsin, over the last 19 years. The plants recorded in the immediate vicinity of 184 Harrier nests reflect these changes. Our 16,000-ha. study area lies mainly in the Buena Vista Marsh, but includes some of the surrounding upland. The marsh was drained, and both it and the upland parts of the study area are now mostly farmland with a high proportion of non-marshy grassland. The low spots tend to become sedge ( Carex spp.) and willow (Salix spp.) swales (Ham- erstrom 1969). We recorded the three most prominent plants within approximately 2 ft. (ca. 60 cm) of the nest cup in order of dominance. Our primary purpose was to facilitate nest find- ing. We rarely measured vegetation height and density. The woody species, aspen and willow, were present as brush rather than trees. We could not identify sedges, gold- enrods (Solidago spp.) and willows to species so lumped them as groups; some grasses were specifically recognized and are shown in Table 1, unidentified grasses are lumped together as a group ( Graminae ). Of different cover species or groups at 184 nests (Table 1) at least 16 were dominants. (We use the term “dominant” here to mean the single most prominent cover plant within 2 ft. of the nest.) The six most frequent dominants (i.e. at more than 5 nests) were willow ( Salix spp.), grasses (Graminae), meadowsweet (Spirea alba), goldenrod ( Solidago spp.), sedge ( Carex and Scirpus spp.), and stinging nettle ( Urtica dioica). Even when not dominant, these six were among the important cover plants at a disproportionate number of nests (Fig. 1). We recorded 56 nests sur- rounded by only one cover species, discounting those species present in only trace amounts (Table 1). All but three nests were in one of six dominant cover types listed above. There has been a shift in the relative abundance of certain nest-site species on the study area, due in considerable extent to herbicide spraying to improve Prairie Chicken (Tympanuchus cupido ) habitat. Changing patterns of farming have also played a part. Since 1959 the Wisconsin Department of Natural Resources has effectively sprayed a substantial portion of the study area to control brush. One result of this program has been a decrease in willows, which, along with sedge, was the most common vegetation at Harrier nests during the first half of this study (Period I: 1959-1968). But Spirea unex- 86 Raptor Research 15(3):86-88 Fall 1981 Hamerstrom and Kopeny — Harriers Table 1. Vegetation found in the immediate vicinity of 184 Harrier nests, 1959-1978. 87 Cover Present at Nest Site Dominant at Nest Site Monotype at Nest Site c N % N % N % Willow (Salix spp.) 65 35.3 40 21.7 15 8.2 Grasses (Graminaej b total (58) (31.5) (42) (22.8) (23) (12.5) Timothy ( Phleum pratense ) .12 6.5 7 3.8 3 1.7 Reed-canary ( Phalaris arundinacea) 6 3.3 3 1.6 1 .1 Poa ssp. 8 4.3 6 3.3 4 2.2 unidentified 32 17.4 26 14.1 15 8.2 Sedge ( Carex spp., Scirpus spp,) 57 30.9 20 10.9 3 1.6 Goldenrod ( Solidago spp.) 56 30.4 32 17.4 8 4.3 Meadowsweet (S pirea alba) 46 25.0 33 17.9 3 1.6 Stinging Nettle ( Urtica dioica) 18 9.8 7 3.8 1 .1 Swamp Milkweed (Asclepias incarnata ) 13 7.1 0 0.0 0 0 Aspen ( Populus tremuloides) 10 5.4 2 1.1 0 0 Other species or groups found at nest sites (each found at less than five nest sites): Bluestem ( Agropyron smithii ); Redtop ( Agrostis alba); Bluejoint ( Calamagrostis canadensis); Bromus spp a inch B. inermis; Oats (Avena sativcP ; Woolgrass (S cii-pus cypennus ); Polygonum spp. inch False Climbing Buckwheat ( P . scandens ); Rosa spp. a ; Strawberry (Fragaria sp.); Raspberry ( Rubus sp.) 3 ; Yellow Sweet Clover (Melilotus officinalisf; Dogwood ( Cornus sp.); Wild Bergamot (Monarda fistulosa); Woundwort ( Stachys palustris); Elderberry (Sam- bucus canadensis); Aster spp. a ; Yarrow ( Achillea millefolium ); Thistle ( Cirsium sp i.); Fleabane (Erigeron sp.) a Dominant at at least one nest. b Parentheses show total of all grasses identified and unidentified. c Plus Oats, Brotnus sp., Raspberry, and Yellow Sweet Clover at one nest each. pectedly increased. The Harriers adjusted to this change and nested more commonly in S. alba and also in Solidago spp. (Fig. 2) in the later years (Period II: 1969-1978). In this latter period, S. alba increased in dominance at nest sites by more than tenfold over the earlier period and increased by almost sixfold in the number of nests at which it was present. Solidago spp. showed a similar trend, whereas Salix spp., Populus tremuloides, and to a lesser extent Carex spp. declined. Fewer nests have been placed in grasses since Period I, particularly with grasses as the dominant cover. By the time nesting Harriers have eggs— roughly the beginning of June— the most common cover plants of both Periods I and II (excluding some of the grasses) normally appear in tall or dense patches, or both. These characteristics may reduce exposure to both mammalian and avian predators. Dense patches of vegetation are not normally used for travel lanes by mammals. From the air the “hole in the field” is conspicuous, but the taller the vegetation, the more directly an avian predator must fly over a nest in order to see it. Brown and Amadon (1968) report that Harriers commonly build their nests in low shrubby vegetation, tall weeds, or reeds rather than in very open sites. Our data agree, and also indicate that the Harrier is highly adaptive as a nester, as evidenced by its ad- justment to the changes that have taken place on their breeding grounds on the Buena Vista Marsh. Literature Cited Brown, L. and D. Amadon. 1968. Eagles, hawks, and falcons of the world. McGraw-Hill Book Company, New York. 88 RAPTOR RESEARCH Vol. 15 No. 3 Hamerstrom, Frances. 1969. A harrier population study. Pages 367-383. In J. J. Hickey, ed. Peregrine falcon populations: their biology and decline. University of Wiscon- sin Press, Madison, Milwaukee, and London. Watson, D. 1977. The hen harrier. T. & A. D. Poyser, Berkhamsted, Hertfordshire, England. j Dominant □ Present N ■ 184 8 M £ 3 a a in x S 3 2 to s e a ft 0 ! & o Figure 2. Fraction of nests at which each cover type was present 1959-1968 compared with 1969-1978. * 1 in .0 in U (top) and dominant (bottom). The period HAVE THE EGGS OF THE ORANGE-BREASTED FALCON (FALCO DEIROLEUCVS ) BEEN DESCRIBED? by Douglas A. Boyce Jr. 1 School of Natural Resources Humboldt State University Areata, California 95521 and Lloyd F. Kiff Western Foundation of Vertebrate Zoology 1100 Glendon Avenue Los Angeles, California 90024 The only published description of Orange-breasted Falcon ( Falco deiroleucus ) eggs known to us is that of Coltart (1952), who presented details on two sets of eggs said to be of this species collected for G. D. Smooker in Trinidad. One of these sets, a clutch of 3 taken on 28 March 1937 in the Aripo Savannah, is now in the collection of the West- ern Foundation of Vertebrate Zoology (WFVZ cat. no. 15,728); the other, a set of 2 col- lected on 21 April 1930 in the Coroni Marshes, is in the collection of the Zoological Museum, University of Helsinki, Finland (ZMUF cat. no. 15,721). The authenticity of these eggs has been questioned by ffrench (1973) because of their small size compared to the body size of the species. The 3 eggs in the WFVZ collection measure 40.6 X 34.7, 41.8 X 35.6, and 39.9 X 34.6 mm, and the 2 eggs in the ZMUF set measure 43.0 X 35.0 and 42.2 X 34.7 mm. All of these measurements fall within the range given for eggs of the Aplomado Falcon ( Falco femoralis ) by Bent (1938) and Brown and Amadon (1968) and are only slightly larger than the extreme measurements known for eggs of the much smaller Bat Falcon ( Falco rufigularis ) (Brown and Amadon op cit., Kiff unpubl. data). Eggs of several falcon species, including one of Smooker’s Trinidad eggs, are shown in Figure 1 to illustrate their comparative sizes. Heinroth (1922) first demonstrated the fundamental relationship between egg weight and body weight in birds, and this was further refined by Huxley (1923-1924). Amadon (1943), Lack (1968), and Rahn et al. (1975) have presented evidence that suggests that each group of related birds (at least to the subfamily level) has a characteristic propor- tionality constant, which expresses the rate at which egg size increases to that of body size increase. It is possible, therefore, to derive individual regression equations to express the relationships between these parameters for particular groups of birds and to predict fairly closely body weight from egg weight, or vice-versa. We obtained data on egg size and female body weight for 12 Falco species, represent- ing the entire size range found in the genus (Table 1), and plotted the log of female body weight against the log of egg length (L) X egg breadth (B), a size index that is highly correlated with actual egg weight (Anderson and Hickey 1970). The resulting regression line (r 2 = 0.92) is shown in Figure 2. The Orange-breasted Falcon data point lies well away from the regression line. Based on the mean weight of 605 g (n = 7) for 'Present address: 4445 Old Gravenstein Highway, Sebastopol, CA 95472 89 Raptor Research 15(3):89-93 90 RAPTOR RESEARCH Vol. 15 No. 3 female Orange-breasted Falcons, the log LB for the species (assuming a sample size of 20) should be 3.26. When this figure is plotted against egg breadth a value of 37.5 mm for Orange-breasted Falcon egg breadth is predicted. When that figure is divided into the product of L X B, an estimate of 48.0 mm for Orange-breasted Falcon egg length is obtained. The 95% prediction interval for these values range from 44.0 to 52.1 mm (L) and 33.8 to 40.0 mm (B); Smooker’s sets fall outside this range in length and just inside in breadth. Table 1. Mean egg size and female body weight of Falco species. Species Code Egg Size (mm) (Length X Breadth) Log L*B ? wt. (g) Log wt. Source American Kestrel F. sparverius A 35.15 X 28.92 3.007 142.2 (13) 2.15 6 Red-footed Falcon F. vespertinus B 35.34 X 29.59 3.038 182.2 (5) 2.26 3 European Kestrel F. tinnunculus C 39.82 X 31.37 3.097 230.4 (20) 2.36 3 Merlin F. columbarius D 40.21 X 30.84 3.094 212.0 (14) 2.33 2 Bat Falcon F. rufigularis E 40.80 X 31.81 3.118 220.0 (13) 2.34 4 European Hobby F. subbuteo F 41.82 X 32.86 3.138 229.0 (10) 2.36 9 Eleonora’s Falcon F, eleonora’s G 41.92 X 34.30 3.160 388.0 (11) 2.59 7 Little Falcon F. longipennis H 44.48 X 33.14 3.169 310.0 (4) 2.49 5 Aplomado Falcon F. femoralis I 44.26 X 34.79 3.188 406.0 (8) 2.61 10 Brown Hawk 0 F. berigora J 51.66 X 39.28 3.308 505-635 (4) 2.89 5 Prairie Falcon F. mexicanus K 52.01 X 40.18 3.320 863.0 (31) 2.94 8 Peregrine Falcon F. p. peregrinus L 51.27 X 40.72 3.320 1010.0 (17) 3.00 5 Gyrfalcon F. rusticolus M 59.17 X 45.92 3.434 1470.0 (10) 3.17 1 'We used the Brown Hawk egg data only in Fig. 3 and Eleonora’s Falcon data only in Fig. 2. Code letters are those used in Figs. 2 and 3. Egg sample size is 20 per species; sample sizes for female body weights are given in parentheses, Sources of data: 1 = Mattox (1970), 2 = Cramp (1980), 3 = Dementiev and Gladkov (1954), 4 = Kiff (unpubl. data), 5 = Brown and Amadon (1968), 6 = Porter and Wiemeyer (1972), 7 = Walter (1979), 8 - Enderson (1964), 9 = Glutz von Blotzheim et ah (1971), 10 = Hector (pers. comm.) In addition to the small size of the eggs, there are other reasons to doubt their au- thenticity. In a long paper on the habits of Trinidad and Tobago birds which Smooker co-authored (Belcher and Smooker 1934-1937), the only allusion to breeding in the Or- ange-breasted Falcon account is the tentative statement, “we think it a resident,” de- spite the fact that the 1930 set had been taken years earlier. The Orange-breasted Fal- con has always been regarded as exceedingly rare in Trinidad, and there is as yet no additional evidence that it breeds there (ffrench 1973). Both sets of eggs were taken for Smooker by a native, apparently the same one in each instance, and Smooker may never have seen the nesting birds personally. Several other instances of misidentification of eggs in the Belcher-Smooker Trinidad collection have been reported (ffrench 1973, Kiff in press), probably resulting from errors by native helpers, rather than dishonesty on the part of the collectors. Three falcon species, the Aplomado Falcon, Bat Falcon, and American Kestrel (F. sparverius) are known to nest in Trinidad. The eggs of the latter are so much smaller than the ones in question that it can safely be ruled out as a candidate for laying them. The Smooker eggs are most similar in size to those of Aplomado Falcons and plotting the measurements of the questionable eggs against mean female Aplomado Falcon body weight yields a point very close to the one seen for the species (Fig. 2). Both nests, how- ever, were said to be in cavities, one (WFVZ no. 15,728) being “30 feet up in a knot- hole in a ceiba tree,” whereas the other was “in the hollow at the base of a palm-branch Fall 1981 Boyce and Kiff — Falcon Eggs 91 about 40 feet up (Coltart 1952). According to Dean Hector (pers, comm.), who has studied the species intensively, there is no recorded instance of Aplomado Falcons nest- ing in such cavities. The nest descriptions are virtually identical to those which Smooker gave for sets of Bat Falcon eggs collected for him in Trinidad and now in the WFVZ collection, but the eggs would be unusually large for that species. We plotted egg breadth against egg length for twelve species of falcons and constructed a 90% predic- tion interval for the genus. The set deposited in the WFVZ lies outside this interval (Fig. 3) and the other set lies on the line. This suggests that these purported eggs may not even belong to the genus! Interestingly, the eggs are most similar in color and size to those of the Yellow-headed Caracara ( Milvago chimachima) (a genus related to Falco ), but that species is rare in Trinidad and is not known to breed there (ffrench 1973). We constructed a 95% confidence interval for a random sample of Yellow-headed Caracara eggs (n = 20) and noted that the Orange-breasted Falcon eggs lie on both sides of the lower limit (42.59 X 34.56 mm). Thus, it is impossible to identify Smooker’s alleged Orange-breasted Falcon eggs une- quivocally, but it is virtually certain that they are not eggs of the Orange-breasted Fal- con and that the eggs of that species await formal description. Acknowledgements We are grateful to Dean Hector and Dave Craigie for commenting on the manuscript and to Clark Sumida for preparing Figure 1. Hector, G. Clark, and M. Kirven provided us with unpublished weight data. Juhani Terhivuo provided us with data from the Zoo- logical Museum of the University of Helsinki. Julie Kiff assisted in measuring eggs. This note was supported by the Western Foundation of Vertebrate Zoology. Literature Cited Amadon, D. 1943. Bird weights and egg weights. Auk 60:221-234. Anderson, D. W., and J. J. Hickey. 1970. Oological data on egg and breeding character- istics of Brown Pelicans. Wilson Bull. 82:14-28. Belcher, C., and G. D. Smooker. 1934-1937. Birds of the Colony of Trinidad and To- bago (in six parts). Ibis 13:572-595, et seq. Bent, A. C. 1938. Life histories of North American birds of prey. Pt. 2. Bull. U.S. Nat. Mus. 170. Brown, L. H., and D. Amadon. 1968. Eagles, hawks and falcons of the world. McGraw- Hill, New York. 945 pp. Coltart, N. B. 1952. Eggs of the Falconinae. Oologists’ Record 26:42-46. Cramp, S. (ed.). 1980. Handbook of the birds of Europe, the Middle East and North Af- rica. Vol. 2. Oxford Univ. Press, Oxford. 687 pp. Dementiev, G. P. and N. A. Gladkov. 1954. Birds of the Soviet Union, Vol. 1. Moscow: State Publishing House. Enderson, J. H. 1964. A study of the Prairie Falcon in the Central Rocky Mountain Re- gion. Auk 81:331-352. ffrench, R. 1973. A guide to the birds of Trinidad and Tobago. Livingston Publ. Co., Wynnewood, Pennsylvania. 470 pp. Glutz von Blotzheim, U. N., K. M. Bauer, and E. Bezzel. 1971. Handbuch der Vogel Mit- teleuropas. Vol. 4. Akademische Verlagschaft, Frankfurt am Main. Heinroth, O. 1922. Die Beziehungen zwischen Vogelgewicht, Eigewicht, Gelegegewicht und Brutdauer . J. f. Ornithol. 70:172-285. 92 RAPTOR RESEARCH Vol. 15 No. 3 Huxley, J. S. 1923-1924. On the relation between egg weight and body weight in birds. J. Linnaean Soc., London 36:457-466. Kiff, L. F. In press. Notes on eggs of the Hook-billed Kite Chondrohierax uncinatus, in- cluding two overlooked nesting records. Bull, of the British Ornithologists’ Club. Lack, D. 1968. Ecological adaptations for breeding in birds. Methuen and Co., London. 409 pp. Mattox, W. G. 1970. Banding Gyrfalcons (. Falco rusticolus) in Greenland, 1967. Bird- Banding 41:31-37. Newton, I. 1979. Population ecology of raptors. Buteo Books, Vermillion, South Dakota. 399 pp. Porter, R. D., and S. N. Wiemeyer. 1972. Reproductive patterns in captive American Kestrels (Sparrowhawks). Condor 74:46-53. Rahn, H., C. V. Paganelli, and A. Ar. 1975. Relation of avian egg weight to body weight. Auk 92:750-765. Walter, H. 1979. Eleonora’s Falcon. The University of Chicago Press, Chicago and Lon- don. 410 pp. Figure 1. Falcon eggs arranged in order of increasing female body weight from left to right (American Kes- trel, Bat Falcon, Aplomado Falcon, Orange-breasted Falcon, Peregrine Falcon, Gyrfalcon). Note the in- congruity of the Orange-breasted Falcon egg location in the sequence. Fall 1981 Boyce and Kiff — Falcon Egg‘ 93 LOG $ BODY WEIGHT Figure 2. Regression line of log egg length times breadth (L*B) with log female body weight for several Falco species. Open circle shows the deviant data point for the Orange-breasted Falcon based upon Smooker’s pur- ported eggs. The asterisk shows the location of these eggs plotted against Aplomado Falcon weight. Egg size of the Orange-breasted Falcon based on female weight should fall on the regression line immediately above the purported clutch. See Table 1 for letter codes. Figure 3. Falco egg breadth regressed with egg length. The dotted lines show the 90% prediction interval for the genus. Note that three Orange-breasted Falcon eggs (black dots) lie outside the line and two lie on the line. The three outlying eggs are in the WFVZ collection. For letter codes see Table 1. MERLINS AS NEST PREDATORS by L. Henry Kermott James Ford Bell Museum of Natural History 10 Church Street, SE Minneapolis, MN 55455 The hunting tactics of the Merlin ( Falco columbarius ) and its preference for small birds as primary prey are well documented (Rowan 1921-22, Allen and Peterson 1936, Bent 1938, Lack 1971, Page and Whitacre 1975, Brown 1976, Oliphant and McTaggart 1977, Hodson 1978, Newton et al. 1978). Most reports of Merlin prey are based on anal- yses of nest remains and pellets; few are based on direct observations of hunting birds. I could find no published reports of Merlins taking nestlings directly from the nests of the prey, as has been reported for the closely related American and European Kestrels ( Fal- co sparverius and Falco tinnunculus ) (Tinbergen 1946, Drinkwater 1953, Freer 1973, Windsor and Emlen 1975). Although the occurrence of nestlings in the diet of Merlins has been reported (Armitage 1932, Roberts 1962, Sperber and Sperber 1963), the data were gathered from nest remains, not by direct observations of hunting birds. During late May and early June 1980 at Big Sky, Gallatin County, Montana, I fre- quently saw a pair of Merlins on the valley floor (elevation 1990 m) in an area of sage- brush (Artemisia sp.) divided by a stream flowing out of nearby mountains, with several beaver ponds and neighboring willows (Salix sp.). A golf course was situated amidst these surroundings, with vacation homes and condominiums scattered around the per- iphery. Many small conifers had been planted on the lawn around these dwellings. On 3 June I noticed a male Merlin seemingly foraging in these conifers— flying from tree to tree. Immediately on landing in a three-meter-high spruce ( Picea sp.) the Merlin was vigorously attacked by a pair of Robins ( Turdus migratorius) and flew off carrying an unidentified object in its talons. I searched the tree and found a Robin nest containing two unfeathered living young. I withdrew and watched from about 20 m away. The Merlin returned in about 30 minutes, flying in low and fast around the corner of a building, and landed in the same tree. The adult Robins resumed their attack and the Merlin turned and defended itself, but shortly flew off again with an object in its talons. A check of the nest revealed a single nestling. I did not see the Merlin again that day, but the next morning the nest was empty. Further investigation in the vicinity revealed many adult Robins and Robin nests in small conifers, but I could find only a single nest containing one well feathered young and saw only one fledged juvenile. Other small birds, especially Cliff Swallows ( Petro - chelidon pyrrhonata), were common in the area. I once saw a Merlin pursuing a swal- low, but it would seem that nestling Robins were easier prey. I wish to thank R. M. Timm and H. B. Tordoff for reading the manuscript. Literature Cited Allen, R. P., and R. T. Peterson. 1936. The hawk migrations at Cape May Point, New Jersey. Auk 53:393-404. Armitage, J. 1932. Merlin taking young from nests. Brit. Birds 25:303-304. Bent, A. C. 1938. Life histories of North American birds of prey. USNM Bull. No. 170:70-95. 94 Raptor Research 15(3):94-95 Fall 1981 Kermott — Merlins as Nest Predators 95 Brown, L. 1976. British birds of prey, Collins, London. 400 pp. Drinkwater, H. 1953. Young bluebird taken from nestbox by sparrow hawk (Falco spar- verius). Auk 70:215. Freer, V. M. 1973. Sparrow hawk predation on bank swallows. Wilson Bull. 85:231-233. Hodson, K. 1978. Prey utilized by merlins nesting in shortgrass prairies of southern Al- berta. Canadian Field-Naturalist 92:76-77. Lack, D. 1971. Ecological isolation in birds. Harvard Univ. Press, Cambridge, Mass. 404 PP- Newton, I., E. R. Meek, and B. Little. 1978. Breeding ecology of the merlin in North- umberland. Brit. Birds 71:376-398. Oliphant, L. W., and S. McTaggart. 1977. Prey utilized by urban merlins. Canadian Field-Naturalist 91:190-192. Page, G., and D. F. Whitacre. 1975. Predation on wintering shorebirds. Condor 77:73-83. Roberts, E. L. 1962. Merlins taking newly hatched passerines. Scottish Birds 2:245. Rowan, W. 1921-22. Observations on the breeding habits of the merlin. Brit. Birds 15:122-129, 194-202, 222-231, 246-253. Sperber, I., and C. Sperber. 1963. Notes on the food consumption of merlins. Zool. Bidrag Uppsala 35:263-268. Tinbergen, L. 1946. De sperwer als roofvijand van zangvogels (The sparrow hawk as a predator of passerine birds). Ardea 34:1-213. Windsor, D., and S. T. Emlen. 1975. Predator-prey interactions of adult and pre- fledgling bank swallows and American kestrels. Condor 77:359-361. BOOK REVIEW The Peregrine Falcon. Derek Ratcliffe. 1980. Buteo Books, Vermillion, South Dakota ($42.50) and T. & A.D. Poyser (£12) 416 pages, 4 color plates 32 bl. and white plates. Few books have been more eagerly awaited than Derek Ratcliffe s major opus on the Peregrine. It has been well worth waiting for; it is a superb book, by far the best mon- ograph on a bird of prey yet published. As might be expected Ratcliffe has handled the difficult task with great skill, concen- trating almost entirely on the North American/European races: F. p. pealei, anatum, tundrius and peregrinus. The remaining races are all briefly described in Chapter 15 at the rear of the book. This means that the text is allowed to flow freely, unhampered by continual reference to the behaviour of other races. The book opens with a realistic account of man’s relationship with the Peregrine, be he egg collector, falconer, pigeon fancier or ornithologist, followed by a discussion on population trends and a detailed summary of the distribution in the British Isles. This is so detailed that one is tempted to try to recognize individual eyries. Information has been gleaned from a wide variety of sources and the author gives generous tribute to all those who made a contribution. For me the book gained momentum from Page 126 onwards when the subject switch- es to feeding habits, nesting habitat and the breeding cycle. The spectrum broadens and comparisons are made between the behaviour of peregrinus and pealei , much of the lat- 96 RAPTOR RESEARCH Vol. 15 No. 3 ter information coming from Wayne Nelson’s thesis on the Lanagra peregrines. On Page 170 Joe Hickey’s system of grading cliffs in suitability for nesting is quoted. But is this system now valid? Dwindling populations may tend to survive longer on high cliffs remote from constant human presence. However, in parts of Great Britain where recolonisation is taking place, recolonising pairs often show a strong tendency to pick contiguous territories to a successful breeding pair despite the paucity of the cliff. Fur- thermore it has been suggested that these birds may be related to the dominant pair and this could be a factor for reducing aggression between them. However, why some first class cliffs remain vacant and some third class ones are tenanted year after year must re- main a subject for speculation. The pair bond in winter is a fascinating subject on which more light needs to be shed. Are certain Peregrines more faithful to their favourite cliff than their mates? My own experience suggests that perhaps they are. One tiercel that I know well has been present both winter and summer on the same stretch of cliff for over 6 years and has had at least 2 different mates if not 3. But the behaviour of individual pairs is so variable no hard and fast rule can be made. The most compulsive reading in the book is the chapter entitled “The Pesticide Sto- ry.’’ Here the author’s sense of personal involvement shines through the text. He is the master detective telling his own story. The photographs are, without exception, new to me and all of a very high order. Donald Watson provides many sketches which are a delight to the eye— full of atmo- sphere. The presentation is excellent and well up to the standard we have come to ex- pect from these publishers. This reviewer has no hestitation in saying that if you are a raptor enthusiast then you must have the book. I shall not be lending my copy to any- one. R. B. Treleaven RRF Annual Meeting The 1981 meeting of the Raptor Research Foundation will be held Friday, October 30 through Monday, November 2, 1981, in Montreal, Quebec, Canada. All sessions and workshops will be held in the Sheraton Mt.-Royal Hotel. The tentative schedule in- cludes workshop sessions on Friday, paper sessions from Saturday through Monday (if necessary) and tours of the Macdonald Raptor Research facilities. Evening films and an art exhibit featuring Canadian artists will also highlight the event. For more information, contact: Dr. David M. Bird, Program Chairperson Macdonald Raptor Research Center Macdonald Campus of McGill University Ste. Anne-de-Bellevue, Quebec CANADA H9X ICO THE RAPTOR RESEARCH FOUNDATION, INC. OFFICERS President Dr. Richard R. Olendorff, Division of Resources (C-932), 2800 Cottage Way, Sacramento, California 95825 Vice-President Dr. Joseph R. Murphy, Department of Zoology, 167 WIDB, Brigham Young University, Provo, Utah 84602 Secretary Dr. Jeffrey L. Lincer, P.O. Box 8, Sarasota, Florida 33578 Treasurer Dr. Gary E. Duke, Department of Veterinary Biology, College of Veterinary Medicine, University of Minnesota, St. Paul, Minnesota 55108 Address all matters dealing with membership status, dues, publication sales, or other financial transactions to the Treasurer. See inside front cover. Send changes of address to the Treasurer. Address all general inquiries to the Secretary. See inside front cover for suggestions to contributors of manuscripts for Raptor Research , Raptor Research Reports, and special Raptor Research Foundation publications. BOARD OF DIRECTORS Eastern Dr. Mark R. Fuller, Migratory Bird Lab., U.S.F.W.S., Patuxent Re- search Center, Laurel, Maryland 20811 Central Dr. Patrick Redig, Department of Veterinary Biology, College of Vet- erinary Medicine, University of Minnesota, St. Paul, MN 55101 Pacific and Mountain Dr. Joseph R. Murphy, Department of Zoology, 167 WIDB, Brigham Young University, Provo, Utah 84602 Canadian Eastern Dr. David Bird, Macdonald Raptor Research Center, Mac- donald College, Quebec, H9X ICO, Canada Western Dr. R. Wayne Nelson, 25 Montcalm Ave., Camrose, Alberta T4V 2K9, Canada At Large Dr. Richard R. Olendorff (address above) At Large Dr. Stanley Temple, Department of Wildlife Ecology, Russell Labo- ratory, University of Wisconsin, Madison, Wisconsin 53706 At Large Dr. Thomas Dunstan, Biology Dept., Western Illinois University, Macomb, Illinois 61455