Captive breeding and restocking of the Peregrine Falcon in Sweden. Peter Lindberg and Ulrika Sjöberg

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1 Peregrine Falcon populations status and perspectives in the 21 st century J. Sielicki and T. Mizera (editors) European Peregrine Falcon Working Group, Society for the Protection of Wild Animals "Falcon" Turul / Poznań University of Life Sciences Press, Warsaw - Poznań 2009, Pages Captive breeding and restocking of the Peregrine Falcon in Sweden Peter Lindberg and Ulrika Sjöberg Department of Zoology, University of Gothenburg Box 463, SE Göteborg, Sweden peter.lindberg@zool.gu.se Abstract The Swedish captive breeding-programme started in 1974 and is still running. In the period a total of 90 Peregrine Falcons (only of the subspecies F. p. peregrinus from wild pairs in Sweden, Norway, Finland and Scotland have been used). No falconry birds with uncertain pedigree were used. Of 49 females 34 laid a total of 1368 eggs, 605 were fertile and 439 young survived until fledging. Average age for egglaying females was 4,8 years and for females producing fertile eggs 6,2 years. Males were on average 7,5 years when sexually mature. Average production of fertile eggs peaked at 8 years and then declined. Average life-time for females was 12 years and the oldest egg-laying female was 16 years. The most productive female produced 54 young. Nestlings (n=279) were released at 26 hack-sites in SW Sweden in % died or were hurt and taken care of within two months of release, while 86% survived until migration started in September- October. A minimum of 8% of released birds was later observed as breeding adults. No significant difference in survival was found between hacked and wild nestlings. The release of falcons was crucial for the positive population increase observed in SW Sweden and SE Norway in 1990 s and 2000 s. Key words: Peregrine Falcon, Falco peregrinus, Sweden, reintroduction, captive breeding, sexual maturity, lifetime, egg production, survival Introduction The decrease of the Peregrine population in Sweden in the 1950 s and 60 s raised concern within the Swedish Society for Nature Conservation.

2 In southwestern Sweden the known population declined from 65 pairs in 1955 to just a few pairs in the mid 1970 s and local extirpation seemed impending (Lindberg 1985, 1988). The species was classified as critically endangered (CR) and in 1974 a national captive-breeding programme was established, based on experience and knowledge from the North American programmes at Cornell University, USA (Tom Cade), Canadian Wildlife breeding station at Wainwright (Richard Fyfe) and German breeding programmes (Christian Saar). The idea was to create a gene bank of Fennoscandian Peregrines and release the offspring. The ultimate goal was to repopulate an area (ca sq km) in south-western Sweden with a wild self-maintaining population of about pairs (ca 50% of the pre-1955 population in that area (Lindberg 1983). Source of falcons The captive stock was established with falcons collected from the distribution area of the nominate subspecies Falco peregrinus peregrinus in northern Europe with most falcons originating from south-western (SW) Sweden (Tab. 1). In contrast to many other captive breeding programs in Europe and North America we have not used falcons from falconry sources, as those might have an uncertain pedigree or origin. The population in SW Sweden probably passed a genetic bottle-neck in the 1950 s (Nesje et al. 2000, Lifjeld et al. 2002, Jabobsen et al. 2008) so we decided to add genes from Norway, northern Sweden, northern Finland and Scotland to the breeding stock. A quite different strategy was adopted by the Peregrine Fund in USA mixing different subspecies from the Pacific coast, Mexico, Spain and Scotland with the original subspecies F. p. anatum (Cade & Burnham 2003), thus creating a non-native sub-species. Numbers of original founders are given in Table 1. A captive stock of about 50 falcons was successively established. This was calculated as a minimum figure due to less than 50% of sexually mature females breeding in captivity (Cade & Fyfe 1978, Fyfe 1978). Captive breeding The breeding programme was initiated in summer of 1974 when a clutch of two eggs were collected from a nest close to the Muddus National Park, Norrbotten, N Sweden (lat 66 o N). One of the eggs hatched and the first founder, a male falcon called Felix, was imprinted and was later used for insemination for two seasons. In the following years, an increasing number of falcons were collected. 678

3 Table 1. Time of collection and origin for founders within the Swedish Peregrine (F. p. peregrinus) captive breeding-programme Reg-no Year Sex Origin Gene-code Collected as M Norrbotten, Sweden A1 egg F Invernesshire, Scotland E1 winghurt juvenile M Grampian, Scotland E2 winghurt juvenile F Lapland, Finland F1 nestling F Invernesshire, Scotland E3 nestling M Invernesshire, Scotland E4 nestling M Kilwenhy, Scotland E5 nestling F Kilwenhy, Scotland E6 nestling F Lapland, Finland F2 nestling M Lapland, Finland F3 nestling F Lapland, Finland F4 nestling F Lapland, Finland F5 nestling M Lapland, Finland F6 nestling F Bohuslän, Sweden S1 egg M Bohuslän, Sweden S2 egg M Trondheim, Norway N1 nestling M Bohuslän, Sweden S3 nestling F Bohuslän, Sweden S2 nestling M Lapland, Finland F7 nestling M Bohuslän, Sweden S1 egg M Lapland, Sweden F8 nestling M Bohuslän, Sweden S3 egg M Bohuslän, Sweden S2 nestling M Norrbotten, Sweden A2 nestling F Norrbotten Sweden A2 nestling M Norrbotten, Sweden A3 nestling F Ålesund, Norway N2 winghurt F Norrbotten, Sweden A3 nestling F Norrbotten, Sweden A3 nestling F Bohuslän, Sweden S1 nestling F Bohuslän, Sweden S1 nestling M Trondheim, Norway N1 nestling F Trondheim, Norway N4 nestling M Trondheim, Norway N4 nestling F Trondheim, Norway N1 nestling M Lapland, Finland F9 nestling F Lapland, Finland F10 nestling M Trondheim, Norway N5 winghurt F Telemark, Norway N6 nestling M Norrbotten, Sweden A3 nestling M Norrbotten, Sweden A4 egg F Norrbotten, Sweden A1 egg 679

4 Figure 1. Source of founders for the captive breeding programme in Sweden Most of the falcons were taken as nestlings (age 2-4 weeks) but a number of birds were also hatched in incubators from eggs collected from wild pairs in Sweden. Some hurt birds of known origin have also been used in the programme. Collected nestlings were placed in breeding cages at an age of 3-5 weeks and besides trying to pair birds from different nests within the same region, no other selection took place and the pairing was almost random. Chicks hatched in incubators were after a period of handfeeding with siblings fostered to pairs in captivity and later paired at an age of 2-5 months. All pairs have been kept in aviaries with covered walls and meshed roofs and had very little contact with humans. The birds have been observed through one-way mirrors and the food (four-weeks chicken, day-old chickens and quail) was presented through plastic tubes. Fertile eggs were produced almost exclusively by natural copulation. Egg-laying females have been manipulated by egg-pulling, double-clutching or triple-clutching in order to increase annual productivity. The first breeding of a pair with fertile eggs took place in 1979 and the first release of falcons started in In the early period of the project ( ), most of the falcons were placed in large aviaries at different places in southern Sweden with interested farmers as keepers (there are no falconers in Sweden as falconry and the keeping of birds of prey is forbidden) and at a breeding station in northern 680

5 Denmark (Allan Pedersen). In 1987 all the birds were moved to a newly built breeding station close to Gothenburg, southwestern Sweden. To concentrate all the birds in one place with dedicated and employed keepers made it much easier to conduct rational and effective breeding and the number of nestlings increased (Fig. 2). This captive breeding station was run between 1987 and 2000, when the project moved to Nordens Ark Foundation, an animal park in SW Sweden, specializing in captive breeding programmes for endangered Fennoscandian wildlife. Release methods Most of the produced nestlings have been released either by fostering to wild pairs or by hacking (Lindberg 1988). Results and discussion In the period a total of 90 falcons (49 females and 41 males) were used in the breeding programme. 34 females laid 1368 eggs, 605 were fertile and 439 young survived to fledging. In the following calculations of fertility rate, hatching success and life-time reproduction we have used data from 75 falcons (38 females and 37 males) from the period Of the 38 females 76% (n=29) produced eggs but only 20 (53%) laid fertile eggs and produced young. Of the males it was 17 (46%) that copulated with females and contributed to fertile eggs and 16(43%) were involved in production of young (Tab. 2). Table 2. Number of females/males involved in production of Peregrine chicks in Total Produced egg % Have laid/contributed to fertile eggs % Produced young No females No males % These figures are comparable with data from Cade & Fyfe(1978) given that about half of the females produce fertile eggs in captivity. In the period clutches were laid with 1231 eggs of which 44,9% were fertile (n=553). Hatching success was 73,4% and 406 young were fledged. Fertility rate (44,9%) is somewhat lower for the Swedish birds compared to falcons in the earlier period of the North American breeding programmes with 55,6% (The Peregrine Fund, USA) and 47,1% (Canadian Wildlife Service) (Cade & Fyfe 1978). However, the latter breeding programmes have used artificial insemination(ai) to increase the fertility rate. 681

6 Number egg fertile young Year Figure 2. Annual production of eggs, fertile eggs and young (n=439) in the Swedish Peregrine captive breeding programme

7 The annual production of eggs and young is shown in Figure 2. Numbers of young increased successively as the falcons became sexually active. Between 1987 and 1995 number of young varied between 21 to 40 but decreased thereafter as a result of ageing of the breeding birds. Time for sexual maturity and fertility The time for sexual maturity (calculated as time for egg laying) and time for producing the first fertile eggs were highly variable between the females. The youngest bird produced her first fertile eggs at two years of age. The average age for egglaying females (n=29) was 4,76 years and for females with fertile eggs 6,2 years (20 females). The males (n=17) were on average 7,47 years when sexually mature. It is well-known that captive birds have a delayed sexual maturity and Cade & Fyfe (1978) showed that the average time for females in captive breeding programmes to become mature is about five years. In a study of wild Peregrines in SW Sweden in the 1990 s the average age for first breeding was significantly lower for females (n=30) with 1,93 years and for males (n=40) with 2,65 years. Clutch size and brood size varies with female age and is generally low in the first breeding years, reaches a peak and then declines. The oldest egglaying captive female was 16 years. Among the captive females (n=20) fertility rate has a peak at 8 years (Fig. 3). A similar investigation of North American captive Peregrines shows that clutch-size, fertility and number of hatched young increase with age to peak at seven years and thereafter decline. Falcons that have experienced copulation have higher reproductive rates than inexperienced falcons of the same age. Productivity also increased with the time that the pair were together and falcons that had the same partner had higher life-time productivity than birds with a new partner. Falcons that reproduced early in life also had a higher productivity than falcons that reproduced later in life (Clum 1995). Age for females and lifetime reproductive success The oldest female to date, died at an age of 20 years and ten other females have lived to ages between 15 and 19 years. The average lifetime for a female (n=33) was about 12 years and during this time she on average laid 7,9 clutches with a total of 32,1 eggs. Of these 15,3 were fertile giving 11, 2 chicks (Fig. 4). If only 20% of these survive to sexual maturity a captive female has a successful life time reproductive output of 2,24 young. 683

8 4,5 4 3,5 3 2,5 2 1,5 1 0, Number Age (year) Figure 3. Average production of fertile eggs for ages among captive Peregrine Falcon females (n=20) , Number 15 11,97 15,33 11, , Average life span/years clutches egg fertile eggs young Figure 4. Average life-span and lifetime reproductive success for 33 captive females 684

9 Number Female reg-no Figure 5. Production of young per female (on the x-axis the registration number of the female is given) The most productive females Number of young produced during the life-time in the period for 20 females is given (Fig. 5). Several of the females hatched in the late 1990's and 2000 are still alive and productive so the figures may change with time but a general picture with a few females producing most of the young can be observed. This uneven distribution causes a dominance for certain genetic traits among the released young, well known to many captive breedingprogrammes. Life-time production is dependent on for the life span of a female but also on the age when she starts to produce fertile eggs and on the type of manipulation conducted (eggpulling, double-clutching and tripleclutching). The most productive female (No 34) produced 54 young, followed by females No 63 and 122 with 43 young each. The five most productive females (25%) produced 53% of the total number of young (n=406), while 15 females, (75%) contributed with the rest. All five productive females reached a relatively high age (14-20 year), and have been sitting with a male (not always the same) for a long period and have been manipulated by egg-pulling and double-clutching. The average time for first laying of fertile eggs was 5,4 years compared to the mean of 6,2 years for all females and fertility being much higher with 74% (mean 45%). The role of the male and the pair constellation also influence the life-time reproductive output. 685

10 Background variables and reproduction Among the background variables that have been correlated to individual reproduction are included the circumstances at collection (egg, nestling, hurt juvenile or adult bird) and eggs hatched by natural or artificial incubation (Tab. 3). Although this is a simplification of all the background variables that have an influence on future reproduction we found that the most productive females were firstly, hatched in the aviaries after natural incubation (100%), secondly, collected as a wild nestlings (66,7%) and thirdly, collected as wild nestlings (64,3%). The most reproductive males derived from wild collected eggs (66,7%) or were collected as 2) wild nestlings (64,3%). Combining both sexes the birds that most succesful were hatched in aviaries (66,7%) or collected as wild adults (66,7%), followed by wild nestlings (65,5%) and collected as wild eggs (62,5%). The least number of reproducing individuals were collected as hurt juveniles (9,1%) or artificially incubated eggs from captive pairs (38,1%). Sample sizes are small and will be further elaborated in future studies. To investigate if the geographic origin could influence individual reproduction each bird in the captive breeding programme was assigned a simplified population- or "gene-code" (S=SW Sweden, A=N Sweden, N=central Norway, F=northern Finland, E=northern Scotland). If for example a male has the code E5N1 the mother came from nest 5 in Scotland and the father from nest 1 in Norway. Each share, 0,5 from E5 and 0,5 from N1 was added and given as a total. In the Figure 6 we can read that genes from S (southwestern Sweden) have the greatest percentage share (36%) while the other (A, E, F, N) have shares between 11-19% (n=64 individuals). To estimate which genetic origin has been most successful we compared the proportion among the captive birds with the proportion of fertile eggs and hatched young. The genetic origin that increased most in the offspring generation compared to the parent generation was E4 with 83%, N4 with 48%, S2 with 32% and A2 with 26% (Sjöberg 2003, Johansson 2006). We expected that the proportion of the genes from southwestern Sweden (S) and from northern Scotland (E) should increase most as the birds had an origin from latitude 57 and were held at the same latitude, while the proportion from northern birds (latitude 66) might decrease. Wild falcons from Scotland and southwestern Sweden have about the same egglaying dates while birds from the northern latitudes lay their eggs one month later. In the beginning of the captive breeding program we tried to pair birds deriving from the same geographical population but this was later changed as a mixture gene-combinations. Tordoff & Redig (2001) have shown that captive 686

11 breeding pairs with different geographic origin and thus gene-composition were the most successful and contributed to a majority of the released falcons in North America. Table 3. Reproduction and background variables for captive Peregrine Falcons (n=75) until 2003 Collected as wild Collected from captivity No Egg Hurt Hurt Natural Nestling (incubator) juvenile adult incubation Incubator Females Reproductive % 50, 0 66, 7 16, 7 66, , 0 Males Reproductive % 66, 7 64, , 4 Females & males Reproductive % 62, 5 65, 5 9, 1 66, 7 66, 7 38, Number A1 A2 A5 A6 E3 E4 E5 E6 F1 F2 F3 F4 F8 N1 N4 S1 S2 S3 Origin Figure 6. Distribution of genetic origin among the captive falcons (N=64). For each individual the proportion of origin or "gene-code" has been added and given as a total Among the captive-produced young (n=406) in our breeding programme between genes (S) from southwestern Sweden dominated with 40% followed by Scottish (E) with 20% and Norwegian (N) with 13% (Fig. 7). Birds from N Sweden (A) and Finland (F) have contributed less than expected according to their proportion among the captive birds. 687

12 Finland 11% Norway 13% SW Sweden 40% N Sweden 16% Scotland 20% Figure 7. Genetic composition among the captive produced young (N=406) The release of falcons In addition to the release of nestlings from the captive breeding programme a number of nestlings from collected first egg-clutches from wild pairs also have been used for fostering or hacking. The method of hacking is well known and usually we have placed between 3-5 nestlings at an age of ca 5 weeks in hack-boxes situated on cliff-sites. In a few cases we have also used hackboxes placed on tall buildings (a factorybuilding, Leksandsbröd, in the province of Dalarna and at a barn in the province of Bohuslän) and on a hacktower in a marsh area (Hornborgasjön, province of Västergötland). Nestlings have been released as fledging in June, July and August and have been fed for 5-10 weeks with chickens until they were self-sustaining. Between 1982 and falcons were released from 26 hacking-sites in SW Sweden in the provinces of Halland,Västergötland, Bohuslän and Dalsland. In addition a number of young were fostered to wild pairs (Fig. 9). 688

13 P. Lindberg & U. Sjöberg. Captive breeding and restocking of the Peregrine Falcon in... Figure 8. A hacking-tower used for releases of falcons at lake Hornborgasjön, Västergötland, S Sweden. Photo P. Lindberg Peregrine Falcon populations - status and perspectives in the 21st century, 689

14 Of the hacked falcons 14% died or were hurt and taken care of within two months of release while the rest (86%) probably survived until migration started in September/October. In North America about 73-81% of the released falcons were estimated to reach the stage of independence and dispersed naturally from their hacksites. Figure 9. Hacking-stations in SW Sweden and number of birds released at each site The most critical period for the falcons is the first week after release. If they are frightened at the release some can fly away and not find their way back to the hack-box. The Goshawk Accipiter gentilis is the main predator during the first week before the falcons have got their flight skills. In the 690

15 period the hacked falcons made up 58% of the total number of fledged falcons in SW Sweden. Their proportion decreased to 34% in as more and more Peregrines fledged from wild eyries. The wild population in south-western Sweden started to increase in the 1990's and the original goal - to create a self-supporting population of ca pairs - was reached in Further releases of hacked birds stopped and our efforts were directed towards central Sweden. Of the hacked falcons 14% died or were hurt and taken care of within twoexperiments with the release of falcons in the province of Dalarna - an area totally devoid of falcons since late 1950's - was started in 1994 and in the 2007 season,129 young have been released. A local wild population of at least 5 breeding pairs were established in 2007 and this local population is estimated to increase by 10-20% annually if we continue to release between young/year. A comparison of survival (based on later observed and individually read breeding falcons) for wild nestlings (n=250) and hacked nestlings (n=277) showed no significant difference (Tab. 4, Dahlgren-Hood 1997). On average 8% of the nestlings were observed as breeding adults, which is a minimumfigure as several of the falcons have dispersed to southern Norway. Survival of hacked falcons released early in the season was significant higher than falcons released later. Table 4. Comparison of survival for hacked and wild falcon nestlings , based on number of adult falcons found breeding until 1997 No of young No found breeding found breeding % Hacked , 9 Wild , 0 χ 2 = 0, 0187, df=1, p=0, 887 Conclusion The captive breeding programme in Sweden and the release of falcons has been crucial for the recovery of the Peregrine population in southwestern and central Sweden and also in south-eastern Norway. Although the number of released falcons has been low compared to many other reintroduction projects in North America and Germany, we have reached the goal in less time than expected. By using falcons from different local populations within the subspecies range of F. p. peregrinus we have avoided inbreeding problems and the south Fennoscandian Peregrine population today exhibit a genetic variation close to the level before the population passed a bottle-neck in the 1950 s (Nesje et al. 2000, Lifjeld et al. 2002, Jabobsen et al. 2008). 691

16 P. Lindberg & U. Sjöberg. Captive breeding and restocking of the Peregrine Falcon in... Figure 10. A hack-box at lake Vänern, Västergötland used for the release of 27 falcons between Photo P. Lindberg 692 Peregrine Falcon populations - status and perspectives in the 21st century,

17 P. Lindberg & U. Sjöberg. Captive breeding and restocking of the Peregrine Falcon in... Figure 11. Mountain hacking box. Photo L. Bertilsson The project was evaluated by the Swedish Environmental Agency in the beginning of the 1990 s and population viability analysis (PVA) showed that the south Swedish Peregrine population probably would have been extinct if no manipulation and releases had been conducted (Ebenhard 1992, 2000). References Cade T.J., Burnham W. (eds) Return of the Peregrine, A north American Saga of Tenacity and Teamwork. The Peregrine Fund, Boise, Idaho, USA. Cade T.J., Fyfe R.W What makes Peregrine Falcons Breed in Captivity? In: Temple S.A (ed.). Endangered Birds Management Techniques for Preserving Threatened Species, pp University of Wisconsin Press, Madison. Clum N.J Effects of ageing and mate retention on reproductive success of captive female Peregrine Falcons. American Zoologist 35, 4: Dahlgren-Hood J Beteenden och överlevnad hos pilgrimsfalkar utsläppta genom hacking. Behaviour and Survival for hacked Peregrines. Master thesis, pp University of Gothenburg. Ebenhard T Projekt Pilgrimsfalk, en utvärdering. På uppdrag av Världsnaturfonden, Naturskyddsföreningen, Naturvårdsverket Peregrine Falcon populations - status and perspectives in the 21st century, 693

18 Ebenhard T Population viability analyses in endangered species management: the Wolf, Otter and Peregrine Falcon in Sweden. Ecol. Bull. 48: Fyfe R.W Reintroducing Endangered Birds to the Wild, A Review: Endangered Birds, Management Techniques for Preservering Threatened Species, In: Temple S.A. (ed), University of Wisconsin Press, Madison. Jacobsen F., Nesje, M., Bachmann L. & Lifjeld J.T Significant genetic admixture after reintroduction of Peregrine Falcon Falco peregrinus in southern Scandinavia. Cons. Genetics 9, 3: Johansson J Släktskapsförhållanden samt analys av de stamboksförda pilgrimsfalkarna Falco peregrinus. Rapport nr 5/2006, pp Svenska Naturskyddsföreningen, Stockholm. Lifjeld J.T., Björnstad G. Steen O.F., Nesje M Reduced genetic variation in Norwegian Peregrine Falcons Falco peregrinus indicated by minisatellite DNA fingerprinting. Ibis 144: 1-8. Lindberg P Captive breeding and programme for reintroduction of the Peregrine Falcon Falco peregrinus in Fennoscandia. Proc. Third Nordic Congr. Ornithol. 1981: Köpenhamn. Lindberg P Population status, pesticide impact and conservation efforts for the Peregrine Falco peregrinus in Sweden, with some comparative data from Norway and Finland. In: Newton I. & Chancellor R.D. (eds.). Conservation Studies on Raptors World Conference on Birds of Prey. Report of Proceedings, Thessaloniki ICBP Techn. Publ. 5: Lindberg P Reintroducing the Peregrine Falcon in Sweden. In: Cade. T.J., Enderson J.H., Thelander C.G. & White C.M. (eds.). The Peregrine Falcon Populations. Their Management and recovery, pp Peregrine Fund, Inc., Boise, Idaho. Moen S.M., Tordoff H.B The genetic and demographic status of Peregrine Falcons in the upper Midwest. The Bell Museum of Natural History, pp Univ. of Minnesota. St. Paul MN. Nesje M., Roed K.H., Lifjeld, J.T., Lindberg P., Steen O.F Genetic relationships in the Peregrine Falcon Falco peregrinus analysed by microsatellite DNA markers. Mol. Ecol. 9: Nesje M., Roed, K.H., Bell, D.A, Lindberg P., Lifjeld J.T Microsatellite analysis of populations structure and genetic variability in Peregrine Falcons Falco peregrinus. Animal Conservation 3: Sjöberg U Reproduktion hos burhållna pilgrimsfalkar Falco peregrinus. Master thesis, pp University of Gothenburg. Tordoff H.B., Redig P.T Role of genetic background in the success of reintroduced Peregrine Falcons. Conservation Biology 15, 2: