The fall and the rise of the Swedish Peregrine Falcon population. Peter Lindberg

Transcription

1 Peregrine Falcon Populations status and perspectives in the 21 st Century J. Sielicki & T. Mizera (editors) European Peregrine Falcon Working Group, Society for the Protection of Wild Animals Falcon Turul, Warsaw 2008, Pages The fall and the rise of the Swedish Peregrine Falcon population Peter Lindberg Department of Zoology, University of Gothenburg Box 463, SE Göteborg, Sweden Abstract The Swedish Peregrine-population increased with 5-10% annually in the 1990 s as a combined result of lower levels of OCs and mercury in prey species and management with captive breeding and release of young esp. in SW Sweden. Estimated population size in 2007 was >175 pairs. Productivity has increased since the 1970 s and average brood-size for successful pairs in was between 2,2-2,7. Males in SW Sweden started to breed at 2,7 years and females at 1,9 years. Females had on average 1,6 partners during the life-time while the males had 1,3 partners. Key words: Peregrine Falcon, Falco peregrinus, Sweden, genetic diversity, inbreeding depression, breeding biology, population increase, productivity, age at first breeding Historical data The Peregrine Falcon was once distributed all over Sweden with the exception of the northern mountain areas. Former population-size has been estimated to be pairs. It was mainly a cliff breeder but part of the population bred in trees and in N Sweden on bogs (Lindberg 1975, 1985,1988). Population decline started in S Sweden already in the 's due to persecution (hunters, pigeon-fanciers) but the main decline occurred after 1945 following the introduction of DDT and several other organochlorines. Thinshelled eggs were recorded in Sweden as early as 1947 and DDE was found in

2 shell-membranes from eggs collected in Finland in In addition, alkyl mercury was used as a seed-dressing agent in agriculture and widespread mercury poisoning among seed-eating birds and small mammals occurred, as well as amongst birds of prey. A combination of lowered reproduction due to DDT and an increased mortality caused by mercury and more toxic organochlorines such as dieldrin and aldrin resulted in a population decline not only in Sweden but in many other areas of Europe.. In the 1950's the population was estimated to be 350 pairs and in 1975, 15 pairs. After the ban of mercury, DDT, PCBs etc in the 1960 s and 1970 s, levels of prey-species decreased, which resulted in both better survival and reproduction among falcons. Figure 1. Attacking female Peregrine at nest in Bohuslän, Sweden. Photo: P. Lindberg Active conservation An action plan involving nest guarding, captive breeding and pesticide monitoring was initiated in 1972 by the Swedish Society of Nature 126

3 Conservation. The declining population became separated into two subpopulations, N and S Sweden with no gene-flow between each other (Fig. 2). The southern population was more or less inbred. In a DNA-study of museum specimens from 1871 and onwards it was shown that the south Scandinavian population passed a genetic bottleneck between 1871 and 1950 due to severe persecution and a second bottleneck after 1950 due to the effects of pesticides (Jacobsen et. al. 2008, Lifjeld et al. 2002, Nesje et al. 2000). Figure 2. Distribution and estimated population size for the Peregrine population in Sweden The aim of the captive breeding programme was to restore a population of >25-30 breeding pairs in SW Sweden. Details of the breeding of >25-30 breeding pairs in SW Sweden. Details of the breeding programme are given in a separate paper. Between 1982 and 1997, about 280 juveniles were released at 26 hacking sites in S Sweden and additional juveniles were fostered to wild birds. Survival of wild and captive-raised falcons was not significantly different and >8% were found breeding in the wild. Double-clutching was also used to increase production of young and to diversify the gene-pool of the captive population. As a result, the wild population in S Sweden started to increase from 6 pairs in 1990 to 29 pairs in 1999 and to 63 territorial and 57 breeding pairs in 2007 (Fig. 5). Rate of increase varied from 5-10% annually 127

4 and will probably continue. Competition and predation from Eagle Owls is severe in many areas. Productivity (=young/occupied territory) has increased and in was between 1,5 and 1,7. Breeding-data for the Peregrines in S Sweden in is given in Tab. 1. Average clutch-size varied from 3,38 to 3,63 and brood-size from 2,25 to 2,75. Figure 3. Two typical breeding-cliffs for the Peregrine Falcons in SW Sweden. To the left is a traditional cliff in an agricultural valley in Halland, the picture to the right is a small cliffface situated on island in a clear-water lake in Västergötland. The falcons are breeding in the remains of a Raven nest. Both these cliffs were unoccupied between 1960 and the end of 1990's. 54 breeding cliff-sites in SW Sweden have an average height of 50 meter (range meter) and 78% have water (lake or sea) beneath the cliff. Photo: P. Lindberg In SE Norway, adjoining SW Sweden, a similar increase has occurred from a few pairs to a recent population of > 60 pairs, of which many have their origin in Sweden. The use of non-native genetic stock has increased genetic diversity and prevented inbreeding depression. The population in N Sweden is associated with falcons in N Finland and N Norway and is genetically different from birds in S Sweden. This population is highly migratory and winters in W and S Europe. A significant population increase started at the end of 1980 s from less than 20 known pairs to > pairs in

5 Figure 4. Some typical breeding-sites for Peregrines in the province of Norrbotten, N Sweden. Most common are cliffs of various heights situated in the taiga but large bogs are also popular nest-sites. The pairs breeding on the bogs are more exposed to harsh weather-conditions and have a lower production of young compared to cliff-breeders. Photo: P. Lindberg 129

6 Number pair young hacked young Figure 5. The Peregrine population increase in S Sweden the 1990 s, the increase was mainly as a result of the captive-breeding programme. Pair = breeding pair. Table 1. Number of territorial pairs and breeding results for Peregrines in S Sweden Mean ±SD is given for egg-clutch and brood-size. Year territorial pairl A breeding pair B successful breedings C (%) successful clutch-size mean± SD (n) D ringed nestlings not ringed (%) brood-size mean±sd (n) E estimated fledged young young/ breeding pair young/ successful breeding (70%) 3, 38±0, 9 (27) , 67±1, 2 (18) 48 1, 78 2, (76%) 3, 63±0, 6 (24) 54 4 (7%) 2, 25±0, 9 (24) 56 1, 65 2, (82%) 3, 61±0, 6 (33) 70 5 (7%) 2, 50±0, 9 (28) 73 1, 87 2, (77%) 3, 58±0, 8 (33) 84* 3 (3, 5%) 2, 59±1, 0 (29) , (69%) 3, 52±0, 8 (25) 93* 5 (5%) 2, 67±1, 0 (30) 77 1, 57 2, (82%) 3, 71±0, 6 (23) 90* 10 (10%) 2, 36±1, 1 (33) 92 1, 88 2, (79%) 3, (3%) 2, , 02 2, (74%) 3, 62±0. 6 (21) (3, 5) 2, 75±1, 0 (41) 114 2, 0 2, 71 A territorial pair, 2 territorial birds at one or more occasions during April-July B breeding pair, started egg-laying, to this category also the sibling pair in Hälsingborg has been included as the birds are used as fosterparents C successful breeding, >1 ringed or fledged nestling D a small number of these young have been transferred to central Sweden or collected for captive breeding E brood-size for ringed birds from first-clutches and not manipulated clutches * only first clutches 130

7 In 1994 release of captive bred birds started in Central Sweden, an area depleted of falcons. Here, the aim is also to create a local self-sustaining population that can increase the gene-flow between the N and S population. 3 2,8 2,6 2,4 Brood-size 2,2 2 1,8 1, Year S Sweden N Sweden Figure 6. Peregrine Falcon brood-size in Sweden Brood size in both N and S Sweden is higher than in the 's probably as a result of significant lower levels of organochlorines in the eggs. Results Based on colour-ringed birds we found that females (n=30) on average started to breed at an age of 1,93 years and bred for 4,3 years (range 1-11 years, n=25). Several females that started to breed after one year (2 nd calendar year), were successful. In all these cases the male was in adult plumage. Females (n=25) had on average 1,6 partners during their life-time but one female had five different partners. Two females have reached the age of 17, one bird breeding in southern Sweden and one breeding in northern Sweden. This latter bird was killed by a car on its wintering grounds in France. Males (n=40) started to breed later, on average at an age of 2,65 years and bred for 4,1 years (range 1-8). On average the male had 1,3 partners during his life-time. The total Swedish population was estimated to be > pairs in 2007 but although the population trend is positive new contaminants such as brominated flame-retardants (PBDEs) and PFOS might hamper a further population increase. 131

8 References 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: 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 Pilgrimsfalken i Sverige. Svenska Naturskyddsföreningen, pp Stockholm. 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., Schei P.J.,Wikman M The Peregrine Falcon in Fennoscandia. 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. 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: 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: