The Occurrence and Reestablishment of White-Tailed Eagle and Golden Eagle As Breeding Birds in Denmark

The occurrence and reestablishment of White-tailed Eagle and Golden Eagle as breeding birds in Denmark Erik EhmsEn, LEnnart PEdErsEn, hans meltoftE, tschErning cLausEn & timmE nyEgaard (Med et dansk resumé: Forekomst og genetablering af Havørn og Kongeørn som danske ynglefugle) Abstract Except for a number of largely unsuccessful breeding attempts during the second half of the 20th century, the White-tailed Eagle Haliaeetus albicilla had been absent as a breeding bird in Denmark for more than 80 years, when a population established itself during the second half of the 1990s. Released from persecution and contaminants the population has grown to 37 pairs in just 16 years. Reproductive success has grown with age and experience of the birds, so that the average number of fledged young per breeding pair peaked with almost two per pair 8-10 years after the establishment of each breeding pair. Similarly, the Golden Eagle Aquila chrysaetos reestablished a small population in Denmark from 1999 onwards after probably having bred here until about 150 years ago. For both species, this success was facilitated by conservation efforts including protection zones around eagle nests, monitoring and public outreach mainly carried out by volunteers from the Danish Ornithological Society / BirdLife Denmark. Introduction in former times, while the White-tailed Eagle bred in The reestablishment of White-tailed Eagle Haliaee- Denmark until it was driven extinct by persecution tus albicilla and Golden Eagle Aquila chrysaetos as in 1912 (Løppenthin 1967). The latter species made breeding birds in Denmark in the 1990s is one of a number of – usually unsuccessful – breeding at- the greatest achievements in modern Danish bird tempts during the second half of the 20th century, and nature conservation. Hitherto, is has been until the first pair of the recent population succeed- questioned that the Golden Eagle bred in Denmark ed in 1996 (Juhl et al. 1996, Génsbøl 2003). The first Dansk Orn. Foren. Tidsskr. 105 (2011): 139-150 140 Reestablishment of breeding eagles in Denmark pair of Golden Eagles nested a few years later (Knud- Also, a chick-ringing programme was initiated in sen et al. 2000). 2007. The results of all these efforts are published in The present paper is largely a summary of data annual reports (e.g. Pedersen & Ehmsen 2010). already published in reports and papers on the oc- In connection with the present review, the lit- currence and reestablishment of these two species erature was scrutinized for information on histori- as breeding birds in Denmark with the aim of mak- cal records. Since the 1970s, regional and national ing these reports available to an international audi- ‘Report Groups’ have gathered bird observations ence (see also Tofft 2002 for an account on Danish from all parts of the country and produced annual White-tailed Eagles in German). reports summarising the most interesting observations (e.g. Christensen & Lange 2010). The observations are now recorded digitally in a web-based da- Material tabase, DOFbasen, holding more than one million The data for this paper were collected by the Danish annual bird records from recent years. Ornithological Society / BirdLife Denmark. Since 1991, Project Eagle has monitored the reestablishment and growth in the Danish eagle populations. Pre-1970 occurrence of eagles in Denmark The monitoring is organized through two volunteer The White-tailed Eagle had probably nested in national coordinators (LP and EE) and a network of Denmark for thousands of years when it became volunteer ‘nest coordinators’ responsible for each extinct in 1912 (Løppenthin 1967), and until the eagle pair, keeping track of the whereabouts of the mid-19th century the species was a relatively com- eagles, their nests and their reproduction. However, mon breeder in most parts of the country. In total, with the recent increase and expansion of the po- 50-60 nesting sites are documented in Denmark pulation it has proved increasingly difficult to keep from the second half of the 19th century (Fig. 1; track of all the pairs, and it is likely that a few pairs Skovgaard 1927, Schiøler 1931), but at that time the have been missed in the latest years. decrease of the population had already begun, es- In addition, national censuses of wintering ea- pecially in regions harbouring the densest human gles have been organized each February since 2006. population. After 1890, only a few pairs bred, all at Fig. 1. Nineteenths century nest sites (open circles; from Skovgaard 1927) for White- tailed Eagles in Denmark, together with present nest sites for White-tailed Eagles (2010; filled circles) and Golden Eagles (red stars). The lack of 19th century sites in southernmost Jutland is confirmed by German ornithologists (the area belonged to Germany during 1864-1918). The position of one nest in SE Denmark is kept secret and marked a little off the true position on the map. Kendte ynglepladser for Havørn i Danmark i 1800-tallet (åbne cirkler) sammen med de nuværende ynglepladser for Havørn (2010; fyldte cirkler) og Kongeørn (røde stjerner). Placeringen af en rede på Møn holdes hemmelig og er markeret lidt forskudt på kortet. Reestablishment of breeding eagles in Denmark 141 fjords in East Jutland, and in 1912 one of the birds in the last pair was deliberately poisoned (Schiøler op.cit.). The main reason for the extermination was shooting and poisoning by gamekeepers, but also collectors took their toll of birds and eggs. A few examples illustrate the intensity by which eagles were shot: at one estate, twelve White-tailed Eagles were shot in 1885, and at another eight were shot in 1889 (Jørgensen 1989). Eagles could legally be shot year round until 1922, when a closed season from 1 February to 31 July was introduced; they were fully protected in 1928. Since then, a pair of White-tailed Eagles nested in southern Zealand in 1952-1960 and another pair on Lolland in 1957-1961, but only the pair on Zea- land succeeded in raising young (in 2-3 of the years (Jørgensen 1989); see also Preuss & Aaris-Sørensen 1981). At the same time, during a few years around 1960, a pair nested at lake Bankel in South Jutland (Tofft 2002). A pair attempted to breed on Lolland again in 1979-1980, but failed (perhaps due to con- tamination of the eggs, Dyck et al. 1988). Concerning the Golden Eagle, earlier reports of breeding in Denmark (until the mid 19th century) were questioned by Schiøler (1931) and rejected by Salomonsen (1963) and Løppenthin (1967). How- ever, since the species is currently breeding in old Fig. 2. Phenology of stationary (filled bars) and migrating forests in Denmark, it may well have done so even (open bars) White-tailed Eagles in Denmark 1952-1966 (N in former times. = 540) and 1995-2005 (N = 14597), shown as percent per In addition to the breeding birds, both White- 10-day period (data from Andersen-Harild (1968) and the tailed and Golden Eagles have always been annual present study). visitors in Denmark. According to Dybbro (1978), the Fænologi for stationære (blå søjler) og trækkende (åbne søjler) Havørne i Danmark 1952-66 og 1995-2005, vist som White-tailed Eagle was a rare visitor during winter procent pr 10-dagesperiode (ældre data fra Andersen-Harild and migration and a very rare, but regular summer 1968). visitor. Most birds occurred on traditional wintering sites in the eastern parts of the country, with a to- dividuals were immature, and most were seen in tal of 20-40 observations per year. Andersen-Harild northern Jutland where the majority were recorded (1968) estimated the number of individuals on the as spring migrants during April and May at Skagen, traditional wintering sites at 7-13 (1-6 adults and the northernmost tip of Jutland (Møller 1978, Jør- sub-adults (≥5th year of life) and 3-7 younger birds. gensen 1989). Wintering birds were concentrated to The birds began to arrive in October, but numbers eastern Denmark and probably came from Sweden did not peak until late January – early February, and and Finland (Jørgensen op.cit.). most birds departed during March and early April (Fig. 2). In northern Jutland, spring migration peaked in March-April (Møller 1978). The White-tailed Post-1970 occurrence of eagles in Denmark Eagles in eastern and southern Denmark probably The characteristics by Dybbro (1978) were largely came from Sweden and Germany, while Norwegian maintained in the last annotated Danish checklist birds may occur in Jutland (Jørgensen 1989, Bakken (Olsen 1992), although the annual number of win- et al. 2003, Bønløkke et al. 2006). tering and migrating White-tailed Eagles now were With a total of c. 20 observations per year the given as 5-30 and 20-40 per year, respectively. For Golden Eagle was a rare visitor in most of the coun- Golden Eagles, 2-5 records per year were given for try during winter and migration, and a very rare the autumn passage, 1-5 for the spring migration at and irregular summer visitor (Dybbro 1978). All in- Skagen, and 1-4 for wintering birds on Zealand. 142 Reestablishment of breeding eagles in Denmark sites, and 78 were seen on autumn migration at eight sites (Lange & Christensen 2008). The increase is illustrated in Fig. 3 which, however, is also influenced by the reporting intensity from the Danish birdwatchers. To get some idea of the development of this reporting intensity, we have used 29 other bird species for which data are available during the entire period, and for which the status has remained more or less stable during the period (data from P. Lange and J.S. Christensen in litt.). According to this, reporting intensity increased by 25 % between 1978-87 and 1988-1997, and by 37 % between 1978-87 and 1998-2006.

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