White-tailed Eagle hunting behavi- our and food choice in Kvismaren Sergio Ovidio Pinedo Valero

I ett nystartat projekt fältsäsongen 2008 undersöktes de häckande havsörnarnas bytesval i Kvismaren. Ob- servationerna har kompletterats med rapporterade jaktresultat i Kvismaren registrerade på Svalan 2007 och 2008. De vanligaste bytena var sothöna och grågås vilket också speglar vilka byten som är mest talrika och lätta att fånga i Kvismaren.

Abstract Kvismaren and to analyze the possible effect The food choice of the breeding White-tailed on populations of interest e.g. Greylag Eagles Haliaeetus albicilla in Kvismaren was stu- anser and Coot. died during the season 2008 in a new project. Different species were the main part in the Material and method White-tailed Eagles’ diet. The most common Observations of White-tailed Eagles searching hunting behaviour observed was direct attacks for food were noted both separately and when on prey, and the species attacked most often carrying out other tasks, in particular invento- was the Coot Fulica atra. In any case, like in ries of Marsh Harrier Circus aeruginosus, ringing other areas, the diet of White-tailed Eagles in of and crane censuses. Activity related to Kvismaren seems to mirror the most common hunting such as direct flight towards waterfowl and most easy taken prey species. flocks or attacks on individual birds were no- ted. Scavenger behaviour (carrion feeding) was Introduction also noted. Other activities such as territorial The White-tailed Eagle population is increa- flights, soaring, resting, or defensive behaviour sing all over Sweden and at present the Swedish against attacks from other birds were also no- population is around 550 breeding pairs (Na- ted. Time and place of observation, type of turvardsverket 2008). In 2007 the White-tailed activity, number and age of eagles and prey Eagle bred successfully for the first time in the species were registered in a database. Kvismaren valley. Also in 2008 the same pair In connection to ringing White-tailed Eagle raised two youngsters. chicks, prey remains were collected around the The species is a versatile hunter and is the nest and identified. After the breeding season, largest bird of prey in the country. It is opp- one more visit to the nest place was made in ortunistic in its search for food (Grubb 1995) order to collect more prey remains. All prey and thus it may be a predator, scavenger, and remains were stored in a freezer and sent to kleptoparasite that eats fish, water birds, mam- the Swedish Museum of Natural History after mals, and carrion. Several studies have been the season. The own data obtained during the carried out with the aim of analyze the diet season 2008, were completed with one more of the White-tailed Eagle in different areas of group of data compiled through a search at north Europe (Sulkava 1997, Wille & Kampp the website of Artportalen (www.artportalen. 1983, Watson 1992, Willgohs 1961). se). The data obtained through this website The aim of this new project is to determine from Kvismaren are from the years 2007 and food choice of breeding White-tailed Eagles in 2008.

22 23 Table 1. Observed hunting activities for White-tailed Eagle in Kvismaren. Type of hunting: Active hunting Scavenger Klepto- Undeter- Number of parasit mined occasions Success?: Yes No Undet Yes Yes Yes Yes Prey species Coot 7 7 Greylag Goose 5 1 6 Undetermined fish 2 1 3 Teal 1 1 2 1 1 2 Roe Deer 2 2 Undetermined bird 1 1 2 Snipe 1 1 Crane 1 1 1 1 Undet bird/mouse 1 1 Total 16 5 1 2 3 1 28

Resultsy The main species affected by the eagle’s klep- A total of 33 observations of eagle food search toparasitic behaviour was the Osprey Pandion activity were noted. Only 28 of these obser- haliaetus. In one case the eagles also stole a prey vations were considered direct attempts to get from a Marsh Harrier. Only in two cases (7 % food. Table 1 shows a list of species attacked of the total) the hunting behaviour observed by White-tailed Eagles as well as number of was scavenging, eagles feeding on the carrion attacks, hunting behaviour and hunting suc- of a Roe Deer Capreolus capreolus. In one case cess. Predator and scavenger behaviour was (4 %) a White-tailed eagle brought a fish to also recorded for the Kvismaren White-tailed the nest, but the hunting behaviour could not Eagles. be determined; the fish may have been caught The species with the highest rate was the alive, by food-piracy or taken as carrion. Coot with 25 % of the attacks observed during The relative shares of different prey (n=24) the seasons, and 100 % of hunting success. types for White-tailed Eagles in Kvismaren are The second species in number of attacks was shown in Figure 1. the Greylag Goose with 21 % of the attacks If food items are grouped by class, and of 83 % hunting success. Teal Anas crecca birds are the most important prey group in the and Bean Goose Anser fabalis, both accumula- White-tailed Eagle’s diet, with 76 %. ted the 10 % of the observed attacks. Other bird species attacked by the eagles were the Discussion Mallard Anas platyrhynchos, Gal- The Sea Eagle hunting strategy is rather opp- linago gallinago and Common Crane Grus grus, all ortunistic; this means that the eagle hunts of them with 7 % of the observed attacks. items of which there are many present and As for the hunting behaviour, 79 % of the easy to catch. Like in other areas, the diet of cases were considered predator behaviour, with the White-tailed Eagles in Kvismaren seems the eagles attacking bird flocks or individuals to be diverse and may be obtained through directly. In the 11 % of the eagles observed, different hunting behaviours. The present data the hunting behaviour was kleptoparasitic. could indicate a specialization in the hunting

24 The old White-tailed Eagle pair that breeds in Kvismaren are sitting in one of their favourite trees waiting for the next time to hunt. Photo: Anders Andersson.

Sea eagle diet in Kvismaren Natural reserve

3,85% Coot 3,85% Greylag goose 7,69% Mallard 30,77% 3,85% Magpie Snipe 11,54% Undetermined duck Undetermined 3,85% Pike 3,85% Roe deer 23,08% 3,85% Teal Undetermined prey 3,85% Figure 1. Food choice of Sea eagles in the Kvismaren area.

24 25 of birds and feeding that agrees with studies Acknowledgments done in Norway (Willgohs 1961) where birds To all the people of Kvismaren who made constituted the greater part of their diet th- my life in Sweden easier and more enjoyable, roughout the year. in particular: Maja Bergman, Maja Tarka, Jan The most common larger breeding water Sondell, Andreas Tranderyd, Bo Nielsen, birds in Kvismaren are Greylag Goose (300 and all the people from Lund University for pairs, estimated number), Mallard (150 pairs) lending me the car and for the barbecue and and Coot (100 pairs). Coot has been recor- football days. ded as the main bird prey for White-tailed Eagles in populations in Northern Europe Contact (Dementavičius 2004). The large, stable po- Adress: Callejón Boteros nº9, pulation of Coot during the study period in 16600 San Clemente (Cuenca). Spain. Kvismaren could stimulate the breeding pair E-mail: [email protected] to specialize on Coots. The Coot also seems to be an easy prey for the White-tailed Eagle to References hunt, if we compare it with the other present Dementavičius D. 2004. Common Buzzard species. During the present study, the Greylag (Buteo buteo) and White-Tailed Eagle (Ha- Goose has been observed successfully defen- liaeetus albicilla): Breeding parasitism or ding their offspring against the White-tailed atypical feeding behaviour? Acta Zoologica Eagle attacks. Coots were never observed Lituanica. 14: 76–79. trying to defend themselves. However Greylag Grubb T G. 1995. Food habits of Bald Eag- Goose was the second most common prey. les breeding in the Arizona Desert. Wilson The Mallard is almost not at all present in the Bulletin. 107: 258–274. material. It may be much more difficult to hunt Sulkava, S, Tornberg, R, Koivusaari, J. 1997. as it easily disappears in the scrub. Diet of the white-tailed eagle Haliaeetus al- The results obtained during the last two bicilla in Finland. Ornis Fennica. 74: 65-78. seasons indicate a preference for birds as a Watson, J, Leitch, A F and Broad, R A. 1992. food resource and for as hunting The diet of the sea eagle Haliaeetus albicilla behaviour, at least during the breeding season and golden eagle Aquila chrysaetos in wes- when the large populations of birds present tern Scotland. Ibis. 134: 27–31 in Kvismaren seems to be the most available Wille, F & Kampp, K. 1983. Food of the food resource. white-tailed eagle Haliaeetus albicilla in The food composition may change in the Greenland. Ecography 6: 81–88. future during breeding season in accordance Willgohs, J F. 1961. Univ. Bergen Arb. Mat.- with future fluctuations in birds populations Nat. Ser. 12: 1–212. or food resources at Kvismaren. That is rela- Naturvårdsverket. 2008. http://www.natur- ted to the opportunistic foraging behaviour vardsverket.se/en/InEnglish/Menu/State- described for the eagles of the Halia- of-the-environment/Habitats-and-species/ eetus (Grubb 1995). At the moment the prey The-marine-environment/ sample size (n=28) is too low to draw any firm conclusion, but in the coming years with more observations, we may be able to analyze cha- racteristics of the diet of White-tailed Eagles in Kvismaren, and how this may affect bird populations.

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