Kleptoparasitism by Bald Eagles (Haliaeetus leucocephalus) as a Factor in Reducing Peregrine Falcon (Falco peregrinus) Predation on Dunlin (Calidris alpina) Wintering in British Columbia

Introduction Kleptoparasitism by animals pertains to the opportunistic or habitual stealing of food from other animals. The kleptoparasite benefits by eating food that it could not have obtained itself or by saving energy by not having to search for or capture that food (Shealer et al. 2005). Kleptoparasitism is particularly common in waterbirds, including gulls, skuas, jaegers, and fri gatebirds (Furness 1987; Calixto-Albarran and Osorno 2000), and it has been documented for numerous Falconiformes (Brockmann and Barnard 1979; Paulson 1985). Among raptors, intraguild kleptoparasitism benefits larger species over smaller species or smaller conspecifics. For instance, in Alberta and British Columbia, Peregrine Falcons (Falco peregrinus) were forced to surrender their prey to pursuing Buteo hawks, and Merlins (Falco columbarius) were kleptoparasitized by pere grines (Dekker 1980, 2009). Similarly, female peregrines commonly rob male peregrines, which are comparatively smaller than females (Cade 1982; White et al. 2002). The interand intraspecific kleptoparasitic habits of the Bald Eagle (Haliaeetus leucocephalus) are well known (Palmer 1988; Buchler 2000). Jorde and Lingle (1998) reported that stealing fish and waterfowl from other raptors was a major food-gathering method of eagles wintering in Nebraska. On the Pacific coast of British Columbia, Bald Eagles commonly kleptoparasitized gulls and crows, as well as conspecifics, and they routinely robbed peregrines of captured seabirds (Dekker and Bogaert 1997; Dekker 1999). On Vancouver Island, eagles pirated 13 (28%) of 46 ducks captured by wintering peregrines, and, in central Alberta, Bald Eagles took four (25%) of 16 ducks from wintering Gyrfalcons (Falco rusticolus) (Dekker 1995; Dekker and Court 2003). On Vancouver Island and in the Fraser River Valley, peregrines lost just-caught ducks and Dunlin (Calidris alpina) to Gyrfalcons and Bald Eagles (Dekker et al. 2012). After a numeric low in the mid-1900s, Bald Eagle populations have recovered in much of North America (Buchler 2000; Watts et al. 2007; Elliott et al. 2011; Hipfner et al. 2012; Elderkin 2014). Bald Eagles are year-round residents at Boundary Bay near Vancouver, British Columbia, and, in the lower Fraser River Valley, nesting territories increased from two in the 1960s to 108 in 2008 (Hancock 2003; Goulet 2009). At Boundary Bay, resident eagles are joined by migrants that begin arriving in October and reach peak numbers in January (Dekker et al. 2012). The wintering population has grown since 1994. In an eight-year census at the Vancouver Regional Landfill, eagles peaked at 453 in 2001 (Elliott et al. 2006). In an ongoing census at the same landfill, 1812 eagles were counted on 1 January 2014 (D. Hancock, personal communication). The growing number of Bald Eagles on the coast of British Columbia and their increasing kleptoparasitic pressure on Peregrine Falcons was investigated by Dek Kleptoparasitism by Bald Eagles (Haliaeetus leucocephalus) as a Factor in Reducing Peregrine Falcon (Falco peregrinus) Predation on Dunlin (Calidris alpina) Wintering in British Columbia