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American White Pelicans force copulations with nestlings.

Article Excerpt
Forced copulation is a behavior used by males of some species as a strategy to fertilize females that would otherwise be unreceptive (McKinney et al. 1983). The proportion of fertilization events gained via forced copulations is likely low (e.g., 2-5%; Dunn et al. 1999), but this behavior is generally considered adaptive and has been reported for several avian orders (e.g., Anseriformes, McKinney et al. 1983; Charadriiformes, Ewins 1993; Passeriformes, Rising and Flood 1998; and Galliformes, Giudice and Ratti 2001). On rare occasions, forced copulation attempts by adults are directed toward conspecific young. We found a small number of reports of adults attempting to copulate with fledged conspecific juveniles (Armstrong 1988, Ewen and Armstrong 2002) and with unfledged chicks (Kinkel and Southern 1978, Besnard et al. 2002). Fledged juveniles may be mistaken for adult females in some species, but there is no obvious adaptive explanation for forced copulations with unfledged chicks. The motivation for forced copulation with unfledged chicks is therefore unclear.

We describe patterns associated with forced copulation attempts on chicks by adult American White Pelicans (Pelecanus erythrorhynchos; hereafter pelicans) in a breeding colony in Saskatchewan, Canada. To our knowledge, this behavior in pelicans has been reported anecdotally once previously (Schaller 1964) and remains poorly characterized for birds.

METHODS

We observed interactions between adult pelicans and chicks in breeding colonies on two islands in the Last Mountain Lake National Wildlife Area and Migratory Bird Sanctuary in Saskatchewan, Canada (51.1[degrees] N, 107.0[degrees] W). The islands were shared with breeding colonies of Double-crested Cormorants (Phalacrocorax auritus) and California Gulls (Larus californicus). We estimated there were 1,360 pelican nests on Island A (10.1 ha) and 240 nests on Island B (3.5 ha) from aerial photos taken on 6 June 2005. The islands were 680 and 550 m from shore, and were observed from the mainland using 45x and 30x spotting scopes, respectively. Two...