Facultative Interspecific Brood Parasitism in Colonial Breeding Waterbirds in Biebrza National Park, Poland

Abstract. Interspecific brood parasitismoccurs when the eggs of one species are laidin the nestof a different species, but evidence of this phenomenon is scarce. Facultativeinterspecific brood parasitismhas been described in Charadriiformes. However, to our knowledge, our study provides the first documentation of facultativeinterspecific brood parasitismin the colonially breeding species we studied. The factors affecting its frequency in relation to colony species composition, nestdensity, and period of the breeding season was analyzed. Between 2006 and 2012, we monitored 2,493 nestsof five species: Northern Lapwing( Vanellus vanellus; n = 745), Common Redshank( Tringatotanus; n = 467), Black-tailed Godwit( Limosa limosa; n = 237), Black-headed Gull( Chroicocephalus ridibundus; n = 932) and Common Tern( Sterna hirundo; n = 112). Facultativeinterspecific brood parasitismwas observed in 1.3% of all nests. Typically, a single egg was laidin a host nest(59.4% of parasitized nests), and a maximum...