Discriminating between Eggs of Herring Gulls (Larus argentatus) and Great Black-Backed Gulls (Larus marinus) in Eastern Canada

Abstract

Abstract. Distinguishing among eggs of large gull species in mixed colonies is difficult because egg size is variable, size ranges overlap and colors are similar. Regional and yearly differences in egg size of Herring Gulls (Larus argentatus) were compared among three regions (Bay of Fundy, Newfoundland, and low Arctic). In two of these regions (Newfoundland and Bay of Fundy), eggs of Herring Gulls and Great Black-backed Gulls (L. marinus) were measured and discriminant analysis models were created to distinguish between the eggs of these two species. Egg dimensions of Herring Gulls decreased from low Arctic (largest) to Bay of Fundy to Newfoundland (smallest). In both species, where a = first-laid egg, b = second-laid, and c = third-laid, a- and b-eggs were of similar size, but c-eggs were significantly smaller; measurements of a- and b-eggs were pooled. The only annual differences were in a- and b-eggs (treated separately) in Newfoundland; there were no annual differences in c-eggs or in a/b-eggs combin...