The incidence of hybridisation in birds differs greatly between orders and is expected to be low in orders comprising few species. The divers or loons (Gaviiformes) are a species-poor group in which apparent hybridisation has been reported infrequently. Here we report on a hybrid diver stored in the collections of the Zoological Museum Amsterdam. The bird shows a heterogeneous set of characters, some shared with the putative parent species White-billed Diver Gavia adamsii and Great Northern Diver G. immer, others being intermediate between the two. A Canonical Discriminant Function analysis positions the bird between these two putative parent species, making a hybrid status quite likely. We evaluate the evidence for hybridisation in the order Gaviiformes and conclude that hybridisation has been suspected in four of the five species, though documentation is limited. If this high incidence could be confirmed, it would rank among the highest of any avian order, contradicting the assumption that incidence of hybridisation in small orders is relatively low.

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