Fig. 1

The incidence of multispecies hybridization in six bird orders (Anseriformes, Galliformes, Charadriiformes, Piciformes, Apodiformes and Passeriformes). In general, most species hybridized with only one other species, but in each of the six bird orders multispecies hybridization occurs frequently. Noteworthy outliers are Mallard (Anas platyrhynchos, 39 hybrids, Anseriformes), Common Pheasant (Phasianus colchicus, 14 hybrids, Galliformes) and European Herring Gull (Larus argentatus, 11 hybrids, Charadriiformes). Records based on the Serge Dumont Bird Hybrid Database (http://www.bird-hybrids.com, Additional file 1)