Bill structure: Evolving
In particular the bill structure appears to be easily and quickly moulded by evolutionary processes. From an ancestral finch-like bird with a short straight beak, the HawaiianHoney-creepers (Family Drepanididae) have evolved bill structures that are adapted to feeding on insects, nectar, fruit and seeds in a period of a few thousand years. Darwin noted similar variation in the bills of the finches of the Galapagos islands. Elsewhere in the bird world the evolution of bill structure has occurred for a much longer time and we therefore see bills adapted to seed-eating (sparrows; Ploceidae), fruit-eating (hornbills and toucans; Bucerotidae and Ramphastidae respectively) insect-eating (nightjars; Caprimulgidae), tearing (eagles and hawks; Accipitridae), probing (stilts; Recurvirostridae), filtering (flamingoes; Phoenicopteridae) and capturing of fish (cormorants; Phalacrocoracidae). The feet of birds also show adaptations to scratching for food (pheasants; Phasianidae), wading (heron; Ardeidae), grasping (eagles), perching (warblers; Muscicapidae) and swimming (ducks; Anatidae).