Woodpeckers of the World: Sexual Dimorphism

Wednesday, 23 July 2014

Sexual Dimorphism

Most woodpeckers are sexually dimorphic in appearance. That is, males and females have different plumage. However such differences are often slight, usually involving more colour on the head or face of the male. In a few cases, such as Williamson's Sapsucker Sphyrapicus thyroideus, sexual dimorphism is extreme, with the sexes appearing very different - males colourful, females plain. Photo of an adult male Williamson's Sapsucker taken in Oregon, USA, in July 2014 by Gerard Gorman.

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Background

Woodpeckers, the Picidae, are Piciformes, an order that includes some of the oldest avian lineages. The Piciformes probably originated about 60 million years ago in the Tertiary period and became distinct from their closest relatives some 50 million years ago. Depending upon which taxonomy is followed, and the fact that the status of some species is unclear, around 240-260 woodpecker species probably exist globally. The Picidae includes three subfamilies: Jynginae (wrynecks), Picumninae (piculets) and the Picinae, the “true woodpeckers”. In terms of size, behaviour, distribution and the habitats they use, the Picinae are a fairly diverse group of birds with six distinct tribes. They are widespread and found from sea-level to high-altitudes but absent from the Arctic, Antarctica, Australia, New Zealand, Papua New Guinea, Madagascar and some other islands. Worldwide woodpeckers are usually, but not exclusively, associated with trees.