SEXUAL DIMORPHISM IN RELATION TO WINTER FORAGING AND TERRITORIAL BEHAVIOUR OF THE THREE-TOED WOODPECKER PICOIDES TRIDACTYLUS AND THREE DENDROCOPOS SPECIES

A comparison of morphological characters shows that Picoides tridactylus is more markedly sexually dimorphic than Dendrocopus leucotos, D. major or D. minor. This is correlated with intersexual differences in foraging behaviour in P. tridactylus, lacking in the Dendrocopus spp. Apparently as a consequence, the sexes are able to share winter territories among P. tridactylus but not among D. major or D. minor; conclusive observations of D. leucotos were not possible. It is suggested that these differences may reflect the distributional history of the species, and the extent of interspecific competition.