Evidence of latitudinal sexual segregation among migratory birds wintering in Mexico

Abstract

aestiva group), Yellowrumped Warbler (Dendroica coronata

Latitudinal sexual segregation during the nonbreeding season, in which males tend to winter farther north than females, is known to occur in many temperatezone bird species. This pattern, however, has rarely been reported in species wintering in tropical regions. We investigated latitudinal sexual segregation in 45 NearcticNeotropical migratory bird species that winter in Mexico, using specimen records freom 35 naturalhistory museums. We found significant latitudinal segregation in nine species: Yellowbellied Sapsucker (Sphyrapicus varius), Swainson's Thrush (Catharus ustulatus), Orangecrowned Warbler (Vermivora celata), Yellow Warbler (Dendroica petechia

coronata group), Blackandwhite Warbler (Mniotilta varia), Ovenbird (Seiurus aurocapilla), Wilson's Warbler (Wilsonia pusilla), and Indigo Bunting (Passerina cyanea). In most cases, males predominated in the northern part of species' winter ranges and females in the south, but the trend was reversed in Indigo Buntings. Discovering the freequency of latitudinal sexual segregation in Neotropical migratory birds will influence understanding of avian ecology and migration systems.