EVIDENCE OF LATITUDINAL SEXUAL SEGREGATION AMONG MIGRATORY BIRDS WINTERING IN MEXICO

A.-Latitudinalsexual segregation during the nonbreeding season, in which males tend to winter farther north than females, is known to occur in many temperate-zone bird species.This pa ern, however, has rarely been reported in species wintering in tropical regions.We investigated latitudinal sexual segregation in 45 Nearctic-Neotropical migratory bird species that winter in Mexico, using specimen records from 35 natural-history museums.We found signifi cant latitudinal segregation in nine species: Yellow-bellied Sapsucker (Sphyrapicus varius), Swainson's Thrush (Catharus ustulatus), Orange-crowned Warbler (Vermivora celata), Yellow Warbler (Dendroica petechia; aestiva group), Yellow-rumped Warbler (Dendroica coronata; coronata group), Black-and-white 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 frequency of latitudinal sexual segregation in Neotropical migratory birds will infl uence understanding of avian ecology and migration systems.