COMPETITION FOR WINTER TERRITORIES IN A NEOTROPICAL MIGRANT - THE ROLE OF AGE, SEX AND COLOR

Hooded Warblers (Wilsonia citrina) defend long-term feeding territories during the nonbreeding season. Experimental removals of territory owners early iri the fall in Mexico resulted in rapid replacement by nonterritorial individuals (''floaters''). The sex ratio of replacement birds was similar to that of territory owners in the same habitat, but virtually all replacements were hatching-year (HY) birds. Females were able to acquire and defend territories in the presence of male floaters. Loss of wintering habitat would likely increase the proportion of nonterritorial birds and, therefore, increase overwinter mortality rates, especially of HY birds. The extent of malelike coloration of females was riot correlated with habitat, indicating that dark females were not more likely to obtain territories in forested habitat where males predominate. Furthermore, the aggressive response of male territory owners toward models did not depend on intruder color. These results suggest that malelike coloration in females does not function in competitive interactions with males. Intense competition for winter territories coupled with reduced survivorship of winter floaters could constrain breeding strategies if young produced late in the summer have little chance of obtaining winter territories.