Territory size and stability in a sedentary neotropical passerine: is resource partitioning a necessary condition?

Long-term pair bonds and defense of territories year-round are common among tropical passerines. The boundaries of these territories tend to be stable, perhaps reflecting the need to defend an area that, regardless of conditions, provides sufficient food resources. If, however, these stable territories are not, even temporarily, sufficiently large, then intra-pair competition for available food may result, particularly in species with no sexual size dimorphism. With such competition, sex-specific differences in foraging behavior may result. Male and female Dusky Antbirds (Cercomacra tyrannina) are not size dimorphic, and pairs jointly defend territories throughout the year. Our objective was to determine if paired Dusky Antbirds exhibited sex-specific differences in foraging behavior. Foraging antbirds were observed in central Panama from February-July 2002 to determine if pairs partitioned food resources. Males and females exhibited no differences in Foraging behavior, with individuals of both sexes foraging at similar heights and using the same foraging maneuvers (glean, probe, and sally) and substrates (leaves, rolled leaves, and woody surfaces). These results suggest that Dusky Antbirds do not partition resources and that territory switching, rather than resource partitioning, may be the means by which they gain access to additional food resources.