Influence of Economics, Interspecific Competition, and Sexual Dimorphism on Territoriality of Migrant Rufous Hummingbirds

Migrant Rufous Hummingbirds (Selasphorus rufus) arrive in eastern Arizona in late summer and establish feeding territories from which other hummingbirds are excluded. Territories vary 100—fold in area and 5—fold in number of flowers. A simple cost—benefit model accounts for observed variation in territory size and number of flowers defended. Both sexes defend territories, but ♂ ♂ utilize denser flowers than ♀ ♀. These differences appear to be related to sexual dimorphism in wing disc loading. Selasphorus rufus appears to have sacrificed efficient flight for aggressive ability as a strategy for competing with resident hummingbird species during its migration. Comparison of feeding territories of S. rufus and other nectarivorous birds indicate similarities which suggest that these systems may be subject to similar economic constraints.