Differential timing of spring passage of Ruby-throated Hummingbirds along the northern coast of the Gulf of Mexico
Hummingbird migration has long fascinated researchers due to the limitations of small body size and high metabolic rate on migratory performance. Yet, few data are available concerning hummingbird migration strategies, especially for species that must negotiate major geographic barriers. To address this problem, we investigated the migration ecology of Ruby-throated Hummingbirds (Archilochus colubris) passing through a coastal banding station in southwest Louisiana following flights across the Gulf of Mexico. Our aims were to describe the phenology of spring migration and explore potential differences in the migration ecology of males and females. During our 10-yr study (19982007), we found that peak hummingbird passage generally occurred in the second half of April and that males preceded females by about three days. However, females arrived in significantly better energetic condition as measured by fat and muscle stores as well as size-corrected body mass. Most birds did not stay at our study site to refuel, only 2% of individually marked birds were recaptured more than a day after initial capture (range = 15 d). Our results suggest that Ruby-throated Hummingbirds exhibit protandrous migration (i.e., males migrate earlier) and that en route body condition may be a consequence of sexual dimorphism in wing morphology (i.e., lower wing loading in females) that allows females to expend less energy during migration across the Gulf of Mexico.