Meeting Abstract
Several studies assume hummingbirds fill their crop prior to roosting, and have included crop filling in nighttime metabolism protocols. To test the validity of this assumption, we examined daytime mass management in both males and females of three SE Arizona hummingbird species that differ in size and ecological role: the black-chinned hummingbird (Archilochus Alexandria, 3.0g; opportunistic forager), the Rivoli’s hummingbird (Eugenes fulgens, 7.5g; trap-liner), and blue-throated hummingbird (Lampornis clemenciae, 8.0g; territorialist). Male Rivoli’s and black chinned hummingbirds maintained mass throughout the day, but appeared to crop load prior to roosting. Blue-throated hummingbirds maintained mass but did not crop load, and fed infrequently during the last 30 minutes of activity, possibly due to unlimited access to resources. Female black-chinned hummingbirds exhibited high variation in mass and no crop-loading even though they were numerically dominant at the feeders during the last 30 minutes of activity. In contrast, female blue-throated and Rivoli’s hummingbirds had higher activity in the beginning and end of the day, but were infrequent visitors to feeders mid-day when temperature was high. These data suggest that daytime mass management and pre-roost crop loading is likely influenced by social interaction and to some degree thermal tolerance. Additionally, since this study was conducted during the breeding season, females were likely influenced by egg production, and all phases of nest construction and attendance.
