THE ESSENTIALITY OF NECTAR AND ARTHROPODS IN THE DIET OF THE ANNA HUMMINGBIRD (CALYPTE-ANNA)

1. Three adult male Anna's hummingbirds (Calyptae anna) were fed each of the following three diets over time: live fruit flies and a 22% sucrose in water solution (control diet), a 22% sucrose solution only, or live fruit flies and water only, and the birds' body mass changes and behavior were recorded. 2. The hummingbirds were able to subsist for 10 days on the 22% sucrose solution with body mass loss but no obvious behavior changes. 3. In the absence of the sucrose solution the hummingbirds made no attempt to catch fruit flies and became listless or torpid within a few hours. 4. The results suggest that hummingbirds have a remarkable ability to survive with no protein in their diets as long as nectar is available.