Maternal Diet Selectivity in Calypte anna

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Abstract
The female Anna hummingbird''s (C. anna) selection of different kinds of food resources for her young from a temporally changing environment in [California, USA] was studied. To see if the female C. anna is selective or simply takes nectar and insects in the proportions in which they are available, the changing patterns of nectar and insect availability to the foraging female were determined during the day, and then compared with the proportions of food types present in the crops of C. anna nestlings. Through a 24 h period, production rates of nectar from Eucalyptus spp. the primary source of nectar in the C. anna''s diet, were relatively constant. Availability of nectar decreased slightly as the day progressed, but remained abundant in the Eucalyptus flowers even by the end of the day. Insects, primarily composed of proteins, increased in availability as the day progressed. Selectivity for nestling dietary composition did occur: the female took different food items in proportion to their availability in the morning, but then changed to active selection of insects in the afternoon. This changing selection of food types is adaptive since it provides a longer-lasting food reserve of proteins to sustain the C. anna nestlings overnight.

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