We report 14 cases of banded female Costa's Hummingbirds (Calypte costae) fledging young from 2 or 3 broods in single breeding seasons during late February to mid-June in southern Nevada, USA. Successfully raising 2 broods in a single breeding season has been reported only rarely for this species, and raising 3 broods is previously unreported in the literature. We also report 8 cases of banded females simultaneously tending young and eggs from 2 nesting attempts. Females constructed a new nest and began incubating while (1) feeding large nestlings in the earlier nest (5 cases), or (2) feeding recently fledged young from the earlier nest (3 cases). One banded female accounted for 5 of these 8 cases. We also report 5 cases of autumn nesting, not previously documented for Costa's Hummingbird, including 5 young fledged from 3 nests in late November and early December. Our results suggest that multiple broods, simultaneous nests, and autumn nesting are viable breeding strategies for female Costa's Hummingbirds, some of which may be year-round residents at our study site in the Mojave Desert. We also suggest that multiple brooding and autumn breeding are facilitated by the availability of hummingbird feeders and cultivated exotic flowering plants in an urban setting.

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