Non-Random Foraging by Hummingbirds: Patterns of Movement Between Ipomopsis aggregata (Pursch) V. Grant Inflorescences

Abstract

Foraging nectarivores can improve net energetic returns above random expectations by avoiding recently depleted locations or preferentially returning to locations least recently visited. Area-restricted search is one possible mechanism to achieve such non-random foraging in a patchy environment. Movement patterns of two species of hummingbirds [Selasphorus platycercus (Swainson) and S. rufus (Gmelin)] between inflorescences of scarlet gilia [Ipomopsis aggregate (Pursh) V. Grant] were studied in montane Colorado in 19791980. The birds preferentially visited tall inflorescences with many flowers. They flew short distances and visited near neighbours unless the inflorescence just visited was of low quality. The latter more often produced flights to distant neighbours, but quality of the current inflorescence did not influence subsequent directionality. Flight direction tended to be forward, but significantly so only in 1980. These patterns kept birds in areas of high quality inflorescences and moved them away from potential areas of low quality. However, movement from low quality inflorescences did not differentially influence the morphological traits of the next inflorescence visited and did not lead predictably to high quality inflorescences. This area-restricted search, based on current inflorescence quality, is only one spatial scale of nonrandom foraging by the hummingbirds. Key-words: Area-restricted search, behaviour, directionality, distance, foraging, hummingbirds, Ipomopsis aggregata, Markov processes, movement rules