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The Effect of Floral Abundance on Feeder Censuses of Hummingbird Populations

David W. Inouye, William A. Calder and Nickolas M. Waser
The Condor
Vol. 93, No. 2 (May, 1991), pp. 279-285
DOI: 10.2307/1368943
Stable URL: http://www.jstor.org/stable/1368943
Page Count: 7
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The Effect of Floral Abundance on Feeder Censuses of Hummingbird Populations
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Abstract

Numbers of Broad-tailed Hummingbirds (Selasphorous platycercus) captured each summer from 1979-1989 at the Rocky Mountain Biological Laboratory were quite variable, ranging from 115 (1981) to 348 (1989), with new birds usually outnumbering returning (previously banded) birds. Capture numbers were negatively correlated with the abundance of four species of flowers they visited, Erythronium grandiflorum, Delphinium nelsonii, Ipomopsis aggregata and Delphinium barbeyi; flower numbers were also highly variable during the study period. Since most of the captures were at feeders, these data suggest that in years with high floral abundance feeders are less attractive, while in years with low floral abundance hummingbirds with nests or territories at greater distances increase their use of the feeders. This interpretation is supported by seasonal variation in use of feeders, which is highest during the beginning and end of the season when floral abundance is lowest. Estimates of hummingbird density based on activity at feeders may thus be affected by the availability of floral food resources.

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