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Standard Metabolic Level and Insulative Characteristics of Eastern House Finches, Carpodacus mexicanus (Müller)

Terry L. Root, Timothy P. O'Connor and William R. Dawson
Physiological Zoology
Vol. 64, No. 5 (Sep. - Oct., 1991), pp. 1279-1295
Stable URL: http://www.jstor.org/stable/30156245
Page Count: 17
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Standard Metabolic Level and Insulative Characteristics of Eastern House Finches, Carpodacus mexicanus (Müller)
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Abstract

Following the release of house finches from southern California (CA) on Long Island, New York, in 1940, the species has become established in eastern North America, including Michigan (MI) and Ohio (OH), despite cold winters. Standard metabolic rates (SMRs) of MI-OH birds, like those of house finches from Colorado (CO) and CA, do not differ significantly between winter and late spring Geographical comparisons are more complex. Standard metabolic rate does not vary significantly among the three populations during late spring Additionally, the winter value for the MI-OH house finches resembles that for CO birds. However, SMR for individuals in these two populations significantly exceeds that for the CA birds, suggesting some linkage between severity of winter climate and metabolic level Analysis of thermal conductance (c) for MI-OH house finches indicates a significantly higher insulation value in winter than in late spring, a circumstance we ascribe to more worn plumage in the latter season. Winter values of c for MI-OH house finches and CA birds are similar. This finding and some previous findings on winter acclimatization in house finches from several localities suggest that geographic variation in their cold response results primarily from metabolic rather than insulative adjustments.

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