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Relationship of Age and Sex to Size and Color of Eastern Phoebes

Kelvin F. Conrad and Raleigh J. Robertson
The Wilson Bulletin
Vol. 105, No. 4 (Dec., 1993), pp. 597-603
Stable URL: http://www.jstor.org/stable/4163351
Page Count: 7
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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.
Relationship of Age and Sex to Size and Color of Eastern Phoebes
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Abstract

We recorded variation in body size and ventral plumage coloration in a population of individually marked Eastern Phoebes (Sayornis phoebe). The venter of Eastern Phoebes is mostly gray with gray mottling on the breast. Most birds have a white bib which, although usually small, may cover much of the breast and abdomen. We found no significant difference in percentage gray area between males and females, but after-second-year (ASY) birds had significantly less gray on their breasts than second-year (SY) birds. Males had significantly longer mean wing lengths, tarsal lengths, and vent--tail lengths than females. There was considerable overlap of wing, tarsal, and vent--tail lengths between the sexes, but the size differences held both overall and separately in SY and ASY birds. We generated a discriminant function which correctly classified 79% (39/49) of females and 95% (22/23) of males. Despite their similar appearance, male Eastern Phoebes are larger than females, at least in the parameters we measured.

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