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A Comparison of Breeding Ecology and Reproductive Success between Morphs of the White-Throated Sparrow

Richard W. Knapton, Ralph V. Cartar and J. Bruce Falls
The Wilson Bulletin
Vol. 96, No. 1 (Mar., 1984), pp. 60-71
Stable URL: http://www.jstor.org/stable/4161871
Page Count: 12
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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.
A Comparison of Breeding Ecology and Reproductive Success between Morphs of the White-Throated Sparrow
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Abstract

We compared breeding ecology and reproductive success between morphs of the White-throated Sparrow (Zonotrichia albicollis). Total arrival time was equally broad for both white-striped (WS) and tan-striped (TS) males, and no difference was found in time of arrival on the breeding grounds between male morphs. WS females were detected significantly earlier than TS females; this is possibly a result of quicker pair formation in TS male × WS female pairs as clutch initiation was earlier in this pair type in one year than in WS male × TS female pairs. Return rates of males to the study areas in successive years did not differ between morphs; return rates of females were very low in all years. Success rates of nests, number of young fledged per nest, length of nestling period, growth rates of nestlings, and weight of nestlings at fledging did not differ between morphs. Thus, the argument that TS males suffer a reproductive cost by occupying "suboptimal" habitat is not supported.

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