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Growth and Sexual Dimorphism of the Boat-Tailed Grackle

G. Thomas Bancroft
The Condor
Vol. 86, No. 4 (Nov., 1984), pp. 423-432
DOI: 10.2307/1366822
Stable URL: http://www.jstor.org/stable/1366822
Page Count: 10
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Growth and Sexual Dimorphism of the Boat-Tailed Grackle
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Abstract

At hatching, male and female Boat-tailed Grackles (Quiscalus major) are similar in size. By day 12, just before fledging, they differ in manus and tarsal lengths, tarsal thickness, and weight, but not in culmen, primary remex 7, and tail lengths. Male and female nestlings attain asymptotic weights of 102.4 g and 65.6 g, respectively, at a rate faster than predicted from the general passerine pattern. Furthermore, these asymptotes are only 54.8% and 65.3%, respectively, of adult weight. The combination of a faster growth rate and an asymptote below adult size means that grackles fledge sooner than would be expected for the general passerine pattern. Clutches of three eggs hatch asynchronously; the hatching of the third chick does not decrease growth rates of the early-hatching chicks. Third-hatched young fledge at weights significantly below those of early-hatching young. Compared to males hatching from the first or second egg, males from the third egg require several more days to attain sizes larger than females.

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