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1 December 2008 Between and within clutch variation of egg size in Greater Rheas
Gustavo J. Fernández, Juan C. Reboreda
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We describe egg characteristics, and analyze between and within clutch variation in egg size and mass in a natural population of Greater Rheas (Rhea americana). We assess the effect of this variation on nesting success and egg success. Yolk represented 29.5% of egg mass whereas albumen was 63.9%. Yolk mass increased with egg width but not with egg length, while mass of albumen increased mainly with egg length. The largest and smallest eggs were 10.3% larger and 25.3% smaller, respectively than mean intra-clutch values. The widest egg was 11.9% wider while the narrowest egg was 20.5% narrower than mean intra-clutch values. There was a significant decrease in egg size between clutches during the breeding season as a result of a decrease in egg length. There was no effect of laying order on intra-clutch variation in egg size, but we detected an increase in the variation of egg length within clutches with clutch size. We did not detect a relationship between egg size and nesting success, and between egg size and egg success. The relatively low intra-clutch variation in egg size and lack of effect of egg size on hatching success do not support the hypothesis that females invest in eggs according to expected chick fitness.

Gustavo J. Fernández and Juan C. Reboreda "Between and within clutch variation of egg size in Greater Rheas," The Wilson Journal of Ornithology 120(4), 674-682, (1 December 2008).
Received: 23 November 2007; Accepted: 1 April 2008; Published: 1 December 2008

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