Avian eggshell thickness: scaling and maximum body mass in birds

The avian eggshell represents a highly evolved structure adapted to the physiological requirements of the embryo and the potential fracturing forces it is exposed to during incubation. Given its many roles, it is not surprising that the eggshell is also central to the current hypothesis about maximu...

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Bibliographic Details
Published in:Journal of zoology (1987) 2009-09, Vol.279 (1), p.95-101
Main Authors: Birchard, G.F, Deeming, D.C
Format: Article
Language:English
Subjects:
Aves
bird
Birds
body size
Comparative analysis
egg shell
Eggs
eggshell
incubation
moa
scaling
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Summary:The avian eggshell represents a highly evolved structure adapted to the physiological requirements of the embryo and the potential fracturing forces it is exposed to during incubation. Given its many roles, it is not surprising that the eggshell is also central to the current hypothesis about maximum avian body mass. Eggshell thickness (L) and strength has historically been scaled as a function of initial egg mass (IEM). However, maximum incubator mass (IM) is likely a better indicator of the forces the shell must be selected to withstand during incubation. We compare the results of analyses of L² (an indicator of shell strength) as a function of IEM and IM. We conclude from IM scaling that megapode and kiwi eggshells are not thin but rather are thicker than expected and in general birds with a clutch size of 1 have thicker shells, and further, that reversed sexual dimorphism in the large, particularly extinct birds may be a strategy to avoid shell breakage during incubation of the largest eggs without creating a shell so thick as to inhibit hatching.
ISSN:0952-8369
1469-7998
DOI:10.1111/j.1469-7998.2009.00596.x