Research Article

Avian egg shape: Form, function, and evolution

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Science  23 Jun 2017:
Vol. 356, Issue 6344, pp. 1249-1254
DOI: 10.1126/science.aaj1945

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  • RE: How to get all your eggs in one basket?

    The introduction to the 1969 edition of The Observer’s Book of Birds Eggs states that “Plovers’ eggs are quite sharply narrowed at one end, and this is apparently because they are rather large for the size of the birds, yet when they are arranged with their “points” inwards, the sitting bird can cover them adequately” 1. Perhaps due to the obscurity of the source, Stoddard2 et al do not discuss this hypothesis. Yet it is clearly supported by one of the main results of their macroevolutionary analysis (see their Table S2-C). Whilst Stoddard et al2 mention this interesting result (“birds with larger eggs than expected given their body mass lay more elliptical eggs”), they do not discuss its significance, and their abstract and the ensuing press coverage focus entirely on the correlation with the hand-wing index and its possible interpretation in terms of biophysical constraints of flight. In claiming to have identified flight as the key driver of egg shape evolution, Stoddard et al2 may have overlooked an important aspect of their own results: more elliptical eggs enhance packing and thereby allow eggs that are large relative to the size of the adult to be efficiently brooded.
    1. Evans, G. The Observer’s Book of Birds Eggs (1969)
    2. M.C. Stoddard MC Science 356, 1249–1254 (2017)

    Competing Interests: None declared.
  • RE: avian egg shape
    • Marc Verhaegen, Medical Doctor, Study Center for Anthropology, B-2580 Belgium.

    Thanks for this beautiful article, which is very convincing. Already in the 1970s, my professor anatomy (Lucien Vakaet, RUCA Antwerp, who did numerous embryological experiments with eggs of quails and chickens) said that the shape of the birth canal of the motherbird was responsible for the shape of the egg (without noticing the relationship with flying however). He also explained the place and orientation (up-down, front-back, right-left) of the developing embryo inside the egg by the way the egg turned inside the birth canal.

    Competing Interests: None declared.

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