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I wonder about that, too, and Google gives me lots of items that seem to debunk that, for example https://www.researchgate.net/publication/318263505_Avian_egg..., which to my amateur eye seems a rather recent and extensive study. It starts with “Hypotheses proposed for the adaptive function of egg shape typically invoke a decrease in egg loss for cliff-nesting birds laying conical eggs that roll in a tight circle; an increase in incubation efficiency when egg shape is associated with the number of eggs in a clutch; or other advantages related to strength, diet, and development. For example, spherical eggs might be advantageous because the sphere is uniformly strong and would be robust to incidental damage in the nest. Spherical eggs, with their minimal surface-area-to-volume ratio, also require the least amount of shell material for a given volume and possibly optimize gas exchange by providing a large surface area for pores. In contrast, conical eggs may be beneficial because they can accommodate an increased concentration of pores at the blunt end, creating a specialized respiratory site for accelerated neural development in precocial birds. Moreover, conical eggs may protect the blunt end (from which chicks usually hatch) from debris contamination or, in colonial breeders, increase resistance to impacts because a larger proportion of the eggshell is in contact with the substrate. Finally, it has also been proposed that adaptations for flight influence egg shape indirectly through the morphology of the pelvis, abdomen, or oviduct.” and concludes “Our macroevolutionary analyses suggest that birds adapted for high-powered flight may maximize egg size by increasing egg asymmetry and/or ellipticity, while maintaining a streamlined body plan” It doesn’t even mention “better protection against drops”. |