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Rook Hind Limbs Grew Fastest Before Hatching, Forelimbs During Most Nestling Development

Rook nestling
Research · Reproduction & development

A study of rook (Corvus frugilegus) development found that the proportions of the head, forelimbs and hind limbs changed repeatedly from the embryo stage through the nestling period. The researchers compared body-part length with overall body size to ask whether each structure grew proportionally, faster than expected or slower than expected as the bird became larger. They identified four distinct phases in these growth trajectories.

Body proportions changed in four phases

From embryonic days 10–13, the measured structures generally showed positive allometry: they lengthened faster than expected if they had simply kept the same proportions as overall body size increased. From embryonic day 14 through the third day after hatching, they showed mostly negative allometry, meaning their length increased more slowly than overall body size. Positive allometry returned from postnatal days 5–23, before growth became approximately isometric during days 25–30 — the stage when body-part proportions changed comparatively little as the bird continued growing.

The different body parts did not share the same relative growth rate within these phases. The hind limbs — the developing legs — grew fastest relative to overall body size during embryonic development, whereas the forelimbs — the developing wings — showed the highest relative growth through most of the postnatal nestling period. This does not mean that one structure necessarily added the most millimetres; it means its size increased fastest relative to the growth of the bird as a whole. These shifting rates changed body proportions even though the broad developmental phases were shared among the traits.

The authors interpret the shifting growth patterns as consistent with different body parts being prepared for function at different times, while whole-body growth also constrains how quickly individual structures can develop. They present this as an interpretation of the changing trajectories rather than a direct test of when each limb becomes functionally mature.

Sources and image credit

  1. Shatkovska, O. V., Ghazali, M., & Mytiai, I. S. (2026). Alterations of growth trajectories in rook (Corvus frugilegus) ontogeny. Journal of Morphology, 287(6), e70141. https://doi.org/10.1002/jmor.70141Primary research article first published 9 June 2026. The study measured head, forelimb and hind-limb growth relative to body mass in rook embryos and nestlings and identified four developmental phases. Hind limbs showed the highest growth rate during embryogenesis, while forelimbs grew faster through most of postnatal nestling development.

Image: Miłośnik Zwierząt974 / Wikimedia Commons — rook nestling, 15 May 2018. Representative image for this story; not presented as an animal or scene from the reported study or event. · CC0 1.0 · Source

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