In baby birds, ambient temperature can set beak size.

Gary Burness of Trent University in Peterborough, Canada, and his colleagues raised 40 Japanese quail hatchlings (Coturnix japonica; pictured) at high (30 °C) or low (15 °C) temperatures. After 51 days, the hatchlings raised in warm conditions had longer bills than the chilled chicks. Beak growth in cold-reared chicks caught up after all birds were moved to an intermediate temperature, but the surface temperature of their beaks was, on average, 7.4 °C lower than that of birds reared at warmer temperatures, suggesting less blood flow.


Cold conditions soon after hatching may irreversibly inhibit blood flow or blood-vessel development in beaks.

Proc. R. Soc. B. 280, 20131436 (2013)