Bird embryos communicate inside their eggs

[Still Waters]

Unhatched bird embryos can not only hear the warning calls of adult birds - they can communicate that information to their unhatched brothers and sisters sharing the same nest, remaining safely tucked away in their shells until it is safe to hatch.

It is a finding that reveals how birds can adapt to their environment even before birth, since, unlike placental mammals, their physiology can no longer be influenced by changes in their mother's body after the egg is laid.

In particular, a team of researchers exposed unhatched yellow-legged gull (Larus michahellis) eggs to cues that indicated high predation risk. Not only did the unhatched embryos communicate these cues to unexposed nestmates, they emerged from their eggs exhibiting much more cautious behaviour than the control group.

https://www.sciencealert.com/baby-birds-can-communicate-with-each-other-from-inside-their-unhatched-eggs

https://www.nature.com/articles/s41559-019-0929-8