Experts discover all the chicks tested underwent genetic changes that delayed hatch time.
Unhatched baby seabirds can warn each other of impending danger by vibrating within their shells, scientists have discovered.
A study of yellow-legged gull embryos, found they reacted to warning calls from a parent and even passed on the message to siblings who had not heard the call.
The researchers collected gull eggs and divided them into groups of three.
A week before hatching, two of the three eggs in each nest were temporarily removed and exposed to a recording of a predator alarm call.
The noise was delivered four times a day at random intervals for three minutes at a time until hatching.
The third egg from each group remained in the nest in silence.
All three eggs were then reunited and left to hatch.
It was found the embryos responded to the external alarm calls by vibrating more.
This information appeared to be passed on to the third egg which had not been directly exposed to the sounds and it then mimicked the vibrations.
Experts from the Animal Ecology Group at the University of Vigo in Spain discovered all the chicks underwent genetic changes that delayed hatch time.
There was also evidence of increased production of stress hormones which is known to make birds more aware of their surroundings after hatching.
The findings were published in the journal, Nature Ecology and Evolution.