It turns out that baby yellow-legged gulls can communicate to each other through vibrating their eggs - prior to hatching.
A new study, published in Nature Ecology & Evolution, discovered this incredible phenomenon.
Not only do they hear the warning cries of adult birds, but now they are known to communicate and warn each other about them.
This research shows the astounding environmental adaptation abilities of these birds prior to coming out of their shells. Placental mammals, on the other hand, can have their physiology influenced by their mother's body after the egg is laid, but not these gulls.
Below is a video of yellow-legged gulls and their eggs (not from the study):
The team of researchers focused predominantly on unhatched yellow-legged gulls, exposing them to cues and high-warning risk sounds.
Unhatched embryos communicated the warning cues to their fellow unhatched brothers and sisters, but once they were out of their shells they displayed more cautious behaviours than those who hadn't been exposed.
Incredible adaptation skills.
The researchers in the study wrote "These results strongly suggest that gull embryos are able to acquire relevant information from their siblings."
How did they communicate? By wriggling in their shells, creating a vibration for their nestmates to pick up.
Yellow-legged gull embryos communicate important information about predators to their clutchmates through vibrations in their eggs https://t.co/xRT3A8s4LN— NYT Science (@NYTScience) July 22, 2019
Lead author of the study, Jose Noguera from the Animal Ecology Group at the University of Vigo, in Spain, said "We were very surprised. We were aware that bird embryos were able to produce egg vibrations, [but they vibrated] even more than we expected."
How did the team figure this out?
The team collected 90 yellow-legged gull eggs from Sálvora Island off the northern coast of Spain and dispersed them into groups of three.
Before hatching, two out of the three eggs were removed from the nest and were either subjected to high-warning predatory calls, or to peaceful white noise, four times a day. The third egg group remained in their nest.
During these tests, the team discovered that the embryos reacted to these noises by vibrating their shells.
It also turned out their 'information' was being passed on to the third chick in the nest - the one that remained unexposed.
How did they discover that the third, unexposed, egg picked up on the information? It wound up vibrating in a similar fashion once the other eggs were placed back into the nest.
Noguera said, "This kind of transfer of information - embryo to embryo - can induce developmental changes that can have potential benefits [to the birds] after hatching."
By being subjected to these warning calls, as well as understanding they were potentially dangerous, it could assist the birds once hatched, as they are quicker to run away and hide.
This phenomenon may occur in other bird species, as Noguera said. His team will now focus on whether chicks can pick up other environmental clues prior to hatching, such as the number of other eggs in the same nest.