A new study seems to demonstrate that gull chicks can communicate information to their siblings—while they’re still in the egg.
There’s evidence that bird parents can communicate information to embryos inside their eggs, which the embryos are able to perceive. A team of researchers at the University of Vigo in Spain wondered if this communication could also somehow exist between the embryos themselves. Specifically, they wondered if the presence of predators could alter certain traits expressed by all of the hatchlings simultaneously.
The work required a very specific experimental setup, all performed on a Spanish breeding colony of yellow-legged gulls, a bird closely related to large grey-backed North American herring gulls. These gull chicks respond to predators by crouching and freezing, but in some years, there might be fewer predators, so perhaps in those years the babies don’t develop defensive behaviors. How defensive the chicks should be would be communicated by alarm calls from adult gulls.
The researchers collected gull eggs and moved them to artificial incubators. Then, they divided the eggs into groups of three, and placed the groups into either an experimental or a control group. In both experimental and control groups, two of the three eggs were placed in a sound-proof box. For only the experimental group only, the researchers played an adult gull’s alarm call. For the rest of the time, all of the gull eggs were in physical contact with each other in the incubator.
The team noticed various differences between the experimental and control groups. All of the embryos in the experimental group (the group that heard alarm calls) took longer to hatch. The DNA of all of the eggs in the experimental group had more added methyl groups, implying more epigenetic activity, or changes to the way their genetic code would be expressed. Finally, once the chicks hatched, the chicks in the experimental group (including the one that didn’t hear to the alarm calls because it was in a sound-proof box), vocalized less and crouched quicker in the face of danger. The researchers thought that their results suggested that the eggs were communicating with one another, presumably through vibrations or vocalizations that the researchers didn’t hear, according to the paper published in Nature Ecology and Evolution.
A pair of researchers not involved in the study thought the experimental design was “elegant,” according to a Nature commentary by Mylene Mariette and Katherine Buchanan from Deakin University in Australia. Researchers already know that bird and crocodile embryos can synchronize hatching, but this kind of communication is more sophisticated. “These results suggest a degree of developmental plasticity based on prenatal social cues, which had hitherto been thought impossible,” they write.
There are obvious limitations to a study like this. It’s unclear whether the differences between the experimental and control groups were specifically due to the alarm calls, or due to the control group sitting in a quiet empty box. It’s also unclear whether the quicker crouching time is actually a helpful anti-predator trait, Mariette and Buchanan wrote. These questions are left to future study.
But regardless, it seems clear that at least some information is being communicated between these eggs—and shows that a bird’s time inside its egg may play an even bigger role in its development than previously thought.