Study suggests embryos communicate with each other while still inside the egg
We know baby birds communicate, often loudly, and mostly about food, but a new study suggests they can also communicate with each other while still in the egg. This method of communication influences the behavioral and physiological traits of newly-hatched chicks from the same clutch of eggs.
It's generally understood that birds and other oviparous (egg-borne) critters receive sensory information from outside the shell to prepare them for the world beyond the nest. Now new research from University of Vigo in Galicia, Spain, suggests that gull embryos are able to acquire environmental information from their egg-bound siblings as well.
In recent years it's been shown that baby turtles can signal each other with vibrations to trigger synchronized hatching, and some birds and reptiles can do the same kind of thing with vocalizations from within the shells, but researchers Jose Noguera and Alberto Velando wanted to know how this egg-to-egg chit-chat might influence more complex factors.
The researchers found that chicks not only hear and respond to the alarm calls of their parents while still inside the egg, but that once hatched, those same chicks were developmentally and behaviorally different to chicks who'd never been exposed to the adult alarm calls. That on it's own is interesting, but what happens when an egg that's been exposed to parental alarm calls is placed into a clutch with another egg which hasn't ever heard these vocalizations? The second egg develops in similar ways to the first. Thus, it seems some kind of communication between embryos is happening, most likely through vibratory cues.
The team used a simple but effective study design to test its theory. The researchers gathered 90 eggs from the nests of yellow-legged gulls (Larus michahellis) on Sálvora Island (off the coast of Galicia in Spain). Back in the lab the eggs were separated into clutches of three and incubated. These clutches were then divided into two groups. One group was assigned as the "exposed to social stimuli of predator presence" group, while the other was the control group.
Then, four times per day, two eggs were taken from each clutch, leaving one behind in the incubator. Those from the test group were exposed to recorded adult alarm calls during these sessions, while those from the control group were exposed to white noise for the same periods. Between the sessions, all of the eggs were exposed to background colony noise in the incubators.
Once hatched, the researchers measured a range of early behavioral and developmental traits in the chicks. The data showed that the embryos that had shared a nest with siblings exposed to the alarm calls developed in the same manner as their siblings. Compared to the calm, white-noise control group (and their clutch-mates) they took longer to hatch, were quieter than the control group, crouched lower when exposed to perceived threats and were smaller overall with shorter legs.
In short, these chicks developed specific, defensive traits as if they'd heard the warning calls themselves. According to Noguera and Velando, this strongly suggests that information about predation risk was being transmitted between siblings, possibly via observed vibrations of embryos in the test group.
A paper on the research has been published in the journal Nature Ecology & Evolution.