Bird Embryos Eavesdrop on Their Parents

Yellow-legged gulls.

Source: Bengt Nyman via Wikimedia Commons.

A new study of seagull families shows that baby bird embryos eavesdrop on conversations between their parents, from inside the egg. Moreover, researchers found that what the embryos overhear during this small window has long-lasting biological and behavioral effects.

Gull Talk

For yellow-legged gulls, raising a family is a two-bird job. The male and female alternately sit and incubate the eggs in the nest. When one parent arrives to relieve the other of incubation duties, the couple performs a nest-relief display in which they vocalize to one another as they trade positions.

These conversations may help parents communicate about foraging opportunities and efficiently divvy up parental care. However, not all pairs are equally communicative; some couples are chatty and have long conversations, while others are less garrulous. Previously, researchers found that how talkative a gull couple is may be related to the coordination of parental care, with parents who vocalize more providing better care to their offspring.

“Because these conversations take place in the nest, and we know that developing embryos can hear, I wondered if the gull embryos can eavesdrop on their parents,” says Francisco Ruiz-Raya, co-author of the study and now at the University of Glasgow. “These conversations could be important as a proxy of the quality of the parents. Maybe the developing embryo can eavesdrop on this information and know it has good quality parents or the opposite, that its parents are a complete disaster.”

Egg-cellent Listeners

Ruiz-Raya, with Alberto Velando of the University of Vigo in Spain, studied 44 yellow-legged gull families on Sálvora Island, Spain. From each nest, they took two sibling eggs and exposed them to different noises in artificial incubators. Half the eggs listened to audio playback of chatty parents, while their siblings were exposed to the sounds of less talkative parents. Just after hatching, both siblings were placed into a gull foster family to be raised together.

“The only difference between the siblings was this short period during prenatal development when they were exposed to different cues of parental communication,” says Ruiz-Raya. “They had a shared genetic background, and they were reared in the same family context.”

Juvenile and adult yellow-legged gulls.

Source: Jules Verne Times Two via Wikimedia Commons

Ruiz-Raya and Velando’s findings suggest that prenatal sound exposure has long-lasting physiological and behavioral effects in gull chicks.

First, they found differences in development: Eggs exposed to chattier parents took longer to hatch. In addition, there were changes in developmental mechanisms between siblings. Specifically, the researchers found increases in hormonal stress response and DNA methylation (a biological change that alters which genes are active at which times) in chicks prenatally exposed to quieter parents.

The researchers monitored the chicks’ growth and nutrition up until fledging to assess how well they communicated with their foster parents. They found chicks prenatally exposed to chattier parents showed more vocal begging behavior than those exposed to quieter parents.

Finally, Ruiz-Raya and Velando examined how prenatal acoustic cues might prepare embryos for the family context into which they will hatch.

“We found that chicks that were raised in chatty families showed a better nutritional status and grew faster, but only those siblings that were exposed to chatty parents in their prenatal life. The sibling exposed to quieter parents prenatally performed worse,” says Ruiz-Raya.

“It's about having the information that prepares you for the postnatal context.”

Yellow-legged gull.

Source: Donald Hobern via Wikimedia Commons.

Eavesdropping Advantages

The finding that chicks with chattier foster parents grow bigger and faster—if those chicks are prenatally exposed to chatty parents—challenges previous thinking regarding parent-offspring conflict. In evolutionary biology, this refers to the tension that arises when the interests of parent and offspring differ, such as when the level of parental investment desired by the offspring is different from what a parent is willing to provide.

Traditionally, embryos have been viewed as passive agents in this conflict, with their development under the complete control of the mother’s hormones.

“It is exciting to show that embryos can obtain information and that they are active agents in parent-offspring conflict,” says Ruiz-Raya.

“The other surprising outcome of this study was that events in this specific, prenatal window can have a lasting effect during postnatal life, likely even into adulthood. It shows that we need to be aware of how important and consequential the social environment is, even for developing embryos.”