Animals have developed unique ways to communicate so they can increase their chances of survival. A new study reveals that birds are able to communicate information while they're still in their eggs. Unhatched bird embryos have adapted to their environment by paying attention to threats, such as predators.
Yellow-Legged Gulls Experiment
When you think of baby birds communicating, you probably imagine them chirping or singing with open beaks. However, this is only a small part of their abilities. Researchers studied the embryos of the yellow-legged gull (Larus michahellis) and discovered that the unhatched chicks could communicate while they were still inside their eggs.
Researchers collected wild yellow-legged gull eggs and divided them into two groups: a control one and an experimental one. Then, they took several eggs from the experimental group four times per day and put them in a box that played the sounds of a predator. The control group was in a box without any sounds. After brief exposures to the calls of the predator, the researchers would put the eggs back into the incubator with the ones that hadn't been taken out.
When researchers exposed the unhatched eggs to threats like the sounds of a predator, the eggs vibrated more after returning to the incubator. They also vibrated more than the eggs that never left the incubator and hadn't heard the predator sounds.
Communication Inside Eggs
Scientists believe that the vibration of the eggs is a form of communication among unhatched bird embryos. The vibrations seem to serve as a warning to the other embryos that a predator is near them. This has an interesting impact on their development, and researchers noticed changes in the experimental groups that the control group didn't have.
For example, both the exposed and unexposed eggs in the experimental group took longer to develop than the control group. They hatched later, were quieter and crouched more. All of these changes indicate a fear of predators that they had not seen but only heard while still inside their eggs. Moreover, all of the eggs in the experimental group showed these changes, including the ones that weren't exposed directly to the sounds of the predator and only noticed the vibrations of other eggs inside the incubator.
It's important to point out that some of the changes in the experimental group weren't positive. The birds had more stress hormones and less mitochondrial DNA in their cells. They also had shorter legs, which researchers believe indicates energy use for responding to threats like predators. Since bird eggs have a limited amount of resources, the embryos exposed to threats had to use their energy to stay safe instead of growing longer legs.
Complex Social Behavior
It's easy to enjoy the beautiful songs of birds without thinking about the deeper meaning. But birds aren't singing for people's entertainment. Instead, they use a variety of sounds and noises to communicate important information and exhibit complex social behaviors.
From declaring their territory to warning others about predators, birds use sound in different ways. Now, research shows they can also use vibration while inside the egg. Since sound is a vibration, it makes sense that birds would use it.
Why would unhatched eggs warn other eggs about a predator? If you only think about survival from the point of an individual, it doesn't make sense. But if you look at how birds have evolved over time, you'll see altruism or behavior that benefits others. Researchers believe that birds who warn their siblings about danger are doing it because they share genes and want the others to survive.
- Nature: Bird Embryos Perceive Vibratory Cues of Predation Risk From Clutch Mates
- Smithsonian: Unhatched Bird Embryos Communicate With Siblings by Vibrating Their Shells
- Scientific American: A Bird's-Eye View of Communication
- Futurity: Social Cues Teach Baby Birds to Sing
- Alderleaf Wilderness College: Bird Communication: An Introduction