Do you have any brothers or sisters? Do you help and play with them, or do you tend to fight or even steal from them? If you were looking at a large group of people, would you be able to find them? Of course you would! But that is not always the case in the animal world. While some animals do recognize their siblings, many actually do not. Even when they do, it is not well studied how this affects the interactions between siblings. These are some topics that many scientists are interested in.
In the city Matera in southern Italy you can find large groups of birds called lesser kestrels (Falco naumanni). Every spring, these birds gather together in rock crevices or holes in abandoned buildings and make their nests, which is called brood nesting. Because all of the nests are so close to each other, the chicks can wander from nest to nest once they are big enough. This means that chicks that are not related can end up in the same nest together. But do these chicks know which other baby kestrels are their brothers and sisters and which ones are not? And if they can, does it change how the chicks interact? These are two questions that a group of curious scientists asked.
To answer their questions, the researchers gathered 15 pairs of baby lesser kestrel siblings for a total of 30 chicks. They randomly selected 2 chicks at a time, placed them in a fake nest, and gave them a mouse to eat. The scientists then videotaped the interactions that happened inside the fake nest between the nestlings. After running many trials, they found something amazing: when the two chicks were siblings, they did not normally steal the food from each other. However, when the two baby lesser kestrels were not related they actually stole the food quite often. Not only that, but almost all the chicks participated in this behavior: of the 30 nestlings that the research team watched, 27 of them stole the mouse from the other chick they were with at least once!
So what does this mean? Well, it shows clearly that baby lesser kestrels are not afraid to compete for food and steal it away from other chicks in order to get their fill. This is because it is a beneficial behavior, or a behavior that is extremely helpful for the chick who performs it. Each nestling wants to grow up to be a strong lesser kestrel adult, so they will work hard to eat enough food in order to do so. However, the nestlings usually only steal food from individuals that they are not related to. Do you know what this means? Baby lesser kestrels do recognize their siblings (just like you do)! Not only that, but they do not wish to directly harm their siblings and therefore will not normally steal food from them, even though stealing the food would help that chick grow stronger. This is called altruistic behavior, or a situation in which one individual does not perform a selfish behavior that then benefits another individual.
So next time you are playing with your brother or sister, maybe take a page out of the lesser kestrel chicks’ book. Do not steal from your siblings or be mean to them, and instead maybe even do something nice – they are, after all, your family!
References:
Romano, A., Morganti, M., Assandri, G., Bazzi, G., Corregidor-Castro, A., Morinay, J., Cecere, J. G., Pilastro, A., & Rubolini, D. (2022). Sibling competition for food and kin selection in nestlings of a Colonial Raptor. Animal Behaviour, 194, 233–238. https://doi.org/10.1016/j.anbehav.2022.10.002.
