Fun with Science Club®


			Cliff swallows know how big their neighborhoods should be. Carrie Straight 05.18.01 Some colonial nesting bird species can have just a few members of a colony or thousands of members in a colony. The number of members in a colony changes with the availability of food, nesting spaces, and mates. Commonly studied colonial birds called cliff swallow Petrochelidon pyrhonota. These small birds nests in variable sized colonies. Two scientists from Oklahoma, USA, wanted to discover why some birds live in large colonies and others live in small colonies. Some researchers that group size changes with available resources (food, space, and mates), there is an optimum size and groups fluctuate around that size, or they might inherit the group size (they want to nest in the same size group they were born in). These two scientists wanted to test the last of these predictions, that group size is heritable. To test this prediction, they set up an experiment by finding cliff swallow colonies. They counted the number of nests in each colony. Then they took some baby birds (nestlings) from small colonies and swapped them with nestlings from big colonies. Each nestling had a mark so that the researchers could identify it later. The following year, when these baby birds were ready to try out their first nesting attempt, the researchers located as many of the marked birds as they could. They again counted the number of nesting adults in each colony. They compared the groups size (number of adults) where the birds decided to nest to the ones they hatched in and the size of the colonies were the researchers placed them after swapping them with the other nestlings. The researchers discovered that birds returned to nest in colonies similar in size to the ones they hatched in, not the ones where they later grew up. These results suggest that the information about what size of colony is a good one to nest in is not learned but passed from their parents through their genes.


			Brown, Charles R., and Mary Bomberger Brown. 2000. Heritable basis for choice of group size in a colonial bird. Proceedings of the National Academy of Science 97(26): 14825-14830.