Many species of animals have ways of making sure they do not mate with a relative. Scientists have identified odor-based recognition of kin in most species, with the exception of birds. But a new study shows the small nocturnal seabird known as the storm petrel can recognize its relatives by smell alone. The study, published online July 15, 2012, in Animal Behaviour (see below), is the first to document the ability to discriminate relatives by odor in a bird.
This ability may help the birds avoid inbreeding and select genetically compatible mates. Storm petrels (Hydrobates pelagicus) remain in the colony they are born in throughout their life, so the chances of encountering a related bird is high. They also mate for life, so choosing an appropriate partner is critical.
Francesco Bonadonna and Ana Sanz-Aguilar, from the Center of Functional and Evolutionary Ecology in Montpellier, France, studied a colony of storm petrels on a tiny island off the coast of Spain called Isla de Benidorm. This colony has been the subject of survey work for nearly two decades, so the researchers had records of which birds were related. In that time, the researchers had never found a related pair nesting together, suggesting the birds had some way of telling apart relatives and unrelated birds.
Historically, birds were thought to have poor olfactory abilities. Under this assumption, scientists did not bother testing whether birds could use odor cues to recognize relatives. But recent studies revealed storm petrels find their food out on the open ocean by means of a sophisticated sense of smell. The birds also have a particular odor, described as warm and musky. It seemed at least plausible that they could use this sense of smell in their social lives, as well.
To test if petrels could discriminate kin from unrelated birds by odor, Bonadonna and Sanz-Aguilar collected bird scents using cotton swabs. They placed a swab with the scent of a relative at the end of one arm of a Y-shaped maze and a swab containing the scent of an unrelated bird on the other. Nearly all the birds chose to avoid the scent of a relative, instead walking along the arm containing the scent of the unrelated bird.
A preference for the smell of nonrelatives could help the petrels avoid inbreeding. Bonadonna and Sanz-Aguilar suggest this could come about through olfactory imprinting on a family scent template. Each storm petrel would recognize its own smell and the similar smell of close relatives, and be able to compare the odor of other birds to this template. Smelling out a nonmatching odor would allow the petrel to find a nonrelated mate among relatives in its bustling seaside colony.