Sniffing Out Ferrets

When we think of animals with a good sense of smell, we typically think of the Class Mammalia. Dogs, for example, are well-known for their ability to pick up and follow scents over long distances. With the exception of some vultures, birds generally are not known for this ability. The conventional understanding is that birds have only a weak sense of smell.

Some new research may change that understanding. Smell could provide a useful tool to lower the risk of predation, if birds could use it. Such a smell would be especially helpful during breeding season to warn of potential nest predators. To find out whether birds use a sense of smell, researchers studied a colony of blue tits (Cyanistes caeruleus) in Spain.

The researchers carried out an experiment with a population of blue tits that raise their young in nest boxes in Miraflores de la Sierra in the Sierra de Guadarrama mountains, in Madrid province. The researchers placed the scent of mustelids (ferrets) inside the nest boxes when the chicks were eight days old, and “the parents took longer to enter the boxes to feed their chicks, and they approached the boxes more often without going inside,” Ms. Amo de Paz told SINC.

Thanks to the images captured by a video camera located several metres from the nest box, the scientists were able to work out the number of times the chicks were fed, and deduced that the birds did not feed their chicks on fewer occasions, although “they spent less time inside the nest while feeding their babies,” according to the biologist. By spending less time in the nest box, the parents lessened the risk of predator attack while still feeding their chicks.

As a control, the researches also added a quail scent to some nest boxes and water to other boxes. The quail scent and water did not deter the parent tits to the same extent as the ferret scent. The researchers later checked all the nestlings again to see if the presence of a "predator" had impaired their physical development. The ones in the ferret-scented boxes were just as healthy as the ones in other boxes, so their development did not suffer as a result.

So does this new information have implications for helping baby birds? There is a common concern that picking up a baby bird or handling its nest might cause the bird's parents to abandon their young. Typical advice reassures people that this is not the case, sometimes with a comment that birds will not smell their touch.

In light of this study, the latter part seems mistaken; at least some birds use their sense of smell to avoid predators. However, the basic advice is correct. Even though the tits in the study sensed the presence of potential predators and were more cautious around the nest, their urge to care for their young was stronger, and they still fed the baby birds. The brief handling necessary to place a nest back into a tree or move a fledgling out of harm's way is unlikely to discourage parent birds from returning.