杏吧原创

The medium tree finch is critically endangered (Image: Image Broker/Rex)

Mosquitoes and parasitic flies can be as deadly for birds as they can for humans. Stowaway mosquitoes brought on tourist planes pose a deadly threat to the iconic birds on the Galapagos Islands. But the innovative birds 鈥� Darwin鈥檚 finches 鈥� have worked out a way to fight them.

The birds are plagued by mosquitoes that may carry disease and by the parasitic fly Philornis downsi, whose blood-sucking larvae can kill entire clutches of young finches. The parasitic fly lays its eggs at the base of a finch nest. Once the larvae emerge, they suck the blood of nestlings.

鈥淭here is often 100 per cent mortality in nests,鈥� says of the Charles Darwin Foundation in Puerto Ayora in the Galapagos Islands.

During field work on the islands of the University of Austria in Vienna and her team noticed something unusual. Birds from four species of Darwin鈥檚 finches were picking leaves from a Galapagos guava tree, Psidium galapageium, and rubbing them into their feathers.

Tebbich鈥檚 team has found that the leaves repel mosquitoes and inhibit the growth of the bloodthirsty parasitic larvae. They presented in Cairns, Australia, but did not want to comment until the study was published.

Early birds

Other birds and animals around the world also rub their feathers or fur with plants to protect themselves from insects and parasites, but actual observations of this behaviour in birds are often anecdotal, Causton says.

鈥淭his is the first time that Darwin鈥檚 finches or any other species of Galapagos songbird have been reported conducting this kind of behaviour,鈥� she says.

鈥淚t is great that these birds are able to cope with a parasite by an innovation, as we want to keep them around,鈥� says of McGill University in Montreal, Canada. Two of the finch species in the Galapagos 鈥� the and the are critically endangered.

The adaptation of the finches to many different niches, which would normally be filled by other birds, helped inspire Charles Darwin鈥檚 theory of evolution by natural selection. And they already have a reputation for being innovative. 鈥淭hey show a lot of behaviours that passerine birds don鈥檛 typically show,鈥� says of McGill University.

For example, vampire finches have figured out a way to supplement their diet with a gruesome iron-rich treat: drops of , especially boobies. The avian vampires peck at the skin around the base of their victims鈥� feathers until they can draw and slurp the blood with their beaks.

They also by kicking at them and pushing them over a cliff.

Another species, the woodpecker finch, to extract arthropods from tree holes. This puts it into elite club of tool-using birds, which includes the likes of crows and ravens.

Only some species and some individuals within particular populations tend to engage in such behaviours, says Hendry.

Harsh environment

Innovativeness might have helped finches survive on the isolated islands, where they were probably blown by strong winds. 鈥淭hey were taken away from a lot of their typical foods and put into an environment with other foods in which conditions were often very harsh,鈥� Hendry says. 鈥淭hey were not able to get enough food so they probably were driven to attempt things that were not typical.鈥�

Lefebvre says the ancestors of the finches must have been innovative too; otherwise they would not have survived when they arrived. 鈥淢any birds that are brought to a new environment fail to survive,鈥� Lefebvre says. 鈥淚nnovativeness in itself allowed the ancestor to be able to make it to the Galapagos Islands and not go extinct.鈥�

Hendry thinks that even now, an estimated 2 to 5 million years since their arrival, the harsh environment of the Galapagos is still forcing the finches to use a diversity of resources in clever ways. 鈥淭hey are in an environment that probably favours innovation and novelty and just general intelligence,鈥� he says.

It鈥檚 not yet clear if the insect repellent is a recently developed response to the parasite or something the birds have done for a long time, Hendry says. The parasite in the 1960s and its negative impact on finches was first noticed in the 1990s.

鈥淭hat would be a really rapid and novel evolutionary response to a new selective pressure that was brought about by humans,鈥� Hendry says. 鈥淭hat would be pretty darn cool.鈥�