A type of seabird can zero in on fishing boats from a distance of about 7 miles (11 kilometers) away, a new study says.
Northern gannets, North Atlantic seabirds with a 70-inch (178-centimeter) wingspan, likely use their binocular vision to determine the boat's speed and fishing activities—and the presence of other birds—before deciding to fly over to investigate. (See "Gannets: Daring Divers" in National Geographic magazine.)
Once gannets arrive at the boat, they often catch fish that have been thrown overboard, plunge-diving into the water at speeds of up to 60 miles (96 kilometers) an hour.
The study—conducted recently off the coast of Ireland—also revealed that the birds don't investigate boats that are drifting and not actively in use.
This study is the first to look at the "halo of influence" that a boat has over seabirds—and its large area surprised the scientists, who published their paper June 2 in the journal Current Biology.
Gannets are "finely tuned to their habitat," said study leader Thomas Bodey, an ecologist at the University of Exeter in the U.K. "In evolutionary terms, boats are a brand-new thing, [but the birds are] perfectly able to adapt to this new opportunity."
Andrew Farnsworth, a research associate at the Cornell Lab of Ornithology in Ithaca, New York, said the study strengthens the idea that "birds are really intelligent" when interpreting their environment.
"In the same way that humans remember things and pick up on patterns and learn, we know that birds can do that too," said Farnsworth, who was not involved in the study.
For the study, Bodey and colleagues caught adult gannets at their cliffside nests and attached GPS monitors to the base of their tails.
The GPS unit takes a position every two minutes, enabling Bodey and colleagues to know how fast a bird is traveling between points and how straight it's going. This clued them in to whether the birds were foraging or simply "commuting," because a foraging bird tends to fly in a tortuous, wiggly path, while a commuting bird flies relatively straight. (See National Geographic's seabird photos.)
The scientists also tallied GPS data that showed where the fishing boats were located. That helped them calculate the distance at which a gannet changed from commuting to foraging behavior. The results revealed that the birds make the switch up to 7 miles (11 kilometers) away.
"We were surprised [the gannet found it] worth checking out the food source from that far away," Bodey said, since fishing boats don't always provide food.
The approach Bodey and his colleagues took could be the beginning of a research trend, says Cornell's Farnsworth.
"There are plenty of times when birders and researchers have been on boats and see seabirds following boats," he said. "Being able to put numbers on that is really amazing and cool. With more technology around and better transmitters and tracking devices, we're going to see more of this kind of thing."
Is this sort of scavenging behavior detrimental to gannets? It's debatable.
Some scientists have argued that it's a "bit like McDonald's—fast and easy but not good for you if you keep doing it." On the other hand, Bodey noted, the northern gannet population is increasing.
He says that with the jury still out, it's best to minimize the amount of foraging the birds do on boats. That's why this research can help governments better plan for marine conservation areas and fishing policies.
One example: Marine planners might pinpoint regions where gannets feed heavily on boats, then tweak fishery regulations so that the boats discard their fish in areas that tend to be less visited by the birds.