Feeding seabirds may give declining populations a boost

Seabirds often have a tough life. They may nest on the side of a cliff, perched over a drop that would be certain death for the rest of us. Their ocean food can be tough to find, especially in years when the weather takes a turn. Some make incredibly long voyages over open water, surprising us with their ability to navigate without GPS.

Add in pressures from humans and climate change, and perhaps it’s not totally surprising that many seabird species aren’t doing so well. A recent study in PLOS ONE, for example, looked at records for 19 percent of the global seabird population — the proportion that is monitored by scientists — and found a 69.7 percent decline between 1950 and 2010.

Scientists have a simple solution: Feed the birds.

The evidence that supplementing seabird diets could help a bird population comes from Simone Vincenzi of the University of California, Santa Cruz and colleagues. Back in 1996, researchers started supplementing the diets of some black-legged kittiwakes on Middleton Island, off the coast of Alaska. In most places, kittiwakes nest on the sides of cliffs. On Middleton Island, though, kittiwakes breed inside an abandoned U.S. Air Force radar tower. Despite the special digs, the kittiwake population on the island declined from 166,000 in 1981 to fewer than 25,000 in 1999 as a result of food shortages and habitat changes.

Kittiwakes are long-lived birds, with life spans of up to 25 years. So figuring out if supplementing nestling diet affects the population at large is a long-term project. Many of the birds fed as part of this project are still alive. But now nearly 20 years into the research, the scientists have been able to tease out some positive data from the effort. They report their findings July 14 in the Proceedings of the Royal Society B.

First, giving the birds extra food wasn’t enough to overcome any natural decrease in the availability of food. In years when there was little fish for the kittiwakes, the number of fledglings per nest declined, whether that nest received extra food or not. But fledglings that received that extra food grew faster than those that didn’t get any.

On Middleton, kittiwakes tend to return to the tower year after year to breed. But it was the unfed birds that returned in higher numbers than the fed ones. The researchers aren’t sure why, but it may be that supplementing the nestlings food decreases the chance that a poor-quality nestling dies early on. Those birds may fledge but not survive well in the wild once they’re not getting a helping hand from a scientist.

Overall, though, supplemented nests produced more breeding birds, and that small difference may be enough to produce long-term benefits for the population, the researchers say. “Food supplementation might be among the few conservation measures that … can help endangered species or populations when facing a strong decline in productivity,” they write.

Food supplementation is bound to be expensive and time-consuming, however. So it would seem to be of limited use as a conservation tool, especially if the factors that are driving seabird declines — such as overfishing of food sources, invasive species and climate change — remain unaddressed.