The Kittiwake: Winging It, Survival-Wise
On a remote, treeless island 60 miles south of Alaska's Prince William Sound, an old military radar tower has become one of the best bird observation sites in the world.
Hundreds of black-legged kittiwakes nest on the tower. As one researcher has discovered, the seabirds may have a lot of flexibility when it comes to responding to a changing environment.
The hulking, concrete tower on Middleton Island isn't much to look at. But in 1986, a few black-legged kittiwakes took a liking to it.
"This is kind of a cool situation where the birds are nesting on a building, where you could go inside and could potentially be looking inside out at the birds," says U.S. Geological Survey biologist Scott Hatch.
These days, the tower is a giant bird hotel, with nearly 600 kittiwake suites. Hatch installed one-way mirrored glass so he can see out, but the birds can't see in.
"These windows are really pretty remarkable. You can get to within inches of the birds you're observing. I like to tell people — sort of tongue in cheek — you can literally do smoosh faces on the window," he says.
Hatch calls kittiwakes the "white lab rats" of the seabird world because they're so common and easy to study. But over the years, the Middleton Island kittiwakes have revealed some intriguing facts about themselves. For one thing, they are really terrible breeders.
"In Alaska, kittiwakes had abject breeding failure. I mean, zero young produced in many colonies for many years, and Middleton Island was maybe the best example of that," Hatch says.
A researcher studying the same bird several decades ago in England found just the opposite, however. Those North Atlantic kittiwakes raised lots of chicks, but they had short life spans — living about 10 years. Hatch realized the Alaskan kittiwakes were probably living longer.
"So I hypothesized, reasonably enough, that they must have very high survival to compensate, otherwise we should have been out of kittiwakes a long time ago," Hatch says.
It turned out to be true. The Alaskan kittiwakes live about 20 years, twice as long as their North Atlantic counterparts. Much of Hatch's research since has been devoted to figuring out why.
This spring, Hatch put GPS bands on several birds. He thinks the birds' reproductive woes have to do with their diet, so the bands will help him learn where they're getting their food and what they're eating.
He also wants to know if feeding the kittiwakes makes a difference. So he began offering fish to some of the birds. It's an all-you-can eat type of arrangement. This spring, the kittiwakes had healthy appetites.
"The bird in A-24 has just eaten seven fish. That's not a record; I think the record was nine fish in one meal," he says.
Hatch wondered if these well-fed Alaskan kittiwakes would start to act more like North Atlantic kittiwakes, and very quickly — within one year — they raised many more chicks. The next question was whether their life span would decrease. The preliminary data suggests the answer is yes.
"The survival rates are coming down accordingly," he says.
This reproductive phenomenon is well-known among different animal species. Mice have lots of young, but short lives. Elephants live a long time, but don't raise many offspring. Hatch says it's rare, however, to discover a single species with two reproductive patterns.
"It's kind of a strategy, it's a game," he says. "Do I put all my eggs into — no pun intended — do I put my effort into breeding, and therefore not live as long, or do I sit it out, live a long time and hope that I'll have adequate reproduction over the long term?"
The conventional wisdom is that if you reduce birds' food supply, their population numbers will suffer. But the kittiwakes' flexibility has allowed them to do well when their favorite fish is plentiful or scarce, in the Atlantic or Pacific. Hatch says usually biologists like himself tell tales of gloom and doom, but the kittiwakes' story may be different.
"Many wildlife populations may operate like this. And so, let's factor that into our thinking, rather than throwing up our hands and assuming all is lost. It could be that populations will adapt in ways they've already demonstrated they're capable of doing, in ways that are a little more palatable than going through the floor when we bugger their food supply," he says.
Hatch doesn't want to minimize very real threats like climate change. But, he says, in some cases, the effect may not be as bleak as many assume. The Middleton Island kittiwakes, with their flexible life spans, may be a good example of that.