Global warming makes the headlines, but at least part of the world has been getting cooler over the last half-century, and migratory birds are noticing. Way down south, in eastern Antarctica, seabirds have begun arriving at their colonies and laying their eggs later on average than in the 1950s, potentially preventing new parents from finding enough food to keep their chicks alive and healthy.
Many kinds of animals are altering their behavior as climate changes (ScienceNOW, October 3 2003). Most research on this topic, however, has been conducted in the northern hemisphere, where ever warmer temperatures have led plants to sprout earlier and migratory birds to return home sooner. The long-term effects of climate change on animals in the southern hemisphere have gone largely unstudied.
That is, until population ecologist Christophe Barbraud of the National Center for Scientific Research in Villiers en Bois, France, and his colleague Henri Weimerskirch of the University of Washington in Seattle took a look at seabirds, such as penguins and petrels, in eastern Antarctica. Making use of a data set collected by several researchers over 55 years, Barbraud and Weimerskirch tracked the timing of the birds' arrival at their breeding colonies and when they began laying eggs.
Their results show a clear trend: Species arrive at their breeding colonies 9 days later, on average, than they did in the mid-20th century. Their egg-laying is also delayed, taking place an average of 2 days later than it did before. (The birds apparently make up for lost time by abridging their mating rituals). The trends are opposite those observed in the northern hemisphere, the researchers report online this week in Proceedings of the National Academy of Sciences.
Why the flip flop? Instead of warming, eastern regions of the southernmost continent are actually cooling, and sea ice is growing, explains Barbraud. This cooling is no less harmful than the warming occurring up north, he says. The delayed arrival of parents means that chicks don't leave the nest until later in the year, perhaps when krill and other food aren't as abundant. "That would have an impact on the size of populations if the trend continues," says Barbraud.
But the extent of this impact "all hinges on what's going to happen in the future," says marine ecologist Angus Atkinson of the British Antarctic Survey. It's hard to distinguish long-term changes from short-term, he says, and climate models for the Antarctic are somewhat controversial because presatellite climate data (from the 1950s and 1960s) is often not trusted.