̽����ѡ

When it comes to climate change, there will be some winners and a lot of losers: The World Wildlife Fund estimates that up 40 percent of Europe’s 426 bird species could disappear with just a 1 degree Celsius increase in temperature. But at least one little bird appears to be bucking the trend.

Ben Hatchwell’s team at University of Sheffield in the United Kingdom have studied the long-tailed tit’s breeding habits for more 20 years. Three years ago, they began a project to study how climate affects the birds’ breeding. 

Populations of the long-tailed tit, a diminutive passerine, ballooned in the last 45 years. There are now twice as many tits living in the U.K. than there were in 1969. And the team thinks a warmer spring breeding season is behind it. 

The long-tailed tit’s nesting season, typically from March to May, is nothing short of a two-month marathon. Their nests, woven from spider silk, feathers, and brush to be elastic enough to expand as their offspring grow, demand a huge amount of labor. In the four to five weeks it takes to build one, a single tit will fly a total of 300 miles shuttling materials back and forth.

With the nest built, an adult female will lay an egg every day for up to 11 days. Then, once the nestlings hatch, the adults will forage for insects from dawn till dusk until the chicks fledge, which takes about two weeks. 

Philippa Gullett, the Ph.D. student in charge of the study, says the warmer breeding season eases the burden on adults. These birds typically exhaust themselves trying to make families—because the tit has a lifespan of only two to three years, the species has to squeeze every last drop of breeding productivity out of their short lives. 

“Previously people have tended to assume that winter is the time that effects the survival of very small birds,” says Gullett, explaining that seasonable cold weather normally winnows the population before breeding can happen. “Really, it’s the warmer spring” boosting tit population numbers.  

The big question: How does the long-tailed tit’s population explosion fit into the larger picture of how climate change is affecting bird behavior? And more practically, Gullet says, what are this finding’s consequences for building effective conservation strategies? The long-tailed tit may not be the only species to benefit from global warming, but its success could provide clues into the failures of other struggling species. “Could similar mechanisms be driving decreases in other species?”

In the long term, it’s the balance of pressures on the birds that drive population growth, says Gullett. “Colder autumns are associated with higher death rates, and there’s a chance of a mismatch between when the birds’ main food, caterpillars, are around and when the birds are breeding.”

But, she says, the tit seems likely to continue its winning streak, and when it comes to climate change, that makes the long-tailed tit a rare bird.