The Amazon rainforest is as pristine (处于原始状态的) a place as most people can imagine, but even there, the effects of a changing climate are playing out. Previous research found that some birds in the Amazon are experiencing drops that may be related to climate change. Now, new research suggests that as the Amazon's dry season has gotten hotter, some species are starting to evolve (进化).
For the new study, researchers studied 77 non-migratory species over a 40-year period. They reported in the journal Science Advances that 36 species have lost weight, as much as 2 percent of their body weight every ten years since
1980. Meanwhile, all the species became smaller in body size, while a third grew longer wings.
The researchers themselves are unsure what advantage the wing length changes give the birds, but smaller birds may have an easier time keeping cool. In general, smaller animals have a larger ratio (比例) of surface area to body size, so they dissipate more heat faster than a bigger animal. Less available food, such as fruit or insects, in dryer weather might lead to smaller body size.
"Think about a fighter plane. It has short wings and is heavy. It has to go really fast to stay high in the air, so it uses up plenty of energy," says ecologist Vtek Jirinec, who led the new study, while a glider (滑翔机) almost uses no power to stay high in the air, because it's got these long wings, and it's light."
For those who wonder why a small body change in a small homebody bird should matter, Jirinec points to how our actions have effects we don't always see － such as changing the size and shape of animals half a world away.
"We think of Amazonia as a pristine place, full of life, untouched by people, away from deforestation," Jirinec says. "But it looks like no, not necessarily."
