In a remote corner of Brazil's Amazon tropical(热带的)rainforest, researchers have spent decades catching and measuring birds. Over 40 years, dozens of Amazonian bird species have declined in mass(质量). Many species have lost nearly 2% of their average body weight each decade, researchers report November 12 in Science Advances. Some species have grown longer wings. The changes could help birds stay cool in a hotter, more changeable climate, the researchers say.
"Climate change isn't something of the future. It has been happening and has effects we haven't thought of," says Ben Winger, an ornithologist(鸟类专家)at the University of Michigan, who wasn't involved in the research but has documented similar shrinkage(缩水)in migratory birds.
To see if non-migratory birds have also been shrinking, Jirinec and colleagues analyzed data collected from 1979 to 2019 in a remote region in the Amazon that spans 43km. The data include over 11,000 individual birds of 77 species as well as climate for the region.
All species declined in mass over this period, the researchers found. Species lost from about 0.1% to nearly 2% of their average body weight each decade. The motmot, for example, shrunk from 133g to about 127g over the study period.
These changes coincided with an overall increase in the average temperature of 1℃ in the wet season and 1.65%℃ in the dry season. Birds' mass decreased the most in a year or two after especially hot and dry seasons, which tracks with the idea that birds are getting smaller to deal with heat stress.
Wing length also grew for 61 species, with a maximum increase of 1% per decade. Jirinec thinks longer wings make for more efficient, and thus cooler, fliers.
"The Amazon rainforest is mysterious, remote and full of biodiversity," Jirined says. "This study suggests that even in places like this, far removed from civilization, you can see signatures of climate change."
8. What changes have happened to Amazonian birds over 40 years?
A.They have lost weight. | B.They have grown prettier. |
C.They have become fewer. un | D.They have become larger. |
9. What do does the underlined phrase "coincided with" in paragraph 5 mean?
A.Contrasted with. | B.Compared with. | C.Corresponded to | D.Contributed to. |
10. What's a reason for the tropical birds' changes?
A.Climate change | B.Food shortage. | C.Massive hunting | D.Scientific research |
11. What might be the best title of the text?
A.Researchers measuring birds in Amazon | B.Climate change shrinking tropical birds |
C.Longer wings improving flying efficiency | D.Human activities damaging Amazon rainforest |