1 . Tropical(热带的)birds deep in Brazil’s Amazon rainforest are shrinking as the world’s climate changes. Researchers studied data for 77 tropical bird species over the past 40 years and found that all of them had lost body mass, with some species losing nearly 2% of their weight per decade.
A 2019 study of birds that had crashed into buildings in Chicago, Illinois, found that they’d lost mass over a 40—year period, but those species were migratory(迁徙的). However, why the birds changed in that way was unknown. Therefore, researchers decided to examine the records of 15, 000 non-migratory birds living in a rainforest within a few hours’ drive from Manaus in Brazil.
The average temperature of the birds’ habitat is 1℃ warmer in the wet season and 1. 65℃ warmer in the dry season compared with that in 40 years ago. What’s more, 13% more rain falls in the wet season and 15% less in the dry season. The birds have lost mass more sharply following extremely dry or wet seasons. This could be a short-term response to changes in their environment, such as a lack of rainfall causing a decline in the number of insects that the birds feed on.
“Mass is a generally good indication of body condition in birds, says Vitek Jirinec at the Integral Ecology Research Center in California, who led the study. "If they’re simply not getting enough to eat, you’d expect them to lose weight.”
Birds of the same species are generally larger at higher latitudes. The leading theory is that their smaller surface — area — to — volume ratio（表面积和体积比）allows them to better conserve heat. The opposite would help smaller species in hot climates to cool and could explain why birds are getting smaller as the climate warms, says Jirinec.
The marked physical change during just four decades show why stopping destroying trees alone won’t prevent the ongoing extinctions of animal species across the world, says Camila Gomez, a scientist who studies evolutionary changes in birds. "This study also shows how human-caused changes in climate are contributing to observed population declines in tropical birds," says Gomez.
1. Why did the researchers study the non-migratory birds?| A．To make the conclusion of the 2019 study. |
| B．To prepare them for their future migration. |
| C．To find the reason for their physical change. |
| D．To seek a way to save the Amazon rainforest. |
| A．High temperatures are rarely seen. | B．It seems much drier in wet seasons. |
| C．Weather patterns get more extreme. | D．Rainfall is increased in dry seasons, |
| A．It enables them to hide easily. | B．It makes them feel less cold. |
| C．It keeps them in good shape. | D．It helps them lose extra heat. |
| A．Global Warming Leads to Population Declines in Birds |
| B．Climate Change Is Causing Some Birds to Lose Weight |
| C．Tropical Birds Are Struggling to Survive Dry Climates |
| D．Migratory Birds Are Experiencing Big Physical Changes |
