Scientists have produced new evidence that climate change is leading tropical bird species that live near the top of a mountain to extinction.
Researchers have predicted for a long time that many creatures will try to escape from a warmer world by moving towards higher ground.
However, those who live at the highest levels can not go higher, and are expected to decrease.
This study found that eight species of birds that once lived near a Peruvian mountain peak have now disappeared.
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Researchers are particularly concerned about tropical mountain ranges and the impacts of climate change.
"The tropical mountain areas are the hottest of biodiversity hotspots, they harbor more species than any other place on Earth," Dr. Benjamin Freeman, lead author of the University of British Columbia, told the BBC.
"It has only become a bit warmer in the tropics and tropical plants and animals seem to be living a bit higher now than they used to."
The species that live in these regions are also extremely vulnerable because the temperature difference between the lowest and highest elevations in tropical regions is not as great as it is in other parts of the world. This means that climbing the slopes may not be as great a solution for species in the tropics as it is in other places.
To test these ideas, the scientists conducted a survey in 2017 on the species of birds that lived in a remote Peruvian mountain.
The team covered the same terrain, at the same time of the year, and used the same methods as in a previous survey, conducted in 1985.
They found that, on average, the ranges of the species had increased the slope between the two surveys. Most of the species found at the higher elevations decreased significantly in both range and abundance.
The researchers say that the recent warming constitutes an "escalation to extinction" for some of these species with temperatures in the area increasing by almost half a degree Celsius between the two surveys.
Of the 16 species that were restricted to the top of the ridge, eight disappeared completely in the most recent survey.
"These birds have climbed the mountain as much as you could predict if the temperature were this master switch that controlled where they live," said Dr. Freeman.
"Those who lived near the first 30 years have left."
The authors warn that rising temperatures will continue to drive widespread "extirpations and extinctions" of animals and plants at high altitudes through the tropical mountains of the Andes.
In contrast, scientists discovered that bird species that live in lowland areas were benefiting from climate change, expanding their ranges and shifting their upper limits higher up the mountains.
However, even species that are now on the move may find that they run out of options over time.
The authors say that if global temperatures increase this century between 2.6C and 4.8C, this could push tropical species to another 500m to 900m on the slopes. This could be too far for some.
Another problem is that many mountains have been cleared of their forests, which limits the ability of the species to ascend.
"You really can not ignore this process if you are thinking about conservation and long-term biodiversity in these areas," said Dr. Freeman.
"The way to deal with this is to keep protected habitat corridors that extend through large elevation gradients."
The study has been published in the Proceedings of the National Academy of Sciences.