It's called the "elevator to extinction." Bird species in Papua New Guinean mountains are getting pushed farther and farther up to escape rising temperatures that may make it impossible for some of them to survive in the future.
Species already living at or near the top of a mountain may eventually run out of higher elevations and face the risk of extinction with higher temperatures. That's according to new research that looked at more than 150 bird species on two mountains in the South Pacific island nation of Papua New Guinea.
"Everything is shifting up. ... The dominant pattern is this kind of musical chairs, and the one at the end is out of luck," said Ben Freeman, a Ph.D. student in ornithology at Cornell University. "What we found is that species are not only moving to higher elevations, but they're disappearing from the lower elevations, as well, and because mountains are pyramid-shaped, there's less area at the top, [so] the forests get smaller and smaller."
He and his wife, Alexandra Class Freeman, also from the Cornell Lab of Ornithology, went to two remote forested mountains in Papua New Guinea, Karkar Island and Mount Karimui, whose birds were studied by the renowned anthropologist Jared Diamond about 50 years ago. That provided a "mangos to mangos" comparison for the Freemans, who published the research this week in Proceedings of the National Academy of Sciences.
Both mountains are approximately 8,000 feet high. The Freemans found that on Mount Karimui, 87 bird species, 70 percent of those studied, moved up the mountain an average of 370 feet. On Karkar Island, 17 bird species, 77 percent of those studied in that area, shifted their range higher by an average of 500 feet.
Four bird species they studied -- the white-winged robin, mountain gerygone, crested satinbird and crested berrypecker -- are now near the summit of Mount Karimui, and higher temperatures could result in the localized extinction of these species during this century, according to the researchers.
In their shift to higher elevations, the birds may have to contend with different food to eat, different diseases to avoid and possibly different predators to ward off.
Reconsidering conservation
Unfortunately, the birds can't just fly to a different island to find similar habitat and temperatures. "The thing with these tropical forest birds is they have wings, but they grow up in one particular spot, and if they're lucky enough to survive, they live their whole life within a stone's throw of that spot," Freeman said.
The scientists don't think there could be any other reason to explain the move except climate change. But they're unsure of the exact mechanism for the shift. It could either be a direct impact of higher temperatures or due to the complex interaction between food sources and competitors.
The mountains are so remote that they're still covered in primary forest and are the same now as they were during Diamond's study in the 1960s; the only difference is that average temperatures have risen in Papua New Guinea 0.4 degree Celsius since then.
Birds "provide a lot of ecosystem services, so they're indirectly beneficial to people," he said. "For me, these are stunningly beautiful species with this long evolutionary history, [and] the local cultures in these areas use the feathers for all kinds of cultural ceremonies."
Papua New Guinea is not the only place where tropical species have been affected by climate change. Peruvian birds, Indonesian moths, Madagascar chameleons and other species in tropical mountains have also shifted upslope, the researchers said. In the western United States, the American pika, a small cousin of the rabbit, can die when exposed to higher temperatures for just a few hours, according to the National Wildlife Federation.
"We need to conserve habitat for the species to move into, so that means conserving entire mountainsides," Freeman said. "Conservation in a climate change age requires more than just conserving a patch of forest here and there."
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