KINANGOP, Kenya — Simon Joakim Kiiru remembers a time not long ago when familiar birdsongs filled the air here and life was correlated with bird sightings. His lush, well-tended homestead is in the highlands next to the Aberdare National Park, one of the premier birding destinations in the world.
When the hornbill arrived, Mr. Kiiru recalled, the rains were near, meaning that it was time to plant. When a buzzard showed a man his chest, it meant a visitor was imminent. When an owl called at night, it foretold a death.
¶ “There used to be myths because these are our giants,” said Mr. Kiiru, 58. “But so many today are gone.”
¶ Over the past two decades, an increasing number of settlers who have moved here to farm have impinged on bird habitats and reduced bird populations by cutting down forests and turning grasslands into fields. Now the early effects of global warming and other climate changes have helped send the populations of many local mountain species into a steep downward spiral, from which many experts say they will never recover.
¶ Over the next 100 years, many scientists predict, 20 percent to 30 percent of species could be lost if the temperature rises 3.6 degrees to 5.4 degrees Fahrenheit. If the most extreme warming predictions are realized, the loss could be over 50 percent, according to the United Nations climate change panel.
¶ Polar bears have become the icons of this climate threat. But scientists say that tens of thousands of smaller species that live in the tropics or on or near mountaintops are equally, if not more, vulnerable. These species, in habitats from the high plateaus of Africa to the jungles of Australia to the Sierra Nevada in the United States, are already experiencing climate pressures, and will be the bulk of the animals that disappear.
¶ In response to warming, animals classically move to cooler ground, relocating either higher up in altitude or farther toward the poles. But in the tropics, animals have to move hundreds of miles north or south to find a different niche. Mountain species face even starker limitations: As they climb upward they find themselves competing for less and less space on the conical peaks, where they run into uninhabitable rocks or a lack of their usual foods — or have nowhere farther to go.
¶ “It’s a really simple story that at some point you can’t go further north or higher up, so there’s no doubt that species will go extinct,” said Walter Jetz, professor of ecology and evolutionary biology at Yale, whose research last year predicted that a third of the 1,000 mountain birds he studied, or 300 species, would be threatened because warming temperatures would decimate their habitats.
¶ Birds are good barometers of biodiversity because amateur birdwatchers keep such extensive records of their sightings. But other animals are similarly affected.
¶ Two years ago, scientists blamed a warming climate for the disappearance of the white lemuroid possum, a niche mountain dweller in Australia that prefers cool weather, and that was cute enough to be the object of nature tours. Many scientists, suspecting that the furry animal had died off during a period of unusually extreme heat, labeled the disappearance the first climate-related animal extinction.
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