Collapse of Desert Bird Populations Likely Due to Heat Stress from Climate Changehttps://phys.org/news/2019-09-collapse-bird-populations-due-stress.htmlAs temperatures rise, desert birds need more water to cool off at the same time as deserts are becoming drier, setting some species up for a severe crash, if not extinction, according to a new study from the University of California, Berkeley.... The researchers' latest findings, part of UC Berkeley's Grinnell Resurvey Project, come from comparing levels of species declines to computer simulations of how "virtual birds" must deal with heat on an average hot day in Death Valley, which can be in the 30s Celsius—90s Fahrenheit—with low humidity. These temperatures are, on average, 2 C (3.6 F) hotter than 100 years ago. The birds that the model predicted would require the most extra water today, compared to a 100 years ago, were the species that had declined the most in the Mojave Desert over the past century. The desert straddles the border between California and Nevada.
The most threatened turn out to be larger birds, and those that have an insect or animal diet.
The team calculated that larger birds, like the mourning dove, require 10% to 30% more water today to keep cool because of the 2 C increase in Mojave Desert temperatures over the last 100 years.
According to the UC Berkeley analysis, birds that eat insects or other animals are more threatened by changes in evaporative water loss because they typically get all of their water from the moisture in their food. They seldom, if ever, drink from surface water sources. A 30% increase in water requirement could mean that larger birds have to catch an extra 60 to 70 bugs per day to survive the increased heat. If those bugs are even around, the birds still have to expend extra energy and time to find them.
The American kestrel, prairie falcon and turkey vulture, all large and carnivorous, have declined, as have large insect-eaters like the white-throated swift, violet-green swallow, olive-sided flycatcher, Western meadowlark and Western bluebird.
Smaller birds that eat seeds or are omnivores are less threatened, according to the model.
Vegetarian birds, such as seedeaters, face a different problem. Because they can drink from surface water sources—springs and pools in desert oases, they can supplement the water they get from their food. But that's only if water is around.
... According to Beissinger, the team's conclusions about these California and Nevada desert birds may apply to species in other regions of the world.
Eric A. Riddell el al.,
"Cooling requirements fueled the collapse of a desert bird community from climate change," PNAS (2019)