The temperature in Death Valley reached 130 degrees on Aug. 16. In the Mojave Desert, a two-hour drive south, it was 109. In September, California's extreme heat continued.
There are birds in those and other western deserts. How do they survive such weather?
Certain desert bird populations won't. They're likely to collapse from the impact of heat and loss of water due to climate change. Scientists from the University of California, Berkeley determined this after studying bird populations in the Mojave Desert last year.
The study found that compared with 100 years ago a third of Mojave Desert bird species are less common today. Heat is stressing them. Additional losses are likely. (A third of Minnesota's breeding bird population would be 82 species.)
Those bird species whose water needs have increased are the species in greatest decline. Water scarcity is driven by sparse rain, high air temperature and low humidity.
Tipping points
Tipping points are when things begin to crash. A dictionary definition is: the critical point in a situation, process, or system beyond which a significant and often unstoppable effect or change takes place.
Douglas Erwin, a paleobiologist with the Smithsonian National Museum of Natural History, put it this way in an address to the Geological Society of America: "Everything's fine until it's not. And then everything goes to hell."
In Minnesota, we created a tipping point by plowing our prairies out of existence. Our prairie bird populations crashed. Numbers reached a point where the remaining population could not support itself on the remaining habitat.
The tipping point could be the plow. It could be weather, as in California.
Habituated to habitat
Birds can move, seek more favorable conditions, but most species have evolved to fit particular habitat difficult to replicate.
Southeast of Tucson, Ariz., the Chiricahua Mountains rise to almost 10,000 feet, 5,000 feet above the surrounding high desert. You drive a switching road to the top.
As the elevation changes, so does vegetation type. You drive through mini-climates. Also changing are the bird species you see. Each lives in its own habitat niche.
On an August trip several years ago, I was comfortable at that mountaintop in a warm cap and gloves. The chickadees we saw up there, easily living with occasional snow, would not survive on the desert floor.
Species that eat insects and animals get water from that diet. (Which is why baby birds survive in the nest without ever getting an actual drink.) Species with a seed diet need supplemental water once they leave the nest.
Weather conditions can reduce or eliminate insect, animal and plant resources.
Coping with heat
Birds, of course, drink water — from your birdbath, a puddle, wherever. Excess heat demands cooling, and water is key to that.
Birds don't sweat. They pant, with their bill open, moving air in and out to capture and expel body heat. Evaporation of water vapor from lungs also removes heat.
Blood loses heat as it flows through featherless areas. Birds cool by opening their wings, exposing more body. They pull up their skirts, so to speak, exposing more of their legs to passing air.
Water also cools birds when they bathe. Birds with webbed feet lose heat by simply standing in water.
In South Dakota several years ago the temperature was 105 degrees one day when we were (unexplainably) birding the prairie. We saw mostly meadowlarks and lark buntings.
They sought shade, but the only shade was made by fence posts. The angle of the sun created a narrow strip of shade for each post.
Birds sat on fence wires, scrunched to the shady side of the posts. Others perched on post tops, wings open, catching what breeze they could.
Birds have evolved to successfully deal with heat. How well they will survive temperature increases that push survival limits, like those in California deserts and possibly coming to a climate near you, is yet to be known.
Lifelong birder Jim Williams can be reached at woodduck38@gmail.com. Join his conversation about birds at startribune.com/wingnut.
