|Sonoran Desert scene. Photo by Chris McCreedy.|
Three years ago, the journal Science published a summary of climate projections for the American Southwest. Eighteen of the 19 climate models used predicted dryer conditions, and the authors stressed that, by the middle to the end of this century, extreme drought conditions could become much more common in the Southwest. It is now the end of the century's first decade, and the National Weather Service's numbers are just in. In many parts of Arizona and Nevada, the past ten years have been among the warmest and driest on record.
This trend could have serious consequences for desert species such as the songbirds that PRBO has monitored in Sonoran Desert washes since 2003. Winter rainfall totals during our study have ranged widely, from a very wet year (2005) to two of the driest winters (2006 and 2007) in over a century. We documented a strong link between winter rainfall amounts and the number and diversity of both migrant and breeding birds in the Sonoran Desert. Also, as winter rainfall decreases, egg-laying begins later in the spring. During the very dry springs, species delayed nesting up to several weeks—and some elected to forgo nesting completely.
|Black-tailed Gnatcatcher. Photo by Tom Grey.|
Can Sonoran birds produce enough young to maintain their populations in breeding seasons shortened by drought conditions? For desert birds like the Black-tailed Gnatcatcher, more rain means greater nest success. Just how droughts limit this species' productivity (e.g., by food limitation, increased threats from predators, nestling intolerance of extreme heat) is the subject of my graduate study at University of Arizona.
Songbirds are short-lived vertebrates, rarely living beyond age four or five years. Multi-year droughts that span their lifetimes and diminish production will further stress desert species already dealing with other anthropogenic threats. Along with effects of climate change, desert wildlife faces large-scale habitat loss, not only from urban development and fire disturbance but also from solar energy installations planned for the desert Southwest (see "The New California Goldrush" by Ellie M. Cohen, Observer 158, www.prbo.org).
PRBO will continue long-term monitoring in the washes of California and Arizona in order to provide the best available information to desert land managers and decision-makers, helping us understand what can be done to protect desert birds.