Dry Winters May Delay Breeding in Desert-Dwelling Birds

From Conservation Magazine:

Just how does rainfall (or the lack thereof) affect desert critters? To find out, University of Arizona researcher Chris McCreedy teamed up with USGS scientist Charles van Riper III, and they turned their attention to the birds. In particular, they focused on thirteen bird species nesting in two spots in the Sonoran Desert, one in California and one in Arizona. From an ecological perspective, the wash systems of the Sonoran Desert are similar to other riparian zones, but surface water is only present during the heaviest of heavy rains. Winter rains fall from November through April and result from cyclones that derive from Pacific storm tracks. Summer rains occur from July through September, and are the result of convective thunderstorms. Winter rains tend to drop lots of water, but gently and over a prolonged period of time; summer thunderstorms are more severe and more localized, but much shorter-lived. The two wet seasons are punctuated by extremely dry autumns and springs.

The researchers collected historical rainfall data for the years 2004-2009 and matched it with data on the first egg laid for each breeding pair of the thirteen species they had monitored. The mean rainfall for each of the study sites was identical, with around 55mm of average annual rainfall (just over two inches). The droughts of 2006 and 2007 saw less than 10% of that amount, while the 2005 El Niño year brought 500% of the average rainfall.

They discovered a distinct negative relationship between winter rainfall and the date on which the nesting season began. In other words, the less wet the winter was, the later the birds began laying eggs. The rainier it had been, the easier the birds began to breed. That pattern held up for each of the thirteen species the researchers considered, which each had to have at least four nests each season. And they suspected that the later egg-laying meant for a reduction in reproductive success. What’s perhaps puzzling is that, elsewhere in North America and Europe, changing climates are associated with earlier nesting, not later. What’s going on?

See more here: http://conservationmagazine.org/2015/01/dry-winters-delay-breeding-for-desert-dwelling-birds/