Saturday afternoon as I descended toward the arroyo I didn't hear a single bird. The land was as silent as a land can be. Only at dusk after I'd pegged my tent in a narrow arroyo branchlet did two species briefly and rather tentatively call. As light failed rapidly, White- winged Doves gently cooed, and some titmouse-like Verdins called insistently with their sharp CHIP CHIP CHIPs, which I interpreted as a warning call -- that a gringo was camped in the arroyo. Verdins occur from the US Desert Southwest to central Mexico. You can see a Verdin at http://sosensky.com/bird-photos/Verdin.htm.
During the next morning's early cool hours birds commonly seen in scrub along the arroyo were House Finches, often perching like big juicy strawberries atop green cacti and agave flower-stems, Northern Mockingbirds, and Northern Cardinals. Turkey Vultures occasionally sailed across the valley, and every now and then I could hear Ravens croaking, even if I couldn't see them.
During much of the day's middle the only birds heard were Cactus Wrens, with their low, gruff GRRU-GRRU-GRRU- GRRU... You can see an illustration of a Cactus Wren -- the birds are surprisingly large to be wrens -- and hear one calling if you have Windows Media installed, here.
In the hottest, most glaring part of middle afternoon it seemed that not a thing stirred. Just as an experiment I chose a thorny thicket in a ravine looking likely to harbor birds and spished -- made the SHHH-SHHH-SHHH sound. Instantly up popped two Cactus Wrens onto their respective Ocotillo stems and replied with their GRRU- GRRU-GRRU-GRRU... Other Cactus Wrens in other thorny ravines chimed in, and for about 15 minutes the whole slope broke out in GRRU-GRRU-GRRU-GRRUs. Then it was quiet again, real quiet.