THERMAL CONSEQUENCES OF DIURNAL MICROHABITAT SELECTION IN A SMALL BIRD

Thermal consequences of microhabitat selection during daily activity w ere quantified for male Phainopeplas Phainopepla nitens breeding durin g (1) spring in the Sonoran Desert, (2) summer in semiarid woodlands w ith mild, ocean-moderated climates, and (3) summer in semiarid woodlan ds isolated from ocean moderation. The interior woodland was markedly hotter during the Phainopepla's breeding season than were the other tw o habitats; for example, maximum air temperature averaged 39.7-degrees -C in the interior woodland and 28-29-degrees-C in the other two areas . Microhabitat selection was similar in the Sonoran Desert and the coa stal woodland, but differed substantially between these locations and the interior woodland. Use of sites exposed to direct sunlight was red uced 56% in the interior woodland compared to the coastal location. Th is reflects reduced use of exposed perches with a resultant increase i n use of shaded sites within vegetation which significantly lowers ope rative environmental temperatures experienced by birds in the interior woodland. Thus, site selection reduces by two-thirds the amount of ti me the animal experiences environmental temperatures above its upper c ritical temperature of 43-degrees-C. Avoidance of exposed sites by bir ds breeding in the interior woodland may interfere with vital activiti es such as foraging and territorial advertisement.