Meeting Abstract
In the Sonoran desert, where current summer surface temperatures can reach 70°C and air temperatures can reach 50°C, it is imperative for birds to defend body temperatures below lethal levels. Cooling occurs primarily by evaporative water loss. Lesser Nighthawks (Chordeiles acutipennis) and Common Poorwills (Phalaenoptilus nuttallii) are exposed to these ambient temperature extremes, particularly in their nesting behavior. An understanding of the thermoregulatory capacity of these two nightjars may offer some prediction of their ability to adapt to changes in climate. Field studies were performed to assess rates of heat dissipation and maximum thermal tolerances using flow-through respirometry. As birds were exposed to increasing ambient temperatures, metabolic rates, body temperature, and rates of evaporative water loss were measured in real-time. Compared to desert passerines, these caprimulgids are able to tolerate significantly higher ambient temperatures and are able to dissipate heat with greater efficiency. This appears to be due, at least in part, to the mechanism of gular flutter, which allows evaporative heat loss with little increase in energy expenditure.
