Social Displays in Red-Winged Blackbirds (Agelaius phoeniceus): Sensitivity to Thermoregulatory Costs

Abstract

Breeding male Red-winged Blackbirds (Agelaius phoeniceus) engage in territorial advertisement and agonistic displays that have ordered benefits. We studied the frequency of these behaviors in relation to thermoregulatory cost by comparing plots of activity vs. microclimate with plots of energy and water cost vs. microclimate, using standard operative temperature, $T_{es}$ , to quantify microclimate. We used a multiple regression model to control for nonthermal environmental factors covariant with $T_{es}$ to clarify the behavior-thermoregulation relationship. We found that male Red-winged Blackbirds shifted from display to shelter seeking and foraging in proportion to increasing thermoregulatory energy cost. Water costs appeared unimportant. Higher-value agonistic display appeared less sensitive to thermoregulatory cost than did lower-value territorial advertisement.