Ecological energetics of the semipalmated plover (Charadrius semipalmatus)

This project represents the first study of the physiological and ecological incubation energetics of an Arctic-nesting migratory shorebird (Semipalmated Plover, Charadrius semipalmatus).;The ability to prolong incubation successfully in subneutral conditions has potential behavioural and life history implications for Semipalmated Plovers, providing a buffer against environmental variation during the incubation period. At a small body size (42-50 grams), with a resultant low degree of thermal inertia, life in cold environments entails high energetic costs which have to be accounted for. Semipalmated Plovers balance the requirements of incubation and against their own fitness costs, a competition for energetic resources reflected in egg homeostasis, parental energy expenditure, behavioural choices 'and ultimately offspring survival.;Key words: Arctic, basal metabolic rate, daily energy expenditure; energetics, lower critical temperature, metabolism, Semipalmated Plover (Charadrius semipalmatus), shorebirds, standard operative temperature, thermography, total evaporative water loss.;A metabolic chamber study determined a lower critical temperature (LCT) of 23.3 C°, a basal metabolic rate (BMR) 47.4 kJ/day-1 and a measured total evaporative water loss of2.5 mL H2O day -1. These results were consistent with high values found for other shorebird species breeding in the Arctic. Daily energy expenditure (DEE) measured in the field averaged 167.8 kJ day-1, or 3.5 times BMR for C. semipalmatus, values consistent with those of other Arctic-nesting shorebirds. Models based on ambient temperature and to a lesser extent body mass best explained DEE, supporting a negative correlation between ambient temperatures and length of incubation sessions. Temporary mate removals suggested that the subneutral cost of incubation for single parents may be as great as that of biparental birds, in agreement with the additional cost model of incubation energetics. The role of nest-site microclimates in the stability of internal egg temperatures was considered using wind speed, solar radiation and surface air temperature values to compute standard operative temperature (Tes). Tes was found to be negatively correlated with measured internal egg temperatures. Infrared thermographic images found total body mean radiative temperatures ranging from 9.8-11.7 °C in different environmental temeratureswith the head region exhibiting the greatest level of temperature radiation and accounting for approximately 39% of the surface area of incubating birds.