Energy costs during incubation in Svalbard and Willow Ptarmigan hens

Abstract

Studies of wild and captive Willow and Svalbard Ptarmigan hens have allowed us to estimate the daily energy cost during incubation. It was similar for the two species, varying between 70-85 kcal per day depending on number of eggs, nest insulation, ambient temperature, number of foraging periods and total time spent away from the nest. Daily energy cost during incubation was 15-20% above resting metabolic rate in non-incubating hens but only 45-55% of that in free-living nonincubating hens. Incubating hens reduced their energy expenditure through high nest attentiveness. A reduction in food intake during incubation led to loss in body weight.