Field Metabolism of Tree Swallows during the Breeding Season

Abstract

Abstract I used doubly labeled water to study the field metabolic rate (FMR) of Tree Swallows (Tachycineta bicolor) on Kent Island, New Brunswick, Canada, during the breeding season. I tested the hypothesis that aerially foraging species have higher energy requirements than other species. For incubating female swallows, carbon dioxide production averaged 201.4 ± 15.8 ml CO2/h. While feeding 5 young, male and female swallows expired CO2 at a rate of 211.6 ± 23.3 and 231.0 ± 26.4 ml CO2/h, respectively. During this period males worked at similar levels to females, but the power consumption of females that fed young was significantly higher than incubating females. For both parents together, the mean number of visits to the nest/h was correlated with CO2 production: ml CO2/h = 201.6 + 2.49 (visits/h). On Kent Island, Tree Swallows had a higher FMR than Savannah Sparrows (Passerculus sandwichensis), suggesting that aerial-foraging birds have a higher FMR than ground-foraging species. For 7 species of hirundines, energy expenditure was associated positively with body mass; log(kJ/d) = 1.34 + 0.53 log(body mass, g). This relationship differed from one for species which use alternative foraging modes (ground foraging and flycatching, n = 11), log(kJ/d) = 0.89 + 0.75 log(body mass, g). Aerial foragers expend from 16-38% more energy/day than do other birds of similar size that spend less time flying.