LOW LEVELS OF ENERGY EXPENDITURE IN A NOCTURNAL, FOREST-DWELLING WADER, THE EURASIAN WOODCOCK SCOLOPAX RUSTICOLA
Résumé
Ecological energetics have been extensively studied in the Scolopacidae, but mostly focused on coastal and wetland species. Living in forests and meadows, the Eurasian Woodcock Scolopax rusticola (mean body mass 317 g) is an exceptional species among waders. Standard Metabolic Rate (SMR, including Basal Metabolic Rate (BMR) and thermoregulation costs, measured at rest in a respirometer chamber) and T3 hormone levels were measured on wild woodcocks wintering in France. While the Lower Critical Temperature followed predictions from allometric equations (17.5°C), BMR was low (1.2 W) and plumage insulation high compared with other shorebirds. T3 was positively correlated with SMR in the laboratory. In the field, we used T3 levels to predict Field Metabolic Rate (FMR); in winter the average FMR was around 2.8 times BMR (3.4 W). The energetic requirements of Eurasian woodcocks are lower than those of typical waders living in windy unsheltered habitats, which in turn may lead to their low BMR. Woodcocks could save energy by resting during the day in sheltered habitat and being active at night, when the costs for thermoregulation are higher.