Field metabolic rate of blue grouse during winter

We measured the field metabolic rate (FMR) of seven free-ranging and two captive blue grouse (Dendragapus obscurus) with doubly labeled water. Average carbon dioxide production (1.016 ± 0.088 L CO2∙kg−0.734∙h−1) of free-ranging grouse was 8% higher but not significantly different (P < 0.05) from captive grouse (0.944 ± 0.058 L CO2∙kg−0.734∙h−1). Ambient temperature was not correlated with FMR (P = 0.268). The mean fat content of free-ranging blue grouse was 39 g (3.4%), which was equal to the energy equivalent of about 3× daily standard metabolie rate (SMR). The FMR of free-ranging grouse averaged 657 ± 62 kJ/d or 1.6 × SMR. The FMRs of free-ranging blue grouse averaged about 25% below FMRs predicted from allometric equations; most were 35–40% below those predicted. We suggest that there is little energetic constraint on blue grouse during winter because they are able to maintain a positive energy balance by minimizing energy costs through effective thermoregulation, microhabitat selection, and reduced activity.