FIELD METABOLIC-RATE OF BLUE GROUSE DURING WINTER

We measured the field metabolic rate (FMR) of seven free-ranging and t wo captive blue grouse (Dendragapus obscurus) with doubly labeled wate r. Average carbon dioxide production (1.016 +/- 0.088 L CO2 . kg(-0.73 4) . 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 X daily stan dard metabolie rate (SMR). The FMR of free-ranging grouse averaged 657 +/- 62 kJ/d or 1.6 X SMR. The FMRs of free-ranging blue grouse averag ed about 25% below FMRs predicted from allometric equations; most were 35-40% below those predicted. We suggest that there is little energet ic constraint on blue grouse during winter because they are able to ma intain a positive energy balance by minimizing energy costs through ef fective thermoregulation, microhabitat selection, and reduced activity .