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
.