Cost reduction in the cold: heat generated by terrestrial locomotion partly substitutes for thermoregulation costs in Knot Calidris canutus

Bruinzeel, L.W.; Piersma, T.


To test whether heat generated during locomotion substitutes for the thermoregulation cost, oxygen consumption of four post-absorptive temperate-wintering Knot Calidris canutus was measured at air temperatures of 25 degrees C (thermoneutral) and 10 degrees C (c. 10 degrees below the lower critical temperature) when the birds were at rest at night and during running on a treadmill, After allowing for body mass, the thermoregulation cost at 10 degrees C was significantly lower in active birds compared with birds at rest, At rest, the birds spent, on average, 0.50 watt (W; range, 0.47-0.57 W) on thermoregulation. During exercise, this cost factor averaged 0.33 W (range, 0.25-0.42 W), The average difference in thermoregulation cost was 35% (ranging from26% to 49% between individuals) and provides an estimate of the amount of substituted heat, A review of nine studies, all restricted to small birds, showed that substitution is a widespread phenomenon, The consequences of such partial substitution for the annual energetics of Knot wintering in the temperate Wadden Sea v tropical west Africa are examined, Compared with a previous additive model, the model which includes substitution (i.e. the use of heat produced during activity) reduces the differences in maintenance metabolism between the two wintering strategies by 17%, from 1.19 W to 0.99 W. VA:IBN