Figure 4.
The daily percentage of time during their active period (01.00–22.00) when snow buntings (Plectrophenax nivalis) at a (a) high-Arctic and (b) low-Arctic breeding site could either sustain an optimal performance level (blue region) or forced to work at suboptimal performance levels (red region) based on either operative (Te) or air (Ta) temperature recordings. Optimal and suboptimal performance is defined as the periods when buntings could sustain levels of work ≥ four-time BMR or less than four-time BMR, respectively, while maintaining thermal balance. (Online version in colour.)