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Figure 2


Fig. 2. Standardised BMR residuals in relation to the time when the BMR value was obtained for individual snow petrels (N=65). Time is expressed in h (0:00–24:00) and rad (0{pi}–2{pi}). The regression line represents a significant effect of the term cosine (time of BMR) on BMR (P=0.05) and indicates a cyclic diurnal rhythm in BMR with the lowest predicted values at 12:00 h and the highest predicted values at 00:00 h. `Night' and `day' measurements refer to BMR measurements that were started during the night (at 22:10 h) and the day (at 11:30 h), respectively. The BMR residuals were obtained from the model in Table 1 (BMR controlled for body mass and body condition). Standardised residuals are divided by an estimate of their standard deviation (s.d.), and have mean=0 and s.d.=1.