Fig. 3. Standardised BMR residuals in relation to age (years) of snow petrels (N=38, range 8–39 years old). The birds are of known age because they were ringed as chicks. The residuals were obtained from the final model in Table 2 (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.