Fig. 3

Eider female blood δ¹³C values. Eider female blood δ¹³C values (N = 69) are, very similarly to lipid free yolk δ¹³C values, affected by an interaction between timing of breeding and female size corrected weight. Heavy females (75^th percentile, dotted line H, open circles) show a clear transition from utilizing more stored reserves (i.e., lower blood δ¹³C values) when breeding early toward an increased use of local feeding (i.e., higher blood δ¹³C values) when breeding later in the season. In contrast, the blood δ¹³C values of light females (25^th percentile, solid line L, black dots) are only negligibly affected by the timing of breeding. Females of median weight (dashed line M, grey dots) exhibit an intermediate association between timing of breeding and blood δ¹³C values