Figure 2.

(a) Patterns in stable nitrogen ratios (δ¹⁵N, green) and (b) concentrations of immunoreactive progesterone (black), corticosterone (red) and oestradiol (blue) across a representative section of bowhead whale baleen (from individual 500). Closed circles indicate hormone concentrations above a baseline threshold, while open circles indicate hormone concentrations within baseline levels. Dark grey box highlights gestation as defined under hypothesis 2; light grey box extends gestation as defined under hypothesis 1. Light grey vertical dashed line demarcates first and second phase of P4 peak.