Fig. 1. Fitted curves for (A) drag D (in Newtons) vs speed U (m s^–1), and (B) drag coefficient C_D vs Reynolds number Re, measured on frozen birds in a tow tank for a common guillemot (COGU) mounted on a sting (from Lovvorn et al., 1999), and for the same COGU and a Brünnich's guillemot (BRGU) towed with a harness and drogue system (from Lovvorn et al., 2001). Vertical lines indicate the range of speeds and Re observed in free-ranging BRGU during descent and ascent (Figs 2 and 3). The equation for the BRGU towed with the harness and drogue is D=1.08+2.55U²–1.38U³+0.276U⁴.