Fig. 7. Energy expenditure (W) of foot-propelled (open symbols) and wing-propelled (filled symbols) aquatic birds during diving. The relationship is best described by the following power function (two variables): energy expenditure=20.36M_b^0.64, where energy expenditure is in W and M_b is body mass in kg; r²=0.87. Note that values are plotted along a log₁₀ scale. The dotted lines indicate the 95% confidence interval. Values are based on table 1 (from Enstipp et al., 2005) and include only respirometry studies. With the exception of two values for A. fuligula (De Leeuw, 1996) and the values for U. lomvia and U. aalge (Croll and McLaren, 1993), all values are based on studies of birds diving in shallow tanks (for references, see Enstipp et al., 2005). Values for the three cormorant species were recalculated for a water temperature of 12.6°C [the water temperature for P. carbo sinensis (Pcs) in Schmid et al., 1995] by using established regression equations [P. aristotelis (Par) (Enstipp et al., 2005); P. auritus (Pau) (present study); P. carbo carbo (Pcc) (data from Grémillet et al., 2001)].