Estimation of the rate of oxygen consumption of the common eider duck (Somateria mollissima), with some measurements of heart rate during voluntary dives

The relationship between heart rate (f(H)) and rate of oxygen consumption ((V) over dot O-2,) was established for a marine diving bird, the common elder duck (Somateria mollissima), during steady-state swimming and running exercise. Both variables increased exponentially with speed during swimming and in a linear fashion during running. Eleven linear regressions of (V) over dot O-2, (ml kg(-1) min(-1)) on f(H) (beats min(-1)) were obtained: five by swimming and six by running the birds. The common regression was described by (V) over dot O-2=10.1+0.15f(H) (r(2)=0.46, N=272, P<0.0001). The accuracy of this relationship for predicting mean (V) over dot O-2 was determined for a group of six birds by recording f(H) continuously over a 2-day period and comparing estimated (V) over dot O-2 obtained using the common regression with (i) (V) over dot O-2, estimated using the doubly labelled water technique (DLW) and (ii) (V) over dot O-2 measured using respirometry. A two-pool model produced the most accurate estimated db, using DLW. Because of individual variability within mean values of (V) over dot O-2, estimated using both techniques, there was no significant difference between mean (V) over dot O-2 estimated using f(H) or DLW and measured (V) over dot O-2 values (P>0.2), although individual errors were substantially less when f(H) was used rather than DLW to estimate (V) over dot O-2. Both techniques are, however, only suitable for estimating mean (V) over dot O-2 for a group of animals, not for individuals.

Heart rate and behaviour were monitored during a bout of 63 voluntary dives by one female bird in an indoor tank 1.7 m deep. Tachycardia occurred both in anticipation of and following each dive. Heart rate decreased before submersion but was above resting values for the whole of the dive cycle. Mean f(H) at mean dive duration was significantly greater than f(H) while swimming at maximum sustainable surface speeds. Heart rate was used to estimate mean (V) over dot O-2, during the dive cycle and to predict aerobic dive limit (ADL) for shallow dives.