Abstract
We studied the changes in heart rate (HR) associated with metabolic rate of incubating and resting adult wandering albatrosses (Diomedea exulans) on the Crozet Islands. Metabolic rates of resting albatrosses fitted with external HR recorders were measured in a metabolic chamber to calibrate the relationship between HR and oxygen consumption (V(O(2))) (V(O(2))=0.074 x HR+0.019, r(2)=0.567, P<0.001, where V(O(2)) is in ml kg(-1) min(-1) and HR is in beats min(-1)). Incubating albatrosses were then fitted with HR recorders to estimate energy expenditure of albatrosses within natural field conditions. We also examined the natural variation in HR and the effects of human disturbance on nesting birds by monitoring the changes in HR. Basal HR was positively related to the mass of the individual. The HR of incubating birds corresponded to a metabolic rate that was 1.5-fold (males) and 1.8-fold (females) lower than basal metabolic rate (BMR) measured in this and a previous study. The difference was probably attributable to birds being stressed while they were held in the metabolic chamber or wearing a mask. Thus, previous measurements of metabolic rate under basal conditions or for incubating wandering albatrosses are likely to be overestimates. Combining the relationship between HR and metabolic rate for both sexes, we estimate that wandering albatrosses expend 147 kJ kg(-1) day(-1) to incubate their eggs. In addition, the cost of incubation was assumed to vary because (i) HR was higher during the day than at night, and (ii) there was an effect of wind chill (<0 degrees C) on basal HR. The presence of humans in the vicinity of the nest or after a band control was shown to increase HR for extended periods (2-3 h), suggesting that energy expenditure was increased as a result of the disturbance. Lastly, males and females reacted differently to handling in terms of HR response: males reacted more strongly than females before handling, whereas females took longer to recover after being handled.
Highlights
To measure precisely factors that affect the rate of energy expenditure of free-ranging animals, it is necessary to obtain instantaneous measurements of energy expenditure in the field.Doubly labelled water can be used to estimate energy expenditure but it provides only an average estimate over the measurement period (Speakman, 1997)
heart rate (HR) can be used to predict metabolic rate if the relationship is calibrated over a range of HRs
All three manipulations were conducted on each study bird, and given the low frequency and short duration of each encounter, we examined whether birds would exhibit the same intensity of change in HR between experimental manipulations
Summary
To measure precisely factors that affect the rate of energy expenditure of free-ranging animals, it is necessary to obtain instantaneous measurements of energy expenditure in the field.Doubly labelled water can be used to estimate energy expenditure but it provides only an average estimate over the measurement period (Speakman, 1997). Heart rate (HR) provides an instantaneous measurement that c.an be used to estimate energy expenditure, because HR and VO2 are directly related, as shown by the Fick equation: VO2 = HR × VS × (CaO2 – CvO2) , (1). HR can be used to predict metabolic rate if the relationship is calibrated over a range of HRs. numero. Us studies have examined the relationship between HR and VO2, and results show that the values for each vary linearly in both birds and mammals (Flynn and Gessaman, 1979; Butler et al, 1993; Nolet et al, 1992; Williams et al, 1993; Bevan et al, 1994). When coupled with behavioural data, HR can be used to the predict energy expenditure of specific activities (e.g. Bevan et al, 1995; Boyd et al, 1999)
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