Heart rate as an indicator for daily energy expenditure by Brent and Barnacle geese

Brent geese (Branta b. bernicla) and Barnacle geese (Branta !eucopsis) on Schiermonnikoog forage on the grass pastures during the winter and switch during early spring to the saltmarsh. In this study we investigated whether this habitat preference can be explained by daily energy expenditure. To estimate the daily energy expenditure, measurements of time-activity-budgets of the Brent geese in the polder area and on different vegetation types on the saltmarsh were conducted during spring 1999. Time-activity-budgets can be translated into caloric terms by measuring the average heart rate for specific behaviour. External heart rate loggers were applied on semi-captive Brent and Barnacle geese walking freely in an enclosure. The resting heart rate was calibrated against oxygen consumption in the laboratory to express the heart rate as caloric costs. Different behavioural parameters could be related to distinct heart rate ranges. Resting had the lowest heart rate, walking had a higher heart rate than foraging. The energetic costs of different behavioural parameters (as assessed by heart rate telemetry) are extrapolated to time-activity budgets of wild Brent geese. When flight is excluded the energy expenditure is lower on the polder than on the saltmarsh. However, flying is very costly, mainly due to disturbance. This results in a higher energy expenditure on the polder than on the saltmarsh., which could play a role in the observed habitat preference for the saltmarsh area as soon as food becomes available there.