The impact of disturbance on the behaviour and energy budgets of Brent Geese Branta b. bernicla

We studied disturbance factors that caused Event Geese along a stretch of the north Norfolk coast to fake flight. Patterns of activity and undisturbed flight were also quantified, to derive energy budgets. The most frequent source of disturbance tons pedestrians. Those disturbances resulting in greatest energy expenditure were also of human origin, but tended to be 'mechanised' (e.g. aircraft, gunfire). Activity budgets for high- and low-disturbance days were compared, which showed that birds feed less and are more vigilant when disturbance is greater. On grass pastures, 68.9% of flight was a response to disturbance, which increased estimated hourly energy expenditure (HEE) from 32.2 to 35.6 J/h (10.8%). On exceptionally disturbed days, HEE increased to more than 44.0 J/h. As a consequence of disturbance, geese may need to feed at night for up to an hour in mid-winter, to balance their daily energy budget. Unless they are able to feed easily at night, disturbance may be one of the primary factors influencing local distribution of Brent Geese. Management implications are discussed.