A study of the impact of human disturbance on Wigeon Anas penelope and Brent Geese Branta bernicla hrota on an Irish sea loch

Abstract

Numbers of over-wintering Wigeon on Strangford Loch have declined from a maximum of 20,000 in the 1970s to less than 2,000 in the 1990s, whereas Palebellied Brent Geese, which occupy similar habitats, have not suffered a similar decline. Human activity has increased around the Loch in recent decades and this may have contributed to the decline of Wigeon which are considered to be less tolerant to disturbance than Brent. This study assessed the types of human activity on Strangford Loch and their likely differential effects on Brent and Wigeon. Results confirmed that Brent are more tolerant of human activity than Wigeon. Wigeon reacted at greater distances from human activity than Brent, were more likely to fly greater distances and less likely to return to their former activity at this site. Human disturbance affected birds significantly because they were usually disturbed while feeding which is limited temporally by tidal patterns. The most common form of human activity was people walking. Based upon observed level of disturbance and their effects upon food intake rates, a simple energy balance model correctly predicted presence/absence of Wigeon, but not Brent in four study areas of suitable habitat quality. It is concluded that disturbance could have contributed to the decline of Wigeon in Strangford Loch, although it is probably not the only factor involved. Future management of refuges must therefore take into account food supply and human access.