Human activity and the drying up of rivers determine abundance and spatial distribution of Black Storks Ciconia nigra on their wintering grounds

Capsule The drying up of rivers results in the fragmentation of home ranges over the winter period, birds avoid areas of high human activity. Aims To investigate the impact of human activity and habitat characteristics on the distribution of Black Storks Ciconia nigra on wintering grounds in West Africa. Methods Seasonal variations in wintering home-range size and habitat selection of seven Black Storks were studied using satellite tracking from 1998 to 2006. A Black Stork population was followed in the field from 2003 to 2005 in the Nazinga Game Ranch (Burkina Faso) and Ghana. Results Adults and sub adults (n = 5) have smaller mean global ranges than juveniles (n = 2) (532.92 +/- 237.17 and 2463.18 +/- 405.10 km2 respectively) and smaller mean core ranges (8.83 +/- 10.01 and 162.14 +/- 131.56 km2 respectively) suggesting that juveniles prospect widely for suitable habitats during their first winter period. In all birds the home range becomes increasingly fragmented from November to February. Two main factors seem to be involved in this fragmentation: (1) Black Storks seem to prefer locations on perennial rivers but many rivers in this region gradually dry out into separated pools at this time of year; and (2) monthly variation of human activity along the rivers. Occurrence of Black Storks is inversely proportional to human activity, irrelevant of whether open habitat is available at the location. When human pressure is moderate, open habitats and low tree canopy favour the presence of Black Storks. Conclusion We propose that conservation measures should include the creation of reserves located along perennial rivers, away from areas of human activity.