Distribución invernal de posaderos, dormideros y áreas de alimentación del Cormorán Grande (Phalacrocorax carbo sinensis) en ríos de Navarra (N España)

Abstract

Wintering distribution of day roosts, night roosts and feeding areas of Cormorants (Phalacrocorax carbo sinensis) in rivers from Navarra (N Spain)
From 1991 to 1996 the wintering population of cormorants in Navarra (N Spain) increased 843%. Five roosts were censused in the 1991-92 winter and nine in 1996-97. Most cormorants (95.4%) stayed within the 0-20 km radius around the roosts during day-time. The mean distance between roosts and feeding areas was calculated in 13.6 km. The mean distance between nearest roosts was 33 km. The distribution of cormorants around the roosts was asymmetric, because more cormorants returned downstream to the roosts than upstream, and this could rninimize the intraspecific competition. Cormorant showed fidelity to day and night roosts and feeding areas. We suggest the distribution of roosts in rivers is conditioned by the distance of daily flight between roosts and foraging areas.