Post-fledging dispersal of Barn Owl in the lower Tagus Valley




The TytoTagus Project arose from studies conducted at Ponta da Erva (Tagus Estuary, Portugal), suggesting its great importance as a foraging area to dispersing juveniles of Barn Owl Tyto alba. Although numbers obtained from car transects vary annually, owls abundance may reach a maximum of ca. 5 birds/km (up to more than 15 birds/km in some patches). Such high abundance values are probably unique in Europe and possibly in the world, and are most likely associated to the habitat features and location of the area: an open farmland landscape with a rich network of ditches located in the estuary of the Tagus and along some of its tributaries.

Although Barn Owls are known to disperse in random directions, several authors refer the tendency of juveniles to disperse along watercourses in order to obtain favourable hunting spots, as a consequence of the good micro-habitat for prey (mainly small mammals) provided by riparian vegetation. The location of the study area close to an estuary may explain the occurrence of these birds, considering the hypothesis that the Tagus River and tributaries may operate as ecological corridors for dispersing juveniles.