Griffon Vulture Gyps fulvus range expansion: population size and reproductive parameters of a recently established population in northwestern Spain.

Full article

Published:

Volume 46(1), June 1999. Pages 81-88.

Language:

Spanish

Original title:

Expansión del Buitre Leonado Gyps fulvus: tamaño de la población y parámetros reproductores en un área de reciente colonización.

Keywords:

Gyps fulvus, new breeding area, northwestern Spain, range expansion, reproductive parameters.

Abstract:

The population of Griffon Vultures has increased dramatically from the 1970´s onwards, although its distribution area has only slightly increased. During 1997 we carried out a census of Griffon Vultures within a 2600 km2 area in the province of León (NW of Spain), in which this species had not been found breeding previously (Fig. 1). We found nine colonies and 41 breeding pairs occupying an area of 477 km2. The Griffon Vulture was first sighted breeding in this area in 1991 (pers. obs.), but it had not been found breeding in the 1979 and 1989 national surveys of the breeding population. This indicates, therefore, that the colonies reported here have been recently established in this area. The new colonies were found at 1270 m.a.s.l. on average and the mean nearest-neighbour distance between them was of 8.42 kms. Colony size varied between 1 and 9 pairs, with a mean of 4.56 pairs. The proportion of pairs that started breeding was 86.2% (n = 29), the breeding success (number of fledglings/laying pairs) was of 0.68 (n = 25), and the productivity (number of fledglings/breeding pairs) was 0.57 (n = 30). No regional variation within the study area was found in these breeding parameters (Table 1). Although reproductive parameter values from different regions and/or years could not be compared properly since they can vary according to biotic (size and density of the colonies), abiotic (weather conditions) and methodological factors, it seems that values for the new population reported here were lower than values found in other Spanish populations (Table 2). The recent establishment of this population did not seem to be related to an increase in the food supply because our estimates of the availability of carrion within the study area indicate that food would have been enough to nourish a Griffon Vulture population at least from the 1970’s. We suggest that the establishment of this population could have been caused by an increase in the number of dispersers coming from increasing populations breeding nearby, combined with favourable conditions offered by the study area: proximity to other populations, availability of food and nest-sites and, especially, a marked reduction of human persecution of the species.