Population expansion and breeding success of Bearded VulturesGypaetus barbatusin the French Pyrenees: results from long‐term population monitoring

Abstract

Based on monitoring of Bearded Vultures over 24 years in the French Pyrenees, we assessed factors explaining temporal and spatial variations in numbers and breeding performance. The number of territorial pairs increased throughout the study period from 16 in 1994 to 44 in 2017. No significant negative trends in mean productivity (fledglings per territorial pair) were detected with increasing population size. Colonization probability increased significantly with breeding population size the previous year and with the regular provision of supplementary food in the territory the winter when colonization occurred. Colonization of new territories simultaneously increased the distribution range and local densities, but we found no effect of number of near neighbours on productivity. Pairs having bred less than 5 years together had a much lower probability of laying clutches, and higher lay rates were observed inside or close to protected areas after accounting for pair‐bond length, so productivity of territories inside protected areas was significantly higher. Nest success decreased with advanced lay date and increased with winter food abundance. Nesting failures in the study area were frequently associated with harsh weather. Additionally, disturbance by human activities was the second most important identified cause of breeding failure. The probability of failing due to disturbance was higher in western areas (where breeding areas are more accessible to humans), outside protected areas, and has increased with time. After a failure due to disturbance, there was a significantly higher probability of not producing a clutch the following year as compared with pairs that had not failed or had failed due to other causes, indicating deferred effects of disturbance. Our results show the benefits of conservation management actions, such as implementation of protected areas or designed supplementary food programmes in winter, to help range expansion. On the other hand, we did not find a significant effect of winter supplementary food on productivity. Management of feeding sites should be adapted to more specific planning, being used only in areas where natural food availability is scarce, avoiding its use close to breeding sites when juveniles disperse, and targeted mainly to help range expansion. Our results also highlight the importance of maintaining or enhancing good populations of wild ungulates and regulating human activities around nesting sites of this threatened species.

Adult coloration of the Bearded Vulture (Gypaetus barbatus) in the Pyrenees: relation to sex, mating system and productivity

“…We hypothesized that such changes are infrequent in a long‐lived and essentially monogamous species, where pair composition is believed to remain stable across years (Terrasse, 2004, Arroyo et al . 2021, S. Duchateau, G. Chéliz, J. A. Gil & P. López‐López, pers.…”

“…2003, Arroyo et al . 2021). Likewise, breeding seasons without clear information of territory occupation and/or in which clutches were extracted for captive breeding and reintroduction projects (Ferrer et al .…”

“…Consequently, unless it changed RU during the course of the study, a given individual could not appear more than once in our dataset. We hypothesized that such changes are infrequent in a long-lived and essentially monogamous species, where pair composition is believed to remain stable across years (Terrasse, 2004, Arroyo et al 2021, S. Duchateau, G. Ch eliz, J. A. Gil & P. L opez-L opez, pers.…”

“…Average productivity (fledged chicks/year) was calculated for each RU across the period 2008-2019 (origin of the data: Gobierno de Arag on/Fundaci on para la Conservaci on del Quebrantahuesos; annual synthesis of M. Razin/Ligue pour la Protection des Oiseaux). RUs with less than 6 years of breeding information (n = 8) were excluded from the analyses in order to retain only reliable productivity means, which also included those territories established in the latest 5 years (n = 4) because inexperienced breeders usually show a lower productivity (Margalida et al 2003, Arroyo et al 2021. Likewise, breeding seasons without clear information of territory occupation and/or in which clutches were extracted for captive breeding and reintroduction projects (Ferrer et al 2014, Gil et al 2019 were also excluded from the analyses.…”

“…Arcese & Smith 1985). On the other hand, it can be argued that in such a long-lived species where pair bonds are believed to be rather stable across years (Terrasse, 2004, Arroyo et al 2021 Ch eliz, J. A. Gil & P. L opez-L opez, pers.…”