An assessment of population size and demographic drivers of the Bearded Vulture using integrated population models

Abstract

Conventional approaches for the assessment of population abundance or trends are usually based on a single source of information, such as counts or changes in demographic parameters. However, these approaches usually neglect some of the information needed to properly understand the population as a whole, such as assessments of the non‐breeding proportion of the population and the drivers of population change. The Bearded Vulture Gypaetus barbatus is a threatened species and its Pyrenean population (the largest in Europe) inhabits parts of Spain, Andorra, and France. We developed an Integrated Population Model (IPM) using data from a long‐term study (1987–2016) in the three countries, including capture–mark–recapture of 150 marked individuals, to assess population size and age structure at the whole population scale, and obtain estimates of survival and breeding parameters of this population. The breeding population experienced a geometric mean population increase of 3.3% annually, falling to 2.3% during the last 10 yr. The adult proportion of the population increased with time, from 61% to 73%. There were 365 (95% Bayesian credible interval [BCI]: 354–373) adult breeding birds in 2016, representing 49% of the adult population and 36% of the total population (estimated at 1,026 individuals, 95% BCI: 937–1,119). The large number of non‐breeding adults probably led to higher mean age of first reproduction than previously estimated, and to an estimated 30–35% of territories occupied by polyandrous trios. Population growth rate was positively and strongly correlated with adult survival, which had a much greater effect on population growth than productivity. The effects of subadult and juvenile survival on population growth were weaker. We found strong evidence for a density‐dependent decrease in juvenile survival, productivity and adult survival, leading to reduced population growth with increased population size. Our approach allowed us to identify important conservation issues related to the management of supplementary feeding sites and geographic expansion of this population. Our study supports the use of IPMs as a tool to understand long‐lived species, allowing simultaneous estimates of the non‐breeding size of the population (which is critical for understanding population functioning), better estimates of population parameters, and assessment of demographic drivers.

Ecological consequences of human depopulation of rural areas on wildlife: A unifying perspective

“…Additionally, not only have predators increased in numbers but big game ungulates, that were hunted intensively in the past, are now thriving (Table 1), such as wild boars (Sus scrofa), red deer (Cervus elaphus), and roe deer (Capreolus capreolus). The increase in ungulate biomass has, in turn, contributed to the recovery of obligate scavengers, such as vultures (Martín-Díaz et al, 2020), along with the additional help of conservation policies, such as supplementary feeding (Margalida et al, 2020), and through the banning of the use of poison. For example, griffon vultures have multiplied their population by a factor of 10 in 40 years (from 3240 pairs in 1979 to 31-37,000 pairs in 2018), and have expanded their range accordingly (Fig.…”

“…Data within brackets indicates the year the estimate was made. Grey wolf data from Á lvares et al 2005, Ministerio de Agricultura, Alimentación y Medio Ambiente (https://www.miteco.gob.es/es/biodiversidad/temas/inventarios-nacionales/censo_lobo_espana_2012_14pdf_tcm30-1 97304.pdf); lynx data from Calzada et al (2007) (https://www.ellinceiberico.com/poblaciones-lince-iberico/); brown bear data from Palomero (2007), Palomero et al (2006), Fundación Oso Pardo (https://fundacionosopardo.org/publicaciones/); Spanish imperial eagle data from González et al (1987), Grupo de Trabajo del águila imperial (Ministerio de Medio Ambiente); griffon vulture data from Del Moral and Molina (2018); bearded vulture data from Margalida and Martínez (2020) and Grupo de Trabajo del Ministerio de Medio Ambiente; ungulate data from Instituto Español de Estadística (https://www.ine.es). (*) The estimate from 1988 (294 packs; Blanco et al, 1990) is methodologically not comparable with those from subsequent decades.…”

A predictive flight-altitude model for avoiding future conflicts between an emblematic raptor and wind energy development in the Swiss Alps

“…A potential limitation of our study, however, may be the under-representation of adult birds in the dataset. Bearded vultures reach adult plumage at the age of 5–6 years [97]. As they develop from the juvenile (less than 2 years) to the adult age, some morphological characteristics that may influence flight behaviour gradually change [98].…”

High long‐term survival and asymmetric movements in a reintroduced metapopulation of Cinereous vultures

“…2009; Bearded vultures, Margalida et al. 2020; or Red‐tailed hawks: Morrison and Baird 2016). The high resighting rate of vultures in the Alps promotes the use of camera traps at scavenger feeding stations, whenever possible, to identify a larger number of individuals.…”