Long‐term demographic dynamics of a keystone scavenger disrupted by human‐induced shifts in food availability

Abstract

Scavenging is a key ecological process controlling energy flow in ecosystems and providing valuable ecosystem services worldwide. As long-lived species, the demographic dynamics of vultures can be disrupted by spatiotemporal fluctuations in food availability, with dramatic impacts on their population viability and the ecosystem services provided. In Europe, the outbreak of bovine spongiform encephalopathy (BSE) in 2001 prompted a restrictive sanitary regulation banning the presence of livestock carcasses in the wild on a continental scale. In long-lived vertebrate species, the buffering hypothesis predicts that the demographic traits with the largest contribution to population growth rate should be less temporally variable. The BSE outbreak provides a unique opportunity to test for the impact of demographic buffering in a keystone scavenger suffering abrupt but transient food shortages. We studied the 42-year dynamics (1979-2020) of one of the world's largest breeding colonies of Eurasian griffon vultures (Gyps fulvus). We fitted an inverse Bayesian state-space model with density-dependent demographic rates to the time series of stage-structured abundances to investigate shifts in vital rates and population dynamics before, during, and after the implementation of a restrictive sanitary regulation. Prior to the BSE outbreak the dynamics was mainly driven by adult survival: 83% of temporal variance in abundance was explained by variability in this rate. Moreover, during this period the regulation of population size operated through density-dependent fecundity and subadult survival. However, after the onset of the European ban, a 1-month delay in average laying date, a drop in fecundity, and a reduction in the number of fledglings induced a transient increase in the impact of fledgling and subadult recruitment on dynamics.Although adult survival rate remained constantly high, as predicted by the buffering hypothesis, its relative impact on the temporal variance in abundance dropped to 71% during the sanitary regulation and to 54% after the ban was lifted. A significant increase in the relative impact of environmental stochasticity on dynamics was modeled after the BSE outbreak. These results provide empirical evidence on how abrupt environmental deterioration may induce dramatic demographic and dynamic changes in the populations of keystone scavengers, with far-reaching impacts on ecosystem functioning worldwide.

Insularity determines nestling sex ratio variation in Egyptian vulture populations

“…Thus, following Blanco (2014), food availability was included as a fixed factor with three levels corresponding to the main stages of the mad-cow crisis, namely (i) prerestrictive period (1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001), before the mad-cow crisis, characterized by a high availability of livestock carcasses in the field for vultures; (ii) restrictive period (2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011), during the mad-cow crisis, when the abandonment of livestock carcasses was limited by new sanitary regulations (i.e., CE 1774/2002) and there was a severe shortage of food for vultures (around 80% of the livestock biomass available before this period was removed; Donázar, Margalida, & Campión, 2009); and (iii) postrestrictive period (2012 onwards), when the use of livestock carcasses for scavengers became more flexible (i.e., CE 142/2011 and RD 1632/2011) and food availability increased gradually (Almaraz et al, 2022;Morales-Reyes et al, 2017). "Year" and "territory" were included as random factors in all models to avoid pseudoreplication.…”

“…Food availability was assessed taking into account changes resulting from the implementation of the European sanitary guidelines after the outbreak of the Bovine Spongiform Encephalopathy (i.e., the mad-cow crisis) in the early 2000s, which limited the amount of livestock carcasses available to vultures and other scavengers (Almaraz et al, 2022;Donázar, Margalida, Carrete, & Sánchez-Zapata, 2009).…”

A long‐lasting, distant journey of a male griffon vulture informs on the success of differential parental investment

“…During June and September 2021, 15 adult griffon vultures ( Gyps fulvus ; seven males, eight females) were captured with a large cage baited with livestock carcasses in the colony located in Hoces del Río Riaza, Segovia, central Spain (Almaraz et al, 2022). We selected adult individuals previously ringed as nestlings (Gómez‐López et al, 2023) or aged by their plumage characteristics.…”

Large‐scale movement patterns in a social vulture are influenced by seasonality, sex, and breeding region

“…Vultures from the Gyps genus (which includes seven species) are among the largest flying birds, showing high sociality and covering large areas in search of ephemeral and unpredictable resources such as carrion (e.g., 162,824 km 2 annually on average in the case of Cape Vultures, Gyps coprotheres ; Jobson et al, 2021 ). The Eurasian Griffon Vulture Gyps fulvus is a monomorphic social species that breeds colonially (Almaraz et al, 2022 ; Donázar, 1993 ; Harel et al, 2017 ; Zuberogoitia et al, 2018 ). The breeding period of the species expands from early December (when first copulates occurs) to late August, when fledglings fly from the nest (Donázar, 1993 ; Zuberogoitia et al, 2018 ).…”

“…The Eurasian Griffon Vulture Gyps fulvus is a monomorphic social species that breeds colonially (Almaraz et al, 2022;Donázar, 1993;Harel et al, 2017;Zuberogoitia et al, 2018). The breeding period of the species expands from early December (when first copulates occurs) to late August, when fledglings fly from the nest (Donázar, 1993;Zuberogoitia et al, 2018).…”