Avian scavengers in a changing world: a multidisciplinary conservation approach in the pyrenees
- Autores: Pilar Oliva Vidal
- Directores de la Tesis: M. Àngels Colomer Cugat (dir. tes.), Antoni Margalida (dir. tes.)
- Lectura: En la Universitat de Lleida ( España ) en 2023
- Idioma: español
- Tribunal Calificador de la Tesis: Santi Mañosa (presid.), Gregorio Mentaberre García (secret.), Beatriz Arroyo López (voc.)
- Programa de doctorado: Programa de Doctorado en Gestión Forestal y del Medio Natural por la Universidad de Lleida
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
Avian scavengers provide essential ecological, economic and cultural services; yet vultures are among the most threatened groups of birds worldwide and their populations have declined significantly in recent decades. An exception are Iberian vultures whose numbers are stable or even increasing and which play a key role in the future viability of European vulture populations (griffon Gyps fulvus, cinereous Aegypius monachus, bearded Gypaetus barbatus and Egyptian Neophron percnopterus). Behind this global collapse lie a wide array of anthropogenic factors, which are accentuating this decline in our human-dominated world. Thus, integrative research linking different disciplines is essential for providing useful insights into the management and conservation of vulture populations in order to design and propose effective management actions. This thesis combines aspects of different disciplines including behavioural ecology, conservation biology, ecotoxicology and the social sciences as a means of fomenting the scientific understanding of significant emerging threats affecting European avian scavengers and providing a set of evidence-based conservation tools. Within this multidisciplinary framework, this thesis first explores how widespread rural abandonment and subsequent passive rewilding due to woody encroachment affect the functioning of scavenger assemblages in mountain agroecosystems (Chapter 1). This chapter provides evidence that landscape type is the main factor governing scavenging dynamics in rewilding situations through its influence on the composition of scavenger assemblages and their scavenging efficiency. While open landscapes favour faster carrion discovery and exploitation by obligate scavengers and attract more scavengers, in shrublands and, particularly, in forests mammals are the dominant scavengers. Thus, woody encroachment after farmland abandonment could reduce the scavenging efficiency of the assemblage and jeopardize the most abundant and efficient scavenger that provides crucial scavenging services and facilitatory processes (i.e. the griffon vulture) while benefitting facultative species, above all mammals. This thesis also demonstrates that, despite the vital regulating service played by griffon vultures in reducing carcass persistence and maintaining healthy ecosystems due to their high carcass consumption rates (Chapter 1), the growing conflict between vultures and livestock could lead to a breakdown in the age-old mutualistic relationship between vultures and humans (Chapter 2). Our findings show that the vulture-livestock conflict is a complex issue accentuated by the typically wide-ranging foraging movements of griffon vultures and the growing amount of fake news and media misrepresentation that lays the blame for livestock killing on vultures. Mitigation in areas with high extensive livestock numbers especially close to landfill sites and, above all, during the birthing season and interdisciplinary awareness campaigns on the coexistence of vultures and livestock are necessary to guarantee the harmony between biodiversity conservation and agropastoral practices (Chapter 2). From an ecotoxicological perspective, this thesis investigates through active monitoring the risk of exposure to second-generation anticoagulant rodenticides in free-living scavenger birds (Chapter 3). Medium-sized avian scavengers such as kites and Egyptian vultures are the species that are most exposed to these pesticides, although of the large obligate avian scavengers bearded vultures showed the highest prevalence. These findings are the first step towards the recognition of the impact of these compounds on scavenging birds and their potential population effects need further investigation. From an ecological modelling angle, our results demonstrate the importance of traditional farming practices of transhumance given its role in increasing carrion availability in mountain landscapes (Chapter 4). However, the seasonal nature of this practice means that the quantitative assessments of food availability must also estimate trophic resources over the whole annual cycle since we found significant seasonal asymmetries. Animal biomass is substantially higher in summer due to transhumance but drops in winter to levels that are unable to satisfy the energetic requirements for the most abundant species (i.e., griffon vultures). The last chapter of this thesis aims to encourage policy managers to adopt strict and effective translocation protocols for restoring European bearded vulture populations without affecting the source Pyrenean population (Chapter 5). Our results show that the extraction of whole clutches and non-territorial adults ( 10 years) is preferable to the removal of juveniles since the removal of this age-class from the wild has significant demographic consequences on the source population. Additionally, we highlight how stochastic variations in demographic parameters (e.g., productivity and survival) can substantially change forecasted results and have significant repercussions on conservation outcomes. Thus, it is vital to update the theoretical ecological models used to implement management actions to increase their credibility, efficiency and objectivity. This thesis underlines, above all, the usefulness of developing multidisciplinary approaches aimed at improving and optimizing conservation management actions from an evidence-based perspective. This will help establish priority conservation lines and ensure the coexistence of avian scavengers and humans in an ever-changing world.