Farmland abandonment and season drive scavenging dynamics in livestock-rewilded landscapes.

Farmland abandonment occurs commonly across European mountain regions, which causes triggering of habitat encroachment through shrub regeneration and natural afforestation. However, its impact on vertebrate scavenger communities and ecological processes, such as the removal of small carcasses remains poorly understood. Through an experimental paired-plot design (grazed vs. abandoned-rewilded habitats), we monitored 99 small carcasses over two seasons (summer and winter) in traditional livestock grazing systems in the Guadarrama Mountains (central Spain) exposed to farmland abandonment. We evaluated how the composition and structure of the scavenger community as well as scavenging dynamics of small carcasses responded to habitat encroachment and seasonal changes. Our findings indicate that habitat encroachment following farmland abandonment significantly altered the composition and structure of the scavenger community and the ecosystem service of carrion removal. Rewilded habitats supported less diverse scavenger communities, with fewer species and individuals, dominated by mammalian facultative scavengers. In grazed habitats, almost all carcasses were consumed within 5 days, while in rewilded areas carrion removal was 2.35 times slower, with longer detection, consumption, and removal times. Seasonal changes amplified these differences, with winter bringing more diverse, bird-rich scavenger communities, but also longer carrion removal times, especially in grazed habitats. Our findings emphasize the ecological importance of small carcasses, which attract a wide range of scavengers, primarily facultative, and play a vital role in the scavenging dynamics of ecosystems. Passive rewilding has been proposed as a management strategy of no human intervention to create self-sustaining ecosystems that support biodiversity, enhance ecosystem services, and increase resilience to environmental change. However, our study shows that farmland abandonment alters small carrion-scavenging dynamics, reducing the effectiveness of carrion removal services and impairing bird scavengers, some of which are of conservation concern. These results highlight the need for land and wildlife managers, as well as policymakers, to consider these effects, particularly given the vast areas undergoing abandonment across Europe, and the potential implications for environmental legislation, such as the recent European Nature Restoration Law. This is crucial to ensure the maintenance of scavengers' diversity and the ecosystem service of carrion removal.