Outdoor recreation alters terrestrial vertebrate scavenger assemblage and carrion removal in a protected Mediterranean wetland

Abstract

Outdoor recreation has increased in recent decades, with an intensification after the COVID-19 lockdown. Previous studies have shown that disturbances from this activity may affect species behaviour and fitness, but its effect on ecological processes has been overlooked. Here, we test the impact of outdoor recreation on terrestrial vertebrate scavenger assemblage and scavenging patterns in El Hondo Natural Park, a Mediterranean wetland located in south-eastern Spain. We placed 185 carcasses monitored with camera traps between February 2020 and May 2021 in two areas: ‘public access area’, where visitors can freely access and carry out outdoor recreation, and ‘restricted area’, where visitors are not allowed. Our results showed that outdoor recreation altered the scavenger assemblage composition, especially affecting large species such as raptors. Non-native species scavenged almost four times more often on carcasses in public access areas than in the restricted areas, showing that human activities promote the presence of non-native species. Furthermore, vertebrates completely consumed 68.2% of the carcasses in the restricted area, decreasing to 46.7% in the public access area. In the restricted area, consumption time was shorter (111.8 vs. 157.5 h) and consumed biomass by vertebrate scavengers was larger (73.9 vs. 52.2%) than in public access area, evidencing that outdoor recreation also affects scavenging processes. Our study shows that outdoor recreation profoundly alters not only the scavenger assemblage but also key ecological processes such as carrion removal. This highlights the urgency of regulating tourism and maintaining restricted areas to preserve biodiversity and ecological processes, especially in highly anthropized landscapes.