Human activity and footprint have differential effects on scavenger assemblages at carrion provided by apex carnivores

Scavengers play a critical role in nutrient cycling and energy flow in ecosystems, yet little is known about the different ways that urban development and human presence may affect scavenger species and their ecological functions. We used video camera traps to monitor scavengers at ungulates killed by pumas ( Puma concolor ) in the Santa Cruz Mountains, California, USA from 2018 to 2024. We quantified four metrics of scavenger assemblages: species richness, Pielou's evenness, Shannon diversity, and total time spent at carcasses. We applied generalized linear models to assess the effects of human activity and human footprint—along with puma visitation, season, and time to first scavenger arrival—on scavenger assemblages. Human activity had significant positive effects on richness, evenness, and diversity, whereas human footprint reduced total scavenger time at kills. Puma visitation also positively influenced diversity and evenness—when pumas are present, larger scavengers are deterred, allowing birds and smaller mesocarnivore species greater access to carrion, but when pumas are displaced by humans, larger scavengers are released from competition and restrict access for other scavengers. These effects highlight complex human-mediated modifications of apex carnivore feeding and scavenger dynamics. Our results show that human activity can simultaneously enhance and constrain aspects of scavenger assemblages, emphasizing the importance of species-specific dependencies on resources provided by apex carnivores. Conserving these interactions is essential for maintaining intact scavenger assemblages and their ecological functions, but conservation actions should recognize the differential effects of human activity and footprint on scavenger assemblages and their behavior.