Average consuming species number across all 13 sites was 4 ± 0.82 species. The number of vertebrates actively scavenging at carcass sites (i.e., consuming species number) ranged from 0 to 8 species. The specific goals of our study were: (i) to evaluate the diversity of the facultative scavenger guild in an ecosystem with fluctuating carrion availability and, (ii) to determine the influence of carcass characteristics, habitat features, and seasonality on carcass selection and scavenging efficiency. In fact, climate change has already been linked to shorter periods of deep snow in winter in Yellowstone National Park, USA (~ 70 km from our study site), leading to a reduction in the number of ungulates dying from starvation and consequently the supply of carcasses to carrion-reliant species during this period 31.
This northern temperate ecosystem supports one of the few intact carnivore guilds in North America 27 but is also a system shown to be highly vulnerable to global climate change 28, 29, 30. This study provides insight into the biotic and abiotic factors influencing the diversity of vertebrate scavengers and their behavior and scavenging efficiency in southwestern Montana, USA. In fact, facultative scavenging is quite common, and nearly all carnivores will capitalize on carrion resources when given the opportunity 8, 14, 25, 26. Conversely, facultative scavengers are species that scavenge when the opportunity arises, but are not solely dependent on carrion for survival these generalists comprise a much more diverse set of species 24. Organisms that rely solely on carrion for survival and reproduction are referred to as obligate scavengers, and the only terrestrial vertebrates categorized as such are vultures 24. Scavenging of carrion is a fundamental process associated with several ecosystem services, including decomposition, nutrient cycling, and disease moderation 4, 22, 23. The possible factors influencing carrion use include the characteristics of the carcass itself 16, 21 (species, spatio-temporal location, disease status or cause of death), the ecology of the scavenging animal (species, body size, sociality, inter- and intra-specific dynamics), and abiotic factors 18, 19 (season, weather, habitat).
Additionally, studies on naturally occurring carcasses are rare 18, 19, 20. While recent studies have shed light on the ecological 4, 14 and economic 15 importance of vertebrate scavenging, findings regarding the roles cues and constraints play in respectively promoting and limiting an individual’s propensity or ability to scavenge vary widely 8, 16 among ecosystems 17. In addition, scavenging shapes inter- and intra-specific interactions through competition 8, 9 and carrion has been shown to have positive and direct effects on the biomass and nutritional content of plants 10, 11, 12, 13. Decreases in the availability of carrion have been shown to alter scavenger population demography and increase mortality 5, 6, 7. The role of carrion in community ecology has only recently gained recognition as a critical resource in terrestrial ecosystems 1, 2, 3, 4. However, growing populations of turkey vultures may lead to increased competition with facultative scavengers over carrion, and could have cascading effects on food webs in this ecosystem. We found that most carcass consumption was via facultative scavengers (bears, wolves, magpies, Corvus spp.) rather than turkey vultures, the only obligate scavengers in the study area. Scavenging efficiency was influenced inter alia by seasonality, distance to water, and elevation. We found that scavenger species diversity was higher at higher elevations and in grassland habitats. We used camera traps established at 13 carcass sites to monitor carcass detection, visitation, and consumption times, during 2016–2018 and generalized linear models to explore the influence of carcass characteristics, habitat features, and seasonality, on carcass selection and scavenging efficiency. Here we investigated differences in scavenging patterns in a complex scavenger guild in Southwestern Montana. Previous research found the cues promoting, or the constraints limiting, an individual’s propensity or ability to scavenge vary widely, depending on anthropogenic and environmental factors. Scavenging of carrion shapes ecological landscapes by influencing scavenger population demography, increasing inter- and intra-specific interactions, and generating ecosystem services such as nutrient cycling and disease moderation.
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