Intraguild scavenging on carnivore carcasses is delayed enough to allow successful dispersal of maggots for pupation

Vertebrate carcasses are a valuable resource for a wide range of organisms, although their consumption rates can vary greatly by the type of carcasses. Studies have indicated that mammalian carnivores rarely consume carnivore carcasses, particularly in the early stages of decay, and thus these carcasses may potentially serve as a reproductive resource for necrophagous arthropods such as blowflies. However, it is unknown whether delays in consumption by carnivores are sufficient for necrophagous arthropods to complete their life cycle in the carcasses. This study addressed this question by monitoring 69 raccoon carcasses using camera traps in Yakumo, southern Hokkaido, Japan, during the summer seasons of 2016–2019. The decay stages of the carcasses were categorized by carefully observing the videos captured by the camera traps, and the timing of maggot dispersion was estimated. The first visitation and first consumption of vertebrate scavengers were also modelled, and the proportion of carcasses visited or consumed by vertebrate scavengers prior to maggot dispersion was determined each year. The proportion of carcasses visited by vertebrate scavengers before maggot dispersal ranged between c. 50% in 2017 and c. 30% in other years. However, only c. 20% of carcasses in each year were consumed before maggot dispersal, and consumption was only partial. The first species to scavenge at carcasses were red foxes and raccoon dogs, with the exception of two carcasses that were first scavenged by large-billed crows. These results suggest that while delayed visitation of carcasses may partly explain delayed consumption, active avoidance of phylogenetically related species may increase the chances of successful maggot dispersal. Our approach of using careful video observations and statistical modelling may apply to a wide range of habitats and could improve our understanding of the ecological consequences of the taboo against cannibalism.