Not avian but mammalian scavengers efficiently consume carcasses under heavy snowfall conditions: a case from northern Japan

Interest in trophic interactions and ecosystem functions derived from carcass consumption by scavengers has been increasing. Here, we conducted the first evaluation of scavenging processes in an ecosystem with heavy snow, located in northern Japan, which is characterized by the limitations of visual and odor cues to detect carcasses. In this study, we verified the behavioral traits and assemblage compositions of avian and mammalian scavengers, which consumed six different carcass types buried in snow. We measured the visits of scavengers using camera traps between 2010 and 2020. The total scavenger richness observed was relatively low (only 12 species) compared to warmer biomes. We observed seven avian scavenger species, but their visit frequencies were extremely low compared with those of nocturnal mammalian scavengers, such as raccoon dogs (Nyctereutes procyonoides) and martens (Martes melampus), which were able to detect carcasses more rapidly and frequently. Our findings imply that large snow piles significantly prevent avian scavengers from detecting carcasses. In contrast, the snow piles could protect carcasses from the freezing air and ensure the occurrence of a basal level of microbial decomposition, possibly leading to carcass decomposition. This probably results in carcasses still providing odor cues for mammalian scavengers with heightened sense of smell. Moreover, considering the high carcass consumption rate (91.3% of full-body carcass; n = 23) and short carcass detection times (approximately 90 h) observed, it is possible that scavenging in heavy snowfall conditions has become systematically integrated into the foraging tactics of many mammalian scavengers.

Interspecific Difference in Seed Dispersal Characteristics between Japanese Macaques (Macaca fuscata) and Sympatric Japanese Martens (Martes melampus)

We compared the characteristics of seeds within faeces between semi-terrestrial Japanese macaques (<i>Macaca fuscata</i>) and sympatric arboreal Japanese martens (<i>Martes melampus</i>) in Shiga Heights, central Japan. We collected faecal samples of the two mammalian species for 1 year (<i>n</i> = 229 for macaques and <i>n</i> = 22 for martens). We then compared the proportion of seed occurrence, life-form composition, number of seeds and species richness within single faecal samples, and the seed intact ratio between the two mammalian species. We detected seeds from 20 and 7 species from macaque and marten faeces, respectively. Macaque faeces contained seeds of multiple strata, while marten faeces contained no herbaceous plant seeds. Seed sizes within faeces showed no interspecific difference. For macaques, seeds were found within faecal samples collected in late spring to late fall, while for martens, seeds were found between summer and winter. The proportion of seed occurrence was greater in summer (both species) and fall (macaques), which implied that the seed dispersal roles of macaques and martens was greater in these seasons. The mean seed number (across species), intact ratio of seeds (high for both species) and seed species richness within single faecal samples of macaques and martens showed no significant differences, but for several species, martens defecated more seeds than macaques and showed higher intact ratio. Our study indicates that sympatric mammals in the temperate regions of Japan contribute differently to seed dispersal in forest ecosystems.

Insectivory characteristics of the Japanese marten (Martes melampus): a qualitative review

Insects are rich in protein and thus are important substitute foods for many species of generalist feeders. This study reviews insectivory characteristics of the Japanese marten (Martes melampus) based on current literature. Across the 16 locations (14 studies) in the Japanese archipelago, a total of 80 different insects (including those only identified at genus, family, or order level) were listed as marten food, 26 of which were identified at the species level. The consumed insects were categorised by their locomotion types, and the Japanese martens exploited not only grounddwelling species, but also arboreal, flying, and underground-dwelling insects, taking advantage of their arboreality and ability of agile pursuit predation. Notably, immobile insects such as egg mass of Mantodea spp, as well as pupa/larvae of Vespula flaviceps and Polistes spp. from wasp nests were consumed by the Japanese marten in multiple study areas. This review shows dietary generalism (specifically ‘food exploitation generalism’) of the Japanese marten in terms of non-nutritive properties (i.e., locomotion ability of prey).