Habitat Selection and Activity Patterns of Japanese Serows and Sika Deer with Currently Sympatric Distributions

The Japanese serow (Capricornis crispus) and sika deer (Cervus nippon) in Japan are usually allopatric. However, a recent expansion in the distribution range of sika deer, combined with an increase in abundance, has resulted in an overlap of the distribution ranges of the two species. We examined the habitat selection and activity patterns of Japanese serows and sika deer using camera traps placed at 83 sites within a 210 km2 study area, where the distribution range of these two species has recently overlapped. Although both species were photographed throughout the study area, we observed a low spatial overlap between them. The Japanese serows selected steep slopes, and the sika deer selected areas far away from human settlements. In addition, the Japanese serows and sika deer exhibited temporal partitioning with diurnal and crepuscular activity patterns, respectively. The observed partitioning could be explained by differences in their species-specific habitat selections, rather than competition, because the photographic capture rate of the Japanese serows was not affected by that of the sika deer and vice versa. These partitioning behaviors are likely to reduce the rate of encounters between the two ungulates, which enables their coexistence considering the sika deer density remains low.

Habitat use and the coexistence of the sika deer and the Japanese serow, sympatric ungulates from Mt. Asama, central Japan

Differential resource use allows for diverse species to specialize in ecological niches and thus coexist in a particular area. In the Japanese archipelago, increasing sika deer (Cervus nippon, Temminck 1836) densities have excluded the Japanese serow (Capricornis crispus, Temminck 1836), but in places where deer population densities are low, the two species coexist. We wanted to better understand their habitats and how these two ungulates manage to coexist. We evaluated the role of habitat use in the coexistence of these two sympatric ungulates on Mt. Asama, central Japan. Deer frequently used the dwarf bamboo-rich communities in autumn and winter, and their habitat use was not associated with topography. Serows frequently used deciduous broadleaf shrub-rich communities and steep slopes throughout the year. Consequently, their habitat use was significantly different in terms of vegetation and topography. Niche breadth suggests that deer tend to be generalists, whereas serows tend to be specialists. Niche differentiation in habitat use between deer and serows may make the coexistence of these similarly sized ungulates possible in Japanese mountainous zones. Therefore, the fine-grained habitat mosaic of different vegetation and topography areas might be the underlying feature that allows the coexistence of these two species.

Spatial organization and mating behavior of the Japanese serow under a low population density

In high-density populations, the adults of the Japanese serow (Capricornis crispus) defend their home ranges against same-sex intruders, and a male’s territory typically overlaps with those of one to three females. We examined the spatial organization and mating behavior of the species in a low-density population by direct observation and radio-tracking over a 4-year period. The home range size of both males and females was more than 4 times larger than that reported in high-density populations. Adult females had ranges that overlapped little, even though they were never observed in agonistic interaction. In contrast, adult males had ranges that overlapped largely except in their core areas, and appeared to be tolerant on encounters, suggesting they did not defend their whole range as a territory. Although males’ ranges overlapped with multiple female ranges, males were only observed following a single female during the mating season. These findings suggest that males directly defended a female rather than a territory, and that the mating system is monogamous. The Japanese serow’s social organization would therefore vary according to ecological conditions.

Food habits of the Japanese serow (Capricornis crispus) in an alpine habitat on Mount Asama, central Japan

We investigated the food habits of the Japanese serow (Capricornis crispus) in alpine habitats using direct observations at Mount Asama, central Japan. We observed the feeding behavior of 13 identified adult serows throughout the year, from April 2016 to October 2017. The animals’ food habits were evaluated by the feeding probability among 2129 observation bouts. The most important food throughout the year was grasses (feeding probability, 57.6%), followed by forbs (43.5%) and dwarf bamboos (11.4%). However, the feeding probability for each food category drastically changed in relation to the season; in particular, grasses and forbs were especially important foods from spring to autumn, whereas dwarf bamboos and conifers were important in winter. These results suggest that the food habits of the serow are flexible and will vary according to seasonal changes in vegetation. The findings also suggest that the feeding ecology of the serow in an alpine area tends to match that of an intermediate feeder rather than a browser, as was reported by several previous studies conducted in forested habitats. However, the food habits of the serows in the alpine habitats were similar to those of other alpine caprids, such as the mountain goat (Oreamnos americanus), alpine chamois (Rupicapra rupicapra) and Pyrenean chamois (Rupicapra pyrenaica). This is the first study to demonstrate that the food habits of the serow are variable according to the season and/or population. Similar to other alpine caprids, the flexible food habits of the serow in alpine habitats are likely an adaptation to an environment with a characteristically unstable food supply.