Mount Fuji Research Institute and Tokyo University of Agriculture reveal sex differences in habitat use of deer at the foot of Mt. Fuji

A joint research team including Researcher Keita Nakamura from the Mount Fuji Research Institute, Yamanashi Prefectural Government and Associate Professor Hayato Takada and Professor Shinsuke Koike from Tokyo University of Agriculture and Technology announced on February 16 that they have clarified sex differences in habitat use by sika deer (Cervus nippon) across a wide area of the northern foothills of Mt. Fuji. By surveying the sighting locations of males and females, the team found that males appear more frequently in areas where they are more likely to be captured by humans, while females appear more frequently in logged areas suitable as foraging grounds, revealing clear sex differences in habitat use. This is the first study to demonstrate that human culling pressure and disturbance drive sex differences in the habitat use of sika deer. The findings were published in European Journal of Wildlife Research on January 10.

Since the latter half of the 20th century, deer family members, including sika deer, have spread to new ranges and their populations have grown rapidly, prompting population control through human culling. It is known that culling produces not only a "lethal effect" of reducing deer numbers, but also a "non-lethal effect" whereby deer spatially perceive the risk of capture and alter their behavior. This non-lethal effect is referred to as the "landscape of fear."

Previous research has shown that management culling has created a "landscape of fear" in the Mt. Fuji area as well, causing deer to avoid culling areas and shift their distribution to higher elevations. However, whether there are sex differences in this spatial response to culling risk had remained unknown.

Sika deer are polygynous, and males and females differ in their reproductive strategies. Because only males that win fights against other males during the mating season are able to reproduce, males need to prioritize food resources even at the cost of risk-taking in order to grow larger bodies. Females, on the other hand, can only give birth to one fawn per year, making it advantageous to live longer and reproduce over an extended period. This difference may also give rise to sex differences in spatial responses to culling risk.

The researchers therefore investigated the relationship between the occurrence of each sex and environmental factors including culling areas, logged areas, the presence or absence of dwarf bamboo (sasa) communities, and slope gradient.

A total of 25 spotlight censuses were conducted in May from 2018 to 2024. When using this method, researchers drive slowly along forest roads at night in a vehicle and observe deer visually using a powerful spotlight. As a result, a total of 549 sika deer were recorded, of which 87 were male, 307 were female, and 155 were of undetermined sex.

Analysis showed that males appeared more frequently in culling areas while females appeared more frequently in logged areas, indicating sex differences in habitat use. The results suggest that males may preferentially use culling areas, which are rich in food resources despite the associated risk of capture, giving priority to improving body size and physical condition in preparation for reproduction.

Furthermore, among the 4,657 individuals taken through management culling in and around the study area from 2015 to 2021, the sex ratio (male/female) was 1.15, indicating a male-biased harvest.

Although the culling areas where males were more commonly sighted and the logged areas where females were more common both share the characteristics of being rich in food resources and having a high risk of capture, there were differences in their spatial distribution. Culling areas were spread broadly across the study area (approximately 51.04% of the survey range), while logged areas were small and scattered (approximately 4.34% of the survey range, totaling 312 sites).

It is thought that culling areas relate to broad-scale habitat selection—that is, "which area to choose as a home range"—whereas logged areas relate to finer-scale site selection —that is, "which area within an established home range to use."

Females avoided culling areas more than males did and made more active use of logged areas suitable as foraging sites. Since the survey was conducted during the period just before parturition when females require high-nutrition food, it is also possible that females were actively using multiple small, logged areas as foraging sites during this time.

For population management, capturing females is the most effective approach. As a result, it is necessary to consider conducting culling in environments that females are more likely to use.

Nakamura commented: "Sika deer are a sexually dimorphic species in which only males have antlers. This study has now shown that there are also clear sex differences in behavior in response to human culling pressure. Given the difference in reproductive strategies, males are thought to prioritize food resources even at the cost of capture risk. I find this fascinating as a piece of research: the findings suggest human activity may be making these behavioral sex differences even more pronounced."

Journal Information
Publication: European Journal of Wildlife Research
Title: Do culling pressure and forest clearing affect sex-specific habitat use in sika deer?
DOI: 10.1007/s10344-025-02048-6