1. Japan's Deer Differ by Region, from Hokkaido to the Southern Islands
Deer in Japan are not a single uniform group. Hokkaido is home to the Ezo deer (ezoshika), Yakushima Island has the Yakushima deer (yakushika), and the Kerama Islands have the Kerama deer (keramajika). The Japanese deer (nihonjika) are distributed across Hokkaido, Honshu, Shikoku, Kyushu, and various islands as regional subspecies [1]. Because this range is so wide, answering the question "Where do deer live?" with just place names becomes difficult. Instead, we change the question to "What kind of places do they live in?" asking about the characteristics of the location rather than just its name.
2. Deer Live at the Edge of Forests and Grasslands, Not in Deep Forest
People often think of deer as animals of the deep primeval forest. However, a management plan from Ishikawa Prefecture states that deer originally make their living area in the "forest edge," where woodlands and grasslands intermingle. Their distribution tends to concentrate in low mountain areas with a forest cover rate of 40–70% [2]. A forest rate of 40–70% means that 40 to 70 percent of that area is covered by forest. This is not a place where forests are dense and continuous, nor is it a place with almost no forest; it is a place where forests and open spaces mix. Lecture materials from the Ministry of the Environment also summarize that the main habitat is the forest edge and note that habitat density varies by season and location due to seasonal movements [1]. The materials do not explain in one sentence why the forest edge is preferred. However, as we will see in the next section, considering the wide range of deer food, a place where both forest and grassland are close together seems convenient.
3. What Deer Eat: Grass, Leaves, Bark, and Bamboo in Winter
Deer are herbivores and eat a wide variety of food, from soft grass and fallen leaves to hard tree bark [1]. According to explanations from Sapporo City, Ezo deer are said to eat about 5 kg (about 11 lbs) of food per day. Their diet includes wild grasses, leaves, buds, acorns, and in winter, bamboo grass (sasa), young branches, and tree bark [3]. Note that the figure of just under 2 kg per day found in some Ministry of the Environment materials refers to dry weight, so it cannot be directly compared to the 5 kg figure. In winter, when food is scarce, the Ishikawa Prefecture plan states that deer often rely on grass family plants like bamboo grass and sedges [2]. Bamboo grass is widely found under beech forests and keeps its leaves in winter, making it a valuable source of nutrition [2]. If the range of food is wide, the places where deer can live also expand. So, was there no "wall" for deer habitats? The wall was snow.
4. Why Areas with Deep Snow Were Long Outside Deer Distribution
Areas with deep snow were a barrier to deer distribution for a long time. A report from the Ministry of the Environment’s Biodiversity Center states that for deer in Honshu (honshujika), sections with deer were almost never found in areas with more than 20 days of snow depth of at least 50 cm (about 20 in) in winter [4]. This is not a law that says "if there are 20 days of 50 cm snow, deer will definitely disappear." It is a survey result showing that when deer distribution sections were overlaid on a map, this pattern appeared. Still, it shows that the boundary between heavy snow areas and deer distribution overlapped significantly. So, what is happening to this wall now?
5. How Deer Distribution Grew 2.46 Times in 36 Years
In Ministry of the Environment materials, the number of deer distribution sections rose to 2.46 times the original number (a 146% increase) between fiscal year 1978 and fiscal year 2014 [5]. In the 2014 survey, the only prefecture where deer were not distributed was Ibaraki [5]. "146% increase" means the same as 2.46 times, not 146 times. Another Ministry of the Environment document states that from 1978 to 2020, the distribution expanded 2.7 times, with expansion in heavy snow areas being particularly notable [6]. Lecture materials describe how deer have spread to snow-covered areas and high elevations where they did not previously live, expanding in concentric circles from areas where they have historically been present [1]. Examples include photographs taken at an elevation of about 2,900 m (about 9,500 ft) at Mount Kita in the Southern Alps [1]. The figures of 2.46 times and 2.7 times come from different study periods (36 years and 42 years) and different documents. Both refer to the number of sections, not the number of deer or the area. The reason why they could cross the wall is not written in these materials. We accept the fact that they are spreading and leave the reason as a question for you to think about by reading the materials yourself.
6. Deer on Islands: Yakushima and the Kerama Islands
Deer also live on islands. The Yakushima deer (yakushika) on Yakushima Island are distributed across the whole island. Warm-temperate evergreen broadleaf forests extend up to elevations of 700–800 m (about 2,300–2,600 ft). Materials from the Forestry Agency’s Kyushu Regional Forest Office state that grazing pressure is increasing in these forests [7]. In the western part of the island, the density is high. Estimates for fiscal year 2008 suggested 100–150 deer per km² (about 0.4 sq miles), and the total population was estimated at 16,000–22,000 in fiscal year 2012 [7]. 100–150 deer per km² means about 6,700–10,000 m² (about 72,000–107,000 sq ft) per deer, which is roughly the size of 1 to 1.5 soccer fields. However, the materials themselves note that these estimates have large errors depending on the measurement method. Body size also differs by island. In a table from Ministry of the Environment lecture materials, Yakushima deer females weigh 19–25 kg (42–55 lbs) and males 24–37 kg (53–82 lbs), while Honshu deer males weigh 45–75 kg (99–165 lbs) and females 35–55 kg (77–121 lbs) [1]. The Kerama deer (keramajika) on the Kerama Islands, according to the Ministry of Land, Infrastructure, Transport and Tourism’s multilingual database, were brought from mainland Japan around the 17th century. They are described as small-bodied, with dark fur and small heads and antlers [8]. In 1972, they were designated a national natural monument. The population, estimated at about 60 in the late 1970s, is said to have recovered due to protection efforts [8]. This is an example of deer that were brought to an island and continued to live there, not deer that were originally on the island.
7. Try Finding the Edge of Trees and Grass Near You to Imagine Deer Habitats
Try looking for the "edge" where tree thickets and grasslands meet in a nearby park or along a river path. Walk along the edge for about 10 steps and compare the types of grass growing in the shade and in the sun. You can see with your own eyes how grass and trees mix at the forest edge. Please do not approach wild animals or give them food. If you want to think about this by reading the materials, there are two questions. First, the materials cited in this article do not explain the reason for the distribution expansion. The Ministry of the Environment materials on "recent trends" organize the process of expansion [5]. Second, try calculating and comparing the 2.46 times increase over 36 years with the 2.7 times increase over 42 years yourself.