A small plant-eating deer species that rarely draws much attention in Japan is now a major source of concern after an explosion in the population in the Boso Peninsula of Chiba Prefecture.

Despite a program to control the invasive non-native animal, fears are growing that muntjac deer are expanding their habitat with a spate of sightings in neighboring Ibaraki Prefecture and possibly Saitama Prefecture, north of Tokyo, too.

“Muntjacs are much more common than wild boar in our daily life,” said Masako Ochi, 52, who runs a strawberry farm in Chiba Prefecture’s Onjuku. “I once came across one nearby while hanging out the laundry to dry.”

Around three years ago, Ochi discovered that a muntjac had broken into her greenhouse to feed on seedlings.

Given that replacing the damaged entrance and its glass door with a new one would cost in the region of 100,000 yen ($630), Ochi opted to simply repair the old door.

“Many people around me have set up tall mesh fences to keep muntjacs out,” Ochi explained. “Others have just given up on growing (vegetables or other crops).”

Muntjacs are native to China and Taiwan and typically measure 70 centimeters to 100 cm long. The deer variant also inhabits Izu-Oshima island south of Tokyo.

Muntjacs in Chiba Prefecture are said to have become feral after escaping from a private tourism facility that used to operate in Katsuura.

The estimated number of muntjacs across Chiba Prefecture soared from 12,600 in fiscal 2006 to 86,000 in fiscal 2023. A lack of natural predators, such as bears, is believed to be a key reason for the explosion in numbers.

Muntjacs were blamed for causing 8.9 million yen in damage to agriculture in fiscal 2023.

The creature’s barking resembles a human shrieking, occasionally resulting in emergency calls to local authorities from startled people hearing the deer’s macabre sound for the first time.

Isumi Railway reported 44 incidents involving muntjacs and wild boars in fiscal 2023 along its track in the eastern part of the Boso Peninsula. The rail operator is currently installing equipment to generate high-frequency noise to scare off the animals.

Chiba Prefecture has devised a specialized plan to eradicate muntjacs and drawn an east-to-west defense boundary at the prefecture’s center to cap their spread.

Additionally, it pays a bounty of up to 6,000 yen for every muntjac captured. The sum includes a 1,000-yen state subsidy to municipal governments.

Upward of 10,000 muntjacs were caught in fiscal 2023. But the figure hardly made a dent in population numbers, given the species’ reproductive capability.

VENTURING FURTHER AFIELD

Muntjac sightings are now relatively common in neighboring Ibaraki Prefecture.

The first report was in 2017. Muntjacs were observed on three occasions in Chikusei city and elsewhere between 2022 and 2023.

Fearing an explosion in deer numbers, Ibaraki Prefecture mounted an incentive system in 2024 under which 2,000 yen is paid to people who provide photos and videos of muntjacs.

Experts were surprised that muntjacs were able to cross the prefectural border.

Yusuke Goto, deputy chief curator at the Ibaraki Nature Museum, noted that young males often travel long distances when they branch out on their own to look for a new place to live.

“Muntjacs are probably moving while trying to avoid detection,” said Goto, 42. “It seems that muntjacs proliferating in southern Chiba Prefecture have migrated northward, crossing the bridges over the Tonegawa river to enter Ibaraki Prefecture.”

Expressing alarm, Goto said male muntjacs had reached Chikusei along the border with Tochigi Prefecture, raising the “possibility that their habitat could soon expand further.”

He also took note of a report of “what appears to be a muntjac” in nearby Saitama Prefecture.

“Containing muntjacs within Chiba Prefecture is first and foremost essential,” Goto said. “We desperately need a program to eliminate them based on data that has been gathered.”

Capturing muntjacs is the only viable approach for the time being while other methods, such as administering vaccines to control their proliferation, are studied, he said.

(This article was written by Miki Takenaka, Takae Kumagai and Junko Miyasako.)