he unique native flora of the 

 Hawaiian Islands, which 

evolved in the absence of ungulates (grazing animals), is highly 

vulnerable to damage by trampling and browsing. Wild ungulates introduced into Hawai`i 

in the past 150 years, including 

mouflon, axis deer, and mule 

deer, have severely harmed the 

native flora. Control measures 

used against feral animals do not 

work as well against these wild 

animals. Trophy hunting tends 

to alter sex ratios and increase 

population growth. U.S. Geological Survey scientists are studying 

these wild ungulates in order 

to develop more effective control measures that help protect 

Hawai`i`s endemic flora.

T

Wild Sheep and Deer in Hawai`i—a Threat to Fragile 

Ecosystems

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 2008–3102

2008

For millions of years, the Hawaiian Islands 

lay undiscovered by humans in the middle of the 

Pacific Ocean. The fauna and flora that found 

their way to the islands and evolved there were 

Introduced Wild Sheep and Deer in Hawai`i

European mouflon (Ovis gmelini 

musimon), closely related to the ancestors of 

domestic sheep (O. aries), are wild sheep that 

originated from Asia Minor. Mouflon were 

subsequently introduced to many areas of the 

world, including Hawai`i. On islands lacking 

native ungulates, populations of introduced 

mouflon have grown rapidly and severely damaged native flora.

Introduced into the Hawaiian Islands beginning in the 1950s, mouflon currently occur wild 

on Läna`i and the Island of Hawai`i. On Hawai`i, 

mouflon and feral sheep were crossbred and 

released on the large shield volcano Mauna Kea 

beginning in 1962. A large hybrid population now 

surrounds Mauna Kea and extends to the northern 

part of the volcano Mauna Loa. In 1968 a population of wild-type mouflon was introduced to the 

Kahuku Ranch (now a unit of Hawai`i Volcanoes 

National Park) on Mauna Loa for trophy hunting. 

These animals now range over the southern part 

of Mauna Loa in the Kahuku area and adjacent 

public and private lands. Both herds have dramatically expanded their range into forest reserves, 

where they are destroying endangered native 

plants such as silverswords (Argyroxiphium spp.).

Axis deer (Axis axis), otherwise known as 

chital, originate from India, Sri Lanka, and Nepal. 

Mouflon (wild Mediterranean sheep), like these in the Kahuku Unit of Hawai`i Volcanoes National Park, 

threaten the fragile native flora of Hawai`i by browsing, bark-stripping, and trampling. The Hawaiian Islands 

originally had no ungulates (grazing animals), but mouflon and several other species were deliberately 

introduced, mainly for recreational hunting. Traditional control methods—including hunting—have proved 

largely ineffective in limiting the increase and spread of these introduced wild ungulates. Photo courtesy of 

Robert Stephens.

Browsing by wild ungulates threatens native 

Hawaiian plants. This mämane tree sapling in Palila 

Critical Habitat on Mauna Kea, Island of Hawai ́i, 

has been stripped of most of its foliage.

unique, and land animals were mostly limited to 

invertebrates and birds. Before humans came, 

the only mammals, apart from seals that hauled 

up on the beaches, were insect-eating bats. When 

Polynesians settled Hawai`i more than a thousand 

years ago, they brought with them domesticated 

dogs, pigs, and fowl (chickens). Rats arrived as 

stowaways. Inevitably, some of these animals 

escaped into the wild and established feral 

populations, which began to have an impact on 

the native flora. After the islands were found 

by Western explorers, the influx of non-native 

species into Hawai`i increased. Since the middle 

of the 19th century, this has included deliberate introduction of several large wild ungulates 

(grazing animals). The native flora, which 

developed in the absence of large land mammals, 

is extremely vulnerable to browsing, trampling, 

and bark stripping by ungulates, and the effects of 

these introduced species has been severe. Some 

domesticated ungulates have been in Hawai`i 

for hundreds of years, but wild species that 

have never been domesticated are now rapidly 

increasing in range and numbers. Wild ungulates 

behave differently and are much more elusive 

and difficult to manage than livestock species that 

were once domesticated and have become feral. 

Thus, Hawai`i’s plants are facing a relatively 

new threat. Controlling these wild ungulates has 

become a major conservation concern.
They have been introduced to many parts of the 

United States (including California, Texas, and 

Hawai`i) and to Australia. Axis deer were brought 

to the Hawaiian Islands from India in late 1867 

as a gift to King Kamehameha V and released 

on Moloka ́i in 1868. Some were moved to 

O`ahu before 1898 and some to Läna`i in 1920. 

Axis deer were also released on Maui in 1959. 

Although axis deer have been wild on Läna`i and 

Moloka`i for many decades, the more recently 

introduced Maui population has rapidly increased 

consequence of their evolutionary history with 

large predators, many ungulates have very high

reproductive rates, causing rapid population 

growth in Hawai’i, where there are no predators. 

The Columbian black-tailed deer 

(Odocoileus hemionus columbianus) is a 

subspecies of mule deer from the northwestern 

United States. In 1961, 35 animals were introduced from Oregon to Pu`u ka Pele Game Management Area on Kaua`i. This herd has grown to 

a population of more than 700 on both sides of 

Waimea Canyon, including Köke`e State Park.

American pronghorn antelope (Antilocapra americana) were brought to Läna`i in 

1959 from Montana. After an initial population 

increase to 250 animals in 1966, pronghorn 

declined to fewer than 12 by 1983 and apparently now no longer exist on Läna`i. Pronghorn 

represent one of the few introductions of a wild 

ungulate to Hawai`i that failed entirely.

Impact on Hawaiian Flora and Fauna

Since 1778, nine percent of the native 

Hawaiian flora has gone extinct, in good part as 

a result of the introduction of non-native species. In addition, where non-native herbivores 

(plant-eating animals) have been introduced, in 

Hawai`i and elsewhere worldwide, there is usually also an increase in the relative abundance of 

invasive plants from their native range, which 

then often outcompete local species. The wild 

in numbers, threatening native forests in natural 

areas. The O`ahu population was reduced to a 

remnant herd in Moanalua Valley by 1962 and 

eventually died out. Although introducing axis 

deer to the Island of Hawai`i was debated for 

many years, it was never undertaken. 

Axis deer in the Hawaiian Islands damage 

agricultural crops and native and ornamental 

vegetation through browse and bark stripping, 

cause erosion, are frequently hit by vehicles, and 

may carry diseases that can infect humans. As a 

Axis deer (fawn) Columbian black-tailed deer

Mauna Loa

mouflon

1968

Maui

axis deer

1959

Lana`i

axis deer 1920

mouflon 1954

pronghorn 1959*

O`ahu

axis deer

after 1898*

Moloka`i

axis deer

1868

Mauna Kea

mouflon and

mouflon-feral

sheep hybrids

1962

Kaua`i

black-tailed deer 1961

mouflon 1962*

Island of

Hawai`i

Starting in the middle of the 19th century, several species of wild ungulates have been introduced into the Hawaiian Islands, eventually inhabiting almost 

all the main islands. This map shows the species and their dates of introduction on each island. Asterisks (*) indicate populations that later died out.

Two species of wild deer have been introduced into Hawai`i, axis deer and Columbian black-tailed deer. 

In their native range, many axis deer fawns fall victim to predators; with no predators in Hawai`i, the 

deer’s numbers can increase rapidly. Photographs courtesy of Charles van Riper III.

161°W 159° 157° 155°

19°

21°

23°

N

0 50 100 MILES

0 100 100 KILOMETERS
ungulates discussed here have caused tremendous damage to Hawai`i’s native flora. On 

Mauna Kea, the habitat degradation in the 

mämane-naio forest, which the endangered 

Hawaiian finch, Palila (Loxioides bailleui) rely 

on, resulted in two court orders to eradicate 

both pure and hybrid mouflon, along with feral 

domestic sheep and goats. Nearly two decades 

of intensive population control were required 

for habitat conditions to improve on Mauna 

Kea. The Mauna Kea silversword (Argyroxiphium sandwicense), an endangered plant, 

still suffer browse damage when even small 

numbers of hybrid mouflon are present.

Where mouflon have occasionally 

invaded fenced areas in the Mauna Loa strip 

of Hawai`i Volcanoes National Park, they have 

destroyed outplanted Ka`ü silverswords (A. 

kauense)—another endangered plant, damaged the threatened Hawaiian catchfly (Silene 

hawaiiensis), and stripped bark from important 

forest trees, such as koa (Acacia koa) and 

mämane (Sophora chrysophylla). A large and 

growing population of mouflon continues to 

threaten and degrade endangered plants such 

as the Ka`ü silversword and the habitats of 

endangered forest birds throughout Mauna 

Loa.

Axis and Columbian black-tailed deer 

cause similar environmental damage. They 

consume progressively less palatable plants 

until no edible vegetation is available. Under 

extreme drought conditions, axis deer will eat 

bark from trees. In addition to stripping bark, 

bucks also rub their antlers on tree trunks 

and branches. This can effectively girdle the 

tree and result in the death of mature trees. 

Deer have their highest concentrations in the 

fragile, seasonally wet areas below the cloud 

forests. Here, they create trails and pathways 

through thick vegetation and cause erosion 

through hoof action. In wet forest areas, the 

trails increase runoff through soil compaction 

and by decreasing the mossy layer available to 

retain water. These trails also damage cultural 

and archaeological resources. The interaction of browsing and soil compaction by feral 

pigs, goats, and axis deer on east Moloka`i 

has reduced the `öhi`a-hapu`u rainforest to 

a grassy scrubland, and runoff of silt from 

this degraded habitat threatens the coral reef 

ecosystem on the southern coast.

Without fences, deer will increase and 

invade new areas, particularly on Maui and 

Kaua`i. Axis deer have been observed to jump 

fences 8 feet (2.6 m) tall. Building fences high 

enough to totally exclude deer is expensive 

and difficult. Therefore, supplementary control 

efforts are often needed within areas enclosed 

by lower fences. Axis deer are also damaging 

existing fences throughout the western slopes 

of Haleakalä on Maui presenting a major concern to natural resource managers.

Biology and Spread of Wild Ungulates

In the five decades since their first 

introduction to the Hawaiian Islands, mouflon 

have become locally abundant, as they have 

on other island groups. In the Kahuku Unit 

of Hawai`i Volcanoes National Park on the 

island of Hawai`i, a founding population of 11 

individuals has increased to more than 2,500 in 

36 years, even while under substantial hunting 

pressure for trophies. Mouflon are polygamous, and their populations can grow rapidly 

when the ratio of females to males is high. An 

abundance of high-quality food can also lead to 

a lower age of first pregnancy and higher lamb 

survival, further increasing population growth.

Axis deer have high reproductive rates, 

which compensate for predation by leopards, 

tigers, and Indian wild dogs in their native 

range. In the absence of predators, as in 

Hawai`i, introduced populations exhibit annual 

population growth rates of 20–30%. On Läna`i 

and Moloka`i, some females reach sexual 

maturity by 4–6 months of age, and most do 

so by the end of their first year. In years when 

forage conditions are good. more than 90% of 

mature females produce fawns.

Axis deer graze and drink water in open 

areas during the twilight of morning and 

evening and rest in cover during the warmest part of the day. They are usually found in 

small family groups of 15–24, and harems are 

uncommon. However, herds of nearly 100 animals are reported on Läna`i and Moloka`i, and 

a herd as large as 300 was recently reported 

on Maui ranch pasturelands. Although axis 

deer are rarely found above 1,160 m (3,800 ft) 

elevation in their native range in Nepal, they 

have been observed above 2,150 m (7,050 ft) 

on Maui. They are present from sea level to 

the highest point on Läna`i (1,030 m; 3,380 

ft), and they exist throughout all but the most 

remote areas of Moloka`i.

In the native range of Columbian blacktailed deer, mountain lions and other predators 

account for as much as 40% of fawn mortality. 

In Hawai`i the deer suffer no predation other 

than human hunting. 

Unlike feral sheep, goats, and pigs, which 

were domesticated before their arrival in 

Hawai`i, mouflon and deer were never domesticated. These wild ungulates present new 

challenges to control efforts in Hawai`i. They 

are able to jump over most fences designed for 

feral animals, and when being pursued, they 

disperse into small groups and hide in dense 

cover. Social behaviors also differ. Mouflon 

segregate by sexes and only form large groups 

when breeding, thus limiting efficient hunting 

periods. Because they disperse widely over the 

landscape alone or in small groups, common 

control techniques that rely on radiotelemetry 

are largely ineffective for mouflon.

The hybrid mouflon-feral sheep of 

Mauna Kea are larger than wild-type mouflon 

and have a wider variety of coat colors. 

Managers are concerned that under intense 

hunting pressure or control efforts, the variation in coat coloration may lead to selection 

for cryptic colors that blend with the environment. These superior physical traits of size 

and color variation are examples of hybrid 

vigor. Although feral sheep and goats have 

been effectively eliminated from Mauna Kea, 

hybrid mouflon continue to expand their 

range and have invaded other natural areas, 

including Hawai`i Volcanoes National Park, 

despite the presence of fences designed for 

feral animals.

0 50 MILES

0 100 KILOMETERS

155°

155°N

156°

156°N

20°

N 20°

19° 19°

Wild introduced mouflon and mouflon-feral 

sheep hybrids are damaging native flora and 

fauna in several areas 

on the Island of Hawai`i, 

including Palila Critical 

Habitat on Mauna Kea 

and the Kahuku Unit 

of Hawai`i Volcanoes 

National Park on Mauna 

Loa.
Control and Management of Wild 

Ungulates

The conservation of rare and endangered 

species in Hawai`i often includes the construction of enclosures that protect only a few 

individuals within a small area. If rare plants 

are relegated to such small areas, there is little 

hope of guarding their long-term survival—

plants cannot effectively disperse and adapt to 

environmental changes under these conditions. 

If, however, wild herbivores are controlled over 

large areas, natural population processes and 

local adaptation can occur, as well as recovery 

for entire native plant communities. To ensure 

long-term survival of native plants, effective 

fence designs and management strategies are 

needed to exclude wild ungulates from protected natural areas in Hawai`i.

Managing wild ungulates for sustainedyield public hunting is problematic, because they 

are extremely difficult to census, hunt, contain, 

and control in the remote and rugged terrain of 

Hawai`i. These ungulates do not stay on public 

land, and in many areas, limited land access 

precludes hunting. Previous efforts at eradication have not generally been successful, because 

of the evasive behavior of the animals. More 

effective hunting programs and control techniques are needed for wild ungulates in Hawai`i. 

Unsupervised public hunting has generally been 

ineffective for controlling ungulates in Hawai`i. 

Although a closely directed hunting program has 

reduced mouflon abundance in the Kahuku area, 

it has also resulted in increased reproduction, 

which could slow future control efforts. This is 

because trophy hunting, which focuses on males 

with impressive horns, can shift the sex ratio of 

populations and contribute to higher population 

growth. If control efforts are directed at females, 

however, growth rates could be reduced.

Population monitoring is critical for 

understanding management actions, growth rate 

trends, and range expansion. It is also important 

to develop effective strategies to reduce the 

expense and effort of control programs and to 

develop and implement monitoring protocols 

that will allow managers to understand the 

effectiveness of different strategies.

The work of scientists in studying the 

wild ungulates of Hawai`i is part of the U.S. 

Geological Survey’s efforts to understand and 

help preserve threatened ecosystems. If effective control measures for these wild ungulates 

are not implemented, it may be difficult if not 

impossible to prevent them from expanding 

their ranges and numbers in Hawai`i. This in 

turn would make it far more difficult to protect 

Hawai`i’s vulnerable endemic flora.

Further Reading

Anderson, S. B., 1999, Axis deer overview 

and profile: [www.hear.org/hnis/

reports/HNIS-AxiAxiV01.pdf].

Hess, S., B. Kawakami, B., Okita, D., and 

Medeiros, K., 2005, A preliminary 

assessment of mouflon abundance at 

the Kahuku Unit of Hawai`i Volcanoes 

National Park: U.S. Geological Survey 

Open File Report OF 2006-1193 

[http://pubs.usgs.gov/of/2006/1193/].

Maui axis deer group, 2002, Initial findings 

for a Maui deer management plan: 

[www.nps.gov/applications/parks/hale/

ppdocuments/ACF214.doc].

Robichaux R., Bergfeld, S., Bruegmann, 

M., Canfield, J., Moriyasu, P., Rubenstein, T., Tunison, T., and Warshauer, 

F., 2000, Reintroducing Hawai`i’s 

silverswords: Endangered Species 

Bulletin, v. 25, p. 22-23.

Sakai, A. K., Wagner, W. L., and Mehrhoff, 

L. A., 2002, Patterns of endangerment 

in the Hawaiian flora: Systematic 

Biology, v. 51, p. 276-302.

Waring, G., 1996, Preliminary study 

of the behavior and ecology of 

axis deer (Axis axis) on Maui, 

Hawai`i: Research report to Haleakala National Park and the National 

Park Service [www.hear.org/

AlienSpeciesInHawai`i/waringreports/

axisdeer.htm].

Steven C. Hess

Edited by

Peter H. Stauffer

Graphic design by

Stephen L. Scott

COOPERATING ORGANIZATIONS

Hakalau Forest National Wildlife Refuge

Hawai`i Volcanoes National Park

For more information contact:

Steven C. Hess 

 (808) 967-7396 x286

U.S. Geological Survey

Pacific Island Ecosystems Research Center

Kilauea Field Station

 P.O. Box 44

Hawaii National Park, HI 96718

Email: shess@usgs.gov

http://biology.usgs.gov/pierc/

This Fact Sheet and any updates to it are available online at: 

http://pubs.usgs.gov/fs/2008/3102

The mouflon population in the Kahuku area of Mauna Loa doubled every 3-4 

years from its initial introduction of 8 animals in 1968 to an estimated 2,586 

in 2004. An assumed annual rate of increase of 21.1 percent (the bold black 

line) best accounts for the known abundance at those two points in time 

(stars) and the removal of about 800 individuals in 1994. 1968 1971 1974 1977 1980 1983 1986 1989 1992

1995

1998

2001

2004

0

1,000

2,000

3,000

4,000

5,000

NUMBER OF ANIMALS

Mouflon in Kahuku area, Island of Hawai`i

Annual growth rate (%)

22.0

21.1

20.0

800 animals removed

A flowering 

Mauna Kea 

silversword 

(foreground) has 

been trampled 

and browsed by 

wild mouflon or 

mouflon-feral 

sheep hybrids. 

Behind it stands 

a surviving silversword. The active 

volcano Mauna 

Loa dominates 

the horizon.