In 1961, Hawaii introduced black-tailed deer to Kauai for sport hunting; a later survey found them across about half of sampled locations

Hawaii is not a place most people associate with deer. But in the soggy, rainy Kauai landscape, there are Columbian black-tailed deer that aren't native to Kauai, and were there at the urging of a decision in the 1960s that very few Americans are aware of. According to a 2001 US Fish and Wildlife Service publication, the deer were introduced in 1961 for sport hunting, and the population on Kauai has since grown to well over 500 animals across the island's western side.

A gift with strings nobody asked about

The deer were introduced as a game species, part of a broader pattern of wildlife introductions in Hawaii. In a similar trend, the axis deer were introduced on Molokai in 1868 and, by the early 1900s, had multiplied in numbers so much that the state was forced to use professional hunters to reduce their populations.

The black-tailed deer on Kauai took a similar path but on a smaller scale. They do not stray from Kauai, but on this one island they established their own permanent niche in the wet upland forests of Waimea Canyon and Alakai Plateau, an area home to plants and insects that occur nowhere else in the world.

The bill nobody sent, until scientists went looking

A more recent, peer-reviewed 2025 study titled “Insights Into Ungulate Distributions Show Range Expansion, Competition, and Potential Impacts on a Sub-Tropical Island,” in Pacific Science, revealed that camera-traps used during surveys of Kauai between 2020 and 2021 recorded the presence of black-tailed deer in about half of all sampled locations on the island, ranking them second after wild pigs in terms of frequency of detection, and their habitat ranges overlap substantially with the habitat of threatened or endangered native species remaining in the state. Decades after their initial 1961 release, and roughly two decades after that 2001 population estimate of "well over 500" was recorded, the deer are still present and still expanding into habitat conservationists are trying to protect, though a current, updated population count is not available.

However, besides being a problem for conservation efforts, the population is also problematic economically. A peer-reviewed economic evaluation titled “Economic estimates of invasive wild ungulate damage to livestock producers in Hawai'i,” published by the National Library of Medicine, estimates that the damage the deer inflict on livestock producers amounts to about $1.42 million per year among survey respondents, which, once other factors are taken into account, such as the costs of fencing, pasture restoration, and lost livestock feed, translates to $3.6-$7.5 million throughout the state.

That statewide figure, however, covers damage from invasive ungulates in general, including wild pigs, feral goats, feral sheep, mouflon sheep, and axis deer across multiple islands, not black-tailed deer on Kauai alone, since the species does not occur anywhere else in the state. Nobody paid those bills in 1961 but they are being covered now.

The story is bigger than one island

The black-tailed deer on Kauai are not themselves the problem; their presence simply illustrates a pattern the US knows all too well from its own experience with kudzu, Burmese pythons, and feral hogs: quick decisions in wildlife management often turn into expensive surprises for future generations.

Hawaii still holds annual controlled hunts for black-tailed deer on Kauai as both a way of managing deer populations and a traditional activity. This seems like an understandable solution to the problem that did not need to exist in the first place.