In 1959, two men released 12 snowshoe hares on a Canadian island; the animals spread, hindered tree growth, and were eradicated in 2007

Introduced to Hay Island in 1959 by two fishermen, snowshoe hares multiplied and spread to Kent Island.

In 1959, two New Brunswick fishermen came up with a simple plan for 12 snowshoe hares. Wesley Ingalls and his nephew, Junior, carried the animals by boat from Grand Manan Island to nearby Hay Island in the Bay of Fundy. They hoped the hares would reproduce and give them something to trap during the winter, when they were not fishing.

A vivid sunset illuminates a lush Canadian island overrun by snowshoe hares, highlighting the contrast between the vibrant coastal landscape and the dead, stalled forest growth. (AI-generated/ Google Gemini)

Instead, the experiment transformed the islands' forests. The hares multiplied rapidly and crossed from Hay Island to neighboring Kent Island. Research published in The Canadian Field-Naturalist found that tree recruitment on Kent Island plummeted after the 1959 introduction and remained low, while trees continued to establish on nearby hare-free Outer Wood Island. It took repeated attempts and nearly half a century before the last hare was trapped in 2007.

How 12 hares became a forest problem

Snowshoe hares were native to mainland New Brunswick, but they had not naturally established themselves on the small islands where Ingalls released them. The absence of competing mammals and the limited ability of local predators to catch them in dense vegetation gave the newcomers an advantage. The hares reproduced quickly. A female could produce several litters a year, and the population grew from the original dozen to hundreds. At low tide, the animals could cross the exposed land between Hay and Kent islands. Soon, the problem was no longer confined to the place where the fishermen had released them.

Deep Dive

How can introduced animals prevent forests and native plants from recovering on islands?

Why can it take so long to remove introduced animals from an island?

How quickly does island vegetation recover after introduced animals are removed?

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The effects became visible in the island’s plant life. The young saplings of the balsam fir and other trees were continually being grazed upon before they could grow and become the next generation of trees in the forest. In 1961, Junior returned to Hay Island to cut the young balsam firs to build a herring weir and found that the stand of trees was no longer able to regenerate like it used to. Researchers eventually compared tree growth on Kent Island with that on hare-free Outer Wood Island.

Why the trees could not grow back

The damage was more than a matter of hungry animals eating a few saplings. The hares became a powerful force shaping the ecosystem. They browsed the growing tips of young white spruce, sometimes reaching branches high above the ground. In some areas, their droppings reached densities of about 50 per square meter. When researchers enclosed small plots so hares could not enter, seedling densities inside the protected areas eventually exceeded 150 per square meter, compared with none outside the fences. These observations, documented by Wheelwright in Frontiers in Ecology and the Environment, showed how strongly the introduced hares were suppressing forest regeneration.

The difference helped rule out other possible explanations for the lack of forest regeneration, including the harsh climate and the Bay of Fundy's salty fog. The hares kept young trees from surviving long enough to replace aging canopy trees. By the 1980s, storms were increasingly knocking down older trees, while few young trees were available to replace them. Forested areas began turning into open tangles dominated by plants such as wood fern and raspberry.

A snowshoe hare in winter, the animals introduced to Hay Island in 1959 that later disrupted forest regeneration. (Wikimedia Commons)

Removing the animal that changed the island

Removing the hares proved much more difficult than introducing them. In 1998, Nathaniel Wheelwright, an ecologist at Bowdoin College, initiated a trapping experiment with the approval of the government of New Brunswick. The trapping reduced the hare population, but it recovered within two years. Again in 2002, the same thing happened. Hares were very difficult to catch; they bred rapidly and could live in the thick vegetation of the island. Wheelwright finally consulted with the vertebrate pest control officials of New Zealand, who told him that it could be done.

However, the final campaign was successful. In 2007, the last snowshoe hare was caught following almost 50 years on the islands. The ecological reaction to this was rather rapid. Without browsing pressure, seedlings and saplings were able to start growing across the forest floor because they were no longer being eaten.