The Rabbit Crusades: The Story of Invasive Herbivores on Kent Island

The L-Transect is my favorite path on Kent Island. It winds though beds of thick mosses of every shade of green, a forest of ferns, and a woodland of conifers, birches, and mountain ash bearded by lichen. This area is alive with birdsong, and it was while accompanying Nat Wheelwright on a bird census that I first noticed a fenced enclosure next to the path. It was packed with spruce and fir seedlings that were practically bursting out of the wire mesh. Outside of the fence plot, the trees were old, more widely spaced, and surrounded by clearings of ferns and moss. Fallen trees and broken stumps littered the understory, a pattern that I had also noticed in the nearby forest around Petrel Path. The key to this ecosystem mystery turns out to be an invasive species that once ran, (or more accurately, hopped) rampant all over the Island.

A foraging Snowshoe Hare  (image:http://bioexpedition.com/snowshoe-hare/)

A foraging Snowshoe Hare
(image:http://bioexpedition.com/snowshoe-hare/)

Snowshoe hares were accidentally introduced to Kent Island in the 1950s when the Ingalls family brought them to Hay Island to start a fur business. The enterprising rabbits ran across the land bridge that emerges between Hay and Kent Islands at low tide, and quickly set about eating all of the seedlings and saplings in sight. Besides mongooses, Kent Island lacked terrestrial mammals, and so there were few predators to control the hare population.

A study conducted by Trevor Peterson in 2006 that looked at tree ring records on Kent Island found that tree recruitment plummeted for the fifty years following the introduction of the hares. The fenced plots that I found along the L-Transect were part of an experiment that compared the density of trees browsed by hares with trees protected from hares. The contrast between the lush enclosure and the sparse surrounding forest provides a clear illustration of the rabbits’ dramatic impact on the environment. When Chuck Huntington, a director of the BSS, began researching Leach’s Storm Petrels in 1953, a dense forest along Petrel Path was his primary study site. Once the hares started consuming all of the saplings, when the older trees that made up the canopy died, they were replaced by raspberry plants and ferns instead of a new generation of trees. The death of the canopy trees also had a domino effect, because sparser tree cover made the remaining trees more exposed to wind, and therefore more likely to topple over. The original Petrel study area was abandoned in the late 1990s and moved to the Shire because so many trees had fallen that the Petrel burrows were too difficult to access. While Petrels still nest there, the impact of the ecosystem changes on their population remains unknown.

As BSS Director, Nat Wheelwright realized that the disappearance of the forest on the North end of the Island was threatening the habitat of many bird species. Eliminating the invasives was to be an enormous operation, with between 700 and 1,000 hares roaming between Kent and Hay Islands. Nat tried several elimination tactics beginning in the 1990s, from setting traps to contracting local hunters and setting dogs on the creatures. He recalled, “At one point I got them down to ten or twenty, and the next year there were 200.” After fifteen years of attempts frustrated by the hares’ extreme fertility, Nat reached out to the head of vertebrate pest control in New Zealand, a country with a long history of dealing with invasive mammals. Nat’s explanation of the Snowshoe Hare problem on Kent Island received a two-line reply: “That should be trivial. You’re not trying hard enough.”

Nat upped the ante by setting traps with apples in the winter, when the hares were especially hungry. The population was so large that the traps had to be emptied three times a day. It was only in 2007 when Bowdoin purchased Hay Island, where the hares had sought refuge, that the BSS was able to eliminate the invasive herbivores for good.

The trees are coming back quickly now that the hares are gone, with spruce and fir seedlings popping up everywhere. Interestingly, while the introduction of the hares threatened research on the Island, so does the re-emergence of the forest after their elimination. The open fields on the South side of the Island, once used for agriculture, are habitat for Savannah Sparrows, the study subjects of a team of Canadian researchers. “We now have to actively manage the fields to prevent the trees from taking over,” says Damon Gannon, the current Director of the BSS. Because Kent Island is so small, landscape changes are very visible. It will be interesting to see the ecosystem changes that occur when the seedlings on the North end of the Island grow and the forest is dense once more.

Sources:

Peterson, Trevor S., Akane Uesugi, and John Lichter. “Tree recruitment limitation by introduced snowshoe hares, Lepus americanus, on Kent Island, New Brunswick.” The Canadian Field-Naturalist 119.4 (2005): 569-572.

http://www.bowdoin.edu/bowdoinmagazine/archives/features/004943.shtml

 

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