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Snowshoe hare population rebounding

Posted: Friday, September 26, 2008

The snowshoe hare (Lepus americanus) is a common resident of the boreal forests of North America. It ranges from the forested extents of northern Canada and Alaska southward to the northern U.S. border states and into the northern Sierra and central Rocky Mountains.

Graph By Toby Burke
Graph By Toby Burke
Annual counts of snowshoe hare pellets show the rise and fall of the central Kenai hare population. This year snowshoe hares are beginning to increase somewhat, but their recovery is probably slowed by the lack of recent large fires that create hardwood browse for winter survival. Vertical bars on graph showed estimated error, based on pellet counts in five grids of 49 1-meter plots.

The snowshoe hare provides a classic example of a species with huge cyclic oscillations in its population densities. These population cycles may be on the order of 20 to one in the southern portions of its range or 3,400 to one in the northern portions of its range. It is amazing to think that field studies have revealed densities of 3,400 snowshoe hares per square mile at the peak of their cycle and densities of one per square mile at the bottom of their cycle, little more than one year later.

In favorable habitat in northern Canada, populations of 10,000 hares per square mile have been estimated by researchers. It has been hypothesized that a less complex food web with fewer buffer species and simpler environmental conditions may be responsible for these spectacular fluctuations in the northern range.

The boom and bust cycle experienced by snowshoe hares and their predators lasts roughly 10 years. This 10-year cycle is also experienced by numerous other prey species such as grouse, ptarmigan, passerine birds, squirrels, small mammals, and even cranes, because predators are forced to switch prey species when snowshoe hares become scarce.

Snowshoe hares are preyed upon by a large array of predators but most significantly by the mammalian predators -- lynx and coyote -- and the avian predators -- great-horned owls and northern goshawks. In addition golden eagles, red-tailed hawks, northern hawk owls, northern harriers, wolves, wolverines, red fox, pine martens, weasels, mink, and even squirrels, also predate heavily upon snowshoe hares, the smallest of these predators only being capable of taking leverets (young hares).

In 1983 Kenai National Wildlife Refuge biologists initiated a series of snowshoe hare research plots for the purpose of determining relative hare abundance in early- to mid-successional forests, which develop within the first few decades after forest fires.

Early-successional forests are the preferred habitat of snowshoe hares not only on the Kenai Peninsula but continent-wide because they provide abundant, accessible hardwood forage, such as willows, birch and aspen, for browsing and cover from predation.

In 1947 and again in 1969, major forest fires altered large forested areas of the central Kenai Peninsula. For the next few decades these forests developed into optimal snowshoe hare (and moose) habitat. Five research grids were established within these burn areas to determine snowshoe hare abundance. Each grid consists of 49 one-square meter plots. Each year during the summer we count all snowshoe hare pellets in these square meter plots and then remove the pellets so that only one year of pellets are allowed to accumulate until the next year's survey.

From these five grids we estimate relative abundance of snowshoe hares from the abundance of their pellets. We assume that when hare pellets are abundant, the hares are likewise abundant, and vice versa. If there was some critter around that ate snowshoe hare pellets, this system wouldn't work.

Interestingly enough, when the results of the five grids are analyzed separately or collectively for the last 25 years, we don't see the classic nine- to 11-year snowshoe hare cycle observed across most of boreal North America, but rather we see a longer cycle of roughly 12-14 years. The Kenai cycle appears to be distinctive because of its long low phase of six to seven years when there are very few hares to be found.

We have been in a low phase since 2001 and only in the last two years have the pellet counts begun to increase. True, we are seeing a few more road kills this year, but we are still along way from the extreme hare highs seen in the Interior or even in the early 1980s on the Kenai. We have no evidence of disease or extreme predator abundance, so the most likely explanation for the slow hare recovery is the lack of good post-fire, early-successional habitat, which is due to a lack of large fires like those of 1947 and 1969.

Toby Burke is a biological technician at the Kenai National Wildlife Refuge.

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Previous Refuge Notebook articles can be viewed on the refuge Web site, http://kenai.fws.gov/. You can check on new bird arrivals or report your bird sighting on the Kenai National Wildlife Refuge Birding Hotline at 907-262-2300.



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