Imported Eastern Cottontails Outcompete Native New England Cottontails

It’s first come, first served, where rabbit habitat is concerned.

New England cottontails thrive in shrublands and young, regrowing forests where low plants, shrubs, and tree seedlings mingle to provide food and cover. Many other kinds of wildlife use such habitats, including the eastern cottontail – a related rabbit introduced to the Northeast in the last century and a species that has proven extremely prolific and adaptable. Today, eastern cottontails now dominate many young forests and shrublands, to the detriment of the New England cottontail in the native species’ six-state range.

Amanda Cheeseman, left, with captured cottontail rabbit.

Amanda Cheeseman, left, studies cottontail rabbits in New York's Lower Hudson Valley.

Recent research in New York’s Hudson Valley confirms a problem that scientists have long known about but have only recently begun to quantify: When conservationists and landowners use certain management techniques to create or refresh habitat for New England cottontails, eastern cottontails may fill up that habitat before native New Englanders get there. The New England cottontails may then be forced into areas of thinner habitat nearby, including stands of invasive alien shrubs, many of which provide poorer food and host greater numbers of noxious ticks.

Amanda Cheeseman, a postdoctoral associate with the State University of New York’s College of Environmental Science and Forestry, studies both New England and eastern cottontails in the Lower Hudson Valley. Using box traps baited with apples, Cheeseman and her helpers captured cottontails of both species. They put 24-gram (0.8 ounce) radio-collars around the necks of mature rabbits and temporarily glued smaller transmitters to younger, smaller rabbits. Then, using receiving antennas, the researchers charted the rabbits’ movements two to three times a week year-round.

At 16 different study sites, Cheeseman’s team monitored a total of 80 New England cottontails and 68 eastern cottontails, logging 5,375 radio-locations between December 2013 and July 2016.

Captured cottontail rabbit

Researchers put radio-collars on cottontails and monitored their use of habitat year-round.

The researchers also sampled vegetation on the sites in both leaf-on and leaf-off seasons: they identified shrubs, trees, and other plants by species, and they characterized the thickness of the habitat by determining the number of plant stems growing per acre. (Top-quality young forest and shrubland habitats can have more than 20,000 stems of small trees and shrubs per acre.)

Cheeseman and her colleagues, Christopher Whipps and Jonathan Cohen of SUNY-ESF, and Sadie Ryan, now with the University of Florida, used computer models to evaluate “fine-scale resource selection” – basically, they looked for trends in the types of habitat occupied by both New England and eastern cottontails at different times of the year.

The researchers reported their results in the September 2018 Ecology and Evolution in an article, “Competition Alters Seasonal Resource Selection and Promotes Use of Invasive Shrubs by an Imperiled Native Cottontail.” (See attachment at bottom of article.)

How do eastern cottontails best New Englands in the race to claim cover? “We don’t think it’s directly through fighting,” Cheeseman says. “Eastern cottontails are more successful at getting to new habitat patches before those patches are ready to support New Englands. The easterns reproduce rapidly, fill up the available habitat, and then the New England cottontails end up using other areas.”

She adds: “Our telemetry studies show that New England cottontails use different parts of their home ranges at different times of the year.” They live in areas thick with plants such as goldenrod in summer and early autumn; then in fall, after frosts knock back summer’s greenery, they shift to areas with dense woody stems – movements that may amount to only a few yards but that can be important in giving eastern cottontails an advantage. “If a New England cottontail gives up its hold on a habitat site in autumn,” Cheeseman says, “eastern cottontails may already have moved into that area by early spring.”

In some of the habitats Cheeseman studied, she found only New England cottontails. Those areas can best be characterized as woodlands with a shrub understory: places where native blueberry, azalea, and mountain laurel shrubs grow under a canopy of trees, mainly oaks, offering cover that’s thick enough to let the rabbits find food, evade predators, and survive winter.

Image

You have to look hard to see the New England cottontail hiding in the lower left portion of this photo. This habitat provides good wintering cover and protection from predators such as foxes and bobcats.

Shrublands, which often occur on old farm fields that have grown up in a mix of native and invasive shrubs, generally support greater numbers of cottontails, but often those rabbits are eastern cottontails. “In our study area, we didn’t have a single typical early successional shrubland that had only New England cottontails,” Cheeseman says. “They all had both eastern and New England cottontails.” In such areas, the New England cottontails ended up occupying only the poorer-quality parts of the habitat – areas that often had non-native invasive shrubs and older, thinner shrubs – that eastern cottontails hadn’t taken.

Ticks were more abundant among the invasive shrubs, and heavy tick burdens can harm a rabbit’s health. Plus, winter food and cover aren’t as plentiful or reliable in such areas.

In their paper, Cheeseman and her colleagues write: “Given the potential for competitive displacement of New England cottontails from early- to mid-successional shrublands where eastern cottontails are present, traditional methods of successional shrub management,” such as clearcutting, controlled burning, and brush-hogging over large areas, are likely to benefit nonnative eastern cottontails over New England cottontails.

Instead, Cheeseman suggests managers and landowners use seed tree cuts, shelterwood cuts, or selective thinning to create gaps in the forest canopy – techniques that don’t create expansive areas of uniform, dense habitat but instead result in clumps of thick habitat scattered across a generally forested landscape.

“In places where eastern cottontails are present, we recommend that managers leave at least 75 percent of the tree canopy on managed sites,” Cheeseman says. “A good management practice might be to go into an area where New Englands live during a snowy winter and cut down two or three trees per acre.” The fallen tops of the trees would provide forage, as cottontails could eat the buds and outermost twigs. The rabbits could also hide beneath the dense felled tops. In spring, light reaching the forest floor would spur the growth of lower plants in the canopy gaps created by removing a few trees.

An area of habitat that is older and a bit thicker than that resulting from clearcutting or shrub-mowing may not be as productive to a broad range of wildlife, but it may help New England cottontails significantly more than it boosts their eastern cottontail competitors.

In areas dominated by nonnative invasive shrubs, such as bush honeysuckle, barberry, and multiflora rose, Cheeseman says, “We recommend removing invasives in 50-by-50-meter patches and rotating these sites throughout a management area, with the intent of slowly shifting the habitat from invasive to native shrubs over time.”

Cheeseman says she was not hugely surprised by her research results, “In many other studies, biologists have found New England and eastern cottontails segregating themselves within habitats. New England cottontails have been known as woods rabbits for years – that’s one of the species’ original common names.”

Cheeseman believes that older shrublands and regrowing trees “20 to 30 years post-disturbance” may be able to keep a New England cottontail population healthy in a given area without providing a boost for competing eastern cottontails. “Late successional habitat may not be as high-quality as younger, thicker habitat,” Cheeseman says, “but it’s better than nothing.”

She and her colleagues state in their Ecology and Evolution article: “Treatments should vary by site,” and, where possible, habitat managers should use an approach that balances a high degree of canopy closure with dense native understory regeneration. Where native shrubs aren’t present, seeding or planting native shrubs and removing or otherwise minimizing invasives may yield habitat that New England cottontails can occupy and use.

Cheeseman reports, “We’re working to help land managers in the region incorporate and monitor wildlife responses to these methods, and, while it’s still early in the process, the response by New England cottontails to these activities has been overwhelmingly positive.”

Adds Anthony Tur, a U.S. Fish and Wildlife Service biologist who has been involved in conserving the New England cottontail for years, “The findings support our understanding of the system, and I think the recommended actions are spot-on. As we move forward in trying to find the best ways to help New England cottontails, the tricky part will lie in balancing conservation goals and objectives with landowners’ desires.”

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Contact Amanda Cheeseman at acheesem@esf.edu and 315-470-4782