Abstract
The New England cottontail (Sylvilagus transitionalis) is a high conservation priority in the Northeastern United States and has been listed as a candidate species under the Endangered Species Act. Loss of early successional habitat is the most common explanation for the decline of the species, which is considered to require habitat with dense low vegetation and limited overstory tree canopy. Federal and state wildlife agencies actively encourage landowners to create this habitat type by clearcutting blocks of forest. However, there are recent indications that the species also occupies sites with moderate overstory tree canopy cover. This is important because many landowners have negative views about clearcutting and are more willing to adopt silvicultural approaches that retain some overstory trees. Furthermore, it is possible that clearcuts with no overstory canopy cover may attract the eastern cottontail (S. floridanus), an introduced species with an expanding range. The objective of our study was to provide guidance for future efforts to create habitat that would be more favorable for New England cottontail than eastern cottontail in areas where the two species are sympatric. We analyzed canopy cover at 336 cottontail locations in five states using maximum entropy modelling and other statistical methods. We found that New England cottontail occupied sites with a mean overstory tree canopy cover of 58% (SE±1.36), and was less likely than eastern cottontail to occupy sites with lower overstory canopy cover and more likely to occupy sites with higher overstory canopy cover. Our findings suggest that silvicultural approaches that retain some overstory canopy cover may be appropriate for creating habitat for New England cottontail. We believe that our results will help inform critical management decisions for the conservation of New England cottontail, and that our methodology can be applied to analyses of habitat use of other critical wildlife species.
Highlights
Conservation of the New England cottontail (Sylvilagus transitionalis) is a high priority in the Northeastern United States (US)
Our study addressed the following research question: are New England cottontail and eastern cottontail likely to occupy sites with high and low amounts of overstory tree canopy cover in areas where the two species are sympatric? We believe that the results have direct implications for efforts to create habitat to conserve the New England cottontail and that the same approach can be applied to analyze the occupancy habitat use of other critical wildlife species
We modelled the occupancy of the two cottontail species at sites with different mean overstory tree canopy densities within 77 m using Maximum Entropy Modelling (MaxEnt) Version 3.3.3k, which is designed for modeling species geographic distributions with presence-only data [26] and produces a number of outputs useful for our analysis including (a) an area under the receiver operating curve (AUC) for both the training and test data, (b) the significance of the prediction using a binomial test of omission, and (c) a response curve that shows how the predicted suitability relates to changes in an environmental variable
Summary
Conservation of the New England cottontail (Sylvilagus transitionalis) is a high priority in the Northeastern United States (US). A number of factors have contributed to the decline of the New England cottontail, including competition with eastern cottontail (S. floridanus), which was introduced from the Southern and Midwestern US to supplement cottontail populations for hunting between 1920 and 1960 [1, 3, 4]. The loss of early successional habitat and habitat fragmentation are generally considered to be the most important reasons for the decline of New England cottontail [8, 9]. A recent study in the state of Rhode Island estimated that the extent of upland shrubland forests in non-coastal areas was declining by at least 1.5% per year and that the average patch size was just 1.2 ha [13]
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