4.1 Spatial overlap and habitat suitability
From our study, we found the importance of young forest and shrublands for cottontail habitat suitability largely reflects what is known about the habitat associations of the two species in the northeastern United States. Both species’ suitable habitat was influenced by the presence of young forests, shrublands, and understory (Cheeseman et al. 2018, 2019a , 2021, Bischoff et al. 2023a , b ). Specifically, proximity to shrublands increased New England cottontail habitat suitability, which increased New England cottontail occupancy and colonization at the landscape scale (Bischoff et al. 2023a ) and abundance at the patch level (Bischoff et al. 2023b ). However, we found not only is the proximity to these vegetation types influential to New England cottontail habitat suitability, but the spatial arrangement of these vegetation types contributed most to habitat suitability for New England cottontail. Specifically, patches of mature forest without understory components within complexes of young forest, shrubland, and mature forest with understory components increased New England cottontail habitat suitability the most. This agrees with many studies that have demonstrated the importance of high vegetation height and canopy closure for New England cottontail, especially in patches co-occupied by eastern cottontail (Buffum et al. 2015, O’Connor 2015, Cheeseman et al. 2018, 2019a , 2021, Bischoff et al. 2023b , a ) and a recent study that found New England cottontail increased the proportion of their home range that included vegetation management areas if some canopy was retained (Eline et al. 2023b ). Because of these findings, guidance for New England cottontail habitat management suggests utilizing shelterwood cuts and leaving residual trees to maintain vegetation height and some canopy closure (Cheeseman and Cohen 2019). Our study supports these recommendations but adds that residual trees clumped in small patches within young forest and shrubland habitat may enhance existing patches and create new patches suitable for New England cottontail.
Despite the benefits of habitat management to New England cottontail, focusing on vegetation management alone will likely not be enough to discourage eastern cottontail populations. We found that eastern cottontail habitat suitability with New England cottontail was high regardless of spatial arrangement of habitat and the distance to young forest, shrubland, and understory habitat. Higher vegetation height was found to decrease eastern cottontail survival and occupancy in several other studies (Buffum et al. 2015, O’Connor 2015, Cheeseman et al. 2018, 2019a , 2021, Bischoff et al. 2023b , a ). However, this association did not translate into measurable differences in suitable habitat between the two species. Thus, vegetation management within strategic areas is still crucial for New England cottontail management to establish connectivity between populations (Ferry 2023) but may need to be coupled with population augmentation or translocation to sustain New England cottontail populations (Bauer et al. 2020). Other states have found coupling habitat connectivity and population augmentation to be a successful strategy for maintaining New England cottontail populations (Bauer et al. 2020). Another potential management action is removal of eastern cottontail to limit or reduce the expansion of the species in suitable New England cottontail habitat. Removal of eastern cottontail was tested at a few patches in Connecticut but was not effective in reducing eastern cottontail abundance (Kilpatrick n.d., unpublished data). Removal of invasive mammalian species has long been a management practice for problematic species, and has largely been successful, but the success depends on the predator response to species removal (Norbury 2001), consistent effort of the program, and controlling large areas (Robertson et al. 2017). The removal of eastern cottontail would contain many complexities and considerations. Eastern cottontail has been present in the northeastern US for over 100 years (Johnston 1972) and has successfully expanded across most of the region. Additionally, the mechanism for removal may be difficult because cottontail hunting is not common in the state and cottontail trapping success is relatively low (Cheeseman et al. 2021). Furthermore, New England and eastern cottontail can only be differentiated confidently through genetic analysis, which requires large amounts of time and resources. Despite these challenges, strategic removal of eastern cottontail in newly managed areas for New England cottontail may offer New England cottontail the advantage of colonizing habitat before eastern cottontail.
Predicting New England cottontail suitable habitat across the state is crucial for planning New England cottontail conservation, management, and monitoring for the future. Some of these highly suitable areas for New England cottontail have not been sampled in recent years, thus areas of highly suitable New England cottontail habitat with limited occurrence data provide opportunities for identifying new populations, locations for eastern cottontail removal, and potential sites for habitat enhancement or New England cottontail reintroductions. The maps of suitable habitat also allow further direction for managing New England cottontail in the two regions of Connecticut where New England cottontail is extant, the eastern and western portion of the state. Differences in New England and eastern cottontail populations in eastern and western Connecticut have been found in other studies (Kristensen and Kovach 2018, Bischoff et al. 2023b ). Specifically, the low habitat suitability for New England cottontail and generally high habitat suitability for eastern cottontail in eastern Connecticut is evidence that explains the decline in New England cottontail relative abundance observed in the eastern portion of the state over the past few years (Bischoff et al. 2023b ). Identifying new areas suitable for New England cottontail in the region of the state where New England cottontail occupancy is not declining will provide enhanced opportunities for management and possibly provide more connections between isolated patches currently occupied by New England cottontail. We argue that additional conservation actions, including augmentation and translocation of New England cottontail, vegetation management to establish, enhance, or maintain inter-mixed habitats, and consideration of eastern cottontail removal, may be needed to benefit New England cottontail.