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Swamp Rabbit Research in the Cache

June 2016 Interview on Swamp Rabbit Research

Liz Hillard, PhD Student and Research Assistant

Forestry Department, Southern Illinois University at Carbondale

What are the unique characteristics of swamp rabbits?

Swamp rabbits (Sylvilagus aquaticus) and the more familiar eastern cottontail (Sylvilagus floridanus) are both “cottontail” rabbits that belong in the genus Sylvilagus. Physically they appear very similar. However, swamp rabbits have a few physical characteristics that differ. Weighing approximately five pounds, they are the largest of the cottontail species, usually twice as large as eastern cottontails. Swamp rabbits also have a cinnamon-colored ring around the eye, and a darker, more rusty brown or black dorsal surface. The big differences between these two species are their ranges and habitat needs. Eastern cottontails are common, inhabit upland open grassy areas, and are distributed throughout the astern and midwestern United States. The swamp rabbit is specific to bottomland hardwood forests (BLH) and distributed from the Gulf of Mexico, northward along the Mississippi River to Illinois and Indiana, eastward to the western piedmont of South Carolina and westward to east Texas and Oklahoma. Southern Illinois lies at the northern extent of their range. Anecdotally, when I’ve trapped and handled both species on the interface of their habitats, swamp rabbits fight fiercely and often vocalize, whereas eastern cottontails remain docile.

Where do swamp rabbits live?

Swamp rabbits inhabit many community types within bottomland hardwood forests, including cypress swamps, canebrakes, wetlands and floodplain/riparian areas. They benefit from large, contiguous patches of bottomland hardwood forest that contain ground cover for concealment from predators. They utilize both young BLH stands that contain a dense understory of tree seedlings and saplings, woody vines, shrubs and herbaceous vegetation, and mature BLH stands that have scattered patches of thick understory growth created by canopy gaps.

Being in close proximity to water is very important for swamp rabbits. They use water as an escape cover from predators and are considered semi-aquatic. The flooding this winter season (2016) allowed me multiple opportunities to observe these animals swimming. They are impressive swimmers, often crossing torrential and fast flowing streams quickly!

How common are swamp rabbits in the Cache region, and what role do they play in the local ecosystem?

The Cache is a stronghold for swamp rabbits at the northern extent of their range. Wherever the above habitat characteristics exist in the Cache, swamp rabbits are abundant. They are important prey in BLH forests and in maintaining the BLH foodweb. Their role as consumers of plants allows the transfer of energy to high trophic levels (predators) such as bobcats, coyotes and owls. Swamp rabbits during my study have been depredated by bobcats, coyotes, and mink.

Are swamp rabbits an endangered species?

Of the 10 million hectares of BLH forests that once existed in the Lower Mississippi Alluvial Valley (LMAV), only two million hectares remain. In Illinois, we’ve seen a 98% loss of BLH forests. Swamp rabbits are not endangered; however, their populations have declined rangewide due to habitat loss and fragmentation of BLH forests. In the northern extent of their range, numbers are low and they exist as metapopulations with limited dispersal. In the core areas of their range (South Carolina, Arkansas, Louisiana), swamp rabbits are abundant. Due to the importance of BLH forest habitat, large afforestation efforts have been taking place in LMAV in the last 25 years.

What aspects of swamp rabbits have you been studying, and what are your key findings?

In the last two decades, reforestation of BLH forests has been implemented within the LMAV to support a wide range of ecosystem services, especially wildlife habitat enhancement. As afforested stands mature, managers are unsure how these will relate to habitat requirements of key species. To better understand how habitats and landscape features associated with forest stands affect swamp rabbit ecology, our objectives are to model resource selection functions and survival probability of swamp rabbits in a contiguous BLH forest that contains a mosaic of mature, afforested, and regenerating forest stands within the Cypress Creek National Wildlife Refuge.

A systematic grid of 769 plots within Cypress Creek continues to be monitored for swamp rabbit fecal pellets, and 62 individual swamp rabbits were captured and 46 radiocollared from December to March, 2014 to 2016. In the initial 2013 to 2014 pellet survey, comparisons showed that the expected number of swamp rabbit fecal pellets in forest stand classes differed significantly from their occurrence within the study area. Regenerating stands were selected in greater proportion to their available area, while afforested stands were selected less than their available area. My research collaborators at the SIU Forestry Department, Dr. John Groninger and Dr. Clay Nielsen, and I will model habitat use and survivorship with a suite of covariates including tree density, average basal area, vertical and horizontal stand structures, and forest patch and landscape contiguity metrics.

Because swamp rabbits are a specialist species that evolved within BLH forest ecosystems, they can be sensitive to the composition, structure and function of the ecosystem in relation to the system's natural or historical range of variation, and thereby serve as indicators of ecosystem integrity and a tool to guide management objectives. Our findings will facilitate an understanding of habitat values associated with different stand ages and structures as a framework that provides an intermediate scale to guide habitat-based management objectives within BLH forest landscapes.

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