Distribution Dynamics of Swamp Rabbits (Sylvilagus aquaticus) in Missouri

Author

Kylie Bosch, Southern Illinois University CarbondaleFollow

Date of Award

8-1-2024

Degree Name

Master of Science

Department

Forestry

First Advisor

Pease, Brent

Abstract

Swamp rabbits (Sylvilagus aquaticus) are a bottomland hardwood forest specialist undergoing contraction at the northern extent of their range. This decline is often attributed to the loss of bottomland hardwood forest and frequent, intense flooding. To mitigate this decline and inform decisions regarding the swamp rabbit’s conservation status, there is a pressing need for long-term monitoring efforts. Although currently listed as imperiled (S2) in Missouri, shifts in occupancy trends may warrant a reassessment of the swamp rabbit’s state rank. The Missouri Department of Conservation has conducted decadal surveys for swamp rabbits since 1991, and the work presented here describes the fourth iteration of this study – 2022-2023. Repeated latrine surveys at 176 previously surveyed sites were conducted from November 2022 – April 2023 across 16 counties in southeast Missouri. Dynamic occupancy models were then used to estimate occupancy, colonization, extinction, and detection probabilities and identify environmental factors driving distribution changes since 2012. Additionally, I examined the impact of including ground latrines in swamp rabbit detection histories for the 2022-2023 survey season in a comparative single-season occupancy analysis. This analysis aimed to evaluate how the incorporation of ground latrines, as opposed to restricting detections to latrines on elevated surfaces, influenced estimates of occupancy and detection probabilities. Swamp rabbits were detected at 148 sites in 15 counties in 2022-2023, with a noted increase in occupancy probability from 0.66 (SE = 0.01) in 2010-2012 to 0.79 (SE = 0.01) in 2022-2023. As expected, site isolation negatively impacted occupancy probability, but predictors for patch richness density, site area, flood frequency, and flood severity had varying levels of support. For example, occupancy probability was negatively influenced by patch richness density but positively influenced by site area, while colonization probabilities were high and positively influenced by both flood frequency and severity. Extinction probability was low but was negatively influenced by flood frequency. Models with occupancy, colonization, and extinction as a function of the proportion of bottomland hardwood forest at a site were not supported. Detection probability decreased from 0.90 (SE = 0.19) in 2010-2012 to 0.78 (SE = 0.13) in 2022-2023. The inclusion of ground latrines in analyses did increase detection (0.68 to 0.84) and estimates of occupancy probabilities (0.95 to 1.00) but the change in estimates of occurrence was not biologically meaningful. Despite concerns about decline at the northern edge of their range, swamp rabbit populations in southeast Missouri appear to be expanding, evidenced by the increased occupancy and promising colonization and extinction rates. While long-term monitoring efforts should continue, managers should consider changing the swamp rabbit’s state rank from imperiled (S2) to vulnerable (S3).