The permeability of surrounding landcover types can influence the probability of animals leaving a patch and dispersing across the unsuitable matrix. The marsh rice rat (Oryzomys palustris) persists in wetlands that are often isolated by upland cover types. The goal was to quantify the permeability of three landcover types (grassland, agriculture, and forest) and calculate the landcover composition of home ranges for a population of rice rats in southern Illinois. Between March 2011 and January 2012, I trapped rice rats up to 95 m from wetlands into unsuitable cover and simultaneously followed individuals via radiotelemetry. I calculated the slope of capture rate (log-transformed) vs. distance from wetland as an inverse measure of permeability and also measured inundation, rice rat abundance, and matrix vegetation density as potential covariates explaining matrix use. I calculated mean home range size for males with the fixed kernel density method and compared landcover within home ranges to what was available in the surrounding landscape. Using generalized linear mixed models, I compared matrix capture rates and permeability levels among cover types, inundation, abundance, and vegetation density. After 13,610 trap-nights, I captured 43 rice rats in the matrix between March and September, with 24 in agriculture, 10 in grassland, and 9 in forest. I did not find permeability differed between landcover types, but did find that rice rats were captured further and more frequently in agriculture than grassland and forest cover. Both population abundance in wetlands and vegetation density < 0.5 m high had positive effects on matrix captures, while lowering water levels increased the permeability of the surrounding matrix. After radio-tracking 25 rice rats, home ranges were 3.01 ±0.57 ha and were the largest for individuals followed in early summer. Emergent vegetation was used proportionally more than would have been expected at random, indicating rice rats preferred emergent wetlands habitat at the home-range level. This study suggests that rice rats are more vagile and move through upland cover types more frequently than previously described in the literature.

The marsh rice rat (Oryzomys palustris) is a semi-aquatic rodent classified as state-threatened in Illinois due to historical wetland loss coupled with being on the northern periphery of its range. The most recent survey for this species in Illinois occurred in 1988, and this study reassessed its status and distribution. From 2007 to 2009, I used live traps to sample for rice rats at previously occupied and random wetland-dominated sites in 5 southern Illinois watersheds. I captured 132 individual rice rats 192 times in 13,248 trap nights. Capture success was 15.10 captures/1,000 trap nights. I detected rice rats within 3 of 5 watersheds, 16 of 48 sites, and 5 new locations. Most rice rats were captured in permanent or semi-permanent emergent wetlands and rice rat occurrence was strongly related with coal mine-associated wetlands. I collected microhabitat measurements at 10% of trap locations and recorded landcover types within and around sites. I analyzed data using t-tests, logistic regression, and occupancy modeling. Percent herbaceous cover and percent visual obstruction (0.0-0.5m) positively influenced rice rat occurrence and were among the most important microhabitat models. The best model in the candidate set of landcover variables included proportion of upland grass in areas surrounding wetlands as a predictor of rice rat occurrence. I believe insufficient evidence exists to warrant removal of the threatened status of the marsh rice rat. However, current management practices, such as wetland restoration, grassland restoration, and mowing of roadside ditches, likely benefit rice rat populations. Slight modification of these management activities may facilitate the eventual delisting of marsh rice rats.