EIU-BioSci poster 057

Seasonal home ranges, habitat use and fractal dimensions of raccoon movement pathways

Roberta Newbury and Tom Nelson
Department of Biological Sciences, Eastern Illinois University

Introduction

One of the reasons why biologists and managers are interested in the raccoon is that raccoons are one of the most common nest predators of ground-nesting birds inhabiting agricultural landscapes in the Midwest. High rates of nest predation result from habitat fragmentation and the creation of edge areas that characterize agricultural land. Agricultural edges provide abundant and diverse food resources for raccoons. Previous research suggested that raccoons may prefer foraging along edges, increasing the risk to birds nesting there.

However, some biologists speculate that most nest predation occurs incidentally as raccoons forage for other food along edges or when they move between rich resource patches such as wetlands. Grassland patches in a row-crop matrix may serve as ecological traps or population sinks for nesting birds if high predator densities contribute to extensive nest predation in these areas. Therefore, management plans designed to conserve edge-sensitive species require reliable information on the relative abundance, habitat use and foraging behaviors of the potential nest predators in a given landscape.

Research Questions

Do home ranges differ in size between sexes and among seasons?
Are there seasonal shifts in the use of core areas?
How do raccoons move through an agricultural landscape?
Can fractal analysis be a useful tool for interpreting movement paths in raccoons?

Methods

Study Area. Prairie Ridge State Natural Area, Jasper County, IL

Capture and handling. Raccoons were live-trapped and anesthetized with Telazol^®. Each captured animal was sexed, weighed, aged and ear-tagged.

Telemetry. Selected animals were radio-collared and located at least weekly. Focal animals were tracked during continuous 12-hour periods (6 PM to 6 AM). Locations were recorded every 30 minutes.

Basemap. Major habitat cover types were digitized with ArcView 3.3.

Home Ranges. 95% kernel home ranges calculated in hectares (ha) using ArcView 3.3 with the Animal Movements Extension using a minimum of twenty locations.

Fractal Analysis. Fractal dimensions of movement pathways were computed with the Fractal Mean Estimator and log-transformed. Fractal dimensions were compared to determine differences between sexes and seasons using the Mann-Whitney Test (α = 0.05).

Results

Do home ranges differ in size between sexes and among seasons? Males had significantly larger overall 95% kernel home ranges than females (p=0.03). Additionally, male raccoons had significantly larger winter (p=0.05) and spring (p=0.03) home ranges than female raccoons (Table 1).

	Table 1. Overall and seasonal 95% kernel home ranges for male and female raccoons at Prairie Ridge State Natural Area using Mann-Whitney Test between sexes (p=0.05).

Are there seasonal shifts in the use of core areas? There appeared to be shifts in the use of core areas on a seasonal basis (Figure 1). Further compositional analysis will supply information as to what habitat types raccoons are keying in to on a seasonal basis.

	Figure 1. Spring and winter seasonal 95% and 50% kernel home ranges for F345. The spring home range (31.3 ha) is located on the left side of the figure in blue along a riparian area. The winter home range of this individual (18.0 ha) is on the right side of the figure in pink and occurred primarily in residential habitat types.

How do raccoons move through an agricultural landscape? Males (n=13) had an average D=1.25 ± 0.03, while females (n=13) had an average D=1.30 ± 0.04. There were no significant differences in the fractal dimension of movement pathways between sexes (p=0.555). There were significant differences in the shape of movement pathways among seasons (p=0.027) (Table 2). Spring and summer pathways were more linear while fall and winter movements were more convoluted.

	Table 2. Seasonal fractal dimension of movement pathways of raccoons showing that seasonal movements were significantly different (p=0.027). Spring and summer movements were more linear as raccoons moved between rich resource patches and became more convoluted as raccoons searched for scarce resources.

Can fractal analysis be a useful tool for interpreting movement paths in raccoons? Yes, fractal analysis allows us to interpret the shape of movement pathways on a seasonal basis. In the spring and summer raccoons tended to follow linear pathways and move rapidly across grassland habitats. Winter and fall movement pathways became more convoluted, indicating searching behavior during these seasons, primarily in residential and agricultural habitats (Figure 2).

	Figure 2. (a) shows a spring pathway with D=1.12, with quick, linear movements across grassland habitats, while (b) shows a fall pathway with D=1.35, characteristic of the convoluted, searching behaviors typical of fall and winter raccoon foraging pathways.

Conclusions

Males had larger home ranges than females.

Seasonal home range size differed by sex. Spring and winter ranges showed the greatest divergence.

Core areas showed pronounced shifts centered around water in spring and summer, agricultural fields in the fall and buildings in the winter.

Males and females moved in similar ways but foraging paths differed between seasons.

Raccoons followed linear paths in the spring and early summer as they moved from dens to rich resource patches. Foraging paths were more convoluted in fall and winter as raccoons searched for scarce food.

This research supports the hypothesis that raccoons are more likely to predate nests while moving between resource patches rather than by actively searching fields for nests.

Acknowledgements

I would like to thank the Illinois Department of Natural Resources, particularly Scott Simpson and Terry Esker for the use of Prairie Ridge State Natural Area. Additionally, my thanks to Eastern Illinois University for research support and funding. I am most grateful to Meghan Tibbs, Tim Buhnerkempe, and Christy Griffith for their field assistance. And last but not least, many thanks to fellow grad students Randy Havens and Kathryn Yurkonis for all of their help in the field!