The Spatial Dynamics of Predator Evasion by Small Mammals in the Adirondacks

Elizabeth Speith

Introduction
The complex interactions that occur between predator and prey are some of the most dramatic, well-studied phenomena in ecology. This study seeks to examine the trends in predator avoidance by small mammals in 4 forest cover types in the central Adirondacks in an attempt to understand some of the variations in small mammal habitat usage.

The Predator
The eastern coyote, Canis latrans, has been a common resident of the Adirondacks since the 1950's, filling in the void left by the extirpation of wolves (Canis lupus) in the early 1900's. These upper level predators have evolved to fill the niche of the wolf in the Adirondacks, and are substantially larger than their southern counterparts, with males growing up to 50 pounds. The diet of the Adirondack coyote consists largely of deer (80-90% in the winter and 40-50% in the summer) and small mammals (15% year round, compared to up to 60% in central New York.)
The eastern coyote relies on a combination of visual, audial, and olfactory cues to capture prey. Mesic meadows and shrub-meadows provide optimal conditions for utilization of all of these senses, and consequently yield the highest predation rates (7.3 small mammal kills per hour compared to 2.2/hr. in grasslands, and 1.4/hr. in forest cover.)

The Prey
The eastern coyote will preferentially hunt for red squirrel (Tamiascuiris hudsonicus) over other small mammals, though like most top predators they will eat many others if presented the opportunity. The prey species analyzed here included the eastern chipmunk (Tamias striatus), red squirre,l red-backed vole (Clethrionomys gapperi), short-tail shrew (Blarina brevicauda), masked shrew (Sorex cinereus), pygmy shrew (Sorex hoyi), smoky shrew (Sorex fumeus), deer mouse (Peromyscus maniculatus), and the white footed mouse (Peromyscus leucopus). Due to the limitations of track recognition needed for analysis, certain species are combined for the purposes of this analysis: all Peromyscus spp. and Clethrionomys spp., and all of the Sorex spp. were combined into 2 separate groups. This results in the following small mammal categories: 1) eastern chipmunk, 2) red squirrel, 3) Peromyscus spp. / Clethrionomys spp., 4) Sorex spp., 5) short-tailed shrew.

The Interaction
The study area consisted of a forest/meadow ecotone at the Adirondack Ecological Center, Newcomb, NY in the central Adirondacks. This study site is typical of a mixed Northern hardwood-conifer forest type, and contained 4 cover types: (1) open canopy/open understory, (2) open canopy/dense understory, (3) closed tree canopy/dense, and (4) understory closed canopy/open understory.
Open-ended track tubes baited with peanut butter and oatmeal were employed in a 6x6 box grid encompassing 2500 m2. In this manner small mammal tracks were captured and species frequency, richness, and diversity were determined. The track tubes were utilized for 2 non-consecutive weeks to avoid familiarization by the study animals, resulting in 16 trap periods. Predator occurrence was simulated by the application of coyote urine uniformly along the edge of the forest/ field interface, replicating natural coyote territory marking. The first 8 trap periods acted as a control (pre-application of coyote urine.)
Total small mammal density was expected to decrease after the application of the coyote urine, reflecting decreased habitat utilization and increased secretive behavior by these animals in an attempt to avoid predator interactions. This effect was expected to be more pronounced in the open meadow (landscape type 1) and decrease in effect along a gradient of structure (Type 2 ®Type 3) to closed canopy/ dense under story (type 3).
Small mammal density, richness, and diversity were compared pre and post-application for the entire site, as well as between the 4 landscape types analyzed. The results were not as pronounced as expected (Figure 1, Figure 2.) The habitat type utilization did not significantly shift after the introduction of the predator scent, with the meadow and closed canopy/open under story areas used the most.
The mouse, vole, and red squirrel usage actually increased post-application across all cover types. The only decrease in activity was demonstrated by the eastern chipmunk. The Shannon-Weiner diversity indices were significantly different (p=.007) pre and post-application and reflect a slight reduction in post-application diversity.
Overall, the coyote urine appears to have had little effect on small mammal utilization of the site. This could be attributed to a few factors such as small sample size, the tendency to ignore olfactory cues as a significant signal of predator activity by the surveyed small mammals, or even a disregard of coyotes as a predator in this Adirondack setting. Introduction of audio (coyote vocalizations) or visual cues (coyote dummies) in conjunction with the usage of coyote scent may have yielded more noticeable results and may be worthwhile additions to studies of predator avoidance in small mammals.

About the The Author
Elizabeth Speith is a senior at SUNY-ESF, and has been involved with biodiversity research in the Adirondacks under the tutelage of Michale Glennon for 2 years.