Small mammal live-trapping research: 2006 update

by Elizabeth Wallace, WildMetro Intern

During the summer of 2006, WildMetro staff and volunteers worked together to conduct 10 different live-trapping surveys at 4 sites in the greater New York area. We focused on sites that were rural or suburban to complement our earlier research which targeted more urban parks. Sites included the Marshlands Conservancy (a Westchester County Parks Department wildlife sanctuary), the Huyck Preserve, Ward Pound Ridge Reservation and Great Swamp National Wildlife Refuge. This research was led by WildMetro Research Director Stefan Ekernas, Research Coordinator Katherine Mertes, President David Burg, Intern Emily Kaplan, and a large number of additional devoted staff and volunteers.

These survey sites varied in size from 69 ha at the Marshlands Conservancy to 2,429 ha at the Great Swamp N.R.W. The Marshlands Conservancy site, located near Rye in Westchester County, has a diverse array of habitats that include forests, meadows and wetlands. Our small mammal surveys targeted forest and meadow habitat. Likewise, surveys at the Huyck Preserve in Rensselaerville, south-west of Albany, NY, at the Ward Pound Ridge Reservation, and at Great Swamp N.W.R. were conducted in and meadow habitat.

WildMetro conducted small mammal surveys using live trapping mark-recapture methods. We placed Sherman traps across a 1 hectare grid with traps set at 15m intervals, for a total of 49 traps per hectare, to facilitate the capture and identification of small mammal residents of each site. The most frequently captured species was the white-footed mouse (Peromyscus leucopus). Although they were most abundant in forested habitats, white-footed mice were also found in meadows, though at lower densities. The abundance of white-footed mice was substantially higher than that of eastern chipmunks and meadow jumping mice (see Figure 1 to right for data from forested habitat at the Huyck Preserve). White-footed mice made up 90% of the captures at this site, and were typically the most abundant species captured at each of the forested study sites.

Meadows generally presented a greater diversity of small mammals than forested habitats. At these sites, we captured meadow voles (Microtus pennsylvanicus), northern short-tailed shrews (Blarina brevicauda), meadow jumping mice (Zapus hudsonicus), and eastern chipmunks (Tamias striatus). These species were all found in the meadow habitat at Ward Pound Ridge, where white-footed mice were absent (Figure 2, also to right). In addition to supporting a more diverse community of small mammals, the relative abundances of each species were also more even in meadow than in forested habitat.

The data gathered from these surveys enhances our understanding of the status of small mammal populations along an urbanization gradient. We found that some species, such as the white-footed mouse, span the urbanization gradient. These generalist species can persist in areas of dense human populations and significant landscape alteration. Other species, such as meadow jumping mice, are more sensitive to increasing urbanization, and are consequently only found in more remote regions, such as suburban or rural protected areas. These surveys are an important contribution towards building our knowledge on how urbanization impacts biodiversity.

Upcoming small mammal research:

In 2007, WildMetro will continue to conduct research in the New York metropolitan area to further understand changes in small mammal density, diversity and distribution in response to increasing urbanization. WildMetro will continue to conduct surveys along the entire urban-to-rural gradient, particularly focusing on protected areas that represent the suburban and rural components of the gradient. To this end, we hope to build on our research at the Huyck Preserve, and Ward Pound Ridge, and to incorporate additional rural sites. We will also survey mammal populations at a suite of new sites using a new survey method called track-tubing. This method consists of tracking animals by looking at species-specific footprints, and is an efficient way to expand our current knowledge of small mammal diversity and distribution. (For more information, see T. Shao’s report on WildMetro’s pilot studies at Marshlands Conservancy and the New York Botanical Gardens.) WildMetro also aims to use camera traps to assess patterns of distribution of larger mammals such as deer, raccoons, foxes, coyotes, weasels etc. Camera traps are cameras placed in a survey area and equipped with an infrared beam. The beam acts as a trigger, taking a picture whenever movement is detected, and the animal is caught on film. Digital images are stored and later downloaded onto computers for analysis.

Scientific research on the patterns of species density and diversity can provide important information that contributes to the management of protected areas. To this end, WildMetro plans to work directly with several parks in Westchester County to apply ecological research to adaptive management of the region’s natural resources. We will study the response of small mammal communities to different management strategies. For an example of an ongoing study on how invasive plant species removal affects small mammals, see T. Shao’s report on WildMetro research at Marshlands Conservancy.

Scientific research can also be a central component of environmental education. WildMetro hopes to expand our current work with local elementary and high schools to develop a research-oriented educational program. In this program, students would set track tubes near their schools in order to study small mammal populations. This would contribute to our growing data on the status of small mammals in urban areas, and would also encourage the involvement of people with their local environment, creating durable links between people and nature.

If funds permit, from 2007 to 2009, WildMetro will conduct a study across 15-20 protected areas spanning the gradient of urbanization, from rural to urban. We will focus on assessing the responses of mammals, birds, amphibians and plants to increasing urbanization. This research will help us identify potential thresholds of urbanization beyond which fauna and flora are critically impacted, and to determine whether different species respond similarly to urbanization.

Research supported by…

WildMetro research is supported by grants from the National Park Service, the Huyck Preserve, the Westchester County Parks Department, the NYC Department of Parks and Recreation, and the Jamaica Bay Institute. Grant support for future research initiatives is pending from EarthWatch, National Geographic, the Hudson River Foundation and the New York State Biodiversity Research Institute.