Small Mammals in an Urban World: Updates from 2006

WildMetro has two updates for our research page. One is a report by intern Tiffany Shao on track-tubing to identify small mammal populations, and the other is a report by Elizabeth Wallace on the 2006 live-trapping of small mammals.

Tiffany Shao Report

Elizabeth Wallace Report


The influence of urbanization, patch size, and habitat type on small mammal communities in the New York Metropolitan Region

L.Stefan Ekernas and Katherine J. Mertes

Popular text abstract

In 2004, WildMetro originated and organized a study investigating small mammal distribution, abundance, and diversity in the New York Metropolitan Region to assess the influence of urbanization, patch size, and habitat type on small mammal communities. Small mammals are a useful model for studying wildlife in urban systems because they can influence vegetation composition, successional dynamics, and the presence and absence of other animals through competitive and trophic interactions.

Working in cooperation with the National Park Service, Friends of Marshlands, Black Rock Forest, and NYC Dept of Parks and Recreation, we conducted 24 small mammal surveys at 12 different urban, suburban, and rural sites between May 29, 2004 and November 15, 2005. We surveyed small mammal communities using capture-mark-recapture methods with arrays of 49 Sherman live traps deployed during 4-day (3-night) trapping periods in forest, salt marsh, shrubland, and grassland sites.

Our surveys revealed clear differences between small mammal communities in different habitat types, as P. leucopus and to a lesser degree B. brevicauda were most common in forests, P. leucopus was most common in shrublands, P. leucopus and M. pennsylvanicus were most common in grasslands, and M. pennsylvanicus and R. norvegicus were most common in salt marshes. P. leucopus was by the far the most abundant species in forests, grasslands, and shrublands, and the species was present at higher densities in sites with denser and more complex understory vegetation. Salt marshes had significantly higher small mammal diversity than all other habitats, and while densities of individual species varied widely between habitat types, overall small mammal density was not significantly different between any of the habitat types.

In forests, both deer density and patch size negatively correlated with small mammal density. Small urban patches are therefore likely to have substantially higher small mammal densities than large patches, but it is unclear whether such high densities are desirable from a conservation and human health perspective. Urbanization, patch size, and deer density did not significantly influence small mammal diversity in forests, indicating that small, urban green spaces can support small mammal communities mostly representative of the region as a whole. Our trapping protocol probably under-represented insectivorous species such as shrews, and our results may not be pertinent for these types of species (particularly those at low density). We will incorporate pitfall traps in future surveys to obtain more accurate data on these species.

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White-footed mouse (Peromyscus leucopus)

Meadow vole (Microtus pennsylvanicus)

Collecting data on small mammals