A Natural History of Millbrook Marsh,
A Wetland In An Urbanizing Setting


As with birds, relatively few mammals are considered to be wetland specialists (Fritzell 1988). The obligate wetland species of Pennsylvania that are expected to occur in this area include the Star-nosed Mole (Condylura cristata), the Water Shrew (Sorex palustris), the Muskrat (Ondatra zibethicus), and Mink (Mustela vison), as well as Beaver (Castor canadensis), and Otter (Lutra canadensis) (PennDOT 1981). Aside from the few wetland obligates, or wetland-dependent mammals, there are others, facultative wetland species, that benefit from the wetland habitat because of increased food and cover availability. Numerous small mammals are facultative wetland species in Pennsylvania, including 8 species of shrews, 11 bats, and 6 rodents (vole, lemming, and mouse species) (Kirkland and Serfass 1989, Serfass and Brooks in press). Those that are expected to occur in north central Pennsylvania are the Big Brown Bat (Eptesicus fuscus), Hoary Bat (Lasiurus cinereus), Indiana Bat (Myotis sodalis), Little Brown Bat (Myotis lucifugus), Pygmy Bat or Eastern Pipistrelle (Pipistellus subflavus), Red Bat (Lasiurus borealis), Silver-haired Bat (Lasionycteris noctivagans), Eastern Cottontail (Sylvilagus floridanus), Snowshoe Hare (Lepus americanus), Meadow Jumping Mouse (Zapus hudsonius), and Woodland Jumping Mouse (Napaeozapus insignis) (PennDOT 1981).

Millbrook Marsh may not be the preferred habitat for some of these obligate or facultative wetland species due to its size and proximity to human development. Habitat requirements for many of them are met, though, and some will probably be found in subsequent inventories. Of the 4 small mammals captured at Millbrook Marsh by Urban (1993), only the Meadow Vole (Microtus pennsylvanicus), is a facultative species. A study of the Muskrat, a wetland obligate species, on Spring Creek (Smith 1954) found Muskrats using the cattail-sedge marsh above the confluence with Slab Cabin Run and Willow (Thompson) Run. There have been 1 facultative, 1 facultative wet and 3 obligate wetland mammals observed in Millbrook Marsh from 1993 to 1998 (Table 6-15) (Brooks et al. 1998).

Only one relatively recent formal study has focused on mammals in Millbrook Marsh. A small mammal inventory occurred in November 1993 using Sherman live box traps, peanut butter and bird seed (Urban 1993). The species diversity was very low in two areas of the marsh, but this could be due to using only one trap type, trapping in only two areas, and at only one time during the year. One of the two study areas was in Millbrook located in the scrub-shrub wetland between Slab Cabin Run and the Mt. Nittany Expressway, where the White-footed mouse, Deer mouse, and Short-tailed shrew were found (Table 6-15). The restored wetland on the east side of Route 322, no longer contiguous to Millbrook Marsh, was the second site. In this area the same small mammals were found with the addition of the meadow vole. Though the meadow vole was not trapped on the Millbrook Marsh side of Route 322, it has been visually observed in Millbrook (R. Brooks, pers. comm.).

Table 6-15
1993-1998 Millbrook Marsh Mammal Inventory, Species or Sign of Mammals Observed (*Urban 1993)

Scientific Name Common Name
Blarina brevicauda* Short-tailed shrew
++Castor canadensis Beaver
++Condylura cristata Star-nosed mole
Marmota monax Eastern woodchuck
Å Microtus pennsylvanicus* Meadow vole
++Mustela vison Mink
Odocoileus virginianus White-tailed deer
++Ondatra zibethicus Muskrat
Peromyscus leucopus* White footed mouse
Peromyscus maniculatus* Deer mouse
+ Procyon lotor Raccoon
Sciurus carolinensis Eastern gray squirrel
Sylvilagus floridanus Eastern cottontail

Species Richness = 13

Å = facultative species
+ = facultative wetland species
++ = obligate wetland species

On to Fauna Discussion