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

Chapter 6


Wetlands support myriad wildlife species, with amphibians and reptiles heavily dependent upon them, and many species of birds and mammals also making use of the wetland for feeding and breeding. Wetlands offer habitat for waterfowl, migratory and other bird species including songbirds and raptors, especially those that eat fish and insects. In Pennsylvania, about 49 % of mammals, 60 % of birds, 59% of reptiles and 100% of amphibians are dependent on wetlands, streams and riparian zones at least partially (Brooks and Croonquist 1990). There are 70 species of endangered and threatened birds in the United States of which 31% are wetland species (Rymon 1989). In Pennsylvania, 48% of all special concern species are associated with wetlands, and 40% of them are wetland specific (Clark and Klem 1986). Of the 13 species of turtles found in Pennsylvania, 12 of them use wetlands at some stage in life (Brooks and Croonquist 1990). Nine are obligate species and 3 are facultative wet species. There are also obligate and facultative wetland species of mammals. Pennsylvania has, for example, 11 bat species, all of which benefit from the concentration of flying insects over water. Ten of them are facultative species (Brooks and Croonquist 1990).

The vegetation and cover types of the wetland often define the habitat a particular species requires, but area is also one of the limiting factors. One example of wetland area relating to wildlife species is a study of wetland birds in Iowa (Nekola 1994). About 100 ha in Northern Iowa has been sufficient for an isolated wetland in maintaining typical wildlife fauna. Another Iowa wetland, only 55 ha, also supports almost typical bird species, although there is a 110 ha lake and another marsh nearby. Other examples are two studies by Watts in the Lower Chesapeake Bay (Watts 1992, 1993). Observations of 105 species were made in saltwater marshes of 0.1 ha to more than 100 ha. Less than 15% of the species were observed in marshes of 0.1 ha. In 1.0 ha marshes, over 28% of the species were found, and in 5.0 and 10.0 ha marshes, more than 60% of the species were observed. In the control marshes, larger than 65 ha, over 90% of the species were detected. Greater species richness was found in larger marshes (Watts 1992). The majority of obligate wetland bird species are most likely supported by marshes between 5 and 50 ha, a relatively rare size, as the more common size is between 1 and 5 ha (Watts 1993). Besides size, habitat diversity does also lead to species richness (Weller 1978, Cashen 1998). Millbrook Marsh, being 36 ha, with diversity of habitats including riparian areas, emergent wetland, calcareous fen, scrub shrub wetland, and upland with some mature trees, has potential for supporting a relatively large number of wetland species.

The fauna of Millbrook Marsh has been only partially investigated up to this point. There have been several inventories, formal and informal, resulting in the somewhat limited species lists. According to the PennDOT study (1980), the potential habitat requirements of over 122 species of mammals, amphibians, reptiles and birds are met. Millbrook Marsh consists of a wide variety of aquatic ecosystems and is, therefore, capable of supporting a wide variety of aquatic and amphibious life, in addition to those animals higher up in the food web. The riparian zones include forested and unforested areas, instream riffles and pools. The marsh consists of various levels of moisture, from seasonal flooding and ponding, to permanent saturation. Variable types and amounts of cover include emergent areas with mainly wetland grasses, shrub wetlands, fen, and forested areas. This area with a variety of habitats is ideal for many reptiles and amphibians. Inventories of Millbrook Marsh amphibians and reptiles are limited and more work needs to be done. Historical data is more prevalent, although not extensive, for fish and invertebrates due to the importance of Slab Cabin Run and Thompson Run as tributaries to Spring Creek.

On to Invertebrates