Sunday, October 21, 2012

Mammal Profile Vol. 2: The White-footed Mouse

For those who do small mammal surveys, it is never unusual to get a white-footed mouse (Peromyscus leucopus, "Mouse with White-Footed Boots"). Both the white-footed mouse and its close relative the deer mouse (Peromyscus maniculatus "Agile Mouse with Boots") are the most populous mammals in North America. So, while they might not be the most exotic species to capture, they certainly play an important role in ecosystems.

White-footed mice are skilled climbers, sometimes caching food or making nests in
tree hollows. Here, a mouse avoids be weighed by climbing the Pesola scale.

Interestingly, the white-footed mouse has not colonized many of the barrier islands off the Eastern Shore, with the exception of four islands (Assateague, Wallops, Cedar, and Fishermans; Moncreif and Dueser, 1994). While there is certainly great habitat for them, they have not been documented on any of the other islands. This is surprising, as P. leucopus has great homing abilities and has well documented swimming abilities. It could be that the intercoastal water conditions are too prohibitive.

There is no scientific merit to this picture, except that the mouse looks funny while
trying to bite the Pesola scale so that it can escape. Actually, wriggling and biting, besides their speed,
is their only defense once captured by predators.

White-footed mice have also have become a public issue these days. Whether it is because of a change in predators, climate, or habitat composition, white-footed mice have come under increasing attention due to the higher incidence of Lyme disease and hantavirus--both of which they are carriers of. Even though their higher densities equate to human health concerns, the mice play an important role in linking food webs, as they their omnivorous diets are transferred to larger predators like foxes, bobcats and raptors (many of whom consume large amounts of the rodents). Economically speaking, mice consume large numbers of seeds from weed plants as well as insects and generally avoid cultivated areas. Despite this, the wildlife disease consequences of their current success is a central facet of current research.

This species favors hardwood forests as well as the edges of forests and fields. On the shore, they are found in myrtle shrublands and marshes. While typically not hallmarked for their presence in coastal areas, they also seem to abound in drier mixed hardwood-pine forests.

Linzey, D.W. 1998. The Mammals of Virginia. The McDonald & Woodward Publishing Company: Blacksburg, VA.
Moncreif, N.D. and R.D. Dueser. 1994. Island Hoppers. Virginia Explorer 10(4): 14-19.
Webster, WM. D., J.F. Parnell, and W.C. Biggs, Jr. Mammals of the Carolinas, Virginia, and Maryland. The University of North Carolina Press: Chapel Hill, NC.

Saturday, October 6, 2012

Mammal Profile Vol. 1: The Least Shrew

Whum chakka um chakka chumchakka whum!
Guosim dig yore paddle deep,
Hurly-burly river wide'n'curly,
There's no time to sleep.
Whum chakka um chakka chumchakka whum!
Rapid wild and fast do go,
Hurly-burly river wide'n'curly,
Bend yore backs an' row.
Whum chakka um chakka chumchakka whum!
Keep her bows up in the foam,
Hurly-burly river wide'n'curly,
Logboat take us home.
Whum chakka um chakka chumchakka ...

-Paddling Song, Guerrilla Union of Shrews In Mossflower, Marlfox by Brian Jacques

I'm not sure if you have read any of the books in the Redwall series by Brian Jacques, but as the main characters are mostly small mammals, you can bet I will shamelessly make references to the series during these mammal profiles (If you haven't heard of the series, it is similar to Watership Down).

So far during our trapping endeavors, we have captured 5 different species of small mammals. One of my favorites, the least shrew (Cryptotis parva, Greek and Latin for "small hidden-ear" shrew), is the first animal I'm going to discuss. The least shrew is in the diverse and complicated order Insectivora (insect-eating and carnivorous mammals). Within that order, they are classified in the Soricidae (shrew) family, a group containing some of the smallest mammals. Characterized by their small eyes, pointed teeth, and long tapered snout, this species relies mostly on its sense of smell and hearing to move and locate prey.

Least shrews are very vocal, using clicks and squeaks to communicate.
In this case, they are mostly communicating, "Stop weighing me and let me go."

The mammals are very small, growing up to 92 mm in length--including tail--and weighing up to 5.7 grams, the weight of a nickel. Although small, they are voracious eaters and busy critters. They are almost always active and only have short periods of rest. Part of this arises from an incredible metabolism: having to eat 50% of their weight or more every 24 hours. The least shrew consumes large amounts of arthropods, worms, and other insects. For some insects that are too large to consume whole, the shrew will eat out the insides. They also are a food source for many other animals, including snakes, raptors, foxes, and skunks.

While the least shrew is often confused with members of the short-tailed shrew genus (Blarina), the least shrew is distinguishable by its tail, which is less than half the length of its body and head. Behaviorally, the least shrew also is rather social, as nests can have up to two dozen individuals. These nests are usually found near logs, rocks, and debris, and they are made out of shredded grass and leaves.

 Unfortunately, due to their energetics, it is not rare to have shrew mortality.
Sometimes the shrew cannot survive the time in the trap, but all possible measures are taken to avoid it.

The old-field habitat in which we surveyed and found the majority
of our least shrews.

The least shrew is mostly found in dry, open grasslands, but they also are found in saltwater marshes.  Typically, the Sherman live trap is not the best method to capture shrews, but we set the trap's trigger to close at a lighter weight.

Linzey, D.W. 1998. The Mammals of Virginia. The McDonald & Woodward Publishing Company: Blacksburg, VA.
Webster, WM. D., J.F. Parnell, and W.C. Biggs, Jr. Mammals of the Carolinas, Virginia, and Maryland. The University of  North Carolina Press: Chapel Hill, NC.
Schemnitz, S.D., 2005. Capturing and Handling Wild Animals. In C. Braun (Ed.).Techniques for Wildlife Investigations and  Management (pp.239-285). Sixth Edition. The Wildlife Society: Bethesda, MD.