The Co-existence of the Rice Rat (Orzomys palustris) and the Florida Muskrat (Neofiber alleni)

Water-loving rodents of many different sizes abounded in Pleistocene marshes and swamps.  It’s likely man overhunted giant beavers (Castoroides ohioensis) and capybaras (Hydrochoreus and Neochoreus) into extinction, but several medium and small species remain.  Beavers (Castor canadensis) and muskrats (Ondatra zibethicus) are still common throughout the southeast, except in Florida where both are completely absent.  However, the presence of round-tailed or Florida muskrats (Neofiber alleni) proves that an aquatic rodent can survive in environments that host significant numbers of alligators. 

The Pleistocene range of the Florida muskrat is a curious example of Ice Age mammal distributions and how they differed from those of the present.  Today, the round-tailed muskrat is restricted to Florida, but during warm climate phases, they use to have a range that extended north.

Datei:Neofiber alleni distribution map.svg

Range map of the Florida muskrat.  During warm climatic phases of the Pleistocene, it was more widespread living as far north as Pennsylvania and Kansas where it shared the range with common muskrats (Ondatra).

Fossils of Florida muskrats were among those excavated from Ladds stone quarry in northwest Georgia.  These likely date to the Sangamonian Interglacial.  Their fossils have also been found in Texas, Kansas, and Pennsylvania and in many of these fossil sites their bones were associated with common muskrat (Ondatra) bones.  This is evidence that the 2 species of muskrats used to co-exist but presently they do not.  Because Florida muskrats are thought to be maladapted to cold climates, they must have only co-occurred with Ondatra zibethicus during extremly warm interglacials when winters were warmer than those of today. 

Florida or round-tailed muskrat (Neofiber alleni)

Round-tailed muskrat nest in Putnam County, Florida.  Photo by Alan Cressler.

Florida muskrats still share habitat with another aquatic rodent–the rice rat (Orzomys palustris).  The latter, though restricted to the south, is more widespread.

Rice rat range map

Rice rat (Orzomys palustris)

The rice rat feeds upon many of the same foods and utilizes Florida muskrat runways and feeding platforms.  They even occasionally build their nests on the roofs of muskrat nests.  Muskrat nests generaly consist of 12-25 inch grass mounds that are accessed by 2 tunnels saturated with groundwater.  Rice rats construct globular nests 6-18 inches in diameter and are located about 6 inches above the flood line.  The preferred habitat of both is a grassy marsh where bamboo cane, sawgrass, cattails, arrowhead, and pickerel weed grow.  Rice rats are omnivorous, feeding on succulent plants, mushrooms, seeds including those of iris and rice, insects, fiddler crabs, snails, fish, and carrion.  Florida muskrats are more vegetarian, eating mainly the stems of water plants and the roots of ferns, but Frances Harper reported that they ate crayfish as well.  Unlike muskrats, rice rats are not specifically adapted to aquatic life–they do not have waterproof fur and webbed toes and they can live in grassy meadows away from water.  But they are good swimmers and divers.

Florida muskrats are members of the vole family.  Most voles are small mouse-sized rodents, and muskrats are just big overgrown voles.  Florida muskrats are gregarious and share feeding platforms with other muskrats.  This behavior is not like that of other vole species including Ondatra which are territorial.  Rice rats are distantly related to white-footed or field mice.  Only 1 species of rice rat lives in North America, but many more occur in South America.  The North American species probably is descended from rodents that colonized the continent when a landbridge formed between the two.

I’ve never seen a rice rat, but I have seen common muskrats (Ondatra) quite often in and around Augusta, Georgia.  I took a boat ride on the Augusta canal a few years ago and saw a score of them.  I see their sign in Woodbridge Lake in Evans, and once I witnessed a hawk carrying a muskrat away.  I’ve seen a Florida muskrat on 1 occasion.  When I was about 10 years old, my grandparents lived on a canal in Inverness, Florida.  As I walked along the bank of the canal in the morning, a round-tailed muskrat swam along beside me and barked at me the whole time.

Frances Harper surveyed the Okefenokee Swamp circa 1920.  He estimated 10,000 Florida muskrats inhabited the swamp but none lived north of it.  However, fossil remains of Florida muskrats, dating to the Boling-Alerod interstadial (~14,000 BP) were found at Clarks Quarry, near Brunswick, which is slightly north of their modern day range limit.  Curiously, their fossils were found with woodchuck fossils (along with mammoth, long-horned bison, etc.).  The climate must have suddenly become much warmer, because woodchucks (which are a cool climate species) were still present in the region, though eventually they would disappear here.  It may be that the Boling-Alerod interstadial was a climate phase with warm winters but cool summers, so both species of rodent were able to live in the same geographic range.

George Leonard Herter writes in his classic Bull Cook and Authentic Recipes and Practices that muskrat is a delicious animal formerly popular to eat among pioneers of Swedish descent who settled in Minnesota.  His method of cooking muskrat was to a) remove the fat, b) boil the hind legs and hams for about an hour, c) season with salt, pepper, and nutmeg, d) sautee in butter and smother in onions and celery.  I assume removing the fat and boiling gets rid of the musky odor.

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2 Responses to “The Co-existence of the Rice Rat (Orzomys palustris) and the Florida Muskrat (Neofiber alleni)”

  1. jamesrobertsmith Says:

    I’ve seen the voles that live in the high elevation areas of the southern Appalachians. They’re elusive, but I’ve been lucky enough to spot them on rare occasions. I saw one some years ago near the summit of Charlie’s Bunion at around 5400 feet above sea level. It was crawling through the low shrubs that grow up there. I also saw what I’ve heard is a unique sub-species of vole at Wind Rock near the Virginia/West Virginia border at around 4,000 feet above sea level. This one was moving around in the cracks of the exposed rock on the summit–very different kind of environment than the the on Charlie’s Bunion.

    I see lots of muskrats here around the NC Piedmont. They’re pretty common and even live within the streams of the Charlotte city limits. They seem to be good at surviving the droughts we’ve had over the past decade by retreating to isolated pools along the streams and creeks in town.

  2. markgelbart Says:

    The only small mammals I get to see near where I live are the ones the cats drag home.

    The most common by far are short-tailed shrews. Eastern moles and house mice are 2nd and 3rd.

    On 1 occasion I found a cat-killed star-nosed mole. Officially, we’re supposed to be slightly outside this animal’s range.

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