University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln

Mammalogy Papers: University of Nebraska State Museum Museum, University of Nebraska State

August 1993

Flat Water Mammals

Patricia W. Freeman University of Nebraska-Lincoln, [email protected]

Russell A. Benedict University of Nebraska - Lincoln

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Freeman, Patricia W. and Benedict, Russell A., "Flat Water Mammals" (1993). Mammalogy Papers: University of Nebraska State Museum. 32. https://digitalcommons.unl.edu/museummammalogy/32

This Article is brought to you for free and open access by the Museum, University of Nebraska State at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Mammalogy Papers: University of Nebraska State Museum by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Flat Water Mammals By Patricia W. Freeman and Russell A. Benedict

Nebraska 's diverse habitats are home for an equally diverse collection of mammals, some of which appear to be expanding their ranges as the habitat changes, especially along the Platte River Valley.

here are many people for whom tle and sometimes interbreed. It is the the terms "God's Country" and stuff that some biologists can only T"Nebraska" are synonymous. We dream about. are not qualified to evaluate that par- To many people speeding along In- ticular metaphysical question, but we terstate 80, the Platte River Valley is can explain why our state is unique anything but exciting. The seemingly from a biological standpoint. monotonous valley is merely an Geographically, Nebraska is so situated obstacle to be traversed in route to in the United States that within its boun- more exciting destinations east or west. daries eastern habitats meet western The convergence of organisms from dif- habitats, and northern habitats meet ferent regions and the fairly rapid southern. change of habitats goes largely un- This diversity of habitats has several noticed because the elevation change is consequences. First, the presence of gradual from east to west. Since much many different habitats means that a of our travel is limited to the Platte Val- wide variety of plants and animals are ley, changes in habitats abutting the val- found here. Since habitat changes fairly ley are not obvious. But the landscape quickly as one travels across Nebraska, does change and so do the organisms. the plants and animals also change, and If we follow the Platte River from in a single day it is possible to visit east to west, we begin in the eastern nearly desert-like habitats in western deciduous forest found on the rugged Nebraska, moderately dry grasslands in bluffs along the Missouri River. These the center of the state and lush prairies oak-hickory forests are typical of much and forests in the eastern counties. The of the eastern United States but extend organisms inhabiting these habitats are along the Platte only for a short dis- also quite different. tance - from the mouth of the river Second, the meeting of eastern and west for about 50 miles. Historically western habitats and northern and these forests were found primarily on southern habitats brings together plants the steep bluffs along the valley. Prairie and animals ordinarily widely separated fires swept the ridgetops above and geographically. This mixing of animals prevented extensive growth of trees. from the four comers of the continent is The elevation of the Platte Valley at its prairie but now largely converted to especially evident along the Platte and mouth is about 960 feet above sea agriculture. In central Nebraska, from Niobrara rivers whose river valleys cre- level, and the hills flanking the valley Grand Island to Paxton, the valley is ate highways of habitat (forests and wet reach nearly 1,200 feet. bounded by mixed-grass prairie and far- prairies) that allow eastern and western For most of the Platte's length, the ther west, from Paxton to the Wyoming organisms to venture out onto the other- banks of the valley are blanketed by border, it passes through shortgrass wise harsh and treeless plains. In these grasslands. In the eastern third of the prairie. In several areas, the valley pas- narrow, fragile strips, normally separate state, the valley passes through a region ses through sandhills prairie including populations meet, occasionally do bat- previously dominated by tallgrass pockets to the north of the river starting just west of Columbus and the large At the western end of the state, the continuous body of the Sandhills start- North Platte Valley once again passes This opossum is not "playing possum" but ing just west of Gothenberg and extend- through an area partially covered by is greatly frightened and when cornered ing to Scottsbluff. South of the river is a forest. The Wildcat Hills are a mix of will hiss and drip saliva. Timid animals, pocket of sandsage prairie from North prairie and Rocky Mountain forest they will try to escape up trees and into Platte to Ogallala. These different dominated by ponderosa pine trees. The brush piles when pursued. Opossums have prairies vary in their composition of elevation of the valley where it passes been steadily moving northward since the plants and in general become shorter in into Wyoming is about 4,030 feet, with Pliocene some 3 million years ago. height as one progresses west. the surrounding hills topping 4,900

AUGUST 1993 ing frequency of flooding on the Platte. Riverine forests extend west along the valley to the Wyoming border along the North Platte, but become shorter in height and harbor different species of plants as we travel west. The river floodplain is also vegetated by dense lowland prairies that are now less abun- dant because of cultivation.

Mammals of the Platte Valley Those habitats support a fascinating diversity of mammals, many of which are small and unfamiliar to most people. Two-thirds of the mammals found in Nebraska (54 of 8 1 species) reach their distributional limits in the state. This means that the ranges of many species abundant in states to the east or west, north or south of Nebraska end in our state. For example the wood- chuck, which lives in much of the east- em United States, can only be found in the eastern third of Nebraska. Many plants, fishes, insects, birds and other organisms also reach their distributional limits here. The result is a unique and subtle blend of biological diversity from all across the continent that whirs past unnoticed as we sit in our air-condi- tioned or heated cars. Contrary to what is suggested by many field guide range maps, the geographic distributions of organisms are not fixed. Populations of living crea- tures rise and fall as conditions vary over time, and these fluctuations can cause the edges of their geographic ran- ges to wander. For exam~le.during a . , w I harsh, dry period, the range of wood- -c.JLr-- chucks could retreat east to such an ex- tent that they would no longer occur in feet. In the southwestem comer of the Nebraska. By monitoring changes in Woodchucks, Marmota monax, (above) are state, a traveler reaches the surprising the distributions of organisms we can sometimes called groundhogs or marmots. elevation of over 5,400 feet - higher track the overall "health" of popula- "Marmot" may be corrupted Latin for than Denver or Albuquerque. tions and determine whether the ac- "mouse of the mountain" or from a The vegetation of the flat floodplain tivities of humans are causing increase French expression meaning to sleep like a within the valley is fairly similar or decline in a species. top. A Native American name is "monax," throughout the state, a fact to which Ironically, many people believe that the digger. Big brown bats (opposite) are most interstate travelers will attest. scientists know everything about common in Nebraska and are beneficial. Floodplain forests dominated by cotton- Nebraska's plants and animals. In A preferred food is the cucumber beetle, wood, willow and other fast-growing reality this is far from the truth. Only a adult form of the corn rootworm. They trees are common and appear to be in- few of the most obvious groups of or- also eat June beetles, stinkbugs and creasing due to planting by humans, ganisms have been surveyed statewide. leafhoppers. control of prairie fires and the decreas- Fortunately for us, however, a com- prehensive survey of the distributions pearance to our common fox squirrel A third squirrel, and perhaps the of mammals of Nebraska was con- but is slightly smaller and colored a most interesting, is the southern flying ducted about 35 years ago by the recent- light gray. It is common in the wooded squirrel. This secretive and beautiful ly deceased prominent mammalogist, J. bluffs along the Missouri River in animal is difficult to locate because it is Knox Jones, Jr., who grew up in Lin- southern Nebraska but is currently un- nocturnal. Flying squirrels can be found coln and attended the University of known along the Platte. The north- along the bluffs of the Missouri River Nebraska. His survey provides a ernmost colony known to us is in in places like Indian Cave State Park, benchmark against which we can com- Fontanelle Forest along the Missouri but they are uncommon. They might pare recent changes in the distributions River in Bellevue. also occur along the eastern Platte of mammals. The eastem chipmunk used to be River, but this is unknown. Flying squir- found over a fairly large portion of ex- rels are insect- and seed-eating mam- Eastern Deciduous Forest - treme eastern Nebraska but has mals that use skin membranes between Some mammals unique to the east- declined for unknown reasons. The legs and tail to glide from one tree to em deciduous forest can be found along most recent sighting of which we are the next. They do not actively fly as a the eastem-most stretches of the Platte aware was in 1991 by Gerry Steinauer bird or bat does. Valley. The eastern gray squirrel and of the Nebraska Game and Parks Com- Another group of secretive and poor- the eastern chipmunk are familiar to mission who spotted one in the Rulo ly known animals inhabiting the eastem many residents of eastern states be- Bluffs Nature Preserve in the deciduous forests includes three species cause they are active during the day. In southeastern comer of the state. It is of bats: the eastem pipistrelle, evening Nebraska, the exact geographical limits possible that both these squirrels have bat and little brown bat. Of the eight. of these squirrels are unknown. The declined due to grazing and timber ac- species of bats inhabiting the southeast gray squirrel is similar in action and ap- tivitv in eastern Nebraska. comer of the state. these three are

AUGUST 1993 limited primarily to the oak-hickory slightly mysterious eastern Nebraska The deer mouse (above) is very similar in forests, and they have been captured mammal. This small rodent has never appearance to its cousin, the white-footed along the Platte. Distributions of bats been captured along the Platte River, mouse. Deer mice are more common in are difficult to determine because they but the possibility certainly exists that it prairies and grasslands, while white-footed are difficult to capture. Only through is there. Woodland voles primarily eat mice are more common in woodlands. regular netting at appropriate locations grass and other plants and live in tun- Both are abundant and are major food over several years can we be sure about nels under the leaf litter on the forest sources for predators. White-footed mice what species are in an area. floor. Although we know they exist are steadily moving westward along These much-misunderstood animals here, mammalogists have caught fewer Nebraska's rivers. Fox squirrels (opposite) are quite beneficial to humans and are than 25 in the state, and probably only are robust cousins of the gray squirrel, no more likely to carry rabies than are five of these captures have occurred in which is found only in eastern Nebraska. the other mammals. In addition, bats the last 20 years. The distribution of the fox squirrel has lead lives so intriguing that few people Two other voles also occur in expanded west and north along riverine can resist these tiny mammals once Nebraska. The meadow vole and prairie woodlands with settlement of the West. they overcome their unwarranted fears. vole are both abundant in areas The woodland vole is an uncommon, dominated by wet and dry grasslands, worth mentioning. The fox squirrel is a mammal that relies on forests for food, classic example of an animal on the shelter and nesting sites. move north and west. This eastern squir- Nebraska's largest squirrel burrows rel was once restricted to forests along in the ground and is known to most the major rivers on the eastern edge of people as the woodchuck or groundhog. the state. With the spread of riverine This squatty mammal can weigh up to forests and intentional releases of this 14 pounds and is found in areas where animal by humans, the fox squirrel has woodlands mix with open country. The now penetrated the Great Plains as far western-most woodchuck we know of west as Wyoming and Colorado. To the is a specimen in the University of north, the fox squirrel has spread out Nebraska State Museum from near along the Missouri River and its Ravenna, north of Kearney. This tributaries into South Dakota and North specimen, combined with other records Dakota. from Greeley, Antelope and Madison Although forests did occur along counties, is proof that woodchucks are prairie rivers prior to the arrival of set- farther west in the state than reported in tlers, they were not continuous enough the survey by J.K. Jones. The likely to allow for the spread of forest- reasons for the spread of this animal are dwelling mammals such as fox squir- the increase of wooded areas along the rels. Quite likely an unforested area rivers and the increase of woodlots only a few miles long is sufficient to planted in agricultural areas.

respectively. Both animals are found throughout most of the state. Floodplain Forests Perhaps the habitat in which the most change in mammal distributions over the last century has occurred is the floodplain forests along the Platte River and other Midwestern rivers. These forests appear to be expanding quickly, especially in central and western Nebraska, allowing forest-dwelling mammals previously restricted to east- ern Nebraska to push west along the valley and in a few cases even to penetrate into Colorado and Wyoming. The expansion of ranges of five

AUGUST 1993 White-tailed deer are widespread in On the South Platte it has been caught on the many species of plants upon the eastern and central United States directly south of Roscoe but not in whose seeds white-footed mice feed. but are largely confined to areas in or forests three miles west. A fifth common woodland-loving near forests. Their cousins, the mule In the forests to the west of the mammal, the opossum, is from a more deer, were once more common in white-footed mouse, two grassland southern geographic distribution. Opos- Nebraska because they live primarily in mice -the deer mouse and the western sums have been moving steadily north open country. White-tailed deer, like harvest mouse - inhabit the rive~e and west in the state and have become rive~eforests, have become more forests but typically in low to moderate more abundant in the last 140 years. In abundant. Whitetails have penetrated a numbers (a trap-line of 40 traps will a longer time frame, opossums have ac- considerable distance into Wyoming capture three to 10 mice in one night). tually been pushing north from the and can now be found in Denver. Mule As the white-footed mouse pushes tropics since North America and South deer, on the other hand, have apparently west, it kicks these mice out of the America joined in the Pliocene Epoch decreased in abundance due largely to floodplain forests probably by sheer some 3 million years ago. The success the conversion of prairies to agricul- numerical superiority (a similar trap- of the opossum is based largely on the tural lands. line will typically catch 15 to 30 white- fact that they are living garbage dis- Another widespread, forest-loving footed mice). posal units and will eat most anything mammal is the white-footed mouse. These "mouse wars" are interesting, they can find. Our research has revealed that it is but they also may have a significant im- Another interesting, but relatively moving farther and farther west in the pact on the forests themselves. When unknown animal inhabiting the state along the Platte and Republican white-footed mice invade an area, the floodplain forests of the Platte Valley is rivers. On the North Platte this mouse total number of mice in a given forest the eastern woodrat, or packrat. This has been caught in a forest directly appears to increase dramatically. This giant mouse can weigh almost as much below Lake Ogallala, but it has not could have a considerable impact on as a gray squirrel and is found only in been found in forests farther upstream. the many animals that prey on mice and the south- and west-central portions of Nebraska where it builds conspicuous, These climatic conditions led to the stick nests on the ground or hidden in demise of most of the eastern or- Short-tailed shrews (opposite) are rock crevices or abandoned buildings. ganisms in Nebraska, but a small rapacious predators of insects and even A closely related population of this population of woodrats survived in the mice more than twice their size. These woodrat resides along the central moist forests sheltered in the steep val- strong-smelling animals can use echo- Niobrara River and represents what ley of the Niobrara. This interesting location (sonar) to navigate in their biologists call a glacial relic. During the population of animals is isolated by tunnels. Kangaroo rats are seed-eaters past 2 million years (the Pleistocene about 150 miles from the main popula- and are typically open-ground Epoch or Ice Age), enormous glaciers tion of eastern woodrats along the inhabitants. In Nebraska they are most advanced south out of eastern Canada western Platte and Republican rivers. common in the Sandhills. and covered much of the northeastern United States. During warm periods, Prairies the glaciers retreated north. The most The changes in grasslands one sees recent ice advance, which reached its while traveling along the Platte Valley peak about 17,000 years ago, was fol- are subtle, and the boundaries between lowed by several thousand years of prairie regions are broad transition warm, moist climatic conditions called zones rather than sharp lines. Likewise, the hypsithermal. During this period, the changes in the mammalian com- eastern plants and animals such as the munities are rarely obvious. Several eastern woodrat spread west, covering grassland mammals inhabit all the much of what is now Nebraska. The prairie types throughout the state. These hypsithermal was followed by several generalists include the 13-lined ground thousand years of hot, dry conditions. squirrel, prairie vole, deer mouse,

AUGUST 1993 western harvest mouse, coyote, badger, some major rivers and have been found Although not common, particularly in the striped skunk, long-tailed weasel, mule as far west as Oshkosh along the Platte. eastern half of the state, porcupines deer, masked shrew and others. They can also be seen running across (below) are rodents that spend a lot of time Other mammals are more special- Highway 30 between Grand Island and in trees where they eat bark. They do not ized and thus limited to one or two Lexington. Like their more familiar chew through trees at the base as beavers grassland types. In the eastern third of cousin, the 13-lined ground squirrel, do. The least weasel (opposite) is a petite the state, the tallgrass prairie supports Franklin's ground squirrels hibernate in carnivore measuring just a little larger only a few of these habitat specialists. their underground burrows from than the mice that make up much of its diet. One of these is Franklin's ground squir- November through early March. These elongate mammals can enter holes rel. This handsome, large ground squir- It is fortunate that the mammals in- in the ground that are less than an inch rel is nearly the size of a fox squirrel, habiting tallgrass prairies are somewhat in diameter, and they also feed on insects gray with a darker gray tail which is not flexible in their use of habitats because and small birds. nearly as long as the fox squirrel's. this grassland type has almost complete- They are seen fairly often running ly disappeared across the country. Only across roadways, such as Highway 6, a few patches remain, and most are too between Lincoln and Omaha and High- small to support healthy populations of way 75 south of Omaha. An excellent prairie plants and animals. Unfortunate- place to see this squirrel is the grounds ly, many plants, birds and insects of the of the Henry Doorly Zoo in Omaha. Al- true tallgrass prairie have not fared so though Franklin's ground squirrels are well because the grasslands they re- considered tallgrass prairie mammals, quire are disappearing. they have extended their range along In the hills bordering the Platte, tallgrass prairies give way to shorter, mixed grass prairies at about Grand Is- land. Here mammals accustomed to drier country start to become more abundant - among them prairie dogs, pocket mice and grasshopper mice. The grasshopper mouse, an unusual ro- dent, has recently been found farther east than was previously known. As the name implies, these gray to brown, short-tailed mice are more carnivorous than most mice and feed on insects and even on other mice. In the southwestem United States, grasshopper mice are more abundant and are known to eat beetles that emit a foul odor. Grasshop- per mice are among the few animals to eat these beetles, and they do it by jam- ming the beetles tail-first into the sand and consuming- them head-first. These fascinating mice also communicate by lifting their heads to the sky and letting by use of their large hind feet, hence black-tailed and white-tailed jack- out a tiny, high-pitched howl. Although the name. The kangaroo rat has large, rabbits. Several of these animals can be this sound is within our hearing range, fur-lined cheek pouches on each side of found in other parts of the state, but it is it typically goes unnoticed. its mouth into which it stuffs seeds to in the western regions that they are In various locations throughout consume later in its burrow. The rear of most abundant. central Nebraska, the Platte Valley its skull is also enormously inflated to Of special interest to mammalogists winds through sandhills. The Sandhills accommodate extremely sensitive hear- is Merriarn's shrew, a rare shrew that is the most unique of Nebraska's ing. Living in the open is dangerous for prefers drier habitats. Only two have habitats, and most of its roughly 20,000 a rodent, and kangaroo rats use their been found in the state. This insect- square miles are within the state bor- sense of hearing and their rapid, unpre- eater has a very pointed snout and ders. A close inspection of the Sandhills dictable jumping to avoid snakes, owls, weighs about three or four grams - shows that this seemingly homogenous coyotes and other would-be predators. less than the weight of a car key! It is prairie is actually a mosaic of dry and Despite these defenses, remains of kan- similar in appearance to the masked wet habitats. The ridges are dry and garoo rats are found frequently in the shrew that can also be found in this vegetated by grasses, flowers, cacti and droppings of many carnivores. area and in most of the rest of the state, yucca with a fair amount of open sand. Also characteristic of the Sandhills but usually in more moist habitats. Also The lake and river valleys are covered is the plains pocket mouse. A relative of interesting in this area is the sagebrush by dense marsh and wet meadow plants the kangaroo rat, this tiny mouse also vole that may occupy this edge of that present a stark contrast to the hills. has cheek pouches. Both rodents feed Nebraska but has never been found, and This mosaic of sharply different primarily on the seeds of grasses and one or two species of bats that may habitats supports a diverse community flowers and can extract enough water occur in the rugged country along the of mammals and makes for surprising from their food to allow them to go in- western edge of the state. neighbors. Kangaroo rats (typical of definitely without drinking. dry, open habitats) can be found just a The shortgrass prairies of western Rocky Mountain Pine Forests few feet from meadow voles (dense wet Nebraska are less well-known than the Rocky Mountain pine forests and meadows) and muskrats (marshes). other habitats of the state, and some savannahs (foresttprairie mix) can be The sandy soils of the Sandhills sup- surprises may await biologists willing found in the Wildcat Hills south of the port high populations of two mice fairly to dedicate the time to do extensive re- North Platte, in the Pie Ridge country uncommon elsewhere in the state. search there. Mammals typically en- in the northwestern comer of the state Ord's kangaroo rat is familiar to anyone countered in this beautiful, desolate and along the Niobrara River. Mam- who has driven the Sandhills at night country include pronghorn (related to mals typical of this region are bushy- and attempted to dodge these large the antelope of Africa), the desert cot- tailed woodrats, porcupine, bobcat, mice as they dash across the roads. tontail, black-tailed prairie dogs, least chipmunk and several bats. In ad- Beautiful animals, they travel primarily badgers, spotted ground squirrels, and dition, the recent shooting of a moun-

AUGUST 1993 tain lion in the northwest comer of the this species in the nation. We do not Armadillos (below), uncommon in our state confirmed the suspicions of many believe that armadillos breed in our state, apparently move north when winters people that these large cats are still , state; more likely a few individuals are mild and retreat south in severe present in our state, probably sneaking simply wander north from Kansas in winters. Although we now have evidence across the border from Wyoming. years with mild winters. Like opos- that armadillos reach north of the PIatte These western forests also used to hold sums, armadillos crossed into North River in Nebraska, we have no evidence such animals as bighorn sheep, wol- America when it joined South America that they breed here. This recent verines, elk, and black and grizzly 3 million years ago. They have been photograph, taken near North Phtte, is bears prior to settlement by Europeans. moving steadily north ever since. Two proof of that movement. Bobcats (opposite) This habitat has not been studied as ex- of the armadillo specimens were found are found all over the state, not just in the tensively as more eastern habitats. dead on roads (one on 1-80 near York) western parts, but they are secretive while the other was found in a hay bale animals and are seldom seen. Other Mammals in Valley County. Several interesting mammals can be Another interesting pair of species found along the Platte that do not fit are the northern short-tailed shrew and neatly into any of the habitat types dis- Elliot's short-tailed shrew. These cussed above. One is a mammal most mouse-sized mammals appear similar people would never guess lives in to moles but have externally visible Nebraska, the nine-banded armadillo, eyes and lack the huge forepaws of a an insect-eating, grub-eating mammal mole. Short-tailed shrews are predators that inhabits the southern United States, that eat insects, snails, earthworms and Central America and much of South mice. They are North America's only America. We now have three records of venomous mammal, and they use their the armadillo in Nebraska, and these poison to kill or subdue their prey. Al- represent the northernmost records for though painful, the bite of short-tailed .I -t C:: L

shrews is not considered dangerous to now able to show that of the 80 species hope we have provided a slightly dif- humans. What is particularly interesting found along the Platte, 10 have ex- ferent perspective of the Platte Valley - about this pair of animals is their panded their ranges. Animals expand- not only does the mammal community geographic distribution. ing their ranges to the west include the along the river change as one travels Elliot's short-tailed shrew lives in opossum, woodchuck, white-footed east or west, it also changes over time. the southern part of the state, while the mouse, red bat, southern bog lemming The movement of some mammals to northern short-tailed shrew lives in the and least weasel. Of these, all but the the west appears to be occurring at a northeastern two-thirds of the state. weasel and lemming are found in the rate of at least a mile every one to Where the two species meet, a sharp spreading forests. The last three may three years. In the natural world this is border marks the end of one species' have always occupied the western edge a fast change. range and the beginning of the other's. of the state, but they are difficult to cap- These mammals live fascinating They can be captured together only in a ture and only recently have we obtained lives which can hold the attention of strip one or two miles wide. The abrupt western records. anyone willing to study them. And, al- changeover from one species to another The northern grasshopper mouse is though it may be a cliche, most of them does not appear to coincide with any ob- the only animal found farther east than have inhabited Nebraska for thousands vious change in the habitat. Apparently previously known. Whether this means of years and are as much citizens of this some sort of "war" is going on between the mouse has moved farther east or state as any of us can be. rn these two species preventing a broad that it was always there and simply es- overlap. Whether it involves competi- caped detection is unknown because tion, interbreeding or some other factor these mice are difficult to catch in the is currently under investigation. For eastern part of the state. Three mam- most of its length, the Platte Valley con- mals were found farther north than pre- tains only the northern short-tailed viously known, the armadillo, hispid shrew. Only in Keith and Lincoln coun- cotton rat and Elliot's short-tailed shrew. ties do Elliot's shrews occupy the valley. Many interesting mammals can be found in Nebraska, but we concentrated Conclusions heavily on the small mammals in this We recently completed a survey of article because they are less well- the mammals of the Platte River for the known, but, in general, are far more U.S. Fish and Wildlife Service and are common than their bigger relatives. We

AUGUST 1993