Reptiles, Amphibians, and Fish
We all have our own definition of the beginning of winter: the first heavy snow, ice on the lake, the last flock of geese heading south, or my personal favorite, the long slow cranking of the car engine. In any case, we know winter when we see it, and we know it’s here to stay.
The change in day-length and the angle of the sun in the sky is dramatic in November. We lose two minutes of daylight per day and by the end of the month the sun is 7 degrees lower in the sky. Although the shortest days are in December, the lowest mean temperature (8 degrees F. at Bismarck) is in mid-January, due to the heat reserve in the soil and surface water. This lag is noticeable by the end of January, when the sun reaches the same point as it does in mid-November, but the average temperature is still nearly 20 degrees colder. We typically have 190 to 200 days with temperatures below freezing, and 45 to 65 days that go below 0 degrees F.
Precipitation in North Dakota is light in the winter, since most storms track to the south. The mean annual snowfall for the state ranges from 30” to 38”. As for our famous blizzards, we have on the average two per winter, as does South Dakota, more than any other state. North Dakota is also well known for wind, with a mean wind speed of 10.8 mph at Bismarck. April, however, is the windiest month, with a mean wind speed of 12.8 mph. December shows a 9.8 mph mean wind speed. At Bismarck, the prevailing direction through most of the year is west-northwest. North Dakota has many hours of sunshine annually, with 58-62% of possible sunshine. November is the cloudiest month (46%) with a gradual decrease in the hours of cloud cover through the winter. Fog occurs on only one or two days per month on the average.
Thanks to long, clear nights, winter is the ideal time to observe northern lights (auroras) and meteor showers. Auroras occur when solar flares increase the flow of charged particles (solar wind) leaving the sun’s surface. These particles interact with the Earth’s atmosphere, centering over the magnetic poles. Fortunately for us, the north magnetic pole is in the Queen Elizabeth Islands of Canada, increasing the chance for a display farther south in the U.S. than in Europe and Asia. The aurora’s distance above the earth determines the color: green or yellow at 50-150 miles high, red at 150-200 miles high. Red is observed only during particularly strong displays. Look on clear, moonless nights, with activity peaking around midnight.
Other celestial events worth watching are meteor showers. Several major showers occur in the winter. Their approximate dates are: Leonid on Nov. 18-19; Geminid on Dec. 13-14; and Quadrantid on Jan. 4. The Leonoids and Geminids can offer spectacular shows. Another phenomenon seen by sky watchers in the winter months is that of a halo: a faintly colored ring of light seen around the sun or moon. This occurs when the light is refracted through the hexagonal ice crystals. A small halo of 22 degrees (about the width of an outstretched hand at arm’s length) is most common, while a large halo of 46 degrees is less frequently seen. Sundogs are partial halos produced by cirrus clouds, sometimes with horizontal rays.
Of all the changes brought on by the coming of winter, the passage of migrating birds is, for many of us, most impressive. Many bird species travel through our area, but a few find North Dakota to be a favorable wintering destination. About thirty species winter in our area: some are year-round residents, others are migrants, while some are irruptive species, or those that come here occasionally, when food or severe weather dictates. About half of the wintering birds survive on hibernating insects, others eat seeds, fruits and tree buds, and a few, like hawks, owls, and hrikes, depend upon small mammals and birds.
The rough-legged hawk breeds in Alaska and Canada and winters here from October to spring. These birds hover in mid-air over animal burrows, then dive as their prey emerges. Their diet is primarily meadow voles (75-95%), as well as mice.
Four gallinaceous birds are year-round residents of the Coteau region: sharp-tailed grouse, gray partridge, ring-necked pheasant, and wild turkey. All need woody, protective cover in the winter and depend upon high-energy winter food like corn, wheat, sunflower, and other seeds. Grouse also eat shrub and tree buds, and may travel several miles in search of food. At night and in severe weather, they move from open areas to brushy draws and dig out a cavity or even dive into loose snow. Under a thick insulating layer of snow, the temperature may be 40 degrees F. warmer than the surrounding air. Ring-necked pheasants depend upon heavier brush, marshes, or ravines for roosting, sometimes burying themselves in snow.
Among the owls, two species, the great-horned owl and the eastern screech owl, are year-round residents with permanent territories. The great-horned owl may begin nesting as early as February. Screech owls nest in hollow trees. The snowy owl is an irruptive, or occasional wintering species. These large birds are active day or night and may be seen perched on rock piles, trees, or posts. The larger adult females winter farther north than the males or younger birds.
Two woodpeckers, the downy and hairy woodpeckers, maintain territories, sometimes joining mixed-species flocks. Both eat insects and sometimes cache food in trees. Courting begins in mid-winter, when their drumming on hollow trees can be heard.
Other insect eaters include the black-capped chickadee and brown creeper. Birds of these species often flock together while feeding, along with nuthatches, which also eat and cache seeds. These birds are among the smallest of birds in cold regions, and have an extremely high metabolic rate, maintaining a body temperature of 104 degrees F. At night they hide in dense shrubs, huddling together in severe weather. Chickadees are able to go into a state of torpor, lowering their body temperature by 20 degrees F.
Other winter birds commonly seen in trees are the pine siskin, common redpoll, and house finch. These gregarious birds eat seeds, fruit and sometimes buds. Each species may roost together at night, and the common redpoll will also burrow into snow.
Ground-feeding birds may be seen in open areas, searching for seeds or insects. Arctic-nesting dark-eyed juncos are among the first to arrive here, re-establishing territories that include four or five foraging sites. The males of this species winter farther north than the females in order to reclaim nesting territories more quickly in the spring.
In open fields and pastures, horned larks, Lapland longspurs and snow buntings search together in large flocks for seeds, ever on the lookout for predators. Even in severe weather, these birds stay in open areas, crouching under tufts of grass. Horned larks do not hop, but walk along the ground, occasionally brushing away the snow with their feet and bills while feeding. Snow buntings will also hit weed stems with their wings to knock seeds to the ground. Another species, the American tree sparrow, is found in large flocks closer to thickets and marshes. This bird uses a double-scratch, or two-footed, method of hopping to expose seeds.
Of all the mammals found in North Dakota, only bats migrate. Six species occur in the Coteau Region. Two species, the little brown bat and the northern long-eared bat, hibernate in caves and mines in South Dakota and perhaps in North Dakota as well. Bats are able to enter hibernation quickly, with their hearts slowing from 180 beats to three beats per minute. They lose up to 35% of their body weight over several months of cold weather.
Shrews, on the other hand, remain active throughout our long winters. These long-nosed, solitary animals live just under the soil surface in a network of burrows 1” to 2” in diameter. Due to their small size (3 ½ “ to 5 ½”, tail included), they must consume more than their body weight each day, feeding on insects, worms and seeds, and they store food as well.
The eastern cottontail rabbit and the white-tailed jackrabbit are also active in winter, primarily in early morning and evening. Their diet consists of buds, stems, and bark, and they rest in “forms” or hollows in grass or cattails. White-tailed jackrabbits are grayish-brown in summer and white in winter.
Our three species of ground squirrels (or “gophers”), Franklin’s, Richardson’s and thirteen-lined, dig extensive networks of burrows through the summer with chambers at several levels. After the accumulation of enough body weight, the adult males enter hibernation as early as July, followed by the adult females and finally the young of the year in September or October. They may lose 40% of their body weight during hibernation. The males emerge in March or April; the females by May. All three species eat and store grasses, forbs and seeds. The tree squirrels, on the other hand, do not hibernate, and use hollow trees during severe weather, huddling with family members.
The northern pocket gopher is a burrowing animal, creating a network of tunnels up to 500 feet in length, with some tunnels six feet deep. They also burrow in the snow pack and deposit 2”-wide tunnel cores of soil which are exposed after snow melt. Feeding on roots, tubers and woody plants, they can be harmful to tree plantings.
Pocket mice are nocturnal burrowers that do not hibernate, but may become torpid in cold weather. They also store seeds, grass and insects underground. Mice, rats and voles are active throughout the winter, nesting together in extremely cold weather. Active mostly at night, they may be out on some winter days. All eat and cache grass, seeds, and insects. Voles make a network of tunnels through grass and snow. The 1”-wide soil cores are visible in the spring.
The long-tailed jumping mice (meadow and western) are solitary creatures, and unlike other mice, are true hibernators. Nesting in loose soil one to two feet under the surface, they hibernate from September or October until May or June. Muskrats can be seen throughout the winter in open water. Building lodges of plant material and burrowing into lake banks, they find protection from predators and severe weather. Active day or night, muskrats eat plants, mollusks and fish.
A common predator in our area is the coyote. An individual may cover a 20-50 square- mile territory in winter in search of rodents, carrion and fruits. Red and gray foxes cache food, and hunt those who visit the caches. They may den in cold weather, but often sleep in the open and out of the wind on sunny days.
Raccoons do not hibernate, but may be dormant for long periods, denning in hollow trees, large rock piles or old buildings. They may lose one-half of their weight during severe winters.
The ever-active weasels are said to have a “great zest for life” (Olaus Murie). The long-tailed weasel and the least weasel are found here. Both have winter coats: the long-tailed weasel is white with a black tip on its tail; the least weasel is entirely white. Both eat and cache small mammals. The larger long-tailed weasel will also eat reptiles, amphibians, birds and their eggs. They hunt in burrows as well as above ground and in trees, and are able to dive and swim through snow.
Mink are closely related to weasels, but are more adapted for semi-aquatic life. Found near lakes, they search for mammals and fish, and dig in the mud for frogs. Other predators include the American badger, the eastern spotted skunk and the striped skunk. All of these animals eat a wide variety of foods, and may spend some or all of the winter in underground dens. The bobcat is the only feline in our area, except for an occasional lynx. This solitary animal is active year-round from dusk to dawn. Thirty to 70% of its diet consists of cottontail rabbits.
By wintertime, a thick, gray coat has replaced the reddish-brown summer coat of the white-tailed deer. Deer spend more time feeding than any other activity, consuming 10 to 12 pounds of food per day, mostly twigs, buds, grains and fruit. Deer are ruminants and can eat a large quantity of food in one area and then quickly move to a safer area. They need to build up a thick layer of fat in the summer and fall to survive the winter. A high protein diet is not required in winter, but high quality forage is needed by spring. In difficult weather, deer will “yard up”, with up to 150 deer in one area. These yards reduce predation and the trails they create allow for movement through heavy snow to food sources. Breeding occurs in November and the bucks lose their antlers in mid-winter. To reduce heat loss, deer will bed down under evergreens or in tall grass on south-facing slopes.
Reptiles, Amphibians and Fish
Reptiles and amphibians take an altogether different tack in dealing with winter. Snakes burrow in loose soil or group together in dens. Mudbanks and old muskrat lodges are used by turtles for winter protection. Salamanders overwinter beneath debris or in rotten logs or animal burrows. Salamander larvae may spend the winter at the bottom of lakes. On a rainy night after ice out, adult salamanders crawl to breeding grounds anytime from March until June. Toads, true frogs and tree frogs also breed after spring rains. In the fall, toads burrow in loose soil while frogs dig into sandy banks or into the bottom of shallow ponds. They awaken in the spring when the temperature and humidity levels improve. Most fish remain active throughout the winter, although some remain on the bottom of the lake in a sluggish state.
A few of the insects of the Coteau are able to migrate: some butterflies, moths, bees and ladybugs, but most overwinter in a resting state. Many species (beetles, flies and some mosquitoes) spend the winter in the adult form hiding under bark or leaf litter. Various fats and sugars in their bodies act as antifreeze lowering the freezing point well below 32 degrees F., even as low as –30 degrees F. Many species survive by laying eggs under tree bark, in webs (tent caterpillars) or on emergent vegetation (damselfly eggs and nymphs) and depend upon snow cover for insulation. Some insects develop as far as the larval or pupae stage, like the mud dauber and some moths, before winter sets in. Most aquatic insects burrow into mud as do soil insects in drier areas. Other aquatic invertebrates overwinter as adults and must move to deeper ponds to survive. Even then, they reduce their activity and have a resistance to cold and the anaerobic conditions that develop under the ice.
One insect remains active on warmer days throughout the winter, a member of the springtail order known as the “snow flea”. These tiny gray or black creatures are found by the hundreds hopping on the surface of the sun-warmed snow. Snow fleas consume algae, pollen and leaf mold. They thrive at 35 degrees F.
One interesting aspect of winter that affects both plants and animals is one we cannot see: freezing of the soil. Frost depth and the timing of freezing depend upon the soil type, aspect, soil moisture, vegetation, snow depth, and of course, air temperature. In our area, one study indicates that the soil begins to freeze in early November and reaches the maximum depth by April. This depth varied by year from 24 to at least 70 inches below the surface. The coldest soil temperature of 25 degrees F. occurred at the 2” depth. Another 4-year study near Fargo showed similar results, although the average date of soil freezing was November 26th, with an average of frost depth of 54” on April 1st. The average maximum freezing depth for North Dakota is 50”, with a maximum depth of 84”.
Snow is an excellent insulator. Temperatures taken in a plowed field covered by 5” of snow resulted in the following: -34 degrees F. at the snow surface, 14 degrees at the soil surface, 32 degrees at 10” depth, and 38 degrees at the 20” depth. This fact is of importance to burrowing, hibernating animals.
Thawing of the soil proceeds down from the soil surface and upward from below due to residual heat. Soil at the 2 to 3 foot level is the last to thaw.
The drop in temperature and the decreasing day-length of autumn affect plants. Some plants, like warm-season grasses, enter dormancy even if the temperatures are warm enough for photosynthesis and growth. The upper part of the plant dies back and overwintering buds are formed at ground level before a killing frost occurs. Cool-season grasses tolerate lower temperatures, growing as long as the temperature is above freezing. Some arctic plants are able to photosynthesize even below 32 degrees F. For most plants, however, little metabolic activity takes place below the freezing point, and relatively little of the sugars and starches stored in the roots are utilized. These compounds and others also protect the plant cells from the harmful effects of freezing.
Winter is a time of drought for plants, with soil water frozen and unavailable. For woody plants, bark, bud scales and waxy coverings help reduce desiccation. At or below ground level, plants survive winter in a variety of forms. Roots, tubers, stolons and rhizomes have protective coverings, and as we have seen, soil temperatures are not severe if there is an adequate snow cover. Seeds of the native plants are especially suited to withstand low temperatures and desiccation, and in fact, may require a chilling period before germination in the spring.
The rigors of winter are something we all understand here on the northern Great Plains. When we stop to observe the native plants and animals, we must marvel at their hardiness and adaptability. And when we dig through the snow (burrow), stock our cupboards (cache), and that car finally starts so we can get to where we’re going (active all winter), we realize that we’re pretty hardy, too.