November Wisconsin Nature Notes
TUNDRA SWANS ON THE MISSISSIPPI RIVER
Few superlatives can sketch for the uninitiated the beauty of the drifting, seemingly translucent formations of white tundra swans that sweep over the Upper Mississippi River National Wildlife Refuge in November. Thousands land to feed and loaf in the shallow backwaters of the river, appearing from a distance like popcorn scattered on the water.
Their attraction in such great numbers to only a few sites in the refuge comes from their love of wild celery and arrowhead tubers, which grow abundantly in shallow, quiet pools found in the river’s backwaters. An adult swan has a large appetite and will feed on nearly six pounds of aquatic vegetation a day. Even though their appetites are prodigious, their energetic digging usually improves the habitat by stimulating the growth of underwater plants, so next year the site will provide a bounty again.
The swans begin arriving along the river the first week of November, but the peak usually occurs in mid-November. They will remain for many weeks, or until ice begins to form, and then it's time to fly east to their wintering grounds in Chesapeake Bay.
Tundra swans (formerly called whistling swans) come by their name honestly, nesting high up on the Arctic coastline in tundra or sheltered marshes. Tundras may fly up to ten hours a day, and, with good weather conditions, can sail along in a V-formation at 60 mph as high as 8,000 feet, thus traveling up to 600 miles a day.
Tundra swans produce a high-pitched call that has been likened to many things: a distant barking of dogs, soft musical laughter, a mellow cooing, or something akin to a Canada goose honk, which amply demonstrates how limited human language is in describing the language of non-humans.
The origin of singing one's "swan song" is attributed to tundra swans, which in their death are described by one scientist as singing a melodious, soft, muted series of notes - "when a swan is shot and falls crippled to the water, it utters this call as it tries in vain to rejoin its fellows in the sky".
Scientists estimate that about 25 percent of the eastern population of tundra swans uses the Upper Mississippi River during fall migration. If you want to see thousands of tundras, your best bet would be the observation platform in Brownsville, Minnesota, just downriver from La Crosse, or Big Lake on the Mississippi River just north of Alma, across from Cedar Ridge Resort.
AMAZING HIBERNATING FROGS
Being a cold-blooded animal in a Wisconsin winter isn’t easy. It requires some remarkable adaptations that at first glance seem physiologically impossible. Take, for instance, spring peepers, those tiny but incredibly boisterous frogs that can turn a spring woodland pond into an echoing din of noise. How do they, and wood frogs, eastern gray tree frogs, and chorus frogs for that matter, survive five months of below freezing temperatures? Well, they freeze, making themselves into “peepsicles.”
How do they do it? Before the ground freezes, they bury themselves a few inches down in the soil where the ground will eventually freeze. They then mostly freeze, too, but they survive by packing their cells with glycogen to keep their internal organ cells from actually freezing. The water that moves between the cells freezes, but the frog's cell structure is not harmed because the sharp edges of the ice can’t damage the organ cells. This procedure, called extra-cellular freezing, is much the same as the strategy used by trees in northern Canada to survive temperatures of minus 80° Fahrenheit.
Still, this strategy only works so well; a dormant peeper will freeze and die at temperatures below about 21° Fahrenheit, so an insulating snow cover and a blanket of leaves is crucial.
Even if they survive the cold, the frogs aren’t home-free. Predators can still get them. Shrews, for example, burrowing about under the soil, readily consume the inactive frogs.
Other frogs employ different strategies. Leopard frogs, green frogs, mink frogs, and bullfrogs simply settle to the bottom of a lake and lie exposed on the mud, often becoming a convenient meal for cruising northern pike, walleye, and musky. Underwater, the frogs breathe through pores in their skin.
When spring comes, the frogs thaw out, or swim up to the lake’s surface. Then they probably yawn and stretch, likely commenting on the fine dreams they’ve had for the last five months.
Consider how remarkable a frog really is. It begins life breathing through gills. Then it changes into a lung-breathing animal. And in winter, it switches to breathing through its skin. Amazing!
SNAPPING INTO WINTER HIBERNATION
A Wisconsin winter poses extraordinary challenges for cold-blooded animals like frogs and turtles. Some species, like snapping turtles, go to astonishing extremes to survive. Snappers hibernate in shallow waters by burying themselves in the mud. While some snapping turtles are still moving around at the beginning of October, they all will have moved to their hibernating areas by mid-October, about half traveling up to two-and-a-half miles to find just the right place.
Hibernating sites have to offer access to oxygen. In lakes and ponds that freeze over, hibernating areas need to be deep enough so the water doesn’t freeze to the bottom. There are only a few favorite sites in each body of water, so many snapping turtles hibernate literally in a pile, often stacked directly on top of each other. Males hibernate on top of females, so it is possible that they serve to protect the females from both predation and thickening ice. While the exact reasons for the group hibernating behavior are unclear, it unfortunately exposes them to predation by otters. At the site of a long-term study of snapping turtles in Algonquin Park, Ontario, the whole population of snapping turtles was effectively exterminated during a single winter when otters ate the defenseless turtles.
During hibernation, a snapper’s body temperature drops to about 34°F, or just above freezing. They also don’t breathe for as much as six months, though they can get oxygen by pushing their head out of the mud and allowing gas exchange to take place through the membranes of their mouth and throat, a process known as extra pulmonary respiration.
No one really knows how wintering turtles survive and why they act as they do. What is death to a turtle? For half their lives, turtles live under ice, buried in mud, not breathing, not moving and likely living without any heart activity. In the spring, they rise to the surface, presumably take a few breaths, and swim away as turtles have done for millions of years. Spring brings many resurrections, but the rebirth of turtles may be one of the most remarkable.
In the warmer months, you can see snapping turtles in many parts of Wisconsin, including at the Conservancy’s Lulu Lake Preserve in the Mukwonago River watershed in southeast Wisconsin.
HARES AND WEASELS GO WHITE FOR WINTER
Snowshoe hares and weasels undergo a fashion change in October, gradually molting their brown fur into white. For snowshoes, first their ears and feet turn white, with their backs the last to change. The process occurs over six to ten weeks, and come mid-March, it reverses. The change occurs due to the length of the day – the photoperiod. When the days become shorter, their melanin, or pigment, production slows, resulting in new growth of fur that lacks pigment and is therefore white. The snowshoes become pure white except for the black tips of their ears.
Three species of weasels also swap their warm summer browns for icy whites: the least weasel, the long-tailed weasel and the short-tailed weasel. The latter species is perhaps best known as the ermine, also the name of its winter fur. All three weasels turn completely white except for the black tip of their tail. Why a black-tipped tail? Apparently the black tip confuses hawks, a predator on weasels, into thinking the tail is the head, and thus they mistakenly attack the tail.
One writer has described an ermine as "a furry snake with legs." While their tiny tracks barely imprint on the snow (just three-quarters of an inch in width and length), ermines display more pound-for-pound fearlessness than virtually any other predator, taking on animals up to 30 times their weight. They are lightning quick and lithe enough to squeeze into the burrows of most small mammals that live under the snow.
Snow-white coats serve as camouflage, but they may also keep animals toasty. It’s thought that white fur, lacking pigment, has more space in its hair shafts. When air fills the empty spaces, it can trap the animal’s body heat and provide insulation from the cold.
A late winter or an early spring makes for a color mismatch that jeopardizes the hare and the weasels, whose milk-white coats stand out starkly against the brown earth. With climate change, by midcentury, the snow season is expected to be a month shorter, and by the end of the century it could be up to 2 months shorter. With the photoperiod dates fixed for molting, that shift could result in hares being mismatched for as much as 36 days by 2050 and for double that amount of time by the end of the century, making them highly vulnerable to predation.
Snowshoe hares and long-tailed weasels can be found in northern Wisconsin. Look for them at The Nature Conservancy’s Catherine Wolter Wilderness Area in Vilas County.