Tuesday, January 8, 2013

Under a Frozen World

Snowy Wetland
Slough off North Asylum Bay
The lakes and marshes become quiet in the winter when the ice covers the lakes and snow blankets the surrounding marshes, but life continues below ice and snow. 

Tunneling through the snow are a number of little mammals.  Mice, voles, and shrews enjoy the relative safety provided by their tunnels.  There they are free from the piercing eyes of hawks, but are still vulnerable to the ears and talons of great-horned owls and pouncing foxes.
On the lake bottoms are the flying insects of summer.  The billions of lake flies of spring are all there as the larva called bloodworms.  Keeping company with sediment, decaying plants and rocks are the larva of caddisflies, damselflies, dragon flies, and mayflies that will emerge from the lake and take flight in spring and summer.  All of these are food throughout the winter for bluegills, perch and other fish. 

Up the food chain there are reptiles we envision hibernating in the mud.  Some turtles and frogs are indeed buried in the mud, but others are piled up sitting on the lake bottom motionless or crawling along at a snail’s pace.  Common map turtles sit on the bottom or wedge themselves amongst rocks and logs.  When disturbed they retreat, and may reveal a northern leopard frog underneath, which will also swim away.  Hardly asleep, these map turtles require more oxygen than painted turtles buried in the sometimes anoxic mud.  The cold and relative inactivity allows them to take in all the oxygen they need from water.  Frogs and softshell turtles breathe through their skin, but softshells also take in oxygen through special adaptions in their throats.   
Oshkosh Ice Night
Frozen Lake Winnebago at Oshkosh

Mammals have no options but to breathe air.  The local aquatic members of the weasel family--river otter and mink--must maintain holes in the ice with their teeth to be able to gain access to the fish, frogs, turtles and other animals they eat.  Muskrats often use the same holes, but they try to stay concealed, and will never walk on ice and snow if they can avoid it.  Muskrats build huts, or lodges like beavers do, but muskrat homes are made of aquatic plant leaves, stems, and roots.  Here they sleep and eat, but they often swim far beyond the range of one breath to obtain the food they need.  For those foraging trips they build cave-like “push ups” for breathing.  They will also build small feeding huts, which are self-explanatory.  A sudden drop in water levels after the ice forms seals off all these structures from the muskrats’ food, forcing them onto ice and snow and into the jaws of coyotes.    

Winter is a harsh time for wildlife, but it can be easier under the ice and snow for those adapted to it.

Previously published in the Oshkosh Scene article.

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