By Megan Hopps
SUN PRESS Newspapers
This winter’s been anything but typical. Between 50 days of sub-zero temps and above average snowfall, Minnesotans experienced one of the harshest winters since the late 70s. The cold and snow led to school cancellations, freezing water lines, extra plowing, sweeping and salting of the roads but it also caused turmoil in the lives of native wildlife.
“For the most part, native mammals and birds are pretty well-equipped for the weather,” said Executive Director Phil Jenni at the Wildlife Rehabilitation Center of Minnesota. “It’s mainly certain parts of the body that we’ve treated for frostbite such as the ears and tails of some species and the feet of certain birds.”
Though it is natural for winter to thin wildlife populations the ones that struggle the most on an individual level are ones that already have underlying problems.
“If an animal has health issues already it’s likely going to struggle in the cold,” Jenni said. “A fox with mange, a bird with a limp, they’re the ones particularly vulnerable.”
And they weren’t the only ones struggling to survive the recent polar vortex.
“Birds can get away from the cold by migrating south,” Jenni said. “The ones that stick around often puff themselves up when perched on branches and tuck their feet beneath them as their feet and legs are the most vulnerable parts of their bodies.”
Birds spend a lot of time trying to protect themselves from the cold. Some will burrow in the snow, others will find spaces in trees. Before the winter hits, they eat fatty seeds so when the temperatures drop they run on reserves. But when it gets that cold, they sometimes out of luck.
Waterfowl however, can also experience a greater threat during severe winters.
“They can be displaced,” said Jenni. “Waterfowl only stick around if they can find open water. They’re fish eaters, so when they can’t reach the fish they become debilitated and emaciated. We have a trumpeter swan we treated because its feet were frostbitten. Due to the cold and snow one of the power plants in the area shut down causing the river to freeze up. Unfortunately, this displaced some of the over wintering flock.”
In most cases dead fish are a result from a normal process known as “winterkill.” When snow and ice cover a lake, they limit the sunlight that reaches aquatic plants. The plants then cut back on the amount of oxygen they produce. If vegetation dies from lack of sunlight, the plants start to decompose, which uses oxygen dissolved in the water. If oxygen depletion becomes severe enough, fish die.
“Shallow lakes are particularly susceptible to this,” said Hennepin County Water Resource Specialist Brian Vlach. “The snow cover prevents photosynthetic activity below the lakes surface. This depletes the oxygen levels.”
Though winterkill is a natural process, it can be worse during winters with abundant and early snowfall. Lower autumn water levels increase the probability and severity of winterkill. Severe frost depths, like ones Minnesotan’s have braved this winter, also cause concern for high amounts of dead fish. Early ice-on and late ice-out dates also can increase the winterkill potential.
How To Help
One of the ways fish winterkill and water foul displacement is prevented is by installing aerators to the lakes.
“Typically the lakes with aerators prevent the lakes from freezing over,” said Vlach.
This helps the lakes oxygen levels stay in a healthy range. Vlach explains that usually the DNR will instal aerators to shallow lakes and lakes that are landlocked, lakes that do not get fresh water from flowing streams or rivers.
“If the lake is landlocked the DNR can come in a restock some of the adult fish populations if they become too severe,” said Vlach.
As for the birds? Jenni suggests keeping the feeders clean and full is always appreciated.
“Feeding wildlife is generally not promoted, but bird feeders are an exception,” said Jenni. “It’s important to keep them clean though, to avoid the spreading of disease.”
Winter causes stress not only on humans, but also on the wildlife we watch, feed, hunt and fish. To learn more about potential threats to certain fish species, birds, large and small mammals, visit the DNR website at www.dnr.state.mn.us.
Contact Megan Hopps at firstname.lastname@example.org