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LAKE VERMILION— Northern Minnesota’s loon population appears to be holding its own, for now, despite the effects of the 2010 BP oil spill, which many had feared would prove devastating to loons. …
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LAKE VERMILION— Northern Minnesota’s loon population appears to be holding its own, for now, despite the effects of the 2010 BP oil spill, which many had feared would prove devastating to loons.
Research in Minnesota and Wisconsin has demonstrated that many of the region’s loons were exposed to petroleum and oil-dispersing agents in the Gulf of Mexico during the 2010 incident. While the exposure proved non-lethal to most loons, it remains unclear whether long-term effects on loons, either from reduced life spans or diminished reproductive potential, are likely. That’s according to Carrol Henderson, director of the Department of Natural Resources’ Nongame Wildlife Program.
For now, such effects aren’t showing up in most loon counts, and this year’s 34th annual count on Lake Vermilion was no exception. About 70 volunteer counters recorded 262 loons on the lake during the count day held Friday, July 15. Two previously scheduled counts were cancelled due to bad weather.
The loon numbers this year were down slightly from last year’s count of 297 birds, but remained well above the ten-year average for the count. Wildlife surveys typically vary from year to year, and the minor variations that do occur are not necessarily indicative of a trend.
Meanwhile, the number of loon chicks also dipped this year, to just 34. That’s a drop from the 46 chicks spotted during last year’s count, but reflects an improvement from the 29 chicks recorded during the 2014 count. It also is slightly above the long-term average of 31 for the number of chicks spotted during the count.
While Vermilion is known to be home to the largest loon population of any lake in Minnesota, the density of loons on the lake appears to be significantly lower than in other parts of the state, according to DNR research. According to data collected from six areas within the loon range from 1994-2015, about two loons are found for every 100 acres of lake surface on average within loon country in Minnesota. But loon density decreases on the Canadian Shield, where the vast majority of the state’s most pristine lakes are found. Indeed, in Lake and Cook County, the research found that loon density was less than one bird per 100 acres of lake surface, ahead of only Kandiyohi County in the southwestern corner of the loon range.
“It’s an interesting scientific question,” said Henderson.
Henderson said it isn’t clear whether the lower productivity of the shield lakes limits loon density, or whether tannins in the water, that reduce the visibility of the prey that loons depend upon, is a factor. The highest loon densities were found in central Itasca County, where an average of 3-3.5 loons were found for every 100 acres of water.
By contrast, given Vermilion’s 40,000 acres of surface area, the loon density on the lake is less than one per 100 acres, similar to lakes in Cook and Lake counties.
“It’s an interesting brain teaser to think about why this would be the case,” said Henderson.