MILWAUKEE -- Swarms of biting flies are attacking loons in northern Wisconsin this season like never before, causing the birds to abandon their nests in record numbers, according to researchers.
The explosion of the black fly population just as the loons began incubating their eggs has caused more than 80 percent of the loons to abandon their nests in Vilas County and more than 70 percent of nests in Oneida County, according to the wildlife scientists who track the tuxedoed birds with the mournful cries.
A cold spring in Wisconsin and rapid warm up in May caused the black flies to arrive en masse, said Walter Piper, a researcher at the School of Earth and Environmental Sciences at Chapman University in Orange, Calif.
"There's always a burst that comes out in May. This happens to be one that is particularly devastating," said Piper, who spends six weeks in Oneida County studying the loons each year.
A species of black flies, Simulium annulus, has a particular attraction to loons, according to research by Michael W. Meyer, of the Wisconsin Department of Natural Resources. His 2012 study published in the Journal of Vector Ecology found the fly species was chemically drawn to the loons.
"It's one of the most exclusive relationships documented," Meyer said.
The fly species has always pestered the loons in the past, but this year it was an all-out assault.
"The intensity of the black flies is the worst I've seen in the 25 years I've monitored loons," said Meyer, who checks the nests of about 150 loons every two weeks throughout the season in Vilas County.
Research shows about 1,200 loons reside in northern Wisconsin, a population that has been doing reasonably well, Piper said. He estimated the number of loon chicks born this year could be reduced by about 30 percent compared to last year.
"It'll set them back. It's been a blow to them," he said.
The loons will re-nest, using the same nest or a new one. But, because the chicks will be hatching later in the summer, they may not be mature enough to migrate or withstand the cool fall weather, Piper said. Loon pairings, male and female, incubate their eggs for about 30 days. The chicks are able to fly in about 11 weeks.
Erica LeMoine, coordinator of Loon Watch at Northland College in Ashland, said loons have been leaving their eggs behind in northern Minnesota as well. Volunteers reported eight abandoned nests recently, LeMoine said. Biologists suspect many more abandonments were likely in Minnesota.
The late 'ice out' in Minnesota followed by some 80-degree days created the proliferation of flies, LeMoine said.
"They're so irritating to the loons. It causes them to abandon their nests because they have to dive (into the water) to get the flies off them," she said.
LoonWatch, its advisory council and volunteers work for loon conservation and protection.
Swarms of black flies were also blamed when endangered whooping cranes abandoned their nests at the Necedah National Wildlife Refuge near Tomah last year.
A few years ago, crane watchers noticed that the birds would build nests and lay eggs, then abruptly abandon their nests. The leading hypothesis pointed to the hordes of biting black flies at the marshy refuge. As an experiment in 2011 and 2012, biologists treated two rivers near the refuge with a soil bacterium known as Bti, which is used an alternative to chemical pesticides. Black fly numbers fell significantly.
Four chicks hatched in 2011, but all eventually died. Several more chicks hatched in 2012, and two survived.
Bti treatments were not used in 2013, the black flies returned and 18 nests were abandoned.
Piper said there is a small rate of nest abandonment by the loons each year for a variety of reasons, including raccoons and other predators, but, nothing that comes close to this year. Piper expected the loon population to eventually recover following a drop in reproduction this year.