MILWAUKEE — In the world of wildlife watching, a “fallout” of birds on spring migration is typically eagerly anticipated by birders.

It often occurs as flocks of birds get stalled out on their northward trek and descend into locales to rest and feed before resuming their journeys.

The occasions can produce the highest number of bird sightings of the year.

What happened Monday to dozens of common loons in northern Wisconsin was something else entirely.

In this case, the fallout apparently was caused by icy atmospheric conditions that coated the birds’ feathers and caused them to lose their ability to fly, according to Marge Gibson of Raptor Education Group Inc. in Antigo.

“They literally fall from the sky,” Gibson said. “By Monday afternoon, we knew we had a major loon emergency.”

The weather late Sunday and early Monday featured some cold spring storms, with about 1 inch of snow and some hail falling in Antigo.

Many birds migrate at night and several thousand feet above ground.

What the conditions were like for the loons early Monday is impossible to tell. But it resulted in at least dozens, and likely many more, to be driven to ground.

In the aviation world, icing is a critical and well-known hazard. It can compromise aerodynamics and weigh down aircraft. De-icing material is often sprayed on planes before take-off in winter. Loons receive no special treatment.

Gibson said she’s seen loon fallouts during spring migration twice previously over the last 25 years.

In one case, a bird was rescued seconds after it fell from the sky.

“It still had a veil of ice around its wings,” Gibson said. “That’s impossible to fly with.”

The unplanned groundings are a special danger to loons. The birds have evolved to swim, dive and fly, not walk on land.

In fact, their leg positioning and body shape make it extremely difficult for loons to move across hard surfaces. They basically have to “wing walk.”

“They are very vulnerable on land,” Gibson said. “As tough as they are, they can’t last long if they are in the middle of some field.”

Grounded loons face another high hurdle: They need lots of space – often up to one-quarter of a mile – to take off in water.

So if the stranded birds are able to find water, but it’s small, they may be able to find food and relative safety, but won’t be able to fly out and continue migrating.

By noon Monday, Gibson had received 35 phone calls about stranded loons. The wildlife rehab center sent out a notice for landowners to check their fields and retention ponds for loons.

Handling a loon is not without danger to humans. The birds’ bills are like a dagger.

If you find a loon on the ground or in a small pond, it’s best to consult a wildlife rehabilitation center for next steps. But among the tips from the Raptor Education Group Inc.: Wear eye protection, a jacket and thick gloves.

Grab the beak first, cover the entire bird with a large towel, jacket or blanket to keep the wings together and prevent injury to the bird or handler.

Rubbermaid containers work the best to transport a loon, but they must have air holes.

By Tuesday afternoon, Raptor Education Group Inc. had taken in 13 loons and more were on the way, Gibson said. Most were in good shape and had fed recently. Five were able to be released after an assessment. Others were kept for additional observation and treatment.

Gibson encouraged people across north-central Wisconsin to keep an eye open for grounded or trapped loons for the next several days.

“These birds were on their way back to their lakes after spending the winter in the south,” Gibson said. “Let’s help as many of them complete that journey as possible.”

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