The heavy weekend snowstorm in northern and central Wisconsin has led to a "bird emergency," says a wildlife expert.

While the annual migration is behind schedule for many birds because of the cold spring, those that have already flown north are in trouble, says Marge Gibson, executive director of the Raptor Education Group, Inc.

"This is absolutely the worst that we've ever seen," Gibson said from her wildlife rehabilitation center in Antigo.

She said the birds are unable to find food or adequate shelter.

"Most of the birds that are migrating this time of year are hardy to a point. They can survive a couple of snowstorms, as long as it warms up shortly after," Gibson said. "But this year, they were faced with not only the heavy snow but the severe cold, and it's been sustained."

Gibson says the wildlife center has been flooded with more than 130 phone calls since Monday night.

"People are seeing robins and warblers, even cardinals that are having a really hard time finding food. They are very lethargic. They are on the ground. They are having difficulty flying," she said.

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Gibson's staff is in the process of picking up more than 50 birds that were rescued from the heavy snow by concerned homeowners.

"BIrds are coming from Marshfield, Stevens Point, Pittsville, Adams Friendship, Wausau, Shawano, Marion and all of the surrounding areas," according to the REGI's Facebook page.

"If you see a bird that is very lethargic and you can pick it up, it has to come in for care," Gibson said. "You can get a cardboard box, put a towel in the bottom, and bring it into a warmed area."

Gibson asked homeowners to help feed robins, which depend on insects and worms.

"Robins can do very well with suet but it has to be broken up into really little pieces," she said. "You can get live waxworms at local bait shops. They’ll also eat live or dried meal worms. Some people are using scrambled eggs."

The Facebook page thanked the Marshfield and Antigo police departments for helping volunteers from REGI, including one staff member who got stuck in the deep snow.