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'An exceptionally good year' for monarch butterflies may see 250 million make it to Mexico

Creighton biology professor Ted Burk, DPhil, tags a monarch butterfly on the Creighton campus, Sept. 13, 2018.While it may not be what it was two decades ago, this year’s anticipated monarch butterfly migration is getting rave reviews.

Over the past week, Creighton University biology professor Ted Burk, DPhil, has been out tagging monarchs and listening to other projections saying the number of butterflies heading south to Mexico may reach as many as 250 million.

“This year has been an exceptionally good year,” Burk said. “The weather has been favorable and if we see 250 million monarchs, that would be the best it’s been in more than a decade. It’s probably the best it will ever get, but it’s still very good.”

Based on the best-known records, the monarch population reached its peak about 20 years ago when more than 900 million of the orange-winged flutterers were counted as they overwintered 10,000 feet up in the mountainous fir forests of western Mexico.

The advent of certain pesticides in farm fields, however, severely limited the monarch caterpillar’s main food source, milkweed, and the population dropped as low as 30 million just five years ago. But with a renewed focus on encouraging milkweed to grow, more caterpillars — and hence, more butterflies — are being observed in the Midwest.

This presently passing-through generation of monarchs represents the great-great-grandchildren of the butterflies who made the long flight to Mexico at this time last year.

This group will spend the winter in Mexico and begin to head north again when the weather warms. They’ll reproduce around the US-Mexico border in the spring and their children push into Nebraska later in the spring. Their grandchildren and great-grandchildren will enjoy the summer here and in parts north, and then the great-great grandchildren will again start the cycle moving south at this time next year.

“It really is a marvelous phenomenon,” Burk said. “We still don’t really have a great idea on how they know which direction they should go, but they keep making the journey.”

Burk has tagged about 100 monarchs annually for the past three years. The process involves catching a butterfly in a net and gently placing a small, numerically sequenced sticker on the underside of the monarch’s wing.

Only about 1 percent of tagged butterflies are recovered in any one year — that is, found dead beneath the trees of the fir forest — and the hope is for every tagged butterfly recovered, many more made it to Mexico, lived on through the winter, and started the return journey in the spring. Burk’s returns have come in at about twice the average recovery rate, with six of the 300 he’s tagged being recovered.

“It’s been fun to see that someone else has seen them along the way and to know they made it,” he said.

This year’s southbound travelers will be making their way through Omaha through about the end of September.

“People should enjoy this over the next two or three weeks,” Burk said. “We won’t see them again until around Memorial Day.”


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