116 3rd St SE
Cedar Rapids, Iowa 52401
Monarch butterfly enthusiasts say it's a thrill to have one of their tags recovered at the imperiled insect's wintering grounds in Mexico.
'We are proud our strong boy made it all the way. It shows we are raising healthy butterflies,” said Karla McGrail, who tagged a successful migrant on Sept. 8 at Noelridge Park in Cedar Rapids.
The butterfly, raised in a Monarch Zone tent provided by the Cedar Rapids-based Monarch Research Project, was recovered March 1 at El Rosario, Mexico, where most of the overwintering monarchs from eastern North America congregate.
Of more than 50 monarchs tagged at Noelridge last year, only one was recovered, said McGrail, a volunteer at the park.
Each year the recovered butterflies are listed on a database maintained by Monarch Watch, a University of Kansas-based organization dedicated to monarch research and conservation and the source of all tags for monarchs in eastern North America.
Monarch Watch research assistant Jim Lovett said Friday that 1,584 tags have been recovered so far this year. The tag recovery rate varies between 1 percent and 2 percent each year, he said.
The tags enable researchers to correlate the capture location with the point of recovery. That data helps scientists determine migration routes, the influence of weather on the migration and the monarchs' survival rate.
Scientists don't fully understand monarchs' complex and arduous migration - typically more than 2,000 miles to a specific site in the mountains of Mexico. While spring and summer generations are short-lived, members of the migrating generation, emerging in late August and September, undergo physiological changes that enable them to live until they reproduce the following spring on their way back north.
Sondra Cabell, who will mark her 34th year as a monarch tagger this fall, recalled the excitement surrounding the first time one of her tags was recovered in Mexico.
'That was before I learned how the tags are recovered. Almost all of them are found on dead butterflies that have fallen from the roost trees,” said Cabell, a naturalist with the Buchanan County Conservation Department.
The thrill of learning that the butterfly made it to Mexico, she said, is tempered by the knowledge that it won't make the return journey north.
Cabell said she and associates have tagged more than 15,000 monarchs since 1983. Of those, 203 tags have been recovered, a 1.35 percent recovery rate, within the typical range cited by Monarch Watch.
In her best year, 2003, Cabell said 48 of her 630 tags were recovered, a recovery rate of 7.6 percent.
Cabell said she typically captures and tags monarchs at two Conservation Department properties - Ham Marsh and Bryantsburg Prairie. In Iowa, tagging takes place from mid-August to first frost when the migratory generation is at large, she said.
Gina Milroy, another Noelridge volunteer, had one of her tags recovered this year and had three tags recovered the year before.
Unlike McGrail, who tags butterflies raised in the Monarch Zone tent, Milroy tags free-flying butterflies captured at Noelridge and Brucemore. She tagged 125 last year and 100 the year before.
Milroy said she was shocked the first time she discovered one of her tag numbers on the Monarch Watch database.
'I double-checked the numbers several times to make sure,” she said.
Milroy said she became fascinated with monarchs when she was growing up in Burlington.
'Hundreds of them migrated through our yard every year. They would clump up in a mulberry tree,” she said.
The monarch population is estimated by measuring the area covered by dense colonies of overwintering butterflies in Mexico. By that measure the population peaked in 1996-97 with colonies covering the equivalent of 44.5 acres and bottomed out in 2013-14 with coverage of just 1.66 acres.
In 2015-16, the population rebounded with coverage of 10 acres but fell 27.9 percent last winter with coverage of 7.2 acres.