One of nature’s least likely spectacles, the fall monarch butterfly migration, is at or near its peak across Iowa.
While butterfly enthusiasts wonder how the frail-looking insects can fly more than 2,000 miles to a remote spot none of them has ever seen, migrating monarchs are becoming increasingly visible, clustering in trees and flitting from flower to flower to refuel their nectar tanks.
“I think we’re close to the peak around here,” said Mike Martin, facilities manager of the Marion-based Monarch Research Project, which encourages the restoration of pollinator habitat while bolstering the monarch population.
As of Tuesday, Martin had tagged 250 migrating monarchs — halfway through the group’s allotment of 500 tags. Two days earlier he said he observed a cluster of more than 150 monarchs roosting in pine trees next to a field of blooming goldenrod and asters.
“They’re pretty easy to catch right now,” said Martin, who earlier in the week netted 50 in 90 minutes in the flowering meadows around the research station.
Monarch expert Sondra Cabell, a naturalist with the Buchanan County Conservation Department, said she and colleagues caught 100 for tagging on a recent afternoon.
Cabell, who has been tagging monarchs for 35 years, said she has observed two migration peaks in recent years — the first in late August-early September and the second in late September.
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As of Wednesday, Cabell said she had used about half her 1,000 tags and expects to use the rest before the migration ends.
Before affixing a numbered tag to the underside of a wing, Martin said he examines each butterfly for its fitness to make the journey to the monarchs’ wintering grounds in central Mexico.
The difficulty of that journey is suggested by the low percentage of tags recovered at the wintering site. Last winter just one of Cabell’s 1,000 tags and just one of the Monarch Research Project’s 500 tags were recovered.
Since most tags are recovered from deceased butterflies, Cabell (who had 14 of 1,000 tags recovered in 2017) said last year’s scant total could reflect low mortality at the wintering site as well as the difficulty of the journey.
Because monarchs can’t survive freezing winters, they fly each fall to the same overwintering sites, where they hibernate until spring.
Triggered by declining day length, monarchs hatched in late summer undergo physiological changes called diapause, which better equips them for the migration and extends their normally brief life span so they can reproduce in the spring.
The average adult monarch butterfly weighs 1/57 ounce, and its brain makes up a slight fraction of its meager body weight. Its tissue-thin wings are better suited to gliding and fluttering than to prolonged flight. Though not one of the migrants has ever been to Mexico, they somehow find their way to the same host trees in which their ancestors overwintered a year and several generations earlier.
Researchers believe they rely on the position of the sun and the earth’s magnetic field to guide them on their journey. Yeah, but still ...