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Oct. 18, 2006

Massive Monarch Migration Pushes Through Texas With Passing Cold Front

AUSTIN, Texas — The cold front that blew through Texas on October 13 pushed many thousands of monarch butterflies south towards their overwintering destination in central Mexico.

“Thousands of monarchs were reported from many locations through the central latitudes of Texas Thursday afternoon and Friday morning” said Mike Quinn, an entomologist with the Texas Parks and Wildlife Department. “The front brought a little bit of rain and a whole lot of monarchs!”

The monarch butterflies were initially reported from a wide band stretching from Sonora to Somerville Lake. Since then, scientists say butterflies have been pouring through Del Rio and Eagle Pass where one observer estimated 500 migrating monarchs per minute. The butterflies are best seen by using binoculars as monarchs frequently migrate at higher than 1,000 feet above the earth.

“A large fall monarch migration is always welcome news,” said Quinn, who noted that this summer’s monarch population was reported by many observers to be near record numbers. “Insect populations can change quickly both up and down,” said Quinn, “as seen with the snout butterflies erupting twice this summer and fall across south Texas and with the occasional monarch die offs in Mexico which last happened in January 2004.”

Female monarchs can lay 400 or more eggs when conditions are favorable, as they were this summer across most of northeastern U.S. and southeastern Canada. Quinn says this illustrates how the monarch, like most insects, has great recuperative powers.

Environmental conditions were particularly favorable in the northeastern portion of the monarch’s summer breeding grounds. This region probably spawned the massive monarch congregation found last week in Southeastern Arkansas. One wildlife biologist estimated the butterflies roosting there at 100,000 strong. This is one of the largest monarch roosts reported in the last few years. These monarchs should be headed down the Gulf Coast in coming days, providing a good show for coastal residents.

The annual monarch population benchmark is determined by the amount of forest acreage the butterflies occupy on their over-wintering grounds in Michoacan, Mexico each December. The Mexican biologists who work on the population estimate generally release their findings in February, just before the monarchs head back to Texas.

Quinn says it’s amazing that the monarchs now passing south through Texas are the very same individuals that will re-cross the Rio Grande five months from now in mid March! With luck, they’ll come back strong next spring!

For more information on monarch butterflies, see the Monarch Watch Web site.

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TH 2006-10-18

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