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Monday, June 4, 2012

A record spring for monarchs!

Monarch.jpgSpring 2012 has been unusual for monarchs, in a good way! We weren't expecting this good news. People have measured the area occupied by monarchs overwintering in Mexico since the winter of 1993-1994, and the winter of 2011-2012 was one of the lowest on record. The average over the whole 19 years is 7 hectares (1 hectare is about 2.5 acres). Last winter (2011-2012), monarchs occupied only 2.9 hectares; only two other years have been this low. However, it appears that a few interacting weather patterns have helped the population rebound in a single generation. First, the drought that's been drying out a large part of Texas ended. This meant that there was lots of healthy milkweed for the monarchs coming up from Mexico to lay their eggs on. Second, just when the next generation of monarchs in the south were emerging, a string of warm days with southerly winds pushed them northward in larger numbers and earlier than we'd seen for many years. Also, it's possible that several bad monarch years in the south meant that there were fewer predators and parasitoids around.

Citizen scientists in both the Monarch Larva Monitoring Project and Journey North reported seeing monarchs up to three weeks earlier than usual, farther north than usual, and in huge numbers. For example, Wendy Macziewski and I visited the University of Minnesota Arboretum on May 15, and saw hundreds of monarchs flying over the grounds. Usually we haven't even seen one monarch by that date. For reports of early and large monarch sightings, check out the Journey North website and compare MLMP state graphs from many years (check out both the timing of the first monarchs, and their numbers:

It looks that this is shaping up to be a good year for monarchs in our part of the country. So far, we've had plenty of rain, and a warm spring meant that the milkweed was ready for the monarchs when they arrived. Your data will really help us understand how monarchs respond to such an usual spring!

Karen Oberhauser

University of Minnesota Monarch Lab

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