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Why So Many Monarchs This Year?
While a large population is good news, Brower cautions that there are risks associated with an early arrival. He is concerned that monarchs may be leaving Mexico early due to the thinning of the forest in their winter sanctuaries. If this is a trend, he is concerned about the implicatons:
"Monarchs were lucky this year, because those that got so far north so early in the season by chance encountered a mild spring," stated Brower. "If a major cold front had come through (which is very possible at this time of the year), then all their breeding could have been in vain, because the fresh and delicate leaves on the sprouting milkweeds would have frozen, and the larvae would then have starved."
During August and September, Dr. Brower and his wife, Dr. Linda Fink sampled monarchs visiting a Buddleia butterfly bush garden at Sweet Briar College, in Virginia, just on the eastern edge of the Blue Ridge Mountains. Here is what they observed:
"What is striking is that the big peak in August represented monarchs in very poor condition and with a lot of mating pairs. Spermatophores could be felt in the females, so clearly they were in their sexual phase.
However, these butterflies also seemed to be migrating, as evidenced by their disappearance around 8 September.
Their disappearance was then immediately followed by the appearance of an obviously fresh group of monarchs
in mint condition. These came in with the southeasterly moving front that I mentioned in my earlier e-mail to you,
and it seemes like the front pushed the old ones out and brought the new ones in.
"As all will know, I consider this dire. Monarchs were lucky this
"If this pattern held for larger parts of the central states to the west of Virginia, then getting in one
or two extra broods this spring and summer season may account for what appears may be a larger than usual migration