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March 5, 2009

Down, Down, Down...
It is hard to find words to describe the mass descent of tens of thousands, likely millions, of monarchs from their clusters. Flying downward does not seem to do it, although that is clearly what they are doing. They ride the air like a kite, but they descend. They float on the air, but ride it downward. They stream in kind of a formation, always downward. If you look upward, their flight appears chaotic with no apparent direction. Nearer the ground they are always streaming downward. They land on moist grass and stick their proboscises into the moisture.

The constant downward movement shows clearly that the once stable winter clusters are breaking up. Each week the colony is lower on the mountainside. This week they were about 100 meters lower than the previous week, both at Chincua and Rosario. Each day they descend and reform lower down. They are headed home – home being the place where they breed.

Mating
There is much mating now. Small males drag their precious cargoes across dusty trails towards a sunfleck. If successful, they accumulate enough heat to warm their muscles so they can fly to a safe perch in the trees above. Here the male will pass a spermatophore to the female and, if lucky, the sperm will fertilize her eggs. But this is unlikely. A female will mate many times because she needs the nitrogen from a number of spermatophores to make egg yoke. (Note: Recent research shows that the last male to mate with a female fertizes the eggs she will lay, so these early matings are usually futile for the male.)

Cascading
There is much cascading now, another sign of colony breakup. There is hardly anything that dazzles more than the simultaneous falling of tens of thousands of butterflies from a roost—as if gravity suddenly pulled with extra force—then all fly off in the same direction before reaching the ground.

But the most constant behavior now, and the behavior that dazzles the most, is the golden flow downward that gives the impression of a blizzard of butterflies – an experience that one is likely never to forget.

This week our group includes the Bonnydale Environmental Education Center in Brattleboro Vermont, a handful of Texans from the Dallas area, and a lone Wisconsinite.

Dr. Calvert