Monday, November 03, 2008

The Dragonfly Migration

Autumn is a time in Idaho when the wonders of migration are everywhere to be seen: Dark-eyed juncos, after spending a winter in Canada, start showing up at birdfeeders. Large flocks of ducks and geese can be seen swimming in ponds, wetlands and rivers. Look closely in the mountains and you may see an increase in hawks, as these birds mass along the ridges before their long southward journey across the sagebrush desert. Soon, herds of mule deer and elk will roam out of the mountains to the valleys, their winter range.

Those migrations are all quite visible--and well-studied. Less well known is the annual flight of the dragonflies. Like birds, many dragonfly species fly south for the winter.

An Idaho species, the green darner, migrates each year to the southwestern United States. There, it lays eggs, which turn into aquatic nymphs. The nymphs hatch in the spring, and return to Idaho. How they know where to go--the adults have long since died so the young have no one to lead the way--remains a mystery.

Just as some marshes serve as resting places for mind-boggling numbers of migrating ducks, some habitats attract huge swarms of dragonflies on their migration. Interestingly, many of these are the same places that attract birds--places like Cape May, New Jersey and Hawk Mountain, Pennsylvania.

Near Hawk Mountain kestrels and dragonflies share similar migration routes. While migrating in the morning, the kestrels do not hunt the dragonflies. But when both stop to rest, the kestrels actively bulk up on the ready supply of these insects.

Dragonflies are enjoying a surge in popularity lately. They're recognized for their voracious appetite for mosquitoes. They're also beautiful and interesting creatures to watch. Contributing information on dragonfly migration is still an area where amateur naturalists can contribute a lot to research. There is even a small but growing group of dragonfly watchers, who keep life lists and go on local and international trips much like birders. There are some fascinating species to be seen--like the huge one above that I photographed in the Llanos grasslands of Colombia.

Not all dragonflies migrate; many nymphs in Idaho are deep underwater, awaiting spring. But when you see a flock of ducks, or a sharp-shinned hawk, flying overhead, look closely: There may be a flight of dragonflies flying nearby.--Matt Miller

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