Wednesday, May 27, 2020

A migration to rival the voyage of the monarchs

I love a monarch butterfly as much as the next Canadian. Canadians tend to think of them as "our" butterflies, mainly because they are so numerous, but also because their arrival is seen as the real start of summer, an all-too- short season precious to all our hearts. I even went down to Michoacán, Mexico, this last February, to see them in their millions in their wintering habitat in the remote jungles of central Mexico.
But monarchs are not the only butterflies that migrate, as I already knew. A Nature documentary on PBS explains just how impressive the much less well-known migration of the painted lady butterfly is. Painted ladies are common butterflies in Britain, Northern Europe and Scandinavia during the summer, and it has long been known that they migrate there from southern Europe in the early summer. However, a huge citizen science operation (and the use of modern radar and weather balloon technology) has revealed that they actually migrate from Morocco and points even further south along the edges of the Sahara Desert in Africa, taking several generations to do so, much like monarchs.
Even more of a mystery was why they seem to just disappear (die?) at the end of the northern summer, only to reappear in Southern Europe and  Northern Africa again ready to start the cycle all over again. It turns our that they, along with millions of other insects, rise up high into the upper atmosphere (above 500m, and well out of the eyesight of ground observers) and take advantage of high-level wind currents to take them back down to Africa, where they arrive, battered and exhausted, after a secret peregrination of up to 7,000 km. (Actually, the distances seem uncertain, and I have seen articles talking about a 9,000 mile round-trip, a 7,500 mile round-trip, 2,500 miles non-stop, etc.)
After this extraordinary journey - over twice the distance travelled by monarchs, crossing the Mediterranean Sea, mountain ranges, and sometimes the Sahara Desert itself, and now recognized as one of the greatest migrations on earth - these fragile insects, weighing less than a gram, are then supposed to find the energy to mate and produce a new generation before they can die in peace.
I now have a new-found respect for the humble painted lady, which we also see here in North America. In fact, these butterflies have managed to colonize every continent except Antarctica and South America, making them one of the most successful and widely distributed butterfly species in the world.
North American painted ladies migrate to the deserts of Southern California, Texas and Mexico, although their migrations are erratic and unpredictable, and seem to be directly influenced by major weather changes, El Niño events, etc. Some years, they don't migrate at all, and somehow the "hive mind" seems to be able to keep track of the group decision.
Painted ladies don't gather together in quite such impressive groups as do monarchs. But their migratory behaviour is every bit as impressive as that of the storied monarch butterfly.

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