More to a monarch than pair of colourful wings

Press, 29 January 1986, Page 18

More to a monarch than pair of colourful wings

By

BARBARA MOFFET,

National

Geographic News Service

The ultimate in flying machines may be neither bird nor plane, but the monarch butterfly. Every autumn, millions of them prove it. Most of the United States monarch population east of the Rocky Mountains travels south, funnelling through Texas on a 2000-mile journey to wintering grounds in central Mexico. On the way they overcome wind turbulence that could turn on the “fasten seat belt” sign on a passenger jet and certainly would overwhelm an ultralight aircraft. Dr David L. Gibo, associate profesor of zoology at the University of Toronto, can verify that. He put together an ultralight — a hang glider with an engine — in the hopes of chasing monarchs through the skies to learn their secrets of flight. After a few attempts to tail them, he retired to the ground to observe them with binoculars. “Once we were waiting for them down in Texas, and a cold

front came through — thousands of them were riding it,” he recalls. “If we had stayed up, we’d have been risking our lives. We went up the next day and were bounced around like leaves."

Professor Gibo’s observations, in Canada and along migration routes on the east coast and in Texas, have shown the monarch to be a master at exploiting wind' currents. Monarchs save energy by riding thermals — rising air masses that lift them to favorable altitudes. They will fly from ground level up to 7000 feet, above many light airplanes. They will flap like birds, at an average 16 km/h to 19 km/h, or soar to conserve energy. When threatened, the butterflies can accelerate to 40 km/h. “Nobody imagined the flight strategy of an insect could be so complicated,” Professor Gibo says. “It’s as complex as anything a bird does.”

The monarch is not bothered by wind shear; its four-inch wing-

span is too small to be affected. The hurricanes that terrify people are opportunities for monarchs. Hurricane Gloria, which roared up the east coast of the United States in late September as the butterflies were beginning their south-westerly trip, probably saved many of them time and energy. "The counterclockwise spin of the hurricane spawned wind currents in just the direction the monarchs needed to go,” says Professor Gibo, whose work is partly supported by the National Geographic Society. "Gloria acted as a warm merry-go-round that could easily have taken them for a 160 kilometres ride." Though they have an uncanny ability to find their way, monarchs occasionally end up in the wrong place. Strong winds have transported a few of the orange-and-black butterflies all the way across the Atlantic to England, where they do not occur naturally. Some scientists believe they

navigate by cues from Earth’s magnetic field, though that is not certain.

Another monarch mystery — exactly where they go in winter — was solved 10 years ago when a lofty, wooded site, its trees dripping with resting monarchs, was discovered in central Mexico. It was already known that most monarchs west of the Rockies spend the season in southern California. None of the millions of monarchs that embark every September for Mexico has ever been there before, and none will return there. Flying by day with stops for foraging on blossoms, they converge each night to rest, sometimes extending their stay if winds are unfavourable. If they reach a barrier, such as Lake Ontario, they may build up in large numbers, turning trees orange.

Their soaring skills are so efficient, Professor Gibo says, that they arrive in Mexico fat and healthy, having gained, not lost, weight on the trip. They

huddle by the millions on the chilly Mexican hillsides, sometimes breaking off fir-tree branches with their weight. Noone knows exactly why they have chosen that area. From November to March they remain in semi-dormancy, resembling masses of pale, dead leaves; but when warm breezes stir, they begin to mate. The males will stay in Mexico to die; the females depart for the journey north, many settling in Texas to lay eggs on emerging milkweed plants. The butterflies born in Texas will continue north, possibly all the way to Ontario. The offspring of those in Ontario will eventually migrate to Mexico, several generations from those that preceded them. Monarchs appear to have the most complex migration and flight strategies of all butterflies, but Professor Gibo has learned from ground observation that at least two other migratory species — the red admiral and the mourning cloak — soar to save energy.