Of all the autumn migrants, perhaps the most remarkable is the monarch butterfly.

Some local monarchs are still emerging from the chrysalis stage this time of year. For about eight more weeks, until mid-October, we can still enjoy the black-and-orange beauty of their 4-inch wingspans over prairies, meadows and gardens. But for the next three weeks the monarch migration is at its peak.

Incredible as it may seem, these fragile wisps of life are as successful at migration as most birds.

Migrant monarchs can live up to 10 months, non-migrants for about 30 days. During the summer there may be two or three generations of new monarchs, thus increasing the final population of migrating monarchs.

August is monarch butterfly month in Minnesota, where the insect was named official state butterfly in the year 2000. We see them between May and October, but it's late summer when their numbers are greatest. Monarchs are now seen roosting in groups, sometimes masses of them. These aggregations tell us their migration has begun.

They travel individually, not in flocks, and fly anywhere from ground level to about 7,000 feet in the air. They save energy by riding thermals.

Every year millions of monarchs make the journey from the eastern United States and southeastern Canada to the fir forests in the mountains northwest of Mexico City to take shelter for the winter.

Jim Gilbert's Nature Notes are heard on WCCO Radio at 7:15 a.m. Sundays. His observations have been part of the Minnesota Weatherguide Environment Calendars since 1977, and he is the author of five books on nature in Minnesota. He taught and worked as a naturalist for 50 years.