You can learn a lot from neighborhood walks and other outings.

I've noticed European mountain ash fruit is a radiant orange, many garden pumpkins are already orange, and Native American bittersweet vines have orange fruit. All are signs of autumn.

Over the years I have learned that most ruby-throated hummingbirds leave northern Minnesota by Sept. 12 and the south by Sept. 25. At this time the hummers are quite active and numerous at our feeding station and others in the Waconia area.

A good share of the Baltimore orioles left for Central America by the first week in September. They are among the night migrants.

There have been many reports by birders of migrating warblers, swallows, gulls, and shorebirds the last few weeks. On Aug. 24 the official tally for the day of migrating common nighthawks counted at Hawk Ridge in Duluth was an amazing 27,580 individuals.

At least 80 % of Minnesota's 300-plus bird species, normally here each year, fly south and millions improve their health by doing so. Migration for some bird species began as early as July. Others will wait until November.

The reason for migration is easy to understand. If certain animals are mobile and have a fluctuating seasonal food supply, the natural result is migration. It's as true today as it was thousands of years ago that the birds that move in the right direction survive.

Most temperate zone birds begin their migrations because of the change in the length of daylight. Others get their signal from the shrinking food supply. Because birds have a tendency to return to the same place because they are familiar with the food supply, available shelter and predators, we often question how they know which way to travel. Navigation is interesting and complex. Landmarks and directions taken from the sun, stars and invisible lines of the earth's magnetic field all help guide various species.

Waves of migrating warblers, vireos and flycatchers are moving through. Because these three groups represent dozens of species, and are small and very active, they can be hard to identify. Even an experienced birder will find a study of these migrants a challenge.

Jim Gilbert taught and worked as a naturalist for 50 years.