Late August is still summer, and warm or hot temperatures still happen frequently. However, the days are getting shorter. A sun slower to rise and quicker to set is telling us of the changing times. It is this daylight pattern that triggers the birds to begin migrations despite the fact that food still abounds.

The migration actually began with tree swallows in July. After an early breeding season, the new crop of swallows gathered with the older ones in family units. Soon these clans mixed with others and utility lines held large numbers of these fast-flying birds. Restless morning flights lasted longer each day and soon the flocks moved on.

Migration in August is varied and involves many kinds of birds. A flock of Canada geese, larger now than in the spring, may begin the southbound route now. Chimney swifts that have circled above our cities and towns for most of the summer have become eager to move on. One day we will see and hear these twittering gray birds, but the next day they are gone.

Warblers that have raised a family in the north woods now begin their movement, too. Family units often blend with those of other species and in the company of local vireos and chickadees, their flocks, often called waves, work their way through the scene. Now wearing autumn plumage, they can be quite hard to discern, even by experts.

Always the opportunists, a few sharp-shinned hawks follow these waves through the woods as well. The really large hawk flights are still a few weeks away, but a scattering pass over now.

One of the grandest migration flights at this time is that of the nighthawks. Though not really hawks, they pass by in huge flocks that perform quite a bit of aerial dynamics as they feed on the wing. With most insects available at dusk, nighthawks appear in their biggest numbers at this time. Many a late August evening has been decorated by these active birds in flocks that reach into the hundreds.

Not quite as dramatic, but just as consistent, is the migration of shorebirds that are southing now, too. Virtually all these small water birds are brown and most remain silent. Some species form large flocks while others are loners. Birds often breed in the far north, even on the tundra, and winter in South America. With such long flights, these shorebirds start moving early in the season. Most stop and feed on beaches along the way and if conditions are good, they will stay a while.

Sandpipers of several species are probably best known, but other shorebirds include sanderlings, plovers, turnstones and dunlins. For at least a month at this time of year all or any of these birds could be on the shores and beaches of Northland lakes. Vast mud flats, sandy beaches or open areas like at Park Point provide great sites for these birds. Here they can get ample rest and the small invertebrate food along the water's edge.

Some sandpipers -- such as the least, western and semipalmated -- are tiny, about 6 inches long, while others may reach up to a foot. But all are out here now and will continue to be along our beaches for the next several weeks. It is well worth our time to look over these flocks with binoculars and see this part of the fall migration.

Larry Weber is author of the "Backyard Almanac." He lives in Carlton County and teaches natural science at Duluth's Marshall School.