Blackbirds are about to begin migration. You could find a flock of them at your seed feeder. They're voracious eaters. Blackbird is a term that can cover a lot of ground. Our blackbirds really are black birds — red-winged, Brewer's, rusty and yellow-headed blackbirds in Minnesota. Other blackbirds can be common grackles. At our feeders in Orono we get visits from red-winged (common from spring forward), rare visits from rusty, and occasional appearances by common grackles, the larger birds with the purple highlights.

Birds of many feathers, explained

So many birds, appearance so often so subtly different. I'm not talking about sparrows or fall warblers. This is about shrikes and honeyeaters and weavers and hummingbirds and flowerpeckers, similarities scattered through the appearances of the 10,700-plus birds illustrated in "The Complete Birds of the World," a new book from Princeton Press.

As the cover tells us, every species is illustrated. This is a big book.

The fascinating part for me was the obvious implied importance of location, habitat, behavior and voice in bird identification. Appearance alone makes that task very difficult for many bird families.

Flycatchers, tyrant flycatchers to be precise, offer common ID problems in both North and South America. In Minnesota assured identification of alder, least and willow flycatchers is often made by the bird's voice.

Paging through this book is an intellectual adventure if you want to ponder the how and why of so many birds looking so much alike. The plumage differences among the seven species of leaf warbler, for example, define subtle. One forages here, another there, alone, in pairs, in flocks. Some in forest, others on specific islands.

Opportunity and competition are two of the factors that have driven avian speciation.

There is brief text for each species in the book. The clues to precise ID are found here.

"The Complete Birds of the World" shows major adult plumages on more than 300 large-format pages containing 25,000 illustrations, principal illustrators Norman Arlott and Ber van Perlo, 640 pages, Princeton University Press, $65.

Jim Williams, Contributing writer