Heinrich tells stories of ravens helping hunters and, where there are no human hunters, wolves. Since they can't kill large animals, it's to their advantage to point out vulnerable prey to the big predators. In places where humans hunt with guns, they've learned to investigate gunshots for a possible meal. Historically, of course, they flocked to battlefields.

Our turkey vultures are still here. We never had them until after DDT was banned. Suddenly, sometime in the 1990s, there they were, nesting in a riverside park near the high school, cruising over the local landfill. At the dump, seagull population dropped from many thousands to a few hundred. The vultures have raised families. Last fall I counted more than 40 over the dump. They leave for a few months in the coldest part of the winter. Now, a cruising vulture in March is a sure sign that spring has arrived. I don't think Thoreau mentioned vultures. Do you see them at all in Atlantic Canada? It may be that they're extending their range north, as did the cardinals and mockingbirds = partly because of human activity providing food and city heat islands, and partly from global warming.