A walk out in the woods during winter usually doesn’t yield a lot of sounds or bird calls; certainly not as much noise as springtime when birds and frogs are in the midst of courtship and breeding. Nuthatches, pine siskins, or the occasional tapping of a woodpecker foraging on a dead tree is the norm. The other day, however, there was the raucous cacophony of a flock of at least two dozen crows calling, while perched in some nearby trees. I checked the trees and others nearby for any interlopers. Crows will call and chase (or “mob”) predators that they see perched, in the air, or on the ground. Many times when crows call in unison from a tree, there will be a hawk or eagle also perched nearby. In this case, there were no predators visible and perhaps they were just trying to rally other crows to the flock.

Nature has many other examples of alarm systems that can be heard now and other times of the year. The slap of a beaver’s tail on the water as a fisherman gets too close to a lodge, or the high pitched “peep” of a green frog as it jumps into the water to escape danger are a couple of examples of giving the alarm and warding off possible attack. There are no green frogs visible at the moment, but the images in this week’s column show some seasonal species that raise the alarm when danger is afoot.