Sex is happening out there, animals congregating and interacting at the beginning of their autumn mating ritual. It is the time of year that ungulates are prancing, snorting, and bugling. Males with their tongues hanging out will are boxing females into the trees. Antlers are clattering (among deer it sounds like a fencing match between pool cues, while elk sound more like a battle with oaken staffs). Animals have begun their migration to lower country, impregnated and readying for winter.

After a long and indolent summer, the forest feels restless. This is when ungulate communication tightens. Males whistle into the woods to hear if another male whistles back. The air smells like rut and the acid of fallen leaves.

An autumn night several years ago I was driving down the road with my son in his car seat when two bucks swung into my headlights. With heads butted nearly to the ground, they locked antlers, dragging and shoving each other into the middle of the road. They did not even glance at my sudden headlights as I stepped on the brakes. I told my little boys to look, that buck deer were fighting. He leaned his body as far as he could out of his buckled car seat and asked why. I told him deer fight this time of year to see who is stronger. Sons try to topple fathers. My boy stared over my shoulder, astonished.

The two animals moved swiftly, throwing each other this way and that, catapulting across the road and out of my headlights. They continued into the black of night where they went on in my imagination, tearing and scrapping like gods through the rest of time.

We may catch a glimpse of a sparrow landed on a branch or a raccoon rolling a trash can, but they quickly slip out of sight. What place do they slip into? What web of interactions are we not seeing?

A recent study put GPS trackers on fishers to get a sense of their intricate daily sojourns. The researchers were surprised by the flexibility "in their willingness to use corridors composed of a variety of habitat types, not just forests." They saw the animals traveling back and forth through woods, over meadows, fields, golf courses and cemeteries. Instead of crossing a six-lane highway, they went under by using old drainage pipes. They knew their way around.

Of course they would. Animals are not dumb. They figure places out.

The closer we look, the more entwined and complex the movement around us appears, dynamic flow in what might have been mistaken for stillness. Movement ecology is the study of how microorganisms, plants and animals travel from one place to another. An entire discipline has been born of this. In 2008, a 76-page issue of PNAS was devoted entirely to it, edited by Ran Nathan who heads the Movement Ecology Laboratory at Hebrew University. Nathan has formed an open-access interdisciplinary journal on the subject. Sea Turtle cooler

Studies range from geomagnetic imprinting to the movement patterns of turkey vultures. An article on imprinting reported that both sea turtles and salmon lock in on the magnetic coordinates of wherever they hatched and later use that information as a navigational beacon. The magnetic field of the natal area is fused into them, a permanent map.

Every species has its unique key and path to follow.

I sit still listening to the many heartbeats of the forest. Summer has, fall has turned, and the world of animals moves ahead.