Going South

The dog days of August are upon us. Scorching temperatures, humidity you can swim in, and thunderstorms powerful enough to uproot houses. Time for Fall migration. I know what you are thinking, its not Fall. Not even close. Yet for some animals, it is time to head for tropic climes or even farther.

Shorebirds—sandpipers, plovers, and the like always lead the way. Nesting on the tundra, above the Arctic Circle, almost at the edge of the ice, they have reared out their broods and are ready for some fun and sun. They pass through the mid-Atlantic starting in late July and by September are pretty much gone. I saw least sandpipers, small brown and white birdlets, hardly bigger than marshmallow Easter duckys, working over the exposed mud flats at Huntley Meadows park last week. They were joined by a solitary sandpiper, a spotted sandpiper, and several killdeer, all partaking in the bounty of the ooze. The leasties are on their way to Peru, the others go as far as the Argentine pampas and Tierra del Fuego.


Other birds I saw that day are busy putting on fat for their own journeys. The chimney swifts chittering overhead are beginning to feel the call of the rainforests and the osprey circling over the open water of the marsh will be going to coastal Brazil by mid-October. Even the hummingbirds, weighing as much as a paper clip, will be flying the 90 miles of open water nonstop from Florida to Cuba.


What prompts an animal you can hold in the palm of one hand to fly thousands of miles twice a year? Sunlight and food. Consider: every point on the planet averages 12 hours of light and 12 hours of night in a day. The actual hours are lopsided except at the equator. The poles get three month each of endless daylight and stygian night. When spring hits the northern hemisphere, daylight exceeds night with a concomitant acceleration of plant growth. More plant growth equals more insects. More insects equals more protein to feed baby birds. A good number of bird species leave the crowded tropical ecosystems and head to the sparsely populated north. They settle in, raise one, maybe two broods, and return to Central and South America at the end of the season. We think of them as our birds going south for the winter when in reality, it is their birds coming north for the summer.

Something is always migrating. Think of the year as the arc of a pendulum. At the top of each swing, there is an instant when gravity and momentum balance and the swing stops. The migration swing stops for about 10 days in mid-July and again at the other end of the arc in mid-January. For those brief periods, all species have gotten where they were going. Then the process begins anew. Now is the time when the pendulum is moving back down and the birds are beginning to move with it.