— It’s September and the fall migration is on.
Migration seems pretty simple, move north in the spring and south in the fall. Once you start looking at it in detail, it’s incredibly complex.
Birds migrate at night. The air is less turbulent and cooler during the night. Put on a down-filled winter coat and flap your arms for seven or eight hours and see how hot you get. Flying by night also allows them to navigate by the stars. Celestial navigation also causes them to get confused by lighted windows and the blinking lights on communication towers, often costing them their lives.
In the spring, birds closely track the calendar, actually the day length. Often we can predict when a species will arrive within a day or so. This is because there is a rush to get to the breeding grounds and establish a territory. Fall migration is much less predictable. Birds hang out, gorging themselves on fruits and seeds, and then catch a cold front when it comes.
Birds can gorge themselves all day and then fly all night. In some cases they can almost double their weight with fat accumulation during the day and then burn that all off that night. Imagine doubling and halving your weight every twelve hours!
Some birds will safely follow the coastline while others will dangerously head off over open water such as the Gulf of Mexico. If a weather front moving in from the north catches them in mid-flight, there’s no place to stop and rest. Millions of birds will run out of energy flying against the headwind, fall into the ocean, and wash up on the beach. There are records of millions of birds washing up on Gulf Coast beaches in a single morning.
The bar-tailed godwit, leaves Alaska and flies straight through to New Zealand. This takes about nine days and is a distance of a little under 7200 miles, without any stops. The blackpoll warbler nests in Alaska, flies east to New Jersey, and then sets out across the Atlantic for a two-day nonstop flight to South America.