Laura Erickson's For the Birds

(Recording of a Ruby-throated Hummingbird)

Astronomers won’t concede that it’s autumn for another two or three weeks, but as far as ornithologists are concerned, fall began August first. Even though goldfinches are still nesting and some robins are caring for their second or third brood of the year, many warblers and shorebirds are already on the move. Fall migration is more leisurely than spring migration– the drive to mate and set up a territory pushes the birds northward each spring at a much more frenetic pace than the urge to return south. The swallows of Capistrano and Hinkley’s buzzards usually arrive within a few days of when they’re supposed to in spring, but their return trip isn’t predictable enough to celebrate. Fall migrants move about as closely on schedule as deregulated airlines do.

A bird doesn’t have a flight crew to check and make sure its fuselage is intact or that its wings and rudder are in top condition, but its bird brain serves the same functions a lot more efficiently than most airlines’ entire maintenance crews. Every summer most birds undergo a complete molt, replacing every one of their feathers. Usually the molt takes place after the energy demands of the breeding season are over but while food is still plentiful. Feathers make up about 10% of a songbird’s full body weight, so replacing them takes a lot of food.

Fueling up is cheaper for a southbound bird than a jet plane. A bird gases up with fat in order to fly long distances. A hummingbird that normally weighs 2 and 1/2 grams must add 2 full grams of fat to fly non-stop over the Gulf of Mexico each spring and fall. An 11-gram Blackpoll Warbler balloons to 23 grams each fall, in order to strike out from New England across the open Atlantic for the Lesser Antilles or Venezuela. They sometimes fly nonstop, but a few Blackpolls, killed by a fatal attraction to a Bermuda lighthouse, were found to have lost about 17% of their original body weight. At this rate of consumption, they could have flown for 105 to 120 hours without a pit stop.

Late summer is the perfect time to start up a feeding station. You can enjoy birds pigging out at your feeder assured that you’re helping them to fuel up. Some people are afraid to feed hummingbirds during migration, just in case the birds are tempted to stay in the Northland longer than they should, but hummingbird physiology makes that impossible. Most adult males left last month–they had all summer to fatten up while the females took care of the babies. The females and growing young can’t take off until they have enough fat reserves, so they don’t light out for the territory until September or even October. Early frosts can kill much of their natural food supply, making sugar water indispensable to their survival. But they’re so well programmed genetically that no feeding station could possibly hold them longer than they need. They may have a bird brain weighing a fraction of a gram, but they’re not stupid.

(Recording of a Ruby-throated Hummingbird)

This is Laura Erickson, and this program has been “For the Birds.”