Other Environmental Themes

A Distant Hum

The rufous hummingbird is a miracle of far-flung travel. The 3.5-inch-long bird, characterized by a bright orange throat and reddish-brown sides and tail, weighs just a quarter of an ounce, yet flies thousands of miles in its annual trek between wintering sites in southern Mexico and breeding grounds in the Pacific Northwest. Some of these tiny birds fly all the way to central Alaska, easily achieving the greatest distance per body weight of any known bird. No other hummingbird travels farther, nor ventures farther north.

The caloric demands of the rufous and other hummingbirds are impressive and arguably oppressive: Each day they drink nearly twice their body weight in nectar, their main food source, acquiring well-needed protein by downing the occasional insect or spider. If they were human sized, they'd have to eat the caloric equivalent of several hundred Big Macs daily.

These calories do not go to waste, instead supporting a frenetic lifestyle that represents the highest energy output of any warm-blooded creature. A hummingbird's heart—the largest proportionally of any animal—beats up to 20 times a second, and its wings may flap 80 times a second, powered by chest muscles that constitute 30 percent of its body mass.

Hummingbirds normally eat every hour during the day, but make special preparations prior to migrations. The rufous then turns carbohydrates obtained from nectar into fat—the most efficient way for it to store energy. To gain weight before the long flight, the bird enters a hibernation-like state called torpor during which energy consumption drops to about one-fiftieth the normal level.

Despite these adjustments, rufous hummingbirds are still extremely vulnerable during migration because their ultra-high energy requirements allow little room for error. The species is declining at the same time that urban development, agriculture, and cattle grazing are swallowing up vital migration corridors. While it is important to save key nesting and wintering habitat, stopover habitat is equally vital. The preservation of even small waystations, where famished hummingbirds can quickly refuel, could spell the difference between successful migration and starvation for these extraordinary voyagers.