A Book For Any Season

Gail Cochrane

Liberty Wildlife Volunteer

“At whatever moment you read these words, day or night, there are birds aloft in the skies of the Western Hemisphere, migrating. If it is spring or fall, the great pivot points of the year, then the continents are swarming with billions of travelers, a flood of birds so great that even the most ignorant and unobservant notice, if nothing else, the skeins of geese and the flocks of robins.”

So opens Scott Weidensaul’s stunning book Living on the Wind – Across the Hemisphere with Migratory Birds.  Weidensaul’s prose is gorgeous and the scope of his topic is immense. He begins his story onsite at the Bering Sea where scores of species summer due to rich feeding opportunities. This is the starting point for migratory journeys that stagger the mind. As Weidensaul notes, birds don’t migrate because of cold weather, but because of food supply, particularly for insect eaters who must reach the tropics to find wintertime meals.

The tiny blackpoll warbler weighs in at one half of one ounce.  It breeds across the northern hemisphere from Alaska to Hudson Bay to New England. In fall the Alaskan birds will cross our continent on northwesterly winds and then cross 2000 miles of Atlantic waters to finally make landfall in Venezuela or Guyana. The birds generally travel at night, waiting for the passage of a cold front and then gaining from the brisk tailwinds that follow, traveling at altitudes up to 5000 feet.  When the northwesterlies run out the warblers gain momentum from subtropical trade winds. Most blackpolls fly on another 1500 miles to Bolivia or Brazil.  In April or May, the birds return to Alaska via a route over the Gulf of Mexico and interior North America. The annual elliptical round trip may cover eleven or twelve thousand miles.

There are birds that fly further. A species of curlew called the bristle thigh flies from Alaska to the South Sea islands around Fiji, motivated and guided by genetically programmed cues. The youngsters are only five weeks old when the parents leave them to fly south. Left behind, they busy themselves putting on fat, gorging on berries and insects. Diminishing daylight hours trigger an instinctive orientation towards the south-southwest and their ancestral wintering grounds. Undeniable agitation sets in and the flock of youngsters takes to the air in short practice flights, testing winds aloft and waiting for the right combination of wind speed and direction. As with other migratory species, the curlews orient themselves with the sun by day and the stars by night. They apparently sense the earth’s magnetic field and perhaps also low-frequency waves generated by trade winds and surf.

“Every rainless autumn night, half an hour after sunset, the land sighs a great, upward breath of birds, which climb to one or two thousand feet before leveling out, their beaks pointed south.”  The observation of migration is made difficult by the fact that most birds travel by night, but nocturnal migration is successful for many reasons. It may help birds avoid predators, or free up daylight hours for feeding and rest. Nighttime skies are cooler, preventing overheating in the laboring birds, and damper, reducing thirst. Winds are typically less turbulent.

In a chapter called River of Hawks, Weidensaul documents hawk watching over the Veracruz area of Mexico. Broad-winged hawks, Swainson’s hawks, turkey vultures, and Mississippi kites migrate through in unbelievable numbers. “Watching the migration was a bit like seeing some great, slithering snake, for the mainstream of the flight shifted sinuously from east to west as the day wore on, moving like a sidewinder tossing its looping body across the land – a serpent of hawks that for hours had no head and no visible tail.”

This is a fantastic book, with so much more in-depth information about birds and their amazing journeys. Read it, gift it, be astounded.