How Birds Migrate, 2nd Edition
Paul Kerlinger
Stackpole Books, 2009
Dateline: Cape May, NJ. There was a 30-knot breeze blowing in from the ocean. Hundreds of thousands of swallows swarmed over the Cape May Meadows, gathering into flocks for the long journey south. On this day they were thick as black flies in the Adirondacks. As we crested the dunes, we rubbed our eyes in disbelief at the sight of thousands of swallows spilled on the sand spreading themselves across the wide beach. They were perfectly still. They were resting. They must have set off and then blown back on shore by the strong breeze. Exhausted, they allowed us to pick them up. We warmed them in our hands, moved them off the foot paths, chased off a curious house cat, and scratched our heads in amazement.
Dateline: Somewhere in the Caribbean. I was the leader of a group of birders on a trip which stopped at several Caribbean islands. One evening I went out on the aft deck after dinner to enjoy a cigar and a little solitude. As I began to sink into a crepuscular reverie, I realized that I had company -- actually, quite a lot of company. In fact, the deck was a happening place. It was full of song birds. They were crossing, perhaps, 500 miles of open water and found our little ship to be a perfect place to rest. (No doubt aware of their stowaway status, none of them complained about my cigar.)
They get eaten. They drown. They die from exhaustion. They get blown off course. They crash into windows. They get diced in wind generators. They get killed by cars. They arrive, exhausted, at re-fueling stations along their route to find them converted to row houses or shopping malls. Many who survive the journey will pass the coming mating season as bachelors, foregoing the reward of generations. How do first time migrants know where they are supposed to be going? How do they find their way? If you are a birder -- even a casual backyard watcher – these and other questions about the phenomenon of bird migration must rattle around in your head each spring and fall because the arithmetic just doesn’t seem to add up. What advantage could justify such an expenditure of calories and the braving of such an extended gauntlet?
Paul Kerlinger’s superb How Birds Migrate gives these questions a thorough, accurate and readable treatment. It is a must-read primer on the subject of migration. Kerlinger is an ornithologist and former director of New Jersey Audubon’s Cape May Bird Observatory. He is frequent contributor to Birder’s World and other birding periodicals. Kerlinger includes chapters on the basics of flight, on route finding, on the benefits of diurnal versus nocturnal passage, on conservation, and the ways in which humans effect migration. As a birder who will drop everything to run to the park in anticipation of a “fallout,” (a “fallout” is a result of a weather front which cause migrating birds to seemingly drop out of the skies and stall until conditions change), I particularly recommend the excellent chapter on boundary layer meteorology – an outstanding primer on weather patterns and fronts and how they effect migration.
How Birds Migrate is also liberally peppered with anecdotal asides or case studies, each of which highlights a particular aspect of or question about migration.
Case Study: Shorebirds provide an excellent example of how a bird’s wing shape is related to habitat. Most shorebirds have long, pointed wings that permit fast and powerful flight. A few shorebirds, however, have short wings and rounded wing tips. The American Woodcock (also called Timberdoodle) is an aberrant shorebird that lives in the forest. Its short wings with rounded tips promote maneuverability in the forest but are not suited for long-distance migration or fast flight. Another feature that makes this bird distinct from other shorebirds is the absence of stiff flight feathers – the primaries at the ends of the wings. Most woodland species have softer, more pliant flight feathers than do birds of open country: soft feathers are less likely to suffer damage from impact with branches, and stiff feathers promote fast flight in open spaces. These forest birds have adaptations that make them more maneuverable than open-country birds of the same size.
Since its publication in 1995, I have worn out two copies of How Birds Migrate from constant thumbing during migration season. I was pleased to see a second edition (published in 2008) which incorporates new findings and adds new material. Although How Birds Migrate, uses a textbook approach, the effect is to leave the reader scratching his or her head in wonder at the interconnectedness and interdependence of all things – evolution, metabolism, timing, accident, habitat, weather, human communities, climate – marveling that it ever worked at all, and wondering how much longer it will continue if we humans further disrupt natural systems for our own comfort. I cannot help but recal a passage written by my old colleague, Pete (J.P.) Myers in “American Birds,” in which Pete elegized the imminent disappearance of the phenomenon of migration:
Not next year, not in the next 10 years, but in our lifetime, Migration, as we know it, will fade away, its threads unraveled, tattered and diminished beyond recognition…The migration events that now occur across the hemisphere each fall and spring – hundreds of thousands of southbound shorebirds in the Bay of Fundy each August, one-half million Sandhill Cranes on the Platte River in March, spring warbler rains in coastal Texas, autumn warbler fallout on Point Reyes, a million Sooty Shearwaters offshore of Pismo Beach each August, to name only a few – these spectacles will become events of the past – avian buffalo reduced to ecosystem irrelevancies if not eliminated altogether.
As conservationists, we hope that rumors of the death of migration are greatly exaggerated. Learning the whys and hows of migration adds to our state of radical amazement. It also commands us to change because knowing imposes an obligation to behave differently. Knowing imposes on us an imperative to be better stewards. Knowledge brings awareness of our role in the natural world and a sense of personal responsibility to keep migration from becoming a biological relic. How Birds Migrate is a first-rate primer on the phenomenon of migration and worth reading and re-reading.
If How Birds Migrate whets your appetite, I also highly recommend Scott Weidensaul’s Living on The Wind (North Point Press, 1999), a favorite book by a favorite author, and Nature’s Flyers: Birds, Insects, and the Biomechanics of Flight by David E. Alexander (The Johns Hopkins University Press, 2002).