Book Review: The Narrow Edge: A Tiny Bird, an Ancient Crab, and an Epic Journey, by Deborah Cramer

Consumed by curiosity could be the motivation for all great natural history books. In her first chapter, Massachusetts naturalist Deborah Cramer says “Each year knots fly from one end of the Earth to the other and back.” Consumed by curiosity, she chases them from Tierra del Fuego to the Arctic “to learn what it takes to go such great distances, where they choose to stop along the way, and why.”

Her portrait of this threatened traveler includes the ecology of shorebirds, the evolution of migration, the cycles of the Earth, the senses of birds, and the impact of humans. It is also an adventure, in pursuit of which she visits sites from Tierra del Fuego to the Arctic, “watching for them from helicopters, listening for them in a small propeller plane equipped with a radio receiver.” She travels by “boat, train, komatik, SUV, and ATV”; more surprisingly, perhaps, she learns “to load and fire…a twelve-gauge shotgun” and finds that on her next stopover, in the presence of polar bears, she misses it. Her writing is vivid, novelistic. The resulting book is everything a natural history should be.

The key to the knot’s survival is that its need for food is greater than that of any sedentary species. Long-distance travel burns fuel, whether petroleum or crab eggs. “Some knots in San Antonio Oeste double their weight before leaving on the next leg of their journey. The prospect of doubling my own weight in a month is both daunting and nauseating…knots increase theirs by almost 10 percent in a day.”

Creatures like knots adapt quickly. The old way of evolutionary thinking was that species could only await the arrival of random genetic mutations for natural selection to work on; now we realize feedback mechanisms do more to push selection toward favorable goals. And knots are individually adaptable as well; they increase weight dramatically to fuel a single-stage, 4,000-mile flight, and once they land they can expand their gizzards by 50 percent if they need to grind low-quality food. Weirder, their muscles can grow rapidly if Peregrine Falcons menace their beach roosts but remain the same if extra muscle mass isn’t needed.

But are even such powers enough to adapt to our swiftly changing planet? The key to the survival of the population of Red Knots Deborah Cramer depicts may come down to how many horseshoe crab eggs remain for them to eat in Delaware Bay, the critical choke point of their migration. When those archaic creatures lumber onto the sands of Delaware Bay in May, their numbers may still look impressive. But the baymen who once harvested up to 2 million of them a year for crab bait now harvest them to obtain limulus amebocyte Books for Birders lysate (LAL), an extract from horseshoe crab blood cells for which there is no easy substitute. It is used to test for gram-negative bacteria, and without it, many of our advances in medicine and surgery could not have taken place.

Synthetic LAL may be coming, but we now know that our impact on other species has reduced their numbers far more than we ever imagined. The Passenger Pigeon was our greatest loss, but we have only recently begun to understand fully how much we devastated the populations of whales and other marine wildlife in the oceans worldwide. The green turtle of the Caribbean numbered some 91 million as late as the 1600s; historical populations of shorebirds are probably beyond present calculation.

We may never, and probably shouldn’t, commodify shorebirds; they mean more. “Red Knots speak to us of distant realms, uniting us along a line that stretches along the entire edge of continents,” writes Cramer. “In a flock of knots lifting into the evening sky in Bahia Lomas, in a lone Whimbrel flying through a hurricane—I find hope and faith that we can face even our most difficult challenges and that a healthy Earth supporting a multitude of species is still possible.”