It is summer here—sweet, sticky, sultry summer—and the terns have noisily returned to their feeding and breeding grounds along the coast of the Pacific Northwest. As I sit at Alki and watch the sun bury itself deep within the reaches of the Olympic Mountains, a flock of seabirds appear overhead and begin to circle the shallows, their heads pointing down, their eyes quick and discerning. Spiraling and swerving high above the sound, silhouetted against a twilit backdrop of cragged peaks and sienna sky, the Caspian terns (Hydroprogne caspia) pick out fish and dive headlong into the water, their long, narrow wings slightly tucked to speed their plunge beneath the waves.
Caspian terns are big birds, the largest of the forty or so tern species found worldwide. They look like gulls from a distance, with their whitish-gray plumage, four-and-a-half foot wingspan, and slow, almost languid flight. A closer inspection reveals the solid black cap of the breeding adult, the heavy orange bill, the shallowly forked tail and sooty, tapered wingtips. Watch them hover near the shoreline at dusk and witness the Caspian’s star turn: a beautifully timed high dive which, when successful, yields a fresh-caught fish to be swallowed whole, on the wing.
Every continent but Antarctica plays host to the Caspian tern, a globetrotting and increasingly gregarious species. Caspian terns in Washington state migrate en masse from South America to summer here, the majority of them hunkering down along the Columbia River estuary in huge, raucous colonies. They prefer areas with little to no vegetation—grass and shrubbery can harbor predators, and because nests are scooped out on the ground, terns find comfort in the austere—and human-made islands and sandbars fit the bill perfectly. In the late 1990s, the estuary’s Rice Island—an artifact of the U.S. Army Corps of Engineers—was home to the world’s largest colony of Caspian terns, numbering more than 17,000 birds. This was fine, except that the terns were eating shitloads of salmon. One study discovered that Columbia salmon smolts constituted between seventy to ninety percent of the tern’s diets. These birds have since been relocated to another colony further downstream, on East Sand Island, with the hope of reducing their impact on sea-bound salmon. So far, the move has been mostly effective: Consumption dropped from 12.4 million smolts to around five million between 1998 and 2007. But now, unexpectedly, other birds have arrived, displacing the skittish terns and commandeering the isle. Gulls and pelicans, along with double-crested cormorants—who eat four times as much salmon as the terns—flock in ever greater numbers to the estuary, where their depredations cost the state fishery millions each year in revenue lost.
The Caspian colonies on East Sand Island may be shrinking, but these birds have proven highly responsive to change. New colonies have sprung up elsewhere along the coast, and overall populations seem stable. I for one welcome their nocturnal flyovers, the stillness of night broken by their loud, croaking calls. They are fair-weather fans, like so many of us: here for the summer, gone come fall.