The Cape and Islands near shore waters are currently experiencing a visitation of Sooty Shearwaters. These remarkable birds are one of the most abundant seabirds on the planet and are found in every ocean. Their only need for land is for use as a platform to lay a single egg; they are dependent on the ocean for all their needs.
Shearwaters take their common name from their habit of tipping from side to side as they follow air currents at the sea surface, thus appearing to “shear” the water. Generally they resemble a stiff-winged, slender-bodied gull. They have long, slim, hooked bills, short tails and very long wings.
Sooty Shearwaters weigh slightly over a pound and a half, have a wingspan of 40 inches and measure approximately 17 inches long from the tip of their beak to the tip of the tail. The lives these birds live is one of a gigantic relay around the oceans of the world.
They nest on remote offshore islands all over the southern hemisphere during the Austral summer. They nest in burrows, which they excavate with beak and sharp claws on their webbed feet. They are nocturnal on the breeding islands and only come in to nesting burrows after dark.
As dusk nears during the Austral summer at places like the Cape Horn Archipelago and at islands off the South Island of New Zealand, mind-boggling numbers of these birds appear as they stage just offshore awaiting nightfall. The ocean’s surface darkens with teeming numbers of these birds as they prepare to visit their nest burrows to relieve a mate or to feed a single chick.
Although graceful at sea as they catch the wind near the water’s surface, they are clumsy on land and awkward on landing and takeoff. Their habit of returning to nesting colonies at dusk and leaving before dawn is a survival mechanism that clearly is a good way to avoid predators, particularly gulls, ravens and skuas. The ability to fly in the dark is also useful for finding food that is primarily available at night.
After breeding they make a Trans equatorial migration to the northern reaches of both the Atlantic and Pacific Oceans allowing them to take advantage of seasonally abundant food resources. The Sooty Shearwater is by far the most common shearwater in the North and South Atlantic Oceans, ditto for the Pacific. Estimates of flocks of these birds numbering in the millions have been reported from many oceanic hotspots for bird activity. There have been aircraft counts describing masses of these birds on the ocean’s surface extending for miles at sea. During migration endless parades of these black birds with silvery wing linings become mesmerizing.
Around the Cape and Islands these birds arrive at the end of May. Generally they stay slightly offshore but on any given afternoon with a telescope one can see them shearing the horizon with strong onshore winds from south shore locations or from Outer Cape beaches. Anywhere south or east facing on Nantucket or the Vineyard can be productive as well.
These highly migratory ocean wanderers are on a rather fixed schedule, even though it appears to human observers that the birds are aimlessly flying above the ocean. They appear like clockwork and records of their occurrence in various ocean locations are predictable within a few days, year after year. Their movements are anything but random and the species has evolved a highly precise migratory route that takes them around the oceans of the world.
