Dolphin Fleet Birdwatching Notes 15 to 30 June 2008
John C. Conlon
Over the past two weeks summertime pelagic birds are seen more regularly and in larger numbers. That’s exciting for everybody! But before getting into that, a reminder… keep a spot in your mind for the unexpected. On the 23rd of June we spotted an immature Glaucous gull. In the brilliant open sea light it appeared entirely white. In reality there is pale brown pigmenting along the wings. Its bright pink with black-tipped bill showed clearly as the bird circled the boat’s bow and port side. Glaucous gulls are usually here in the winter months and very rarely into May, so a late June sighting is a real treat.
The widely spaced Wilson’s storm petrels and shearwaters are now here in steady and larger numbers. Wilson’s storm petrels are regularly seen in evenly dispersed, though still low numbers in upwellings along the edges of Stellwagen Bank. And several days ago, while whale watching off the southeastern corner of the bank, in an area with 20 or more humpback whales, I got my first look at several mixed flocks of Greater and Sooty shearwaters. Each raft had some 200 or more birds. Other mixed flocks were in the air above the feeding whales. These same airborne flocks also offered some gulls and terns!
Greater shearwaters will average some 18 inches in length, 42 inches in wingspan and about 1.8 pounds. They are mottled grey-brown across the upper wing with darker tips, have a black cap and tail tip with a white nape and rump patch. They are quite white with marked black lines underneath.The Sooty shearwaters are smaller at 17 inches in length, 40 inches in wingspan and 1.7 pounds They are almost uniformly dark grey above and mostly grey beneath,though you will see that the length of the wings’ center is white.
As the humpbacks, using their bubble nets and clouds, fed, they collectively pushed thousands and thousands of six inch sand lance toward the surface. The foraging seabirds had an easier time feeding. Air bubbles will concentrate the sand lance (or sand eels), force them toward the surface and confuse them. The shearwaters will plunge dive from as much as 30 feet in the air or pursuit dive from the water’s surface and then use their wings and feet to propell themselves through the water to get the fish.
The sand lance themselves weigh mere ounces but these shearwaters are ravenous in their hunt. It has been estimated that collectively, shearwaters, including those we see here, will annually consume some 992 tonnes of sand lance, and another 247 tonnes of small herring, and 90 more tonnes of small mackerel from the northeast pelagic ecosystem. That’s 1,329 tonnes (almost 2.7 million pounds) of fish. But remember that shearwaters are virtually absent from the area for about 5 five months each year (December through April). So really that’s 1,329 tonnes of fish in less than seven months.
While shearwaters do form large feeding flocks that are easy to see while whalewatching, we should look around. Scan the open seas with your binoculars. Soaring individuals sometimes are seen by the hundreds where a passing glances would produce almost none. Look close to the water’s surface. Updrafts above even small rolling waves allow shearwaters to soar great distances. In stronger winds their “dynamic” soaring is aided by winds moving above the water. Shearwaters glide from height downward on outstretched narrow glider wings. They gain speed as they decend. Turning into the wind their momentum carries them slightly foreward while the updraft again lifts them higher for the next longer downward and foreward glide. By using the wind’s energy these long arcing loops allow shearwaters to cover great distance with less of their own energy.
The aerodynamic capabilities of these two shearwaters are even more impressive when we consider that both nest in the far south Atlantic Ocean. The Greaters nest in the mid-south Atlantic areas of Nightingale, Inaccessible, Tristan da Cunha and Gough Islands while the Sootys nest in the Staten, Wollaston and Deceit Island areas off Cape Horn, South America. The annual migration of both species brings them up much of the east coast of South America, up the east coast of North America, and across to western Europe before looping back across the open Atlantic toward eastern South America and back to their respective breeding islands. The waters off Cape Cod are used as a late autumn staging area for nonbreeding Greaters, while some nonbreeding Sootys are also thought to stay north of the equator in nonbreeding season.