Monday, May 20, 2013

By E. Vernon Laux
Published: July 23, 2009

Time waits for no bird. Bird migration, especially the southbound movement of shorebirds, is in full swing in late July. While the dog days of summer may be upon us, for migratory birds it's a critically important time as they feed voraciously at favored locations, often doubling their body weight in as little as ten days. They bulk up, accumulating a subcutaneous layer of fat, storing it as energy required to fuel their incredible flight and grow new feathers.

Cory's Shearwaters, which are surrounding the Island this year, are designed for life at sea. The "tubenose" mounted on the top of its beak drinks saltwater and excretes concentrated salt. Photo by E. Vernon Laux

The birds are able to utilize this fat like your car uses gasoline as fuel for travel. Often at this time of year, birds of the same species standing side by side on a mudflat will look very different. One will appear much larger than the other. One individual may have just arrived on Vineyard shores overnight while the other has been here feeding and fattening, and may be about to depart on a nonstop southern flight of thousands of miles. Their weights can vary up to 100 percent.

This makes the identification of these stylish and graceful birds even more challenging. Physical sizes vary according to what stage of arrival or departure condition the birds are in. Being cognizant and aware of this an important factor when determining what species one is looking at. The birds seen in our area are just visiting briefly for a week or two as part of a remarkable annual journey that takes them tens of thousands of miles on a circuitous route.

Shorebirds are such strong flyers and incredible navigators that they are able to find where they want to be and arrive exactly when they want to be there to take advantage of abundant food resources. So, once the birds have survived a migration they pretty much are able to duplicate the timing and route from year to year.

On the Vineyard, birders hope for strong thunderstorms or even hurricanes to force these remarkable migrants to detour to Island shores. Birds are able to detect and avoid nasty weather by being equipped with built in barometers. They will interrupt their migration and go to ground at the nearest landfall when confronted by such life threatening storm systems. The best time to find shorebirds on the Island is during and immediately after such foul weather.

Offshore waters

On Saturday, July 18, a dedicated pelagic birding trip took off from Hyannis harbor at 4 am, headed south. The Helen H motored across Nantucket Sound, up Muskeget Channel between the Vineyard and Nantucket, and headed south to the warm waters at the edge of the Continental Shelf. They discovered a petrel in the genus Pterodroma, southern birds that can be found with regularity off Cape Hatteras. This black-capped petrel, a fifth record for the state, was the first of its kind to be seen by a boatload of observers off Massachusetts, and the first ever photographed in Massachusetts waters.

This had the trip off to a rousing start despite the rather bleak weather for the first four hours. Other highlights were a total of 19 Audubon's shearwaters, another southern species that occasionally appears at the shelf edge in summer. They are not known to occur north of Cape Cod. This total is the most ever reported from New England and specifically these southern shelf waters south of the islands.

The trip also recorded 232 Cory's shearwaters, 240 greater shearwaters, 16 sooty shearwaters, three manx shearwaters, 475 Wilson's storm-petrels, 58 Leach's storm-petrels, and a Pomarine jaeger. There are lots of birds not far away to the south. If you are fortunate to get a trip out there fishing, sailing or whatever, keep some binoculars and a digital camera at the ready.

Land birds

Land birds are also on the move and a couple of land birds were seen about 15 miles south of the Vineyard on the aforementioned pelagic trip. They were too far away to be conclusively identified. Optimum conditions for land bird movement are the passage of a cold front with light to moderate northwest winds. On mornings after this kind of weather the Vineyard experiences some of the finest birding anywhere on the continent.

As the nesting season continues to wind down, all birds are engaged in the process of growing new feathers, called molting. In between feeding bouts they are resting and preening - taking care of their all-important feathers. They depend on feathers for insulation, protection, and mobility. Only birds have feathers and they are an incredibly versatile, strong, lightweight physical adaptation that has enabled these animals to fly, making them far and away the most mobile creatures on the planet. Until next time - keep your eyes to the sky.