Birds : Spring fallout
Things are right in the world for both birds and birders in the middle of May. It is an exciting time of year for birders, whether novice or veteran, as migrant birds pass by and summer resident species return for another breeding season. It is as if the night sky becomes an avian highway and the Island serves as both rest stop and final destination.
The vast majority of land birds migrate in darkness. From a terrestrial mammal's perspective, nocturnal migration represents a mysterious and largely unseen phenomenon that begs the question of how the birds are able to perform such a dangerous and seemingly miraculous journey. The fact that they perform this remarkable feat is indisputable and research into nocturnal bird movements is just beginning to unravel the smallest threads.
It is a large part of the wonder of a May morning, knowing that millions of birds were on the move during the night. This creates alertness and sensitivity by the observer to what is going on in the natural world. It is a special season that passes all too quickly.
The spring migration went ballistic this past week as long-awaited arrivals occurred all over the Island and the entire region. There was a spectacular fallout of Neotropical migrants transported farther east than many of the birds would have liked, and the birding has been predictably terrific.
On Mother's Day, May 11, it rained summer tanagers on both the Vineyard and Nantucket. David and Julieanne Mehegan of Hingham visited Cape Pogue and were delighted by a male summer tanager and a blackburnian warbler. This was the second summer tanager reported on the Vineyard this spring. Also on May 11 three different summer tanagers were discovered at three different places on Nantucket, the first ones reported from that island this spring.
From people watching their feeders to more active field observers scouring migrant traps, all have reported lots of birds. Most impressive have been Island-wide reports of rose-breasted grosbeaks, scarlet tanagers, indigo buntings, and orchard and Baltimore orioles. These colorful and distinctive birds arrived in numbers this past week and have been delighting observers fortunate to have them in their yards.
Photo by E. Vernon Laux
The number of migrants passing through has been impressive. Warbler species that nest farther north have been detected as well as species that have returned to the Island to nest. Warblers that were seen this past week included Magnolia, blackburnian, yellow, American redstart, black-throated blue, black-throated green, black and white, prairie, yellow-rumped, pine, ovenbird, and northern waterthrush. Typically, the next two weeks will see the largest movement of spring warblers. So, if one could only bird for one week or one day during the spring, these should be the weeks that are necessary to get out in the field. Any favorite spot that one frequents will be a little different this week as birds that are continuing further north stop for a brief visit.
Each species has an optimum time of arrival for returning to the breeding grounds. Generally speaking, the farther north a species nest, the later in the season it will pass by or over the Vineyard. While the weather is improving daily, 1,000 miles north of here, where many of the passing land birds are heading, conditions are still not hospitable for these insectivorous birds.
So, as the season advances, boreal and Arctic nesting species time their arrivals for the end of May or early June. They bide their time at ancestral stopover points or take their time moving north in a series of leisurely nocturnal flights whenever good weather allows. But as the days grow longer and May turns to June they become driven to get back north and will move in almost any weather.
This has a lot to do with explaining how birds end up on the Vineyard in the spring. A look at a map of North America, specifically the eastern half, shows the land mass. The continent expands both east and west at the top or northern half.
Most land birds move up the middle of the continent and then branch off to where they are going. Land birds stay away from the coast in spring as the result of countless successful migrations. The birds that survived to pass on their genes to perpetuate their species stayed away from the dangerous and inhospitable ocean and adjacent coastlines.
Species that nest in Maine, New Brunswick, Nova Scotia, Prince Edward Island, Newfoundland, Labrador, Greenland, Quebec or farther north on Baffin Island must cover a lot of distance. They prefer to stay overland where they can find food and shelter, but they are capable of long over-water crossings. They routinely make these crossings in the fall migration but not as frequently in spring. However, as the end of migration nears and the rush to arrive at the breeding grounds becomes imperative, water crossings become less of an issue.
Which is why the birding along the Massachusetts coastline and offshore islands is usually much better in mid to late May than earlier in the month. The reverse is true at inland locations where the best birding occurs in early to mid-month. Additionally, non-breeding immature overshoots often appear at this time of the year.
With the abundant bird song that characterizes both dawn and dusk at this season, many kinds of birds that are here but are seldom seen are heard with surprising frequency. Bob-white (quail), a species that has been declining on the Vineyard and over most of its range for decades, can still be heard proclaiming their existence. They are not common, but can still be heard calling in many areas, especially in more rural spots along the south side of the Island.
The tidal flats on the Island are alive with shorebirds now. The resident nesting American oystercatchers, willets, and piping plovers are already sitting on eggs. The vast majority of birds on the flats; black-bellied plovers, dunlin, sanderlings, least sandpipers and assorted others nest on tundra far to the north. They are feeding voraciously in preparation for their final push to the breeding grounds.
They may linger here until late May or early June, and then make a rapid flight to breeding areas that are just becoming snow free. These birds are superb athletes with a synchronous schedule amongst all members of the same species, allowing them to arrive, court, lay eggs and hatch young in the shortest time possible.
Every day brings with it the promise of new birds. As May progresses the speed of migration increases as birds' hormonal levels increase. So as the end of the month nears, so does the number and variety of bird species present, especially here on the Island. It is a fantastic time of year.
Until next week - keep your eyes to the sky!