by Bob Engel, Marlboro College Professor Emeritus of Biology and Environmental Science
This time of year is magical. An all but lifeless dormancy is flipping to its other personality: brilliant, lush green and all that depends on that. That’s you and me, psychologically, but it also makes life possible for whole swaths of nature. That includes most of our birds, especially those that rely on insects and other arthropods.
As I write this, they are flying, mostly at night, in our direction. The early birds have already arrived. These (sparrows, blackbirds, sapsuckers, phoebes and others) have retreated to the U.S. sunbelt, just as many Vermonters do. But the ones just starting to arrive, often from great distance and presumably at great cost, are tropical birds that view Vermont as a bountiful, tropical paradise for two or three months. Most of them winter in the Caribbean, southern Mexico, and central America. A handful come from as far away as Peru. How they get here is another story, but coming they are — in the millions.
The timing of their arrivals is loosely cued to the availability of food and the habitat that supports it. The males especially are caught between a rock and a hard place. Get here early enough to procure a decent territory (with food, nesting sites, etc.), but not so early as to get caught in horrible cold snaps, late snow storms, and a foodless world. The females come a bit later, sometimes because they have been segregated by the males into inferior winter habitat where they must remain for up to two weeks to get enough food to start the trip (e.g., American Redstarts in Jamaica).
They can arrive in surges that are quite dramatic. Sometimes the birds are forced down for feeding by stormy weather. If you happen to encounter one of these groups — I did a couple of years back on the coast — the trees and shrubs are just dripping with birds all looking to fill their tanks. In the instance I mention, there were at least 10 species of warbler jostling with each other for a place to land and look for food. It was a birding clinic; they were just twenty feet away.
This arrival is starting to happen here. Many migrants use the Connecticut River as a navigational device and stop for feeding along its more accessible, undeveloped shoreline.
Locally, one of these places is just across the river in Hinsdale, N.H. Oblivious to the carcass of Vermont Yankee, birds can be very common where the river abuts or has insularized an old rail bed. A walk along that can be very productive, and we at Southeastern Vermont Audubon go out for five successive Saturdays in late April and early May to see the patterns of arrival of both the few birds that stay right there, and the majority that are just taking a break.
By doing this, we can see the start of surges, their peaks, and then finally a few stragglers. Each surge might take about two weeks. For example, yellow-rumped warblers surge through in the last ten days of April and the first week or so of May. Palm warblers, headed for the muskeg of Canada, do just about the same (some birds of both of these species winter in our “sunbelt”). But last year, we recorded our highest tropical migrant diversity on 5/9 and 5/16. Lots of vireos, warblers, and thrushes. By 5/23, the newly arrived Hinsdale residents were sweeping their floors and everyone else had moved on.
The Museum has planned a morning guided walk on 5/21 in Grafton that would allow us to see and hear these amazing creatures (living links to the dinosaurs) in full summer swing. They will have just established their territories, and won’t yet be comfortable with their neighbors. Most will have mated, and nest construction will be in process. In some instances incubation will even be underway. Of course, our tough, fully temperate residents might well be further along. Because of the vulnerability of incubating adults, their eggs, and their helpless young to predators and parasites, the whole thing happens in a flash. We will be there to see this in prime time.