Thursday, February 4, 2016

Absence of sea ducks attributed to weather, climate

            Rhode Island’s south shore is typically a haven for wintering sea ducks. It’s not unusual to observe flocks of hundreds of eiders and scoters and dozens of harlequin ducks grouped together feeding amid the crashing waves. But not this year. At the usual places where observers go to look for the birds – like Brenton Point, Sachuest Point, Beavertail, and the Charlestown Breachway – duck numbers are alarmingly low.
            Many of the active birders in the region repeatedly scour the coastline looking for the usual flocks of sea ducks, but they are reporting just a few handfuls of the birds, which is not nearly what they have come to expect.
According to Scott McWilliams, an ornithologist at the University of Rhode Island, there are multiple possible explanations for the absence of sea ducks in the area, explanations that involve the warm weather in December, environmental changes due to global warming, and even behavioral preferences among the different species of birds.
Black scoter by Alan D. Wilson
The three species of scoters – surf, black and white-winged – are attired in black plumage with white markings on their head and variable amounts of orange on their beaks. They often flock together with common eiders, which are black and white with a pale greenish tinge behind the head and neck. And the most sought-after of the sea ducks, the harlequin, is an attractive combination of slate blue, chestnut and white in patterns reminiscent of their namesake character. None of the five species seem to mind the blowing wind and cold temperatures of the New England winter, and harlequins especially seem to prefer the surf zone.
McWilliams isn’t worried, however, that duck populations have suddenly declined in Rhode Island waters this winter. Instead, he believes the birds are simply spending the winter elsewhere.  He said that the warm temperatures early in the winter likely played a role. Rather than migrate all the way from their breeding grounds in Canada, the birds probably took advantage of the warm weather in December and lingered along the coast of the Canadian Maritimes, Maine and Massachusetts, where many of them likely remain.
That’s almost certainly true of common eider. “Once they find a spot they like, they stay there,” McWilliams said. “Each bird tends to spend the entire winter within a very small area. So the 200 eider that you see one day at the Charlestown Breachway are the same 200 eider that will be there every day of the winter.”
Black scoters, on the other hand, are wanderers.  McWilliams and his colleagues have tagged a number of scoters and eiders to track their activity as part of a region-wide study of bird movement patterns, and they found that black scoters appear to move around based on local environmental conditions. “So they may be here in Rhode Island waters for a few weeks and then take a jaunt to the Chesapeake Bay for a few weeks, and then maybe return,” he said. “They probably pay close attention to changes in the environment and move around based on the conditions.”
The colder weather in January has prompted some eiders and scoters to move further south to their more typical wintering locations in recent weeks, but McWilliams said that most haven’t gotten much beyond Cape Cod just yet. And most may not make it to Rhode Island at all this year.
Rhode Island seldom has large numbers of wintering white-winged scoters, so this year’s numbers aren’t far off from an average year. McWilliams said that most white-winged scoters spend the winter off Cape Cod, and based on the data from birds he has tagged, they are in their usual places this year.
One other element that may be confounding the situation is climate change. The URI researcher said that increasing temperatures and the longer ice-free season in northern waters may mean that many species of coastal seabirds are finding open water further and further north. Scientists studying biological activity in northern waters say that food appears to be readily available to seabirds that choose to spend the winter months to the north. So the birds may not have to travel as far south as they used to in winter. Since migration is the most dangerous time in a bird’s life, many may choose to cut the trip short and spend the winter to the north of their usual range.
So the dearth of sea ducks in Rhode Island waters this winter may be a sign of things to come, McWilliams said. Bird watchers in the region might have to get used to seeing fewer seabirds in local waters in winter. On the other hand, it may also mean that more birds that migrate to points south of Rhode Island may end up wintering in the local area instead.

The article first appeared on EcoRI on January 30, 2016.

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