Tracking scoter mortalities

26 06 2014

In mid-June, our favorite duck hunter, Jack Renfrew, wrote to tell us that his son had seen about 50 dead Black Scoters on the rocks near Woods Hole, Massachusetts. This past week, we received an email passed along by Rick Keup down in South Carolina letting us know that the state wildlife authorities were looking into scoter die-offs on their shores as well. Their agency managed to get a few carcasses and have shipped them to the National Wildlife Health Center in Wisconsin for diagnostics. Hopefully, we’ll have some answers for you soon, but as we’ve learned time and again in such cases, there may be no clear answers in the end.

In the meantime, we’re left wondering. Is this scoter phenomenon the same in the north versus the south? Is there a difference in age or sex between the northern and southern birds? In body condition? In a whole host of other factors?

Because I am a nerd, my birthday present last year was this informative but not very flashy volume:

In it, I have learned that Black Scoters tend to venture farther south in the winter than our other scoter species, with substantial numbers (up to 30,000 birds) found as far south as Georgia. There are reports of the birds even in Florida in eBird, though the species is comparatively rare there. The heart of their wintering terrain runs from Maine to Virginia, in any case, so South Carolina is certainly pretty far south for them. As for timing, the species breeds here in the East on lakes from Ontario to Labrador, and they mass for that northward migration in the St. Lawrence starting in mid-April. By mid-May, most of the birds have traveled to and are headed onward from the St. Lawrence. By the end of June, few birds would be expected to remain down south, and eBird records tend to reflect that:

Screen Shot 2014-06-26 at 11.56.38 AM

The Nisbet et al text reports that “very few (usually <10 together) oversummer in the main wintering areas off the eastern United States." Any birds still remaining in the southern states at this point in the year, then, may well be abnormal. But are these birds starving? Sick? Ill-equipped to make the migration or to attempt breeding? There has been some chatter along these lines amongst the birders and wildlife pros contemplating the problem, and factors like this winter's harsh weather and its impacts on sea ducks have been bandied about. Nathan Dias, who birds the southeastern coast, wrote,
"This is the second summer in a row that numbers of Black Scoters over-summered in SC. Some have been lethargic and spent a lot of time on the beach, while others have looked healthy and hale all summer long. John Cox, Chris Snook, I and other CRBO folks saw them in multiple locations in Cape Romain NWR last year (Key Inlet, Marsh Island, north Bulls Island) and down at Kiawah and Sullivan's Island as well. But there are definitely more of them this summer – they are all over the SC coast."

Whether we're looking at a couple aberrant years, or a new normal remains to be seen.

As we learn more, I will be certain to share it along, my dear readers.



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