Wild Side: The osprey cometh

It’s just a question of when.


It’s hard to think of a species more beloved among Vineyarders than the osprey. This long-winged, black-and-white bird was, like many other raptors, nearly exterminated in the 1950s and 1960s by indiscriminate insecticide use. Following the ban of the worst chemicals in the 1970s, this fish-eating hawk has bounced back with gratifying vigor.

The species occurs worldwide, on all the continents except Antarctica. Four subspecies seem to be generally recognized, including ours, which ranges across North America; a Eurasian and an Australasian subspecies; and a gorgeous, nonmigratory West Indies form with a much whiter head than our birds have.

For Ludlow Griscom and Guy Emerson (“Birds of Martha’s Vineyard,” 1959), osprey was mainly a transient on the Island, with just a few nesting records from the 1950s, a pattern that prevailed into the early 1970s. From that point, a rebounding population combined with a campaign by Gus Ben David and others to erect nest poles for ospreys has steadily increased our breeding population, with Rob Bierregaard’s exemplary monitoring efforts tallying more than 100 active nests in recent years.

In the North American population, migration is complex, but in general, ospreys nesting at higher latitudes are strongly migratory, while lower-latitude breeders are much less so, and may make only local, seasonal movements as they follow resources. The movements of the Vineyard’s ospreys have been splendidly illuminated by the work of Bierregaard and his collaborators (including the late and very much missed Dick Jennings). More than 20 years of radio-tagging has shown a clear pattern of movement, sometimes involving prodigious overwater flights, to (mostly) northern South America for the winter.

Return journeys are idiosyncratic in terms of timing, but data on Rob’s website shows birds leaving on spring migration in late February or March, and taking anywhere from a couple of weeks to well over a month to complete the trip. In 2015,one bird, Snowy, dilly-dallied in Cuba (where she had sometimes wintered), but then moved from Cuba to Cape Cod in just six days, covering as many as 400 miles in a single day.

Yet historically, the arrival date for ospreys in our region has remained quite stable. Vern Laux always declared his birthday, March 17, to be Official Osprey Arrival Day here, though the birds often showed up late to the party. The earliest solid record I can come up with for Martha’s Vineyard is March 14, which Soo Whiting and Babara Pesch deemed reliable enough to include in “Vineyard Birds II.”

The picture isn’t much different across Massachusetts generally. The online data portal eBird contains almost 140,000 Massachusetts checklists that include osprey; exactly zero of those checklists date from the first week of March, and there is only the thinnest smattering of reports from any other time in the first two and a half months of the year. The legendary Edward Forbush, in his 1927 “Birds of Massachusetts and Other New England States,” cites a Bay State osprey record from March 7; this is no doubt reliable, and indeed that bird may well have been shot and examined in the hand, since that’s how ornithologists rolled in those days. But it stands out even a century later as an exceptional record. Arthur Cleveland Bent’s account in the aging but still valuable “Life Histories of North American Birds of Prey” (1961), evidently overlooking the record in Forbush, mentions no Massachusetts ospreys earlier than a March 16 bird in Taunton.

Recent years, though, have seen a steady and intriguing trickle of Vineyard osprey reports in February and early March. Little is impossible when it comes to bird movements. And in an era of climate change, weird things are expected. But so far, none of those early reports has been supported by photographs, multiple observers, or sound recordings. Being conservative about unusual wildlife records, I remain skeptical but open-minded.

The problem with the Vineyard’s February or early March reports is that they come at a time when our breeding birds either haven’t yet left their wintering grounds, or if they have, are barely started on a journey of many hundreds of miles and at least a fortnight’s duration. And while it’s true that our winters are trending milder and our springs earlier, an osprey in Brazil wouldn’t know that, so one wouldn’t expect these changes to alter an osprey’s departure date.

Meanwhile, it would take a singularly foolish bird from one of the less migratory populations in the Southeast to head northward at this point in the season, into colder weather and less productive waters. So once the last, lingering southbound migrants have left in December or, very rarely, early January, it’s hard to think of a plausible mechanism that would bring ospreys here with any regularity until the usual arrival time, around the middle of March.

So what’s up? Are all, some, or none of those early reports valid? Happily, the Vineyard is equipped with a large community of alert and capable birders. If there truly is a change afoot in osprey migration behavior, it won’t be long before there is concrete evidence. In the meantime, unsubstantiated reports that conflict with a longstanding historical pattern should be treated seriously but with caution.