It may sound strange to refer to one of our most conspicuous songbirds as “enigmatic,” but there you have it: There is a lot about the Northern mockingbird that just doesn’t make sense to me.
When present, especially during the breeding season, the species is impossible to miss. Males, famous for the sustained and varied vocalizations that give this species its name, sing incessantly from prominent perches such as treetops, wires, and rooflines. Mockers are also notoriously territorial: Both sexes will relentlessly harass hawks, cats, and even people too close to a mockingbird nest, flying into the face of the perceived threat while giving a harsh, grating alarm call.
Even in winter, mockingbirds are generally easy to find, since their preference seems to be for suburban housing developments — a plentiful, accessible, and easily surveyed habitat type. Mockers thrive on the semi-open conditions in this setting, and relish the fruits and berries produced by many popular landscaping plants. It is probably this affinity for modern human land-use patterns that drove the initial expansion of mockingbirds into New England, which was noticed by ornithologists well before the end of the 1800s.
But while many such instances of Northward range expansion seem linked at least in part to climate change, mockingbirds colonized much of our region before the effects of climate change had become evident. And puzzlingly, in recent years, at least in the Southeastern portion of Massachusetts, it appears that the species has grown somewhat less common despite generally milder winters and the steady march, or more accurately full-throttle charge, of suburbanization. My sense is that the downward drift of mockingbird numbers has been especially evident on the Vineyard, although the picture is a complicated one.
Our winter population, at least as measured by Christmas Bird Count results, has behaved strangely. In the early years of the Vineyard count, which was launched in 1960, mockingbirds were scarce — recorded every year, but usually in very low numbers. Numbers skyrocketed, though, from 10 individuals on the 1979 count to 93 the following year. Over the next quarter-century or so, scores of mockingbirds were counted consistently, and tallies often exceeded 100. After that window, though, numbers dropped sharply again, and have hung mainly in low double digits (with a particularly pitiful count of just three in 2013).
To be sure, one would expect mockingbird numbers to fluctuate with the severity of the season. Though the species is not strongly migratory, individual birds will make seasonal movements in response to the onset of winter (such movements do not necessarily follow the expected North-to-South pattern, however). And of course, being at heart a Southern species, the mockingbird is vulnerable to freezing or starving during prolonged snow cover or extreme cold.
But the vagaries of our winter weather would not account for that fairly consistent, long-term rise and fall of mockingbird numbers. What the bird-count data show is not the pattern one would expect for a species that benefits from milder winters and increasing suburbanization, both of which have progressed steadily in recent decades.
It has been several years since mockingbirds were regular in my Oak Bluffs neighborhood, where once this bird was common enough and noisy enough to verge on being annoying. Having managed only one mockingbird in my Vineyard Haven territory on this winter’s Christmas Bird Count, I headed up-Island on an early January day to see how many mockers I could find.
While the thickets were productive that day once the sun warmed things up, and the birding generally quite good, I managed only three mockingbirds. All three were in dependable locations for this species, one mocker contentedly eating privet berries at Menemsha, the other two in thickets around the circle at the Gay Head Cliffs (where I almost never fail to find this species).
But vast amounts of habitat seemingly suitable for this species failed to produce any mockers. Broader sources, such as iNaturalist records of this species, paint a similar picture: Despite their onetime abundance, mockingbirds have become rather local on the Vineyard, with most recent records coming from a relatively small number of dependable, often intensively developed locations. I rarely find this species in a truly natural setting.
While drab in appearance, the mockingbird is easily recognized. Adults of both sexes, and immatures once they have fully fledged, all look similar: gray on the back, white underneath, long-tailed, and sporting flashy white tail edges and rectangles on the outer portion of each wing. Really the only thing you could confuse with a mockingbird would be a Northern shrike (a very rare winter visitor on the Island) or a loggerhead shrike (even rarer). So it isn’t like mockingbirds are being overlooked.
The species is local here, but not truly rare, and overall mockingbird numbers in the region remain solid. So there is no cause for concern over the status of this bird. But the mockingbird is a puzzling example of a species that doesn’t respond to ecological changes in the way you’d expect.