Martha’s Vineyard is famous among birders, with a well-earned reputation for both a skillful birding community and a tendency to attract rare birds. While arriving rarities are by their nature unpredictable, patterns in what rare birds tend to occur at particular seasons are well-known. April, for example, invariably brings a smattering of southern warblers to the Vineyard, individuals that “overshoot” their normal range as they migrate northward on warm spring winds.
Even more interestingly, those patterns can change over time, and these changes can occur quite rapidly, relative to the usual pace of natural change. Such has been the case with vagrant hummingbirds, not just on the Vineyard but across the East Coast.
Just a few decades ago, it was assumed that the one hummingbird that breeds in the East, the ruby-throated hummingbird, was the only hummer likely to be encountered east of the Great Plains and the Gulf Coast. But starting around the 1980s, hummingbirds from the West, where diversity in this odd avian family is much higher, began turning up in Eastern states with increasing regularity, mostly in the fall and early winter.
Late-season records of ruby-throated hummingbirds have increased, too, reflecting a steady increase in the breeding population in much of New England. But most ruby-throats have left the region by mid-October, and a hummingbird seen after that date in Massachusetts is now more likely to be a vagrant than our common local species.
While these vagrant hummers have occurred widely in the East, records concentrate along the coast, meaning that the Cape and Islands region receives its full share. Most recently, a feeder near Christiantown has hosted the Vineyard’s third black-chinned hummingbird, a Western relative of our familiar ruby-throated hummer. First noticed in late November, when reports of a mysterious late-season hummer came from several observers in the area, the bird eventually settled in around the feeders of Gary Mirando, who photographed it resoundingly.
The photos were critical because hummingbird identification, especially when immature or female birds are involved, is difficult. Subtle marks such as the extent of white in tail feathers or the shape of the tips of flight or tail feathers can be crucial for firm identification. Following previous records for this species in 2005 and 2007, this black-chin stands out as one of the exceptional Vineyard birds of 2016.
Famously tiny and frail, hummingbirds seem like improbable candidates for long-distance vagrancy. But some species of this group are strongly migratory and capable of amazing nonstop flights (our ruby-throated hummingbirds, for example, often cross the Gulf of Mexico during migration, necessarily nonstop since there is no place to land along the way except the odd oil platform).
Assessing the rise in vagrant hummers over the past few decades is difficult. For one thing, birding and birdfeeding have both grown as activities, so the number of observers has increased, which would tend to produce more reports. On the other hand, populations of some Western hummingbirds have declined steadily in recent years (the rufous hummingbird, for instance, the most commonly occurring vagrant, is declining in numbers at the rate of about 2 percent per year, according to Breeding Bird Survey data), which would tend to make vagrants less numerous.
On balance, my take is that there is a real change going on here, with increasing percentages of some Western hummers migrating more East than South. The choice is probably a bad one from the perspective of individual birds; while a hummer can hang on deep into December if it has a reliable food supply, the odds of surviving a New England winter are slim for hummers, which rely on small insects and nectar from flowers for sustenance.
But if you consider entire species rather than individual birds, the picture may be different. Under unusual conditions, hummers can survive and indeed even return repeatedly to the same wintering location. One rufous hummingbird wintered for at least six consecutive years in a greenhouse on the Massachusetts mainland. And farther south, where milder weather makes winter survival easier, there are many instances of such “wintering site fidelity” among hummingbirds.
A reasonable conclusion, then, is that the rise of vagrant hummingbirds in the East is a natural process of exploration by a group of related species. Probably in response to the changing climate and associated alterations in wind patterns, increasing numbers of hummingbirds are testing nontraditional migration routes and wintering locations. And at least some of these birds, probably benefiting from increased availability of hummingbird feeders and late-blooming flowers, are surviving the winter in these new locations, gradually altering the migration pattern of an entire species.
Vagrants like the recent Christiantown black-chin, then, reflect a significant change in the life histories of hummingbirds. Climate change, changes in human behavior, and innate flexibility built into the genes of the hummingbirds themselves interact to make a class of rarities steadily less rare.
The Christmas Bird Count
In December 1900 ornithologist Frank Chapman of the American Museum of Natural History suggested that we as a nation replace the Christmas tradition of bird shoots with a new tradition of a Christmas bird count. More than a century later, the National Audubon Society’s Christmas Bird Count is going strong. The day-long tabulations are undertaken between Dec. 14 and Jan. 5; the 57th annual Martha’s Vineyard count will be done on Friday, Dec. 30. If you haven’t joined a group counting birds in the field, it’s not too late: count the birds are your feeder between 2 and 4 pm, and report your results to Felix Neck Sanctuary (508-627-4850). For more information see the Biodiversity Works website.