Winter, generally speaking, is a season I could live without. But I’ve always had a fascination with the ways wildlife responds to adversity, and the early January cold snap represented a fine opportunity to contemplate this subject. After several days of merely cold weather, the mercury bottomed out on the night of Wednesday, Jan. 7. Our porch thermometer in Oak Bluffs dipped to slightly below zero before sunrise Thursday morning; reports from elsewhere on the Island suggested that virtually the entire Vineyard hit zero or below.
My first thoughts were for a particular bird implausibly lingering at this latitude: a first-year male Baltimore oriole that has been frequenting feeders in West Tisbury for several weeks now. A familiar sight and sound on the Vineyard in summer, when they nest in deciduous trees across the Island, Baltimore orioles are ill equipped for winter. With long, pointed beaks, they’re optimized for eating insects, and struggle to eat the seeds that represent the bulk of the available food supply in winter.
Accordingly, orioles are strongly migratory. The heart of their winter range is Central America, though the species is regular in Florida and the West Indies in winter. But oddly, the Baltimore oriole is a bird that has always been prone to lingering in the North in small numbers, and in recent years, it seems like this imprudent behavior is growing more common. Perhaps not quite annual on the Vineyard in early winter, Baltimore orioles are approaching that degree of regularity, and the sight of one of these orange avian gems in early January is no longer much of a surprise.
The West Tisbury bird (it seems that only one individual was involved) was reported from several feeding stations, eating suet and doing its best with seeds. The last report I heard came from early on the morning of Jan. 8, so it survived the night of the deepest cold. Whether it lived beyond that is not clear, and even if it did, it may have relocated. So we may never know its fate.
How does a bird like an oriole, essentially a tropical species that disperses northward to breed during the summer, handle the deep freeze? The availability of a reliable food source, preferably with high-energy options like suet, is surely a critical element. Given enough calories to keep its internal furnace running, a bird can withstand surprisingly low temperatures, and the kindhearted birders providing food for the West Tisbury oriole were surely keeping it alive.
The real sticking point for such a bird is nighttime, when the temperatures dip to their lowest and when
protracted darkness makes it difficult or impossible to forage for ten hours or so at a time. About the only thing an oriole or similar species can do to survive the night is hunker down in a sheltered spot, fluffing out its feathers for maximum insulation and probably settling down on its perch so that its bare legs and feet, vulnerable to frostbite, are covered by belly feathers. At first light, feeding as heavily as possible is critical, and if conditions allow, soaking up whatever warmth can be gleaned from the winter sun is a help.
So much for the how; the other question is why? Migrants that linger into winter are often injured or sick birds, not fit for undertaking the journey south. But many, perhaps most, of the birds like the West Tisbury oriole appear perfectly healthy, and it seems probable that they simply lack the instinctive impulses that should trigger migration. The outcome of failing to migrate is usually not a happy one for the individual bird. But from the larger perspective of an entire species, defective instincts are probably a good thing: that’s the sort of variation that allows a species to adapt to climate change or the loss of traditional wintering areas, with the occasional misdirected bird surviving to discover new sites or strategies for surviving the cold months. Defective migrants, in other words, may be part of the evolutionary strategy of birds.
Interestingly, some species are more prone to linger than others. The orchard oriole, for example, is a close relative of the more common Baltimore oriole, but unlike the latter species it is almost unheard of in the Northeast in early winter (though it often turns up on the West Coast as a vagrant). Likewise among the warblers, some species, such as black-throated blue warbler, seem to linger with some regularity, while others — say, bay-breasted — seem to bail out for warmer climes with complete reliability. To some extent, migratory patterns may explain the differences, with the species that winter farthest to the south least prone to linger. But in the absence of actual records, it would be hard to predict reliably which species would be most likely at our latitude in winter.
In any event, I’m rooting for the West Tisbury oriole. He’s got high-quality food sources and even a few heated birdbaths available, if he can find them. And he’s demonstrated great tenacity and resourcefulness — even if he missed the memo on migration.