Wild Side: Yellow-throated warbler

Yellow-throated warbler. —Matt Pelikan

Well, he’s back again. 

In one of the more bizarre episodes in the history of Martha’s Vineyard bird life, a male yellow-throated warbler is once again on territory amid the tall pitch pines of a residential neighborhood in Vineyard Haven. Found again last week, this charismatic bird has been showing well, singing persistently, and exhibiting his characteristic penchant for flying in to take a close look at his own observers. You’d almost think this bird enjoys being watched; he certainly enjoys visiting the Vineyard.

According to my colleague Luanne Johnson, this bird was first found at the end of April in 2019, and has been observed annually since then. How long he remains on his territory each year is not entirely clear; one limitation of data collected from recreational birders is that the reports stop coming once a bird loses its novelty. But reports typically extend into late May or June, showing that the bird is territorial, and not simply passing through.

I’ve noticed no distinctive marks on the bird that allow absolute certainty that it’s the same bird returning. But given the rarity of the species here, and the consistency of the bird’s arrival date, location choice, and behavior, it seems inconceivable that multiple individuals could be involved.

The yellow-throated warbler is essentially a species of the Southeastern U.S. The breeding range of the bird extends north along the East Coast into southernmost New Jersey and southwestern Pennsylvania. In southern New England, the species occurs as a rare but quite regular “overshoot” migrant in the spring, its arrival here sometimes associated with coastal storms or strong southerly winds. Fall records do occur, but are less frequent. A relatively short-distance migrant, the species retreats mainly to Florida, the Yucatán Peninsula, and the Caribbean islands for the winter. 

Several poorly defined and somewhat disputed subspecies occupy the overall range of this species. Some birds, typically with relatively long bills and tiny but distinct yellow patches in front of their eyes, breed mainly in East Coast pine habitats. Another form, breeding more in the interior, including the western slope of the Appalachians, prefers sycamore woodland along stream drainages, has a shorter bill, and lacks the yellow facial spots.

As is typical of avian subspecies, these forms intergrade and intermingle. But the Vineyard Haven bird, with a notably long beak and clear yellow in front of his eyes, seems to be a solid member of the coastal, pine-loving group, and probably feels quite at home among the pitch pines in his chosen territory.

Two things are unusual about this bird. First is the length of his history. First found as an adult in the spring of 2019, he could have hatched no later than the 2018 breeding season, and possibly earlier. So as he makes this spring’s trip to the Vineyard, he is approaching at least 6 years of age. This longevity verges on exceptional for a wild songbird; regarding this species in particular, the account in the Cornell Lab of Ornithology’s authoritative Birds of the World website cites 5 years and 1 month as the oldest individual known to the account’s authors. So the Vineyard Haven bird may be one of the oldest yellow-throated warblers on record.

But perhaps even more notable is the fact that this bird sets up shop on the Vineyard every season. We are hundreds of miles from the northern edge of the typical breeding range of the species. The inescapable inference is that, having mistakenly flown too far north during the 2019 spring migration, this individual simply liked what he found enough to keep returning.

With at least six full migration cycles to his credit, this bird certainly wins points for his survival abilities. 

But what about reproductive success, which is really the gold standard for defining success in the natural world? In this area, it must be said that our bird has chosen a high-risk strategy, establishing a territory in a place where his species occurs only as a rare vagrant. The odds are slim of a female yellow-throated warbler happening along to mate with, and at this bird’s advanced age, time is surely running out for chances to pass along his otherwise exceptional genes. (Though if a female did appear, our bird would enjoy the complete absence of competition from other males.)

Territorial and even actual breeding records for this species far north of its normal range are not unprecedented. And overall, it appears that yellow-throated warbler is gradually but steadily extending its range northward. Viewed in that context, the reliably returning Vineyard Haven bird is unusual, but perhaps best viewed as a cog in the overall evolutionary strategy of his species. Individuals like this one are the vanguard of range expansion, usually failing to reproduce, but sometimes establishing outposts that help the species overall adapt to altering habitat conditions and climate. I wish this genial bird the best of luck.