Blue-winged Warbler

The Blue-winged Warbler announces his presence with an insect-like “beeee zzzzzzz” sung from a shrub or sapling at the edge of an old field. At some point in the past this would have been sufficient for an identification, but now things are more complicated. But first, a bit of history is in order.

The Blue-winged Warbler was unheard of in New England in the early 1900s, but was already gradually expanding northward from the Appalachians in response to forest clearing. At the same time or slightly earlier, the closely-related Golden-winged Warbler was moving east out the Great Lakes region. Eventually the two species met in the Northeast and soon began to hybridize, and therein lies the source of our inability to identify either species by song. Hybrid individuals have plumages that a widely divergent from the adults. They are also fertile and readily mate with either parent species, and it didn’t take long for the situation in the overlap zone to become quite confusing. To make matters worse, there is no consistency in song types, so that “textbook” “beeee bzzzzz” you heard earlier could just as easily be a Golden-winged or a hybrid. You need to find the singer and see what it looks like – and check it carefully for signs of hybridization.

Because of this complex interaction between the two species, their ranges have continued to shift at local and continental scales. In the 1980s both were restricted to extreme southeastern New Hampshire, but 10 years later the only Golden-wings were in the Connecticut Valley – and soon thereafter disappeared from the state entirely. Blue-wings expanded up the Connecticut and Merrimack valleys as well, but then retracted south in in the early 2000s. Most Golden-wings are now around the western Great Lakes, while Blue-wings are patchily distributed from southern New England to Arkansas and Wisconsin.

Much of the shifts in the Blue-winged Warbler’s range are the result of changes in habitat. For an early successional species it is fairly specialized, preferring areas of saplings over those dominated by shrubs. It would appear there is thus something of a “sweet spot” around 10-20 years where a regenerating forest is ideal. As this habitat appears and disappears, so do Blue-winged Warblers, and this may explain most of this species’ brief period of relative abundance in the Granite State.