Warblers can be hard to find.
First of all, they are small. Slip three in an envelope, and a single 39-cent stamp would be sufficient to cover the postage. And they are binocular-shy, possessing a special talent for disappearing among dense foliage.
Misleading names add to the challenge of seeing a warbler. The Connecticut warbler shows up in Connecticut only during fall migration. The magnolia warbler favors northern conifers. And the Tennessee warbler nests nowhere south of the Adirondacks.
The Canada warbler is a refreshing exception to this pattern of misnomers, breeding from northern British Columbia east to Nova Scotia. Although its range is not confined to Canada, the areas it occupies in the U.S. evoke the Canadian landscape. These include cool, moist forests of the Northeast and upper elevations along the Appalachian chain south to Georgia.
But Canada warbler numbers have been dropping throughout the East ever since monitoring began in 1966. The loss of forested wetlands and changes in upland habitat may be contributing to declines that are averaging 4 to 7 percent per year.
In New Hampshire and Vermont, Canada warblers start returning from their tropical wintering grounds during the second week of May. They are most abundant in red maple swamps, especially those containing a smattering of lowland softwoods. Wet forests feature four main elements that attract Canada warblers: exposed song perches, a dense shrub layer, an abundance of insect prey, and a structurally complex forest floor.
Wet-forest canopies are frequently interrupted by small openings, primarily as the result of beaver activity and the windthrow of shallow-rooted trees. These gaps in the canopy expose elevated perches from which male Canada warblers sing emphatic variations on chip-chuppety swee-ditchety. From these perches, males display their slate-gray upperparts, a bright yellow breast, and a black necklace that gets bolder with age. The female’s plumage is duller, as befits the camouflage more suited to her shrub-skulking habits.
Willows, alders, and other wetland shrubs thrive in canopy gaps, providing ample cover for foraging Canada warblers. Teeming insects ensure a reliable food supply for both adult warblers and their young, which are raised at ground level in the shelter of hollows, hummocks, woody debris, and clumps of fern and sedge.
Ongoing loss and fragmentation of forested wetlands may help explain four decades of Canada warbler decline. But changes in drier, upland forest habitat may also be underlying the observed trends. Like several other of the region’s shrub-dwelling songbirds, Canada warblers may have benefited from the temporary abundance of shrubby habitat created by mid-century farm abandonment, meaning that there may have been more warblers than normal when monitoring began in the 1960s. Vast areas of young forest have now reached middle age and no longer provide the complex understory structure that Canada warblers require.
Numerous studies link Canada warblers to shrubby, upland openings, including those formed by both natural and human disturbance. Birders accustomed to finding Canada warblers in lowland settings may be surprised to encounter them in brushy treefall gaps within old upland forests, or even in mountain forests damaged by wind, ice, or rockslide. Besides abandoned pastures, human-created habitats include regenerating logging roads and recent timber cuts. Canada warbler abundance is relatively high in logged areas 5 to 20 years following a harvest operation, especially in places where some overstory trees are retained. Elevated perches and thick underbrush are key habitat elements in harvested areas, just as they are in natural settings.
Plymouth State University researchers, working in Canaan, New Hampshire, have found that Canada warblers inhabiting regenerating harvest zones achieve levels of pairing and fledging success similar to those breeding in an adjacent, unharvested swamp. Though the rate of breeding success is similar, the wetland appears to be more productive than the upland forest overall, because small and overlapping territories enable Canada warblers to breed at a higher density in the wetland. The small size and packed configuration of wetland territories could indicate greater resource availability in some wet forests, compared to upland harvest zones.
Landowners interested in helping to stabilize Canada warbler populations can set aside streamside or lowland forests, especially mixed woods with a semi-open canopy and dense undergrowth. Large treefall gaps and partial timber cuts can provide upland alternatives, particularly when shrubs, saplings, and woody debris are generously provided. Remember, these are Canada warblers. They like their woods cool and moist, messy and buggy.
When managing bird habitat, it can be hard to balance ecological, economic, and aesthetic considerations. But those who succeed are assured rich rewards, including the opportunity to view one of the Northeast’s most handsome songbirds, perched and singing on a sunlit branch. At least until it dives back into the underbrush.