By Michael Burke
We looked skyward, our futile gazes drawn by a hidden bird’s persistent, penetrating trill coming from somewhere in
the endless palette of greens of the tree canopy that soared 80 feet or more overhead.. The song wasn’t pretty, but it was unmistakable. The note rose in intensity until it suddenly dropped to nothingness.
We were in the National Arboretum, the 400-plus-acre oasis in Northeast Washington, DC. The path we walked led us to a break in the foliage. We craned our necks anew and were rewarded with glimpses of tiny warblers flitting about in nearby treetops.
The voice and habitat alone were enough to convince us that we were looking at northern parulas (Parula americana), but we stopped to get a better look at these colorful wood warblers.
Northern parulas are tiny. Weighing about a third of an ounce, they measure just four and a half inches from their bills to the end of their black tails. When a bird is that small and 80 feet overheard, you’d better be equipped with good binoculars and cooperative lighting. Fortunately on this day, we had both.
One of the birds stopped its aerial dance in search of insects and perched obligingly on a terminal twig. He was still far away, but he held still long enough for closer inspection.
The yellow throat and chest caught my eye first. The head and wings were a cool blue-gray, contrasting with his white belly. The wings sported two white wing bars. Arcs of white also circled his eyes. The yellow of his throat blended seamlessly into the lower bill. The upper bill, in contrast, mimicked the blue-gray of the cap. Across his chest, reddish and black bands interrupted the yellow. His back was olive green.
The females look the same; except they don’t have the chest bands and the colors are a bit more subdued.
Like other warblers, parulas are Neotropical migrants. These birds head for Central America and the Caribbean each winter. On the return trip north in the spring, northern parulas look for a specific habitat.
In the southeastern United States, they seek tall trees with Spanish moss. Farther north, when the Spanish moss gives out, other epiphytes, particularly old man’s beard lichen, serve the same function. The females use the abundant epiphytes as nesting materials. In trees with extensive epiphytes, a nest constructed of such materials doesn’t look conspicuous.
In Central America and especially in the Caribbean, loss of habitat is reducing population density. In the United States, the loss of epiphytes, primarily to air pollution, strips the forests of an essential evolutionary element. Breeding bird survey data show a distinct band in New York State and lower New England where there are no parulas successfully breeding. Acid rain has killed off the sensitive lichen. And where there is no lichen, there are no parulas.
The area without parulas coincides with the worst cases of acid rain in the nation.
Poorly regulated power plants in the Midwest have poured pollution into the upper atmosphere for decades. Prevailing winds carry these plumes of pollution to the Northeast where the sulfur and nitrogen oxides are eventually washed out of the sky, with the damage concentrated in Central New York and across a swath of New England.
The acid rain has a devastating effect on the lakes in the region, robbing them of much of their native aquatic life. The high-pH rainwater has also been lethal to epiphytes. Parulas have lost nesting habitat while humans suffer from smog and soot. Thankfully, regulators have begun to crack down.
The parula in the arboretum didn’t face those challenges. He left his perch to resume gleaning insects from the high foliage. Another trill rose to its crescendo before suddenly disappearing.
To some, the abrupt ending of the bird’s song suggests this delicate species might suddenly be eliminated by a combination of pollution and habitat loss.
I hear a different meaning. These are tiny but rugged birds built for survival as well as beauty.
They spend the summer producing another generation and then make the long migration from the Chesapeake to the Caribbean and back. They will have to work around areas that humans have destroyed or despoiled.
But next year they will be back, at the top of the tree, announcing anew their presence. It’s the song of a survivor, and I find it inspiring in spite of its noisy nature.
Mike Burke is an amateur naturalist who lives in Cheverly, MD.
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