Of a Feather: Yellow and green with a black cap

Photo by Mike’s Birds
Flocks of white-throated sparrows have been flying up in front of me as I walk the dog most mornings. I always look for white-crowned sparrows among them, but I haven’t seen any yet this year. I like to see the white-crowns because they are a boreal novelty. They breed well north of us in northern Quebec and winter only as far north as Long Island.

Earlier this week I encountered a mixed flock of kinglets, mostly golden-crowned with at least one ruby-crowned among them. Tagging along with them were at least two Wilson’s warblers — I saw one male and one female — which was a new bird for me.

I confess to sighing when I see warblers in fall migration, because so many of them are transformed into little green birds with or without wing bars and only flecks of their breeding plumage finery. Mercifully, Wilson’s warbler plumage in the fall looks much the same as that of the breeding bird: bright olive green above and yellow below with a black cap that looks like a beret worn right on top of the head. The female is quite similar, but often lacks or shows only a trace of the beret. They are small birds, less than 5 inches long, with short bills.

They once shared a genus Wilsonia with Canada and hooded warblers, but it was dissolved within the last decade. Wilson’s and the Canada were reassigned to Cardellina and the hooded went to Setophaga. What is now Cardellina pusilla was first described in 1811 in southern New Jersey during migration by Alexander Wilson. Wilson called it the “green black-capt flycatcher” and placed the New World species in the European genus of flycatchers. In pre-Darwinian days, naturalists expected to find European species or ones very similar to them everywhere on Earth, as evidence of Creation. Wilson’s misidentification can also be blamed on this warbler’s relatively broad bill and prominent rictal bristles, which enable it to feed on the wing like a flycatcher. The warbler was reassigned in 1838 to a genus created in Wilson’s honor by Charles Lucien Bonaparte.

Alexander Wilson, born in Paisley, Scotland in 1766, was considered the greatest American ornithologist before John James Audubon. Like Audubon, he was also a painter. Unlike Audubon, he was also a poet, which is what caused him to emigrate to the United States. In Scotland he was a weaver by trade, but wrote verse that protested poor conditions in the mills, for which he was arrested. He subscribed to a Romantic way of life and devoted himself to his art and to science. He died at age 47 of over-work and poverty.

Charles Bonaparte was the nephew of the Emperor Napoleon I and a gentleman scientist. He traveled to the United States in 1822 and managed to describe a new species of storm-petrel on the voyage over. He named it after Alexander Wilson. In fact, Wilson’s warbler is the only passerine named for him; all the others are shorebirds or seabirds.

Bonaparte never lived in poverty, but he did work very hard and in 1849 even joined the Italian Republican cause in the defense of Rome against the invading army of his cousin Louis Napoleon. When he died at age 54 he had created 165 genera, 203 species and 262 subspecies. He named the genus for mourning doves Zenaida, after his wife. Bonaparte’s gull is named for him.

Like their Scottish discoverer, Wilson’s warblers are famously energetic, making them difficult to spot, but they are also known to forage lower in the canopy than most warblers. The pair that I saw earlier this week was indeed down low in the birch saplings at the edge of our meadow. As promised, they were constantly on the move, appearing in the open for a few seconds before diving into the underbrush again. They are known to sing during the spring migration, but not in the fall. But their small size, stubby bill, and bright and simple coloration are distinctive.

This boreal species breeds as far south as the Northeast Kingdom of Vermont, very northern part of New Hampshire (Coös County), and northern Maine. It nests in alder swamps on the ground, building a large structure in the sphagnum moss made out of grass, dead leaves, fine stems, and moss.

In most areas, alders are a successional species, so the preferred habitat of the Wilson’s warbler is a transitional one. Mario Cohn-Haft, writing in the “Atlas of Breeding Birds in New Hampshire,” suggests that clearing of low-altitude forest can create suitable plant assemblages a few years after logging or burning. But more stable alder communities are found around boreal beaver ponds.

As with many boreal species, the range of this species extends further south out west, following the coniferous forests down through the mountain ranges of the west coast and the Rockies. The western birds are slightly larger and brighter colored, almost orange in some cases. They also build nests above the ground, up to five feet up in shrubs, and lay fewer eggs.

Three subspecies were long recognized, but molecular genetic studies have shown that there are at least six distinct populations that have separate breeding locations and remain segregated on their wintering grounds. Our eastern birds winter on the Yucatan Peninsula of Mexico, but those breeding in the Pacific Northwest, the Sierra Nevada, and coastal California spend the winter in Baja California Sur and along the west coast of Sinaloa, Mexico.

The 2014 “State of Birds Report” listed Wilson’s warbler as a common bird in steep decline. The population has decreased by 61 percent since 1966 with losses being greater in the west. The “Birds of New Hampshire (2013)” calls it a rare summer resident in the state and reports declining numbers during migration.

Bill Chaisson has been a birdwatcher from the age of 10. He is a former managing editor of the Eagle Times and now lives and works in the town of Wilmot. Contact him at [email protected].