Many birdwatchers are obsessed by North America’s beautiful, abundant spring warblers, and one of the most elusive is the smallest, the Northern Parula.
By Rex Graham
“It is my favorite warbler,” said Becky Marvil, Executive Director of the Acadia Birding Festival in Maine. “Seeing one creates a buzz with all festival goers, not just advanced birders, and it is seen or heard on nearly all of our field trip locations. We often can find a nest, too.”
However, birdwatchers in a broad region of the Ohio River Valley up to the Great Lakes no longer see Northern Parula during its breeding season. The bird species must go elsewhere to find their required nesting material: lichen.
Several birding tour companies, including Birding Research and Nature Tours, provide one-week guided birding tours to see the Northern Parula and dozens of other bird species in the Cape May, N.J., area. The Northern Parula also breeds in the Southeastern, Atlantic and Northeastern states and much of southeastern Canada.
Northern Parula, Bird Photography Challenge
Warblers – North America’s most beautiful and abundant spring migrants – can hop, flit and slip past many photographers without anything close to a pose for a high-quality photo. The Northern Parula is one of the most difficult to photograph because of its small size, treetop feeding and rapid movements.
“This required Vera and me to get within 10-12 feet of them to take any kind of meaningful shot since our 300mm lens, despite the 1.4 converter was especially limiting for a bird this small,” wrote photographer Bob Thornton in Chasing Warblers, which he co-authored with Vera Thornton. “However, the warbler is most confiding, not timid at all, and is as easy to approach closely as any of the warblers we sought.”
American ornithologist Henry Mousley called the Northern Parula “the little feathered mite.” It feeds on insects amid massive, dense stands of broadleaf trees or conifers. To get a great photo or make a visual ID, birdwatchers and bird photographers need magnification, fast reflexes, patience, and most importantly luck.
The Northern Parula is usually heard before seen. Its brief buzzy trill rises in pitch and ends in a sharp slur. Paul Marvin recorded a Northern Parula singing during a steady rain at the Merritt Island National Wildlife Refuge in Florida in March 2014. He also saw the bird.
The species breeds in the eastern half of the U.S., and the southern quarter of Canada’s eastern provinces. The dynamic map of eBird sightings includes sporadic spring sightings in all western U.S. states and Canadian provinces. It occasionally nests in northern coastal California in moist forests with trees draped with thin pendulous lichen. A lichen is a symbiotic association of fungi and algae. They are sometimes called tree beards or Old Man’s Beard.
The Tropical Parula, a non-migratory cousin that breeds from southernmost Texas to northern Argentina, also requires similar epiphytic thin pendulous lichens in which to build nests. All Parula nests resemble those of an Orchard or Baltimore Oriole. The Tropical Parula lacks the white eye crescents of the northern species, which acquired the migratory trait and more northern breeding distribution.
Female Parulas weave thin species of lichen strands into cup-like nests, but the precise way they weave is a mystery. “The whole lichen mass would often vibrate violently and appear to be manipulated from within,” researchers reported in The Condor in 1958 after observing one female Northern Parula build her nest in northern California. Parula nests, woven within clumps of thin pendulous lichen and lined with grass, don’t look like birds’ nests. However, they can be spotted by experienced birdwatching guides.
Nova Scotia birdwatcher Maxine Quinton, author of the children’s book Dottie, It’s Time for School!!!, has not only photographed Northern Parulas amid their favored lichens, but she has also photographed one of their nests. Her photo of the nest is a revealing piece of citizen-science documentation that provides a revealing example of why the bird species no longer breeds in northern Ohio, Indiana, Illinois, Iowa, and southern Minnesota, Wisconsin, and most of Michigan.
Northern Parula Lichen Requirement
In order for the female Northern Parula to initiate breeding behavior she requires the presence of a sexually active male, proper nest sites, thin pendulous lichen in which to build her nest, and an adequate food supply for the young. Those four requirements are met in northern California, where Northern Parulas frequently nest even though it is not within their traditional breeding territory.
However, a requirement of nesting female Northern Parulas – thin, pendulous lichen – has been essentially wiped out of a broad patch of its traditional range in the industrial heartland of the Eastern and Midwestern U.S. by air pollution. Huge amounts of Sulfur dioxide are emitted by coal-burning power plants, steel mills, foundries, and coking ovens. The air pollution eliminated or nearly eliminated 25 of Ohio’s 225 species of lichens, including all six species of Usnea, after 1950.
“It’s enough to make a grown man weep,” said Jason Hollinger, a lichenologist in North Carolina.
Air pollution was not as harmful to rigid, shrub-like lichens that have a thick cortex or outer covering: they tend to be pollution tolerant. “The thin, pendulous ones the Northern Parula apparently prefers have a thin cortex, or in the case of Usnea longissimi, are lacking a cortex altogether,” said Hollinger. “Thin cortex or even none allows Usnea species to absorb moisture and nutrients from the air more readily, an excellent adaptation for misty humid environments, but alas also enables them to absorb and be damaged by pollution much more readily, too.”
Ironically, lichens’ ability to absorb nitrogen-containing molecules from rain, fog and snow, makes then not only a nutritious food source for animals, but also an efficient natural fertilizer of forests.
Hollinger said the Northern Parula nest photographed in Nova Scotia by Quinton is either U. trichodea, U. longissima, U. filipendula or U. subfloridana – all thin, pendulous lichens with almost no skin of protective cortex. Two of those species – U. longissimi and U. subfloridana – were eliminated from Ohio after 1950, according to a 1990 paper in The Ohio Journal of Science.
Northern Parula Weaves Lichen Nests
One of the lichen species commonly found in the Northeast U.S. and southern Nova Scotia, Usnea trichodea, also is used almost exclusively as roosting cover by the Tricolored Bat in Nova Scotia.
Epiphytic lichens are one of the least appreciated residents of moist forests.
A 1989 study published in The Bryologist, reported 65 species of lichen found in the Cuyahoga Valley National Recreational Area, which is between Akron and Cleveland. However, 119 lichen species previously reported in the heavily polluted area were not found. Lower levels of sulphur dioxide and other air pollutants are expected to help lichens rebound in Ohio.
Indeed, the decommissioning of the Coniston Smelter in Ontario, Canada in 1972 led to a significant rebound in lichen richness and diversity, according to a 2014 report in Environmental Science and Pollution Research.
Ornithologists hope the Northern Parula’s disappearance from the Ohio River Valley during the breeding season will be reversed as air pollution levels decline in the region. However, lichen experts don’t predict a quick recovery.
“Usnea species are reliant on old forests,” said Trevor Goward, Curator of Lichens at the University of British Columbia Herbarium. “While pollution may be on the wane, and pollution-sensitive lichens may begin to recolonize, these Usneas may well remain absent until forest structure is also restored.”