Ever fewer chimneys may force Chimney Swifts to return to large, hollow trees

For millennia, Chimney Swifts roosted and nested in caves and hollow trees. Then European colonists added buildings with chimneys to the landscape, and the birds adapted. Now they make their homes almost exclusively in chimneys, but they haven’t abandoned trees entirely.

Researchers from Bird Studies Canada who reviewed journal articles, books, breeding-bird atlases, and other sources were able to find 59 reports of tree-nesting swifts in eastern states and provinces between 1803 and 2013. Among the observations are accounts from John James Audubon, Spencer Baird, George Miksch Sutton, and other notable ornithologists.

Writing in the online journal Avian Conservation and Ecology, the researchers report that the birds used live and dead trees of 13 species, including white pine, elm, birch, hemlock, maple, and cypress, and that all but six trees were in remote areas. Some had broken tops, forming chimney-like openings. Others had cavities caused by weather damage or broken limbs.

Entryways could be surprisingly small. “Some swifts entered through apertures less than 5 cm [2 in] in width, requiring them to land on the surface rather than flying in directly,” note the researchers. “In some of the observations, Chimney Swifts used entrances created by Pileated Woodpeckers located on the sides of trunks.”

The one thing the trees had in common was size: They averaged more than 41 feet in height and 1.6-5 feet in diameter at breast height (about 4.5 feet above the ground).

Trees meeting the birds’ size requirements are relatively rare in logged and unlogged forests today. That’s significant because the availability of suitable chimneys is declining and breeding-bird surveys have shown the swift’s population has dropped almost six percent per year in Canada over the last four decades. If the species is forced to re-adapt to a life in trees, forest managers will want to know what trees the birds need.

A version of this article appeared in “Birding Briefs” in the December 2014 issue of BirdWatching. Subscribe.

Originally Published October 14, 2014