For some time, I've been curious about the specific makeup of the lichen communities of Ruby-throated Hummingbird and Blue-gray Gnatcatcher nests. The literature contains abundant reference to the fact that these species use lichens in nest construction, but I've yet to see a study that analyzed the lichen species and composition.
So, a few weeks back, I put out a request to the Ohio birding community, and was rewarded with a few dozen nests that were made available for study.
Enter Ray Showman, without doubt one of the leading lichenologists in the U.S. Ray lives in Vinton County, Ohio, and recently retired as a biologist with American Electric Power. AEP originally hired him to study lichen populations in the vicinity of coal-burning power plants. Lichens are quite vulnerable to air pollution; thus they serve as readily studied barometers of environmental conditions.
Between the gnatcher and hummingbird nests, we found a total of five species, and all but one were used commonly by both species. The Hoary Rosette Lichen pictured above differs in that it grows tightly appressed - flat - to the bark. It would be difficult for a hummer or gnatcatcher to pry pieces of it away from the tree.
Both of these bird species site their nests on small lateral tree branches, typically well away from the trunk. The lichens that we found in their nests are species that thrive on branches, and at least in one instance, don't occur as often on large trunks. It stands to reason that these are the lichens most desirable for nest construction, as they occur in the immediate vicinity of the nest site, thus making for better camouflage.
Also, all of the lichen species used in nest construction produce elongated lobe tips that arc away from the bark. This growth habit makes for easy plucking and removal for birds that have small, delicate bills. All of the lichens we found are very common, too, and readily available to the birds.
Lichens tie these tiny birds to a much larger ecological picture involving plant communities, and man's impact on air pollution. Ray and I are working on a paper for publication in the Ohio Cardinal that will describe our study and findings in detail, and explore the birds' ecological relationship with lichens.