Want to support nesting songbirds? Shoot for a minimum of 70% native plant cover in your landscaping, and 94% would be better, according to a recently published study by the University of Delaware’s Desirée Narango and others. For their study, the scientists chose Carolina chickadees as a representative suburban songbird. Homeowners across the southeastern U.S. delight to see them in our yards and at our bird feeders. Like most songbirds, chickadees provision their nestlings with insects from the landscape around their nest.
Study results show that baby chickadees reared in landscapes with less native vegetation are food-limited and much less likely to survive. So much so that the authors termed landscapes with less than 70% native vegetation as “food deserts” and “habitat sinks”. A habitat sink is a place with habitat sufficient to attract animals but insufficient to support their survival or the survival of their young. Habitat sinks are bad for a species because breeding pairs do not produce enough young birds to replace their parent’s generation. It would actually be better for the chickadees not to have that habitat available at all.
The study’s message is clear, if suburban residents want to continue to enjoy the company of native songbirds, they must support plenty of high-quality native landscape. Habitats with greater than 94% native vegetation were shown to be sources, in other words, places where the chickadees produced enough young to replace their parent’s generation.
To collect the data, the scientists worked with the Smithsonian Institution’s Neighborhood Nestwatch, a citizen science program. 159 homeowners in suburban Washington, D.C., installed and monitored chickadee nest boxes. The scientists measured native plant cover, insect abundance, bird diet, site occupancy, and reproductive success at each site. Many readers will recognize one of the co-authors, Doug Tallamy, from his now classic book, Bringing Nature Home. The study appeared in the August 2018 edition of Proceedings of the National Academy of Sciences, one of the world’s most respected publications.
By Sara Tangren, Ph. D., Sr. Agent Associate, Sustainable Horticulture and Native Plants, University of Maryland Extension, Home & Garden Information Center
Baisden, Emily C., Douglas W. Tallamy, Desirée L. Narango, and Eileen Boyle. 2018. Do cultivars of native plants support insect herbivores? HortTechnology 28(5) 596-606.
Carignan, C. (2018, Nov. 12). The Nativar Dilemma: The Case of My Purple Ninebark & The Leaf Beetle [Maryland Grows Blog].
Narango, Desirée L., Douglas W. Tallamy, and Peter P. Marra. Desirée. 2018. Nonnative plants reduce population growth of an insectivorous bird. Proceedings of the National Academy of Sciences of the United States of America.
Tallamy, Doug. 2009. Bringing Nature Home. Timber Press. 288pp.