A new study shows how quickly songbird populations fall off when gardens are planted with exotic trees and shrubs
By Adam Cohen
They say the early bird catches the worm. For native songbirds in suburban backyards, however, finding enough food to feed a family is often impossible.
A newly released survey of Carolina chickadee populations in the Washington, D.C., metro area shows that even a relatively small proportion of nonnative plants can make a habitat unsustainable for native bird species. The study, published last week in Proceedings of the National Academy of Sciences, is the first to examine the three-way interaction between plants, arthropods that eat those plants, and insectivorous birds that rely on caterpillars, spiders and other arthropods as food during the breeding season. Based on data collected in the backyards of citizen-scientist homeowners, the researchers arrived at an explicit threshold: In areas made up of less than 70 percent native plant biomass, Carolina chickadees will not produce enough young to sustain their populations. At 70 percent or higher, the birds can thrive…