To feed their young, many species of birds hunt for insects in people's yards, which comprise much of the American landscape. A new chickadee study from the Washington metropolitan area suggests that to promote biodiversity, homeowners should plant native species. Insectivorous birds prefer breeding and foraging in native shrubs and trees, researchers found, because they support more caterpillars.
"It's imperative during the breeding season that they have these caterpillars and other insects to provide the protein that nestlings need to grow," said Desiree Narango, first author on the paper published in Biological Conservation.
Narango, a PhD candidate and research fellow at the University of Delaware, and her colleagues at the Smithsonian Migratory Bird Center were curious about the impacts of nonnative plants on breeding birds' food resources. From 2013 to 2016, the researchers examined plants, insects and birds in over 200 yards belonging to citizen scientists in Washington, Maryland and northern Virginia. They installed nest boxes at each site to attract their focal insectivore, the Carolina chickadee (Poecile carolinensis) and observe its reproduction and foraging on caterpillars and other prey.
"We show that in general, nonnative plants support fewer caterpillars," Narango said. "We also found that the number of caterpillars a tree supports will predict how much a chickadee prefers to forage in that tree. Chickadees are foraging more often in native plants and more likely to breed in yards more dominated by native plants as well."
The chickadee is a common native bird adapted to the city, but the scientists also documented almost 100 other bird species using residential backyards during the study that could benefit from greater abundances of insects. These included migratory birds of conservation concern, such as the wood thrush (Hylocichla mustelina), Acadian flycatcher (Empidonax virescens), American redstart (Setophaga Ruticilla) and scarlet tanager (Piranga olivacea).
"Ornithologists have suggested insufficient stopover habitat during migration might be contributing to declines," Narango said, "so we want to provide plant communities supporting the insects these birds need even if they are just passing through."
Although this research project was one of the first conducted on residential land, she said, it agrees with previous findings indicating that nonnative plants harbor less diverse insect communities and that aggressive invasive plants cause insect and bird declines.
"The amount of native plants used in ornamental landscaping in urban yards can have considerable effects on insectivorous birds," Narango said. "If you're interested in supporting biodiversity, you can start in your backyard by managing your property to provide food for wildlife."