Alliance for Community Trees News

Native Trees Best Support Bird Populations

By Conni Kunzler | November 13, 2017

Source: Shireen Gonzaga, “Want birds in your yard? Plant native trees,” EarthSky; Desiree L.Narango, Douglas W.Tallamy, Peter P.Marra, “Native plants improve breeding and foraging habitat for an insectivorous bird,” Biological Conservation

Newark, DE (November 8, 2017) – A recently published study confirms that native trees are most effective in hosting caterpillars, an important food for birds. The study, focused on yards in the Washington, D.C. metro area, shows that native trees and shrubs were the best producers of caterpillars and other insects that are valuable as food for wild birds.

The research by scientists at the University of Delaware and the Smithsonian Migratory Bird Center, appeared in the journal Biological Conservation.

Desiree Narango, a doctoral student at the University of Delaware, is the paper’s lead author. She works with Doug Tallamy, a professor of entomology at the university’s Department of Entomology and Wildlife Ecology. Tallamy is the author of Bringing Nature Home, a 2007 book that makes a strong case for growing native plants in home gardens to help support wildlife that face dwindling natural habitats. Narango’s work is also associated with a citizen-science program called “Neighborhood Nest Watch,” run by the Smithsonian Migratory Bird Center.

Over ninety percent of insect species co-evolved with a specific plant species or a group of related plant species; their larvae — caterpillars — adapted over the insect’s evolutionary history to overcome the chemical defenses of its host plant(s). These insects, however, have not had a chance to develop a tolerance for the chemical defenses in many recently-introduced plants, and are therefore unable to consume them.

During the breeding season, birds depend on insects, a rich source of protein, to feed their young. Over a four-year span, Narango and her team observed where breeding birds foraged for food in 203 yards of homes in the Washington D.C. metropolitan area. She documented which plants provided the most food, such as insects and caterpillars, for the birds.

In a press release, Narango said, “native trees are better, hands down, but even among the native trees, there are some that are better than others [in the in the Washington, D.C. metro area] so things like oaks and cherries and elms are highly productive for caterpillars. They have lots of good food for the birds.”

Narango was struck by the large variety of different trees she encountered in the gardens. “We focus on woody plants — so trees and shrubs — and we’ve documented over 375 different species in these 203 yards. Which is crazy.”

Most non-native plants, such as zelkova, ginkgo and lilac, did not provide any food for breeding birds. “Those species are true non-natives so they’re not related to anything here, and they provide almost nothing in terms of caterpillars for birds,” said Narango.

Narango was also struck by the large diversity in insects and birds she encountered. Ninety-eight different bird species were documented in the study. “A lot of people think you need to go to the woods to see beautiful butterflies or beautiful birds, but they’re actually in people’s backyards, too.”

Most homeowners interested in growing native plants, however, face the challenge of finding them because many big box stores don’t sell them. However, she noted, “There are a lot of really great small nurseries that have many native plants that are productive in terms of caterpillars and are also very beautiful. You definitely don’t have to sacrifice beauty to get plants that are ecologically beneficial. There’s a lot to choose from so you can have beauty, you can have fruit and then also have food for birds, too. It’s all interconnected.”

Bottom line: Wild birds in suburban areas are highly dependent on native plants that host insects that are an important source of their food.

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