Non-Native Plants reduce Food availability for Birds

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Doug Tallamy, Desiree Narango and Peter Marra* have provided more definitive data about the importance of native trees and shrubs for the livelihood of insect-eating birds. In this case, their research focused primarily on the Caroline Chickadee (Poecile carolinensis). In their report Nonnative plants reduce population growth of an insectivorous bird printed in Proceedings of the National Academy of Sciences of the USA (PNAS) Doug and his team concluded:

Doug Tallamy says a Black-capped Chickadee (Poecile atricapillus) pair brings 390-570 caterpillars to their young per day for 16 days. Photo by Doug Tallamy.

“We monitored reproduction and survival of Carolina chickadees within residential yards and found that when nonnative plants increased, both insect availability and chickadee population growth declined. We also found that populations could only be sustained if nonnative plants constituted <30% of plant biomass. Our results demonstrate that nonnative plants reduce habitat quality for insectivorous birds and restoration of human-dominated areas should prioritize native plants to support local food webs.” (PNAS)

*Doug Tallamy and Desiree Narango are both researchers with the University of Delaware, while Peter Marra is director of the Smithsonian Migratory Bird Center.

Evolution and Insects

We all know that most plant-eating insects evolved with the species of plants they eat. The Monarch butterfly and its dependence upon milkweed as its host for its larvae is a good example.

Non-native plants smell and taste differently from native plants; some are even toxic to native insects. They also typically don’t provide the same nutritional value. Consequently, landscaping with non-native plants will support fewer plant-eating caterpillars and other insects. This means fewer insects for insectivorous birds, which means either less healthy birds and fewer fledglings or simply fewer birds in the landscaping.

Conclusion

To support sustainable food webs and to support wildlife, the researchers concluded landscaping must contain at least 70 percent native plants to enable insectivorous birds to successfully reproduce and to sustain their population.

Native oaks, cherries, willows, elms, birches, hickories, black walnuts and viburnums are the native trees and shrubs we should be using in our landscaping — residential, industrial and municipal. These native trees and shrubs support the most caterpillars and predatory insects.

Thanks Ken Sikora for bringing this new data to my attention. See also CATCH THE BUZZ – Non-Native Plants in Homeowners’ Yards Endanger Wildlife – Both Birds and Bees, UD Researchers Report in Bee Culture The Magazine of American Beekeeping.

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