Desiree Narango, together with a small army of citizen scientists from Neighborhood Nestwatch, is taking a look at the ecological wildlife value of trees and shrubs planted in the lawns of homeowners throughout the Washington D.C., Maryland, and northern Virginia area. Desiree is one of Professor of Entomology Doug Tallamy’s graduate students at the University of Delaware. She’s on a mission to document the value of residential yards to birds.

Black-capped chickadee

A black-capped chickadee. (Photo by Vodeck.)

Desiree has discovered that the plants supporting a greater variety of caterpillar species are the most attractive to chickadees that rely on caterpillars to feed their young. Through her studies of 203 yards, she also found that native species of trees and shrubs attract more caterpillars than non-native species.

“One of the most ubiquitous threats to biodiversity today is the conversion of native plant communities into plant assemblages dominated by non-native species. Such conversions have triggered debate about the benefit of managing non-native species, particularly when it is unclear how well introduced plants support wildlife and management is financially and logistically challenging,” the authors write in their introduction.

Top 15 woody plants for caterpillars:

  1. Quercus—532 (both): Oak
  2. Prunus—456 (both): plums, cherries, peaches,apricots, almonds, etc.
  3. Salix—455 (both): willow
  4. Betula—411 (both): birch
  5. Populus—367 (both): poplar, aspen, cottonwood, etc.
  6. Malus—308 (both): apple
  7. Acer—297 (both): maple
  8. Vaccinium—294  (native): cranberry, blueberry, etc.
  9. Alnus—255 (native): alder; in the birch family
  10. Carya—235 (native): hickory
  11. Ulmus—215 (both): elm
  12. Pinus—201 (both): pine
  13. Crataegus—168 (native): hawthorn, thornapple, etc.
  14. Rubus—163 (both): raspberries, blackberries, etc.
  15. Picea—150 (both): spruce
    From: Smithsonian Migratory Bird Center Lepidoptera Index dataset   

The study documented more than 375 different tree and shrub species in the 203 yards. Natives fostered more caterpillars and were therefore preferred, but even they differed in their impact.  Prunus, Quercus, and Ulmus were the most preferred natives for the vast numbers of caterpillars they harbor.

While some non-natives also provide for caterpillars, some, like Zelkova, Ginkgo, and Syringa, don’t provide resources for breeding birds.

Non-native species that have native relatives, like ornamental cherries and Japanese maples provide on average 40% fewer caterpillars than their native relatives. “If you had a choice between a black cherry and a Japanese cherry and if you’re interested in food for birds, then you should choose the native version,” Desiree wrote in a blog post.

UD’s Desiree Narango looks at how residential yards impact food webs by Adam Thomas for the University of Delaware.

Native plants improve breeding and foraging habitat for an insectivorous bird by Desiree L. Narango et al in Biological Conservation. DOI: 10.1016/j.biocon.2017.06.029