All over the world, habitat is being rapidly lost to human activities like urban development and deforestation. In addition, native vegetation communities are being replaced with introductions of plant species that are not native to North America, either by intentional (horticultural landscaping) or unintentional (exotic invasions) means.
The majority of herbivorous insects (for example, caterpillars) are specialist feeders, which means they are only able to feed on a specific species or group of plants. When native plant species are removed from a landscape, specialist insects may be lost as well if they are unable to adapt to feeding on the newly introduced species.
Although the loss of biodiversity in itself is important, removing insects from the landscape is of particular concern for birds that rely on insects for food. Many birds are mostly or entirely insectivorous, especially during the breeding season when nestlings are growing and food demand is highest.
Dr. Peter Marra from the Smithsonian Migratory Bird Center has started a new National Science Foundation-funded collaboration with Dr. Doug Tallamy, an entomologist at the University of Delaware, along with Ph.D. student Desiree Narango, to investigate how non-native plants may be affecting food resources for backyard birds.
This new study works in conjunction with the Neighborhood Nestwatch program to study a common insectivorous bird: The Carolina chickadee. Nestwatch participants with native and non-native landscaping in Maryland, the District of Columbia and Virginia have agreed to host nest boxes that attract chickadees to nest in their backyard monitor them over the breeding season.
In this study, individual chickadee pairs are color-banded and followed over the nesting season to determine:
- which trees they prefer to forage on,
- which kind of insects they feed their young, and
- how successful they are at reproducing in neighborhoods with different densities of non-native vegetation.
The work will utilize a variety of different methods to test these questions, such as using stable isotopes to track trophic contributions of trees to different consumers, and video cameras to record food items and nest visiting rates by chickadees. In addition to the birds, they are also sampling caterpillars to determine what species feed on different types of trees and how the numbers of caterpillars change throughout the year.
This study will contribute to our understanding of the role of non-native plants in trophic food webs and novel ecosystems. Future findings will also be useful to homeowners and land managers that are interested in improving their backyards to provide food for resident and migratory birds.