The black-capped chickadees coming to your seed feeders get 20 to 25% of their nourishment there. There is research to support the numbers.
Those birds have a usual nesting territory of 6 to 10 acres. This is where they look first for food.
If they’re not finding the remaining 75 to 80% of their daily dietary needs from natural sources within that territory they must look for it elsewhere. That takes time and energy for breeding birds.
The source for the information discussed here is Desiree L. Narango’s Ph.D. dissertation examining the relationships among birds, bugs and plants. She wrote about the future of conservation and the importance of residential yards in conservation efforts. Her postgraduate work was done at the University of Delaware.
One of the villains in this story is buckthorn, a notorious non-native that is prolific here. Every buckthorn tree, large or small, in a bird’s nesting territory is preventing native plants from growing and thriving.
The insects that these birds need to feed their young cannot be found on buckthorn, a European species. Our insects and birds evolved with native plants.
It’s pretty simple. Buckthorn and other non-native plants can and will influence behavior, diet and population growth of chickadees and other native bird species.
The more non-native vegetation, the fewer birds and species numbers.
Allowing native plants in gardens and yards to be dominated by non-native species is “one of the most ubiquitous threats to bio-diversity today,” Narango wrote.
It doesn’t matter if you plant non-natives or simply ignore them, it’s bad either way.
Her study was done in Washington, DC, focusing on that area’s chickadee species, the Carolina chickadee. The two chickadee species share many behaviors and characteristics.
“Native plant groups were more preferred in 97 percent of chickadee territories observed,” Narango wrote. Birds also drill in trees. In her study the birds foraged most frequently (28%) in oaks.
In yards where chickadees occurred, non-native plants were avoided as a foraging source, and chickadee plant preferences were highest for native plants supporting the most caterpillars, she wrote.
“Homeowners interested in increasing the native bird food available in their yard should … prioritize the planting of productive native plant species,” she wrote.
In sites dominated with non-native plants, foraging arthropods — insects and spiders — disproportionately selected the native plants available, Narango wrote.
Fewer native plants can result in higher competition among native insect species for food. It also can mean reduction of insect/arthropod populations, she wrote.
Using more native plants can lessen the effect of competition by simply expanding the foraging base. In brief, more native plants are better.
She explained that plants described as wildlife-friendly often produce seed or fruit “well past breeding season,” when it would be of most value to birds.
Chickadees avoided breeding in areas high in non-native plant numbers, even when nesting cavities (always in short supply) were available, her research found. Food for chicks apparently was a stronger determinant than nesting opportunity.
“Homeowners who choose to landscape with non-native plants are not providing suitable habitat for species that require a diet of insects during breeding,” she explained.
More than 96% of terrestrial bird species in North America raise their babies primarily on arthropod prey, she wrote. Insects and spiders provide the amount and quality of necessary nutrients.
“In addition,” she wrote, “chickadees are known to lead other bird species to foraging locations. Thus, chickadee breeding behavior may serve as a model for the relationship between plant quality and habitat for insectivorous birds in general.”
Her research provides compelling evidence that homeowners should make native plant species a priority in home landscaping. We can improve bird habitat, thereby attracting more birds, by using more native plant species.
More broadly, Narango found that a large urban landscape with more non-native vegetation, fewer trees and more concrete and asphalt had fewer chickadees and fewer breeding chickadees.
Her study included house wrens, American robins, gray catbirds, Northern cardinals and house wrens. Generally speaking, these birds did better when feeding on native vegetation.
For suggestions of native plant species, visit http://strib.mn/3L9VQ3b or https://bit.ly/39Pk9Gx.
More than half of the world’s population lives in cities and suburbs (Grimm et al., 2008). An estimated 80% of our population will live in urbanized areas by 2050 (United Nations Department of Economic and Social Affairs Population Division, 2019). Bird-friendly yards will become even more important.
Lifelong birder Jim Williams can be reached at [email protected]