Researchers at the University of Washington report that suburban development is forcing lovebirds in the Seattle area to split up and miss their best chance to raise a family.
We’re not just talking figuratively here: These are real birds – specifically, a category of songbirds called “avoiders” that tend to form monogamous relationships.
Such birds include the Pacific wren and Swainson’s thrush in the Pacific Northwest. They’re generally shy of humans, and rely on groundcover and brush for breeding locales.
A team of UW researchers led by wildlife biologist John Marzluff tracked the movements and mating patterns of six common bird species at 26 forested sites east of Seattle over the course of a decade, from 2000 to 2010. Some of the sites experienced rapid development during that time frame.
When fallen trees and ferns gave way to streets and lawns, that eliminated the kinds of habitat that avoider birds prefer. The birds traveled farther than usual to find places to nest and mate — about 150 yards (meters) on average, according to the researchers.
The avoider birds typically failed to reproduce for at least a year after relocating, and Marzluff and his colleagues suspect that the disruption caused by development is the reason why.
“These birds don’t like to move once they have established a territory,” Marzluff said in a news release. “But when it comes to having enough food and safety for a nest, and being able to attract a mate, that’s when things get tough. That’s probably when they decide to move.”
Meanwhile, other types of birds known as “adapters” or “exploiters” tolerated suburban development much better, and even thrived. Such birds include the song sparrow, spotted towhee, dark-eyed junco and Bewick’s wren.
The UW study, published Dec. 28 in the open-access journal PLOS ONE, focused on the Seattle area, but the researchers suggest that the results are relevant to other cities and suburbs across the U.S. The findings help explain why development hits some species of birds much harder than others.
“To conserve some of these rarer species in an increasingly urban planet is going to require more knowledge of how birds disperse,” Marzluff said. “I expect that as we look more closely, we will find birds that are compromised because of us.”
Yet another study led by UW researchers, published this week in the Proceedings of the National Academy of Sciences, found that rapid urban development can accelerate the pace of evolution for plants and animals.
For this study, the researchers analyzed 1,600 observations of changing traits, and correlated them with human-caused effects on the environment ranging from climate change to infrastructure construction.
Here are three examples of changing traits:
- Rising average temperatures are prompting the seasonal onset of reproduction to occur earlier in 65 species of migratory birds in Western Europe.
- The use of galvanized transmission towers that contain zinc is creating novel habitats characterized by high zinc tolerance in plant species.
- The size of brown trout is being affected by fish ladders, which subsequently affects predators and prey.
“Our findings of rapid and substantial adjustment by many plants and animals to the challenges of living in an increasingly urban world demonstrate the power of natural selection where we live, work, worship and play,” Marzluff said in a news release.
In addition to Marzluff, the authors of the PLOS ONE study, “Breeding Dispersal by Birds in a Dynamic Urban Ecosystem,” include Jack DeLap, M. David Oleyar, Kara Whittaker and Beth Gardner.
Marina Alberti, director of UW’s Urban Ecology Research Laboratory, is the lead author of the PNAS study, titled “Global Urban Signatures of Phenotypic Change in Animal and Plant Populations.” In addition to Marzluff, the other authors include Cristian Correa, Andrew Hendry, Eric Palkovacs, Kiyoko Gotanda, Victoria Hunt, Travis Apgar and Yuyu Zhou.
