More than a decade of observation in Seattle suburbs shows where sensitive bird species won’t go
Our take
The Puget Sound region is growing, and that growth inevitably impacts the natural world around us. It's a reality we’re increasingly confronted with, as seen in recent efforts like Tacoma closes portion of Old Town Dock to help seal and her pup and the innovative coral conservation work happening in Florida, where Florida researchers bring endangered elkhorn coral ashore to protect them. Now, a new study out of the University of Washington offers crucial data for navigating this tension – demonstrating that bird species aren't simply reacting to *whether* development occurs, but *how* it’s configured. Twelve years of observation in Seattle suburbs reveals that specific landscape features – things like the density of housing, the presence of green corridors, and the size of individual lots – significantly influence whether sensitive bird species will establish territory. This isn't just about protecting cute birds; it’s about preserving biodiversity and the ecological services these species provide, all while acknowledging the need for continued development.
The study’s findings are particularly compelling because they move beyond broad pronouncements about habitat loss. It’s not enough to simply say "don't build here," when that's often not a feasible option. Instead, this research provides actionable insights for developers and urban planners. For example, maintaining larger lots and incorporating connected green spaces—even relatively small ones—can create pathways for birds to move between fragmented habitats, increasing their chances of survival and reproduction. The research highlights the importance of considering the cumulative impact of development patterns, suggesting that seemingly minor design choices can have significant consequences for wildlife. This is a shift towards a more nuanced and proactive approach to conservation, one that integrates ecological considerations into the planning process from the outset. It emphasizes the potential for "smart growth" strategies that minimize environmental impact while still accommodating population increases, a critical consideration for rapidly growing regions like the Puget Sound.
The implications extend beyond just avian conservation. Birds are often considered “indicator species,” meaning their health and abundance reflect the overall health of the ecosystem. If birds are struggling in a developed area, it's a strong signal that other wildlife and even human health may be at risk. The study’s focus on suburban environments is also significant. These areas often receive less attention than pristine wilderness, yet they represent a crucial interface between urban and natural landscapes. Protecting biodiversity in suburban areas isn't just about preserving nature; it’s about creating more livable and resilient communities for people. It reinforces the idea that conservation and development aren't mutually exclusive—they can, and should, be pursued in tandem. This research provides a concrete framework for achieving that balance, offering a blueprint for developers to create more bird-friendly, and ultimately, more sustainable communities.
Looking ahead, the challenge will be translating these research findings into widespread practice. Will developers voluntarily adopt these guidelines, or will regulatory frameworks be needed to incentivize or mandate changes? The cost of implementing these strategies—larger lots, green corridors—may be perceived as a barrier, but the long-term benefits—increased property values, improved community health, and a more resilient ecosystem—likely outweigh the short-term costs. It's a question of prioritizing future well-being over immediate profit, a shift that requires a collective commitment from developers, policymakers, and the community as a whole. How can we best ensure that this valuable research informs the next generation of development in the Puget Sound region, and beyond?
Nearly 30 years ago, a simple question sent University of Washington researchers into the Puget Sound lowlands to look for birds. With Seattle’s population swelling and housing developments pushing into once-forested suburbs, researchers wanted to know how land conversion was impacting birds, and whether the type of development mattered.
The researchers returned to various development sites three to four times a year to log which birds they saw and heard. They found that when developments preserved native vegetation and tree cover between homes, a wider variety of bird species remained. The difference was most significant to sensitive species that tend to avoid humans — like the Wilson’s warbler and Swainson’s thrush — which fared better in conservation-minded developments.
This study highlights a dynamic that is often overlooked under the assumption that all development is bad for habitat.
“This work shows that birds care how land is developed, which gives developers a choice during the planning process. There are tradeoffs between developments designed for humans and those designed with the ecosystem in mind, but balancing the two can benefit both,” said senior author John Marzluff, UW professor emeritus of environmental and forest sciences.
The results were published May 31 in Scientific Reports.
For the study, researchers organized birds into three groups based on their adaptability. Avoiders included native forest birds such as chickadees, wrens and woodpeckers; adapters included sparrows and robins; and crows, pigeons and hummingbirds were among those classified as exploiters because they can benefit from development by visiting bird feeders and foraging on scraps.
The researchers returned to lowland sites several times a year during the spring and summer breeding season to look and listen for birds. Pairing visual and acoustic signals gave them a more complete bird census.
During the initial years of observation, when the habitat was changing but before construction began, species diversity increased at all development sites, but prolonged disturbance sent many native species into decline. This effect was more pronounced when housing density increased.
“The greatest species diversity was right in the middle years of development, likely due to an increase in habitat heterogeneity,” said lead author Jack DeLap, who completed this work as a doctoral student of environmental and forest sciences at the UW and is now an associate professor at Seattle University. “Our Pacific Northwest forests aren’t terribly diverse as forests go, but when you start to mix that up by clearing trees, it opens the canopy to another suite of species.”
As construction progressed, avoider and adapter populations declined. Avoiders showed the most uniform response, but adapters were more split — some declined while others persisted. Exploiters were present in both development types, contrary to the researchers’ hypothesis that they would fare better in denser developments.
These results come at a pivotal moment for Washington’s avian residents. Earlier this year, Birds Connect Seattle issued a report describing declines in bird abundance and diversity throughout the city. Average bird counts are down 21% since the 1990s and species richness has dropped 18%. At the same time, developers are buying up tracts of timberland to build homes.
Just last week, bidding closed on the auction of 4,833 acres of forest in the Snoqualmie Valley, which could allow construction of up to 30 new homes.
“It’s becoming less and less profitable to keep land for timber than it is to sell it for home development,” DeLap said.
Even if development compromises habitat quality, knowing which factors support biodiversity could help developers balance profitability and ecosystem health.
These results underscore the need to consider sensitive species when planning projects, and caution surveyors against assuming that all birds within a guild will behave the same way. Changing the land will change the ecosystem, bringing birds together that might not have shared habitat otherwise.
“Given that a lot of forest land will likely be converted in the coming years, I hope this will help folks recognize what they stand to gain and lose through development,” DeLap said. “There might be other configurations worth evaluating, but now at least we know what happens on the landscape in these two scenarios.”
Additional co-authors include Sarah Converse, a UW professor of aquatic and fishery sciences and leader of the USGS Washington Cooperative Fish and Wildlife Research Unit.
This study was funded by the U.S. National Science Foundation and the University of Washington Rachel Wood’s Endowed Graduate Program and James W. Ridgeway Professorship.
For more information, contact DeLap at jdelap@seattleu.edu and Marzluff at corvid@uw.edu.
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