Natural History

A Historical Timeline of Bainbridge Island Bird Populations

Pre-1850s: Indigenous Stewardship and Natural Disturbances

• Indigenous Stewardship: The Suquamish, who have inhabited Bainbridge Island and the surrounding areas for thousands of years, practiced sustainable methods such as selective harvesting and resource sharing. These practices preserved diverse habitats and supported stable native bird populations.

• Wildfires as a Natural Disturbance: For thousands of years, wildfires were one of the most significant natural disturbances shaping the island's landbird populations. Frequent low- and moderate-severity fires had localized effects on species, while occasional high-severity fires created large open habitats with standing dead trees and woody debris. These features of high-severity fires attracted species such as Lewis's Woodpeckers and Western Bluebirds.

• Distant Natural Disturbances: Bird populations on the island have always fluctuated due to environmental changes in distant breeding and overwintering grounds. For example, droughts in critical waterfowl breeding areas, such as the Prairie Potholes region, caused fluctuations in the number of ducks wintering on and around the island.

Mid-1800s: Settlement and Logging

• With the establishment of the first lumber mill in 1854, followed by additional mills and shipyards, the number of settlers on Bainbridge Island grew rapidly, accelerating the transformation of the landscape. Early logging operations targeted shoreline areas to take advantage of waterways for transporting timber. This deforestation quickly degraded habitats for species like Spotted Owls and Marbled Murrelets, which rely on large, undisturbed old-growth forests for nesting.

Late 1800s–Early 1900s: Industrial Growth

• Loss of All Mature Forests: The complete removal of old-growth and mature forests across the island eradicated critical habitats for species such as Vaux’s Swifts and Sooty Grouse.

• Clearcuts and Regeneration: The open spaces created by clearcutting supported species such as White-crowned and Golden-crowned Sparrows but lacked the structural complexity and hosted a different species composition compared to open habitats formed by wildfires. Over time, these clearcut areas regenerated into hardwood and mixed forests, attracting birds like Warbling Vireos and Downy Woodpeckers.

• Shoreline Development: Construction of mills, shipyards, and other development disrupted estuarine and beach habitats, negatively affecting shorebird populations.

• Hunting and Introduced Game Birds: Overhunting significantly reduced populations of species such as Band-tailed Pigeons and American Wigeons. Game birds like California Quail and Ring-necked Pheasant were introduced and flourished temporarily in agricultural areas.

1916: Migratory Bird Treaty Signed

• The treaty between the U.S. and Canada marked a significant milestone in bird conservation, limiting hunting and other activities that threatened populations. It benefited migratory species such as waterfowl and songbirds that passed through or overwintered on the island.

Early 1900s–1940s: Agricultural Expansion

• Forest Conversion: Large areas of regenerating hardwood and mixed forests were cleared for farmland, creating fields that supported species such as Mourning Doves and Savannah Sparrows but disrupted habitats for species beginning to colonize the regenerating forests.

• Wetland Changes: Settlers drained and plowed wetlands, including bogs and marshes, to create farmland, impacting wetland specialists like Marsh Wrens and Common Yellowthroats. However, they also constructed ponds for irrigation, livestock, and aesthetics. These artificial ponds provided unexpected habitats for species like Wood Ducks and Hooded Mergansers.

• Non-Native Plants: The introduction and proliferation of invasive species like English Ivy and Himalayan Blackberry transformed local ecosystems. While these plants offered new resources for adaptable birds like American Robins, they also diminished food and shelter options for less adaptable native species, including Varied Thrushes.

1950s–Present: Suburban Development and Habitat Fragmentation

• Urban Expansion: The rapid suburban development of former farmlands introduced new food sources, including garbage and bird feeders. These changes created favorable conditions for adaptable bird species like American Crows and Black-capped Chickadees.

• Continued Shoreline Development: The alteration and fortification of shorelines for housing disrupted natural beach processes, reduced eelgrass beds, and diminished critical habitats for species such as Brant and Pigeon Guillemots.

• Introduced Species: European Starlings and House Sparrows, introduced to the Americas, established themselves in suburban areas, where they competed with native birds for food and nesting sites.

• Canada Geese: Before the 1950s, Canada Geese were uncommon migrants. The introduction of the Great Basin subspecies transformed them into common year-round residents.

• Pesticide Impacts: The widespread use of pesticides like DDT devastated populations of raptors, including Ospreys, Bald Eagles, and Peregrine Falcons.

1980s–Present: Shifts in Conservation and Species Dynamics

• Habitat Restoration: Community initiatives restored wetlands and protected green spaces, including Grand Forest and Gazzam Lake, creating essential refuges for native birds.

• Raptor Recovery: Bans on DDT allowed raptors such as Bald Eagles, Ospreys, and Peregrine Falcons to recover significantly.

• Decline of Wintering Western Grebes: Since the late 1970s, wintering populations of Western Grebes in Puget Sound have declined by nearly 95%. This decline appears closely linked to the decreasing availability of forage fish, such as Pacific herring, which can comprise more than 50% of their winter diet.

• Species Range Expansion: Anna’s Hummingbirds, California Scrub-Jays, and several other species expanded their ranges due to milder winters, the availability of bird feeders, and ornamental plantings.

• Arrival of Barred Owls: Barred Owls arrived on Bainbridge Island in the early 1990s, thriving in mixed forests but competing with native Western Screech-Owls for territory and resources. Their westward range expansion was driven by various human-caused environmental changes.

Contemporary Threats

• Large-Scale Threats: Many bird species face significant risks from climate change, including disrupted food resources, altered predator dynamics, and shifts in breeding habitats. Additional threats, such as avian flu, habitat loss, and pesticide use, also pose growing challenges, particularly for migratory species.

• Local Threats: Habitat loss from urban development, window collisions, and predation by domestic and feral cats remain persistent challenges to bird populations. Additionally, off-leash dogs and boating traffic often disrupt birds like gulls, shorebirds, and ducks, preventing them from establishing safe roosting and feeding sites. These localized pressures compound the broader effects of climate change and other large-scale disturbances.

Conclusion

Over the last 200 years, bird species on Bainbridge Island have undergone significant changes. For numerous reasons, some species, such as Rufous Hummingbirds and Golden-crowned Kinglets, have experienced steep declines, while others, like Brown-headed Cowbirds and Caspian Terns, have increased or remained stable. These changes highlight the profound impact of human activity and environmental shifts on bird populations, emphasizing the importance of continued conservation efforts to protect the island’s avian diversity.

The following bar chart is from the highly recommended book, The Birds of Vashon Island, by Ed Swan.