Purple martin colony being relocated

A charismatic colony of purple martins along Ruston Way is moving. The dark purple and blue birds are North America’s largest swallow and often spotted among decrepit wooden poles at Dickman Mill Park, Titlow Beach and Chambers Bay.

They are a native bird that has been migrating back to Tacoma and other areas of the West Coast for thousands of years, arriving each spring from Brazil and usually departing by late August. The birds – beloved for their pest control and throaty chirps known as the Dawn Song – live in wooden nest boxes or plastic gourds made by humans, which are often attached to pilings and dock remnants.

Last week, the Washington State Department of Natural Resources began removing about 1,200 pilings treated with creosote, a toxic chemical that keeps water-logged wood from decaying, from the waters around Dickman Mill Park.

To preserve the longtime purple martin colony there, conservation staff from Point Defiance Zoo & Aquarium and Northwest Trek Wildlife Park teamed up with Communities for a Healthy Bay to remove 18 bird houses and gourds.

The boxes and gourds will be fixed up and put back on new posts in a tidal estuary about 500 feet south of their current location.

“Purple martins are important and valued here in Tacoma and we are dedicated to monitoring and protecting them,” said zoo conservation coordinator Zach Hawn. “They are a species that restores balance to our ecosystem, and we want to continue to provide that habitat that is essential for the success of these colorful, playful birds.”

Point Defiance Zoo & Aquarium has been working with purple martins since it launched a community monitoring program in 2013. Volunteers are trained in how to collect data about the local birds and their behavior and are asked to monitor one of the three locations at least twice a month.

All the data is shared with the Washington Department of Fish and Wildlife (WDFW), which lists purple martins as a Species of Greatest Conservation Need due to their low population in the state and vulnerable nesting sites. The designation means human intervention is necessary for the birds to succeed.

“I can’t overstate how important our partners and local groups are in helping us manage purple martins,” said Michelle Tirhi, a wildlife biologist for WDFW. “This collaboration is vital to keeping Washington’s purple martin populations stable and possible increasing these birds’ numbers in the future.”

No comprehensive population survey has been done to determine exactly how many purple martins nest in Washington each year, but the conservative estimate is 600 adult birds. That means Tacoma could have as much as 16 percent of the state’s population.

A statewide comprehensive survey has been proposed in Washington for 2026 or 2027, Tirhi said.

Thanks to Point Defiance Zoo & Aquarium’s community monitoring program, there are about 34 purple martins nesting at Dickman Mill Park, nearly 50 at Titlow Beach, about 20 at Chambers Bay and another 6 to 10 at the Point Defiance Boathouse.

Another colony exists on Hylebos Waterway but has not had regular monitoring in recent years.

“We have a sizable proportion of the state’s population of purple martins in the city of Tacoma,” said Sam Hain, conservation specialist at Point Defiance Zoo & Aquarium. “It’s a huge bastion for this species that needs our support right here in our backyard.”

The purple martins’ population started to decline in the Pacific Northwest in the 1930s when forestry operations removed large amounts of timber that housed natural cavities traditionally used by the birds as nests. Around the same time, non-native birds such as house sparrows and starlings were introduced to the area and competed with purple martins for resources and nesting habitat.

With a loss of habitat, purple martin numbers dropped so low that local scientists and bird enthusiasts began building homes for the birds in an effort to recover the species. That helped the western populations rebound but also made them reliant on human-made housing.

Purple martins nest as a colony, which is why boxes and gourds are grouped together. The birds like to be close but not too close, otherwise their squabbling intensifies and amounts to something Hawn and Hain laughingly call a “soap opera of the Sound.”

To help aid and manage purple martins, the number of boxes and gourds in each colony are limited to ensure there are enough to support the population encouraging birds to use natural cavities as the population grows.

Once DNR finishes removing the creosote-soaked pilings from Dickman Mill in February, conservation staff from Point Defiance Zoo will install new 6×6 posts and reinstall the boxes and gourds so they’re ready when purple martins return this spring.