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Golden-crowned kinglet (Regulus satrapa). Photo: Minette Layne (CC BY-NC 2.0)
Golden-crowned kinglet (Regulus satrapa). Photo: Minette Layne (CC BY-NC 2.0)

Golden-crowned kinglets in Puget Sound have seen a steep decline since 1968

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The number of golden-crowned kinglets in the Puget Sound watershed has declined by more than 91% over a recent 50-year period, according to data from the North American Breeding Bird Survey. The data was reported by the Washington Department of Fish and Wildlife, which tracks the information for the Puget Sound Partnership’s terrestrial bird indicator. The indicator was established to monitor the health of Puget Sound’s species and food webs.

The findings come amid widespread bird declines across North America. Overall, bird numbers across the Continent dropped by almost 30% over the last half-century, a loss of more than three billion birds that biologists in the journal Science called “staggering.”

The figures for Puget Sound show an even steeper rate of decline for the kinglets, which inhabit Puget Sound’s interior forests. Over the 50-year period from 1968 to 2018, golden-crowned kinglets declined by an average of 4.78% per year, according to WDFW biologist Scott Pearson, who compiled the information for the Partnership’s terrestrial bird population abundance indicator. That amounts to a population loss of 91.36% over the duration of the survey. The declines were measured in “routes that occur, or partially occur, within the Puget Sound watershed,” according to the Partnership’s website.

Map of North American Breeding Bird Survey (BBS) routes that occur, or partially occur, within the Puget Sound watershed.

The golden-crowned kinglet is described by the American Bird Conservancy as “one of the world’s smallest perching birds,” and lives in Puget Sound’s coniferous forests year-round. It feeds mostly on insects in trees and shrubs and must eat almost constantly to feed its high metabolic rate. It is one of three normally common forest species measured by the Partnership’s Vital Sign indicator. The other forest indicator species include the varied thrush, which declined by less than 1% per year over the study period, and the brown creeper which saw moderate increases of about 2% per year. The Vital Sign indicator takes an average of the status of all three birds as a way of measuring the health of the food web in interior forest habitats. Driven by the drop in kinglets, the overall indicator showed a decline of 46% over 50 years.

Other bird species measured by the indicator are several “human-associated species” including the American crow, European starling, rock pigeon, house finch and house sparrow. Biologists say those birds adapt more easily to human development and can nest on human structures or eat discarded food in garbage. On average, those birds were more stable but still declined as a group by 8%. The Partnership has classified the status of the terrestrial bird abundance Vital Sign indicator as “Getting Worse.”

According to Pearson, the decline in kinglets is “not well understood” but could be driven by factors such as loss of forest habitat and pressures from climate change leading to forest fires or increasing winter storminess.

The decline in forest birds tracks roughly with the Partnership’s Land Cover and Development Vital Sign indicator which shows an estimated decline in forest habitat in Puget Sound of 836 acres per year. “To the region it [forest bird declines] suggests that we are losing our predominant land cover,” Pearson says.

Percent change per year (1968-2018) in population abundance of three forest interior bird species. (Graph courtesy of the Puget Sound Partnership and the Washington Department of Fish and Wildlife.)

Kinglets are also prone to die-offs during severe winter events such as ice storms. “If trees freeze up, the birds can’t get to the bugs to eat,” Pearson says. “We have had a number of unusual winter events,” a phenomenon that is predicted to increase in frequency, according to climate change models.

While golden-crowned kinglets have dropped precipitously in Puget Sound and are declining generally, they are still relatively common across North America. “It’s hard to imagine we would get to a world without kinglets,” says Pearson.

However, the story of the golden-crowned kinglet in Puget Sound may be one of many playing out across North America. According to the 2019 article in Science  that described the massive loss of billions of birds across the Continent, the declines “are not restricted to rare and threatened species—those once considered common and wide-spread are also diminished.”

One positive sign for the kinglets may be that the loss of forest habitat in Puget Sound, while still ongoing, is less severe than it has been in previous years. According to the Partnership, forest declines in the watershed have dropped to about 38% of what they were in the early 2000s. “If this decline in habitat loss continues, it will be interesting to see if the rate of forest associated bird populations begins to stabilize,” Pearson and his colleagues wrote on the Partnership’s website.