The chances of spotting a mourning dove or Brewer’s blackbird in The City have been sliced in half since about 25 years ago, likely because trees planted in the late 1800s are all failing at once.
It’s one of several speculations that came after the official results of the Golden Gate Audubon Society Christmas Bird Count reported that the number of species and the number of birds in The City have also plummeted.
When more than 10 birders took their binoculars out before dawn for the annual count in December, they observed 159 species among 49,313 birds, down from 172 species and 50,416 birds in the prior year among 170 square miles in the Bay Area.
“The trees in The City weren’t just planted in the 1880s but through the early part of 1920. It’s a relatively even-aged forest all hitting maturity at about the same time, that started back in the 1980s,” said Dan Murphy, compiler for the count.
However he also said that removing mature pines, cypresses and eucalyptus trees could have been the reason why the red-shouldered hawk numbers increased from an average of eight birds to an average of 49 within the past five years.
Murphy speculated an invasive, tough grass called Spartina alterniflora — a hybrid of native and Atlantic cordgrass — has driven the clapper rails out of the count entirely.
“It creates a habitat sink … and for some reason it prevents [the clapper rails] from being able to breed properly,” he said.
There weren’t any Neotropic birds either. They’re from an area that includes South America, the West Indies, Central America and tropical Mexico — like warblers, tanagers and orioles — but their population fluctuations were not related to the hybrid grass.
Volunteers count birds and bird species every December within a 15-mile radius of The City.
Source: Golden Gate Audubon Society