Protected lands help bird populations recover and thrive in the long term, a study by the Petaluma-based Point Blue Conservation Science found. Over the course of a quarter century, researchers at the Palomarin Field Station in Bolinas surveyed bird populations in the Point Reyes National Seashore, Golden Gate National Recreation Area, Mount Tamalpais State Park and Marin County parks. Compared to average population trends throughout coastal California, about two thirds of the bird species studied in these parks fared better over time. Nine of the 14 species the scientists studied did better in protected areas than the overall average. All nine of these populations remained stable or increased locally, rather than declining slowly. “The long-term data sets are really the only way we can look at these big changes that are occurring related to climate change, related to habitat loss,” said Mark Dettling, an avian ecologist at Point Blue and the study’s lead author. “You can’t do that with shorter, five- or 10-year data sets.” Mr. Dettling said scientists often assumed that protecting more land would help safeguard bird populations, which have seen widespread decline in recent decades. Last year’s Audubon Christmas Bird Count at Point Reyes was cancelled due to the pandemic, but the 2019 season saw just 188 species, down from over 200 in years past. Federal and state mandates mean that 30 percent of California’s lands and waters must be protected by 2030. The Point Blue researchers sought to confirm whether the assumptions behind conservation are true by conducting point count surveys at dozens of locations on protected lands around Marin, and comparing them over the years with regional averages. More than half of Marin County’s land is protected by parks or open space preserves, and much of the coastal protected land is uninterrupted by development or resource extraction, which makes it particularly bird-friendly. “That’s something that’s kind of unique in Marin,” Mr. Dettling said. “A lot of these protected areas are contiguous.” Although the majority of species fared better in protected areas as expected, two species, the black-headed grosbeak and olive-sided flycatcher, actually had worse-than-average population trends. Mr. Dettling said more studies are needed to determine why that is. Though the two species, which are migratory, might be spending summers in protected areas in Marin, scientists would need to track them with transmitters to determine whether they are also wintering in protected areas in Mexico or Central America, and whether their migration routes are safe. “Especially with migratory species, they’re spending half or more of their life cycle outside of Marin County,” he said. Although his study overall confirms the value of habitat conservation, Mr. Dettling said, there are other factors that can harm bird populations and extend far beyond Marin. Climate change may already be affecting food sources like berries and insects, even in parks. “Protected areas might not be able to buffer that climatic change,” he said.