Bird Population Monitoring 

Bird population monitoring informs Marin's public land management strategies.

Birds are sensitive to changes in their environment. Long-term monitoring is an important component to tracking the health of wildlife populations, and understanding how they are responding to changes in their habitats and climate. Monitoring bird population trends over a sustained period of time provides data about ecosystem ecology, as well as the status of individual species. Public land managers in Marin, including Marin County Parks, have long partnered with Point Blue Conservation Science to gain a better understanding of Marin's birds, and how they are faring across a diverse range of habitats. This has resulted in two key initiatives:
  • Abundance Patterns of Landbirds in the Marin Municipal Water District   
  • Northern Spotted Owl Monitoring
Banner Photo Credit: Andre Gregoire

Abundance Patterns of Landbirds

How Are the Birds Doing?

Point Blue Conservation Science has been tracking long-term trends of landbirds on Marin Municipal Water District Lands on Mount Tamalpais for over 20 years, and found that the majority of these populations are either growing or stable. This is great news, given the widespread declines of many species throughout California and the nation.

Which Locally-Nesting Landbird Species Are Changing?

Birds are excellent indicators of their environment, so changes in bird populations are often indicative of other changes, such as food, habitat, or weather. Additionally, migratory birds may show increases or declines due to changes in areas where they spend another part of their year, many miles from Marin County.
Anna’s Hummingbirds is increasing overall in California and the West, and that may be due to an increase in hummingbird-friendly gardens. Wilson’s Warbler is one of several species of breeding warblers that is also increasing on Marin Water lands (the others being Audubon’s, Black-Throated Gray, and Hermit warblers). The Olive-sided Flycatcher, while lower in overall abundance than some other species, is a California Bird Species of Special Concern, and declining in many other parts of their range. Other species with increasing trends include Hairy Woodpecker, Hermit Thrush, and Oak Titmouse.
The two species of declining jays is noteworthy, and may be related to Sudden Oak Death in Marin County, which kills oaks and tanoak trees that produce acorns, a source of food for jays and other animals. Additionally, West Nile Virus was also first isolated in California around the same time that these species started to decline. But, while declining over the entire study period, both species appear to be slightly increasing in more recent years. The California Towhee is encountered in neighborhoods throughout Marin. Long-term monitoring can reveal important trends in species often thought of as common. Those populations cannot be taken for granted. Other species with declining trends include Ash-throated Flycatcher and Downy Woodpecker.

Landbird Species Analyzed

Acorn Woodpecker
Chestnut-backed Chickadee
Pacific Wren
Anna's Hummingbird
Golden-crowned kinglet
Spotted Towhee
  • Acorn Woodpecker
  • American Robin
  • Anna's Hummingbird
  • Ash-throated Flycatcher
  • Audubon's (Yellow-rumped) Warbler
  • Band-tailed Pigeon
  • Bewick's Wren
  • Black-throated Gray Warbler
  • Blue-gray Gnatcatcher
  • Brown Creeper
  • Bushtit
  • California Quail
  • California Scrub-Jay
  • California Towhee
  • Chestnut-backed Chickadee
  • Dark-eyed Junco
  • Downy Woodpecker
  • Golden-crowned Kinglet
  • Hairy Woodpecker
  • Hermit Thrush
  • Hermit Warbler
  • House Finch
  • Hutton's Vireo
  • Mourning Dove
  • Northern Flicker
  • Oak Titmouse
  • Olive-sided Flycatcher
  • Orange-crowned Warbler
  • Pacific Wren
  • Pacific-slope Flycatcher
  • Pileated Woodpecker
  • Purple Finch
  • Red-breasted Nuthatch
  • Rufous-crowned Sparrow
  • Song Sparrow
  • Spotted Towhee
  • Steller's Jay
  • Swainson's Thrush
  • Warbling Vireo
  • Wilson's Warbler
  • Wrentit

Northern Spotted Owl Monitoring

Marin Northern Spotted Owl Population Appears Stable

Site occupancy by Northern Spotted Owl pairs in Marin County remains relatively high and stable, suggesting that this federally and state Threatened species is doing relatively well here. Unfortunately, Northern Spotted Owls are declining throughout most of their range, but Marin County remains a bright spot. 

Northern Spotted Owl Pairs by Land Manager

Northern Spotted Owls are found in forested habitats all over Marin County, on state, county, and federal parklands, as well as on private and municipal lands. Not all potential habitat is surveyed every year, so actual numbers of pairs per land management agency or landowner may differ from the survey data.

Northern Spotted Owl Breeding Success

The number of Northern Spotted Owl pairs that nest successfully each year is highly variable, and depends on weather, food availability, and other factors, but the overall average is relatively high in Marin County (averaging 46%) – a bright spot for this threatened species – compared to other parts of their range. Data were collected on California State Parks, Marin County Parks, Marin Municipal Water District, National Park Service, municipal, and private lands.

Northern Spotted Owl Nesting Trees

Northern Spotted Owls usually choose to nest in conifers, but sometimes use oaks, bays, and madrones as a nest tree.

Read the Reports

Point Blue Spotted Owl Report Cover
National Park Service Spotted Owl Report Cover

Parks Measure A: Funding Natural Resources Research

Measure A has allowed Marin County Parks to support important work in natural resources monitoring and research on Marin's public lands. As the Bay Area faces the challenge of climate change, this work has become more important than ever. Learn more about land and habitat restoration projects funded by Measure A.

Partners and Collaborators

One Tam brings these four agencies together with the nonprofit Golden Gate National Parks Conservancy to leverage the skills and resources of each partner and inspired community members to support the long-term stewardship of Mt. Tam. Learn more at
One Tam partner logos
Point Blue's mission is to conserve birds, other wildlife, and ecosystems through science, partnerships, and outreach. Point Blue has been assessing changes in the environment and advancing conservation through bird and ecosystem studies since its founding as Point Reyes Bird Observatory in 1965. Learn more at

For more information about Marin County Parks, visit
Link to Marin County Parks website.