Measuring the health of Mt. Tam

Maintaining a healthy, vibrant and diverse Mt. Tam begins with understanding how key ecological resources are faring, and how we can better care for this iconic and beloved place.

One Tam partners and Bay Area scientists have come together to try to answer the question: How healthy are Mt. Tam's natural resources?



The health of Mt. Tam’s birds can be looked at in a variety of ways. Below is an assessment of the overall health of the mountain’s avian communities obtained by combining the health assessments of a number of bird communities.

Additional details about the health of these bird communities is available through links in the photos above. There are also links to two individual species of birds for which enough is known to asses their condition and trend: Osprey and Northern Spotted Owls.

The Overall Health of Mt. Tam's Birds

Why Was This Indicator Chosen?

Birds are recognized as indicators of ecological change (Carignan & Villard, 2002). They also provide a wide variety of important ecosystem services including devouring pests, pollinating flowers, dispersing seeds, scavenging carrion, cycling nutrients, and modifying the environment in ways that benefit other species (Whelan et al., 2015). Agencies within the One Tam area of focus have a relatively long history of bird monitoring, enabling estimates of population trends for multiple species across a range of vegetation communities.

What is Healthy?

A healthy population of birds on Mt. Tam would be stable or increasing over the next five years. Given environmental stressors beyond our control, it may not be realistic to try to maintain a certain abundance for all species. However, overall population size and fitness are likely to be important components of a species’ ability to track environmental change (Williams et al. 2008).

What is The Current Condition?

Overall, Mt. Tam’s birds are currently in Good condition.

What is the Current Trend?

Birds on Mt. Tam currently appear to be experiencing No Change in their trend.

How Sure Are We?

Confidence in this assessment is High, as Mt. Tam’s birds have been fairly well studied, and because of the large number of species considered in this assessment. Bird species were aggregated to reach a summarized confidence level for individuals sharing similar traits, as well as overall. Individual species confidence levels were summarized from the species traits-status database.

What is This Assessment Based On?

  • Marin Municipal Water District (Cormier et al., 2014)
  • National Park Service (Gardali & Geupel, 1997) and just riparian areas (Humple & Porzig, 2012)
  • Marin County Parks (Gardali et al., 2010)

What Don’t We Know?

Key information gaps include:

  • Data on grassland-associated species, wintering and migratory bird populations, and time series data for agencies other than the Marin Municipal Water District
  • Population demographics such as survival and reproductive success


Learn More

Species Traits-Status Database


Carignan, V., & Villard, M.A. (2002). Selecting indicator species to monitor ecological integrity: a review. Environmental Monitoring and Assessment 78, 45-61. Available from:

Cormier, R. L. (2015). Northern Spotted Owl monitoring on Marin County Open Space District and Marin Municipal Water District Lands, 2015 Report. Petaluma, CA: Point Blue. Available here.

Gardali, T., & Geupel. G.R. (1997). Songbird inventory and monitoring at the Golden Gate National Recreation Area: Results from the 1997 field season. Petaluma, CA: Point Reyes Bird Observatory (PRBO)

Gardali, T., Jongsomjit, D., & Stralberg. D. (2010). Developing habitat-based landbird models as planning tools for the Marin County Open Space District and the Marin Municipal Water District. Petaluma, CA: Point Reyes Bird Observatory (PRBO). Report to the Marin County Open Space District and the Marin Municipal Water District. PRBO Contribution #1736.

Humple, D.L., & Gardali, T. (2006). Landbird monitoring in the National Park Service’s San Francisco Bay Area Network. A summary report of the 2005 field activities for: Golden Gate National Recreation Area, John Muir National Historic Site, Pinnacles National Monument, and Point Reyes National Seashore. Petaluma, CA: Point Reyes Bird Observatory (PRBO). Available from:

Whelan, C.J., Sekercioglu, C.H., & Wenny, D.G. (2015). Why birds matter: from economic ornithology to ecosystem services. J Ornithol doi:10.1007/s10336-015-1229-y. Available from:

Williams, S.E., Shoo, L.P., Isaac, J.L., Hoffman, A.A., Langham, G. (2008). Towards an integrated framework for assessing the vulnerability of species to climate change. PLoS Biol 6(12), e325. doi:10.1371/journal.pbio.0060325. Available from: