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?

Native Mammal Diversity

Native Mammal Diversity

Marin Wildlife Picture Index Project Photo

Why Was This Indicator Chosen?

In September 2014, cameras were placed in a variety of habitat types throughout the Lagunitas Creek corridor as a part of the Marin Wildlife Picture Index Project (MWPIP). Looking at a suite of native mammals through the MWPIP provides a more complete picture of how terrestrial ecosystems on Mt. Tam are doing compared to looking at a single species, and also provides information on rare and non-native species.

What is Healthy?

The full suite of expected native mammals is present, and there are no non-native mammals. Rare species are also found in suitable habitat types. MWPIP occupancy estimates are stable and indicate that all tropic levels (from small prey species to large predators) are represented at appropriate scales.

What Are the Biggest Threats?

  • The lingering effects of historical impacts including land use changes, hunting, and trapping
  • Habitat loss and fragmentation, which can be particularly detrimental to species such as mountain lions that require large home ranges
  • Disease, including those spread by contact with pets
  • Rodenticide and pesticide exposure, especially for mammals that live near residential areas
  • Visitor use, which can affect the abundance and behavior of mammal communities (George & Crooks, 2006; Reed and Mehrlander, 2008; Lenth et al., 2008)
  • Invasive plant species that alter wildlife habitat, and invasive animals that outcompete native species for food, water, nest or burrow sites, and shelter

What is The Current Condition?

Results from preliminary data so far show most expected native mammal species are present in the One Tam area of focus, with an abundance of small mammals (prey species). Opossums and cattle have been the only non-native mammal seen so far (Townsend, 2015). The current condition of Fair reflects these promising early results combined with the fact that we have seen very few rare species such as spotted skunks and mountain lions.

Mammal species and number of individual detections captured on camera in the first three months of the Marin WPI project (Townsend, 2015)

What is the Current Trend?

Trends are Unknown because there are not yet enough data from the Marin WPI to assess a trend in Mt. Tam’s mammals.

How Sure Are We?

Our certainty in these conclusions is currently Moderate because only early data are available.

What is This Assessment Based On?

Preliminary results from three months of MWPIP images (only three months are available so far because of the large amount of time it takes to catalog, verify, and analyze the data).

What Don’t We Know?

Key information gaps include:

  • The effects of climate change on mammal habitats on Mt. Tam
  • Numbers and distribution of small mammals, as MWPIP cameras most reliably capture mid- to large-size animals (those over 1 kg)


Marin Wildlife Picture Index Project The River Otter Ecology ProjectFelidae Conservation Fund
Mammals Indicator Overview

Learn More


George S. L., & Crooks K. R. (2006). Recreation and large mammal activity in an urban nature reserve. Biological Conservation, 133(1), 107–117. Available from:

Lenth, B.E., Knight, R.L., & Brennan, M.E. (2008). The Effects of Dogs on Wildlife Communities. Natural Areas Journal, 28 (3), 218-227. Available from:

Reed, S.E. & Merenlander, A.M. (2011). Effects of management of domestic dogs and recreation on carnivores in protected areas in northern California. Conservation Biology, 25(3), 504–513. Available from:

Townsend, S.E. (2015). The Marin wildlife picture index project, pilot for monitoring wildlife in Marin County: Interim analysis (Final administrative draft). Marin County Parks, Marin Municipal Water District, State Parks Samuel P. Taylor, Golden Gate National Recreation Area. Oakland, California.