Capturing Biodiversity on Camera at Rancho Corral de Tierra

By Wildlife Ecologist Bill Merkle and Biologist Eric Wrubel, Golden Gate National Recreation Area; with Science Communication Specialist Jessica Weinberg McClosky, San Francisco Bay Area Network

Mountain lion photo from a wildlife camera at Rancho from the 2014 Golden Gate National Parks BioBlitz.

September 2023 - It’s tough for a park to meet its mission to conserve wildlife habitat and support sensitive species when no one is quite sure what creatures live there. Nor is it easy to learn what lives where when so many species' superpowers include avoiding human observation. Early on, such challenges weighed on National Park Service biologists working at Rancho Corral de Tierra, which became part of Golden Gate National Recreation Area in 2011. But now, answers are on the horizon. In August 2023, we launched the San Mateo Wildlife Inventory project to document Rancho’s wildlife—with help from wildlife cameras and community members.

Rancho Corral de Tierra, located about 20 miles south of San Francisco, spans nearly 4,000 acres. It encompasses elevations ranging from 60 feet near the coast to over 1,700 feet atop Montara Mountain. And it supports a similarly wide variety of habitat types, from the dominant coastal scrub, to riparian woodlands, freshwater wetlands, coastal grasslands, non-native forests, and manzanita chaparral. The site also offers important landscape connections to the San Francisco Public Utilities Commission Watershed and California State and San Mateo County park lands—eventually linking into other protected areas on the San Francisco Peninsula and the Santa Cruz Mountains.

To find out how wildlife use Rancho’s diverse, interconnected habitats, we opted to emulate One Tam’s successful, wildlife camera-based Marin Wildlife Watch project. Wildlife cameras are excellent for capturing information on secretive species. We deployed 24 of them across a 0.5 km grid over the park lands, covering a range of habitat types, elevations, and levels of human development.

National Park Service Wildlife Biologist Rachel Townsend sets up a wildlife camera in the upper elevations of Rancho. The cameras are located on game trails or habitat edges that mammals are likely to traverse.

NPS / Eric Wrubel

Our standard wildlife cameras are best suited to capturing medium-to-large mammal activity at Rancho, but we’re also interested in the site’s herpetofauna (reptile and amphibian) activity. So in addition, we are deploying ten specially configured close-up cameras. Using methods from the California Department of Fish and Wildlife, we’re setting these up in conjunction with drift fence arrays to help funnel the small herps toward the camera for better camera triggering and clearer views.

It’s all about the wildlife.

The San Mateo Wildlife Inventory project is strictly to help Golden Gate better understand and conserve Rancho Corral de Tierra’s biodiversity. While we have placed them away from trails, the wildlife cameras are triggered by motion and heat, and have the potential to capture photos of adventurous park visitors and pets. We do not use the photos to identify individuals or their pets.

Golden Gate staff and interns set up a herp camera. The camera is in the green box, and the drift array funnels reptiles and amphibians (and some small mammals) to the camera.

NPS / Darren Fong

Wildlife camera images are captured on flash cards that we collect every three months and upload to a cloud database. There, they are processed through artificial intelligence software, which provides suggested identifications for each image. We then go through the images and verify the identifications. We are seeking interested community scientists to volunteer to help verify image identifications. This is a great way to engage with the project and learn about the wildlife using Rancho. We will provide training, and look forward to possible future cataloging parties, where groups of individuals get together to catalog images.

Once the images are cataloged, we will analyze the data to develop a species list (species richness) and calculate detection rates for each species. For more common species, we’ll also estimate occupancy across the site, or how common a species is relative to others in a given area.. For the sensitive species we detect, we’ll pay special attention to their numbers, locations and habitat preferences. As we accumulate more years of data, we will also be tracking trends in biodiversity over time.

San Mateo Wildlife Inventory goals

With our wildlife cameras, we aim to:

• Inventory the mammal (>1 kg) and herpetofauna communities at Rancho Corral de Tierra.

• Gain information on rare and sensitive species at the site.

• Monitor trends in species abundance and diversity over time.

• Identify invasive species like feral pigs.

• Engage the community with fun photos of rarely-seen wildlife and invitations to participate in our community science effort to identify the photographs that we capture.

One particular species of interest at Rancho will undoubtedly be the mountain lion (Felis concolor). From past smaller efforts with wildlife cameras, as well as reports from our local community, we know that they are here. As apex predators, mountain lions are important components of terrestrial ecosystems. In addition, the regional mountain lion population—the central coast Ecologically Significant Unit—was recently identified as a candidate population for listing under the California Endangered Species Act. But mountain lions may also instill fear and present a risk to wandering pets. We hope to use what we learn about mountain lion activity at Rancho from this project to inform lion coexistence outreach.

For more information

• Contact Eric Wrubel with questions about the San Mateo Wildlife Inventory project, or to learn about volunteering to identify project images

• Learn more about mountain lions in California

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