The MVSD Western Pond Turtle Study

A female pond turtle was tagged with a GPS unit

A baseline population study conducted by Wildlife Biologist Jeff Alvarez in 2009 revealed that some 90 to 120 adult western pond turtles depend on habitat provided by MVSD’s Moorhen Marsh. This 21-acre freshwater wetland was constructed in the 1970s to provide valuable aquatic habitat for native fish and wildlife. The marsh receives 1.2 million gallons daily of advanced secondarily treated effluent as its primary water source.

Remains of a pond turtle nest after predation from a skunkIn 2011, MVSD recognized that to provide the best wildlife habitat possible, a new Management Plan was required for Moorhen Marsh. The plan was completed in 2013 and identified the need for pond dredging and levee stabilization. Kelly Davidson, District Biologist for MVSD, was concerned about how such activities would affect the pond turtle population. She wanted to know how the turtles were using the habitat throughout the year. Were they breeding and nesting on site? Were they overwintering in the ponds, on land, or off site? How the turtles used the wetland throughout the seasons would determine how and when the dredging, levee work, and other maintenance and enhancement activities would proceed. The best way to figure out what the turtles were doing, and when they were doing it, was a telemetry study.

The non-native red fox The first attempt to answer some of these questions began in 2012. With grant funding from the Contra Costa Fish and Wildlife Committee, MVSD purchased five very high frequency (VHF) radio telemetry units to monitor the turtle’s activity. However, this method did not prove as successful as hoped, as the VHF units used to tag turtles proved unreliable. Though significantly more expensive, GPS is a more effective and efficient form of tracking compared with the VHF units, as long as the turtle is big enoughto carry the added weight of the larger GPS unit. Fortunately, Moorhen Marsh is home to some very large turtles!

A newly hatched pond turtleFisheries and Wildlife Biologist Bert Mulcahey at East Bay Municipal Utility District generously offered to loan MVSD the first five GPS units. These units were placed on one male and four female turtles in May and June of 2013. An additional four GPS units were placed on female turtles in May of 2014.

Thanks to the ongoing study, MVSD now knows that turtles are in fact, nesting in the limited upland habitat of the marsh. Sixteen pond turtle nests were detected in 2013 and 21 nests were found in 2014. Because female turtles do not incubate or tend to the nest after the eggs are laid, predation of nests is very common. Unfortunately, many of the nests in Moorhen Marsh were predated.
Through intense monitoring efforts, MVSD biologists and consultants were able to find five actively nesting females in June and July of 2014. To protect nests from predators, they were covered with special cages designed to allow hatchlings to get out once they emerged. The nests are incubated by the sun, and viable eggs could hatch in 80-100 days. Interestingly, most of the hatchlings will remain sequestered in the nests over the fall and winter and will not emerge until spring of the following year. For more information on turtle nest predation in Moorhen Marsh, CLICK HERE to read a short article published in the Herpetological Review.

The Western Pond Turtle was recently separated into two species, the Northern Pond Turtle (Actinemys marmorata) and the Southwestern Pond Turtle (Actinemys pallida). The southwestern pond turtle is in serious decline throughout its range, which likely includes Contra Costa County. Soon, MVSD hopes to determine which species calls Moorhen Marsh home. Check this site regularly for more updates on this and other aspects if the study!

Jane with female pond turtle (blue GPS unit) after the turtle successfully nested in Moorhen Marsh. The GPS unit was removed and the turtle was released the same night. Photo by Kelly Davidson.Special thanks to MVSD Wetland Resources Intern Jane Lien for her significant contributions to this site.


About Telemetry

Many species of wildlife are studied using radio telemetry. This technique includes the use of a tag that can be glued to an animal (turtles), applied with a collar (bears and other large mammals), attached with a vest (California Condor), or placed internally (fish).

Radio telemetry units come in two different types: VHF and UHF. A VHF unit is usually smaller than a UHF unit and the emitted signal is captured through the use of an antenna and receiver. This is the type of telemetry unit we used to study turtles in 2012.

To collect data on turtle locations, a biologist walks through the area and uses the antenna to scan for a signal. When a signal is detected, the direction of the antenna is a clue to the direction of the animal. Three or more readings of the signal are needed to determine the precise location of the tagged animal. VHF units are less expensive but require many more hours in the field to collect data.

UHF uses GPS technology. GPS allows biologists to pre-program a unit to collect location data as frequently as is needed for a given species. For pond turtles, every hour during the day can provide location points.

With this method, biologists download the data from the unit remotely–using an antenna, or by collecting the unit from the turtle and plugging it directly into a laptop. UHF telemetry units are a more expensive technology than VHF, but provide much more data with far fewer hours in the field. These units are often much larger and heavier than VHF units because of the increased battery size.

We applied GPS units to five pond turtles in 2013 and four pond turtles in 2014. One of the goals for the MVSD study is to assess the advantages and disadvantages of both technologies as we gain a better understanding of how turtles use the different habitats of Moorhen Marsh throughout the year.

First Turtle Photo Gallery

How to Attach GPS to a Western Pond Turtle

Video courtesy of Telemetry Solutions – Concord, CA. Visit Telemetry Solutions Website here.

For more information on Jeff Alvarez and his company, The Wildlife Project, visit his Website here.

Learn More – Websites of Interest

2010 Bay Nature Article by Matthew Bettelheim

California Department of Fish and Wildlife Amphibians and Reptiles Species of Special Concern

Oakland Zoo Conservation Program

Oregon Wildlife Institute

Oregon Zoo Conservation Program

Sacramento Regional County Sanitation District Western Pond Turtle and Red-eared Slider Study

San Francisco Chronicle – EBRPD Pond Turtle Study

The Slaven’s Western Pond Turtle Project – Washington State

Washington State Recovery Plan

Western Pond Turtle Literature Compiled by Matthew Bettelheim

Wildlife of the San Francisco Bay Area – Western Pond Turtle

Recommended Reading List

Bettelheim, Matthew. 2005. The Western Pond Turtle, Clemmys marmorata, a Natural History of the Species. Matthew P. Bettelheim, Walnut Creek, CA, pp 28.

This is a comprehensive yet very readable natural history for scientists and non-scientists alike. It is a great place to start and is highly recommended. To purchase the booklet, visit:

Bury, R.B., Welsh, H.H., Germano, D.J., Ashton, D.T., eds., 2012, Western Pond Turtle- Biology, Sampling Techniques, Inventory and Monitoring, Conservation, and Management: Northwest Fauna No. 7, Olympia, WA, The Society for Northwestern Vertebrate Biology, pp 128.

This is a recently published synthesis of the known information on the Western Pond Turtle. It is probably best geared towards biologists, land managers, and serious amateur herpetologists and naturalists. For information on purchasing the manuscript visit:

Ernst, Carl H., Jeffrey E. Lovich, and Roger W. Barbour. 1994. Turtles of the United States and Canada. Smithsonian Institution Press, pp 578.

A comprehensive compilation on the turtles of North America. It is an indispensable reference for all turtle enthusiasts and herpetologists.

Holland, Dan C. 1994. The Western Pond Turtle: Habitat and History. Final Report. Portland, OR: US Department of Energy, Bonneville Power Administration.

This report summarizes the natural history and behavior of the Western Pond Turtle by one of the noted authorities on the species. Readers may be able to access the report here:

Stebbins, Robert C. 2003. Western Reptiles and Amphibians. Peterson Field Guides. Houghton Mifflin Company, Boston, MA, pp 533.

The best field reference for reptiles and amphibians of the western United States. Well known for its excellent color illustrations by the author.

For those who just can’t get enough information on the Western Pond Turtle, visit Matthew Bettelheim’s site at You will find a very thorough list of published works including: journal articles, technical reports, published and unpublished theses, media articles, and historical documents.