Its turtling season at the Oakland Zoo again! Each summer our zookeepers team up with biologists and students from Sonoma State University to study the western pond turtle. Turtle nesting season is in full swing and California’s only native aquatic freshwater turtle has been an enigma to researchers for years. This is the fourth consecutive year that zookeepers have spent in Lake County and our knowledge of this species of special concern has increased exponentially. Here is just a short run down of a few of the things we have learned about western pond turtles through our collaborative research:
First, we were surprised to discover just how dry the nests were. Aquatic turtles are usually expected to have very moist nests, but not our western pond turtles. Based on our observations at the site, we created a very dry vermiculite mixture in which to incubate the eggs we collected. Several experts expressed concern about the lack of moisture in the mixture, but our guess was correct and we had a 90% hatch rate the first year.
One little known fact about many reptile species, western pond turtles included, is that the sex of the hatchling is determined by the temperature at which the egg is incubated. Along with our dry vermiculite mixture, we also set up five separate incubators at five different temperatures. The hatchlings were carefully marked with numbered dots so we knew exactly which clutch and incubator they came from. The hatchlings were then raised here at the zoo for about ten months, until they were big enough for a small endoscopic surgery to determine their sex. This data was then correlated with the incubation data and we now know the exact temperatures that produce male turtles versus female turtles.
As time went on, our project expanded and we also began to incubate nests in the field. This requires careful placement of high tech temperature and humidity sensors inside the nests and then covering the nests to secure them against predators. The wide range of temperatures in even a single day took us by surprise. Who would have guessed a difference of up to fifty degrees in one twenty-four hour period.
This is a project that is near and dear to our hearts, not only because it is a native species, but also because it is a project that zookeepers can be directly involved in. Just days ago, two keepers went to the lake to use telemetry equipment to track nesting females while other keepers were here at the zoo caring for last year’s hatchlings, who will be released at the end of this month. As we continue to progress in this conservation project, we hope to learn even more about this special animal.