It's Turtles All the Way Down

Turtle monitoring season has come to a close. Our counts were going up – seven turtles, nine turtles, eleven turtles basking at once – enough for a football team! But internships end, and their programs expire with them. Also, CalTrans (California Dept. of Transportation) began some new work along the same shore of the lake where our turtles bask, and turtles prefer a more serene setting. Finally, the winter weather has settled in; cool and rainy.

Eleven. Last year, the biggest survey counted 38 turtles basking at once. This year, eleven turtles. So how many turtles are left?

It’s pretty clear that the attrition is due to raccoons. As David Harelson (Wildlife Biology Technician with the Presidio Trust) said, “You can see raccoon tracks all along the lakeshore. They’re smart, and there are a lot of them.” As the surviving turtles grow bigger, they’ll be less vulnerable to predators. But it does raise a question: if the Western Pond Turtles at Mountain Lake do live long enough to reach sexual maturity, how well will their offspring do? Hatchling turtles are like pot stickers to herons and grebes, not to mention the raccoons.

Estimating the total number of turtles based on our monitoring is like trying to guess the population of a town by watching the number of sunbathers at the local beach. On hot, sunny days, more residents show up on the shore – but never all of them at once. On rainy days, nobody is at the beach*, but that doesn’t mean that the town is empty.

Over beers at the local Irish pub/bluegrass joint, I spoke to David and Jonathan Young, a Wildlife Ecologist with the Presidio Trust about the turtle population. Jonathan hedges his bets. “If we saw eleven, maaaaaybe there are fifteen or sixteen turtles left.”

David is more sanguine. “I think it’s like a dolphin pod. For every dolphin you see at the surface, there are five or six below the surface. So, with the turtles, I’m thinking there are 20 or 25 out there.” He added, “you know, CalTrans has to have a biologist on site, and he says he’s seen turtles in the reeds while the work crews are there.”

And the reeds are where this author pins his turtle hopes. Presidio biologists (and volunteer Citizen Scientists, like me) observe turtles from the far shore of the lake, through a spotting scope. And all we can see are the logs that have been strategically placed for turtle basking. But behind the logs is a wetland nearly the size of a football field, created as part of the restoration effort at Mountain Lake. The reeds are mature now, ten feet tall. The mud is as swampy as you like – as sticky as molasses, and as aromatic as a manure spreader. These reeds are really hard for me and other Presidio workers to travel through; definitely not raccoon-friendly. I think there are turtles back there, playing it cool. 

So is this a success story? Mountain Lake is a little lake in a major urban center. No matter how much we work at habitat restoration, we’ll never create a truly wild space. And the habitat we create is going to require ongoing care. But the results are worthwhile – reintroducing native species increases the diversity of the environment. With a diverse set of plant species, something is always in bloom for the pollinators; something is always in seed for the birds and the field mice. More birds stop at Mountain Lake now, where there’s a wider variety of insects to eat, a bigger array of potential nesting sites. Diversity fosters redundancy. Redundancy means resiliency; an ability to compensate when one resource goes sideways. 

They call us habitat restoration volunteers “Presidio Park Stewards.” And stewardship is what this is about. We can’t return Mountain Lake to a pristine condition, even if we could agree on what that meant. But we can make it hospitable for as many native plants and critters as possible. And there are some clear success stories. The three-spined sticklebacks are thriving. And the Pacific Chorus Frogs are going gangbusters.

So this will be the last turtle blog for a while. But the Presidio is buzzing with more stories to tell. 


*You might assume that turtles don’t bask in the rain, but testing assumptions is what the scientific method is all about. So one afternoon, when the water temperature was 10°F warmer than the air, and a cool mist was falling, I tested this hypothesis and counted turtles. I saw none.