Absence of Evidence

Five. The current record for "most turtles seen at once" this season is five. In the best-case scenario, these five represent a little more than 10% of all the Western Pond Turtles that should still be doing their turtle thing at Mountain Lake.

So, seeing five turtles doesn't mean that there are only five turtles (of the 54 released) still alive. 

I spoke with David Harelson, a Wildlife Biology Technician with the Presidio Trust. As it happens, hs passion is herpetology - all things reptilian. His perspective on the Western Pond Turtles at Mountain Lake is helpful. 

"Remember, it's still 'fogust' [fog+August] in San Francisco. When we get longer days of sunny weather, in September and October, I expect that we'll see more turtles basking at a time."

Turtles bask for different reasons. The obvious reason is "to get warm." But turtles don't need to bask in order to be active. Turtles can spend the day in the water, looking for food, without needing to sunbathe. And basking has other purposes. Like humans, turtles use sunlight to generate their own vitamin D. Turtles bask to kill off algae that grows on their shells. And after a big meal, basking may help speed the digestive process.

So, on the foggy days typical of July and August in San Francisco (sorry Outside Lands), there's not much to gain by basking: it's not much warmer than being in the lake itself. So an absence of evidence of turtles is not evidence of an absence of turtles.

It's too early to assume that the Mountain Lake turtles aren't going to make it. Like many animals, once Western Pond Turtles reach maturity, the odds that they'll live a long time improve. In the case of Western Pond Turtles, 50 years in the wild is a fair estimate. Turtles take the long view.

The turtles at Mountain Lake are still youngsters; at 3-4 years old, they won't be mature enough to breed for another 6-10 years. Right now, though they're too big to be prey for most birds, they are still vulnerable. As David said,

"The predation is real. These turtles are still small enough to be carried off by a determined raptor. The real risk, though, is raccoons. Raccoons are smart, and can work at a turtle, scraping out its carapace like a pumpkin."

As Fue said, five confirmed deaths is more than expected. Last winter's record rainfall may have done in some of the turtles, and the raccoons still pose a threat. But turtles have been around a lot longer than us, a lot longer than raccoons. The turtle strategy is sound. The turtles should be fine.

Still, we count the turtles we see, not the turtles we assume are out there somewhere. David was able to capture one of the Western Pond turtles - a big male with an dented shell - and attach a new radio transmitter. That's one more data point; one more turtle we can track without needing to spot it while basking.

I've been observing these turtles for a few weeks now. But I'm hooked. I'm rooting for these little guys, hoping I get to see them grow up to be old farts. And as our best "summer" weather approaches, I look forward to spotting more of my turtle neighbors soaking up the sun, while it lasts, like the rest of us San Franciscans.