What’s up my turtles?
“So, what’s up with the turtles?”
I’ve been monitoring the Western pond turtle population at Mountain Lake for three years. 2017 was a mystery — where are the turtles? 2018 was a triumph — plenty of turtles. So, what about this year? The short answer? It’s complicated.
Until 2015, there were no Western pond turtles in San Francisco. They’d been eaten by ‘49ers and other new arrivals (when turtle soup was a thing in the US). Where their ponds weren’t filled in, the Western pond turtles found themselves competing with East Coast turtles that out-ate, out-grew, and out-bred* the Western pond turtles. Western pond turtles had been absent from San Francisco for generations.
In the culmination of a massive habitat restoration project, in October 2015, 54 young turtles were released into Mountain Lake, a small pond in San Francisco’s Presidio. And Presidio biologists have been keeping tabs on them ever since.
But turtles don’t write postcards, and they don’t do instant messaging. They spend most of their time in the water, out of sight. So monitoring the welfare of the turtles becomes a bit speculative.
Turtles are gonna turt
Turtle monitoring means counting the number of turtles basking on a given sunny afternoon. How many turtles were out today? How does that compare to last month? Or last year? In October 2018, I counted 29 turtles. But this year, the most turtles I’ve seen at once is 19. Has there been some drastic decline in the turtle population? A change in behavior? Do the turtles have a new spot to get some sun, far away from the prying eyes?
“The first thing you need to know about turtles is, turtles are going to do whatever they want.” This was how Dana Terry summed up turtle behavior. In 2015, Dana was a biology grad student at Sonoma State University.
Dana was instrumental in the reintroduction of Western pond turtles, working with Nick Geist, a professor in the Biology department at Sonoma State. The two biologists gathered the Western pond turtle eggs and provided advice as the turtle hatchings were raised at the Oakland and San Francisco Zoos. Safe from predators, the baby turtles grew quickly. Because the turtles could grow up in a space that was warm year-round, by the time they were 2 years old, they were as big as 4 year old turtles in the wild.
After another four years in the lake, the turtles are big enough now to evade most predators, so Dana believes that the population is stable. “30-odd turtles surviving out of the 54 we released in 2016 is a great result.”
The improving health of the lake may be making turtles harder to spot. We can only see the turtles sunning themselves on floating logs along the shore. But Western pond turtles will gladly bask on floating vegetation. As Mountain Lake has become healthier, the beds of tule reeds are taller and deeper. Turtles could be basking in comfort, just out of sight.
Caught in the act
Knowing what the turtles are up to is a lot of guesswork. But once, this May, one turtle gave away the plot. A sharp-eyed neighbor spotted a turtle crossing a lawn, more than 20 yards from the lakeshore. Western pond turtles are aquatic — they prefer to be in the water, where they’re fast and agile. Water is where the food is, and where the turtles are safest. If a Western pond turtle ventures far from land, it’s for a good reason.
This turtle was on her way back to the lake after laying eggs.
The neighbor held onto this rogue turtle until one of the Presidio biologists could take a closer look. The female turtle wasn’t carrying eggs, confirming that she’d laid her clutch by the time she was picked up. After a few measurements, and a quick shell buff,** she was released back into the lake.
Mud butt
There are plenty of advantages to wearing body armor. Turtles have been into it for 200 million years. But ease of hole digging isn’t one of those advantages.
Nonetheless, female turtles dig nests. Female Western pond turtles scrape out a hole with their hind feet, as deep as they can manage. Then they lay their eggs (6 or so) and refill the hole. As a final touch, the female urinates on the nest, creating a sort of dirt plug that seals the hole. The mothers then head back to water. If they’re picked up after laying, it shows, and these ladies are called “mud butts.”
After 4 months, the eggs in her clutch hatch. But the baby turtles stay underground, feeding off their remaining yolk over the winter. In the spring, they dig out and head for the safety of the lake.
How do the baby turtles know which way the lake is? Scientists have no idea. Really. Turtles are gonna turt.
Send more turtles
The hope is that the Mountain Lake turtles breed successfully. They can live up to 70 years, so time is on their side. And there’s lots of room for turtles.
“Carrying capacity of the lake? 200 turtles, easy. There are enough crayfish to feed them all,” said Professor Nick Geist, at a recent celebration of Mountain Lake’s restoration.
There may also be spare turtles available. As Jon Young, Wildlife Ecologist with the Presidio Trust explained, there are multiple turtle reintroduction programs underway in the Bay Area. There are still ponds in Northern California with robust numbers of Western pond turtles. These ponds are reservoirs to rebuild numbers of Western pond turtles, and re-establish populations in their former homes.
If more turtles are caught than are requested for a given program, these “extra turtles” can freelance, as it were. For instance, they could bolster the numbers at Mountain Lake.
Fingers crossed.
*The Red-eared Slider is the most common invasive species in North America. Usually seen as pets, they’re hardy, they grow big, and they lay eggs by the dozen, compared to the handful laid by Western pond turtles.
**The biologists didn’t buff her shell. But they did handle her gently and call her sweet names.
