Last fall, our tracking club decided to study the shorelines of Nicasio Reservoir, with its extensive drought-exposed lakebeds and amazing amount of bird and mammal activity near the water and up in the brushy banks. Tracks stretch in a progression from high-water shorelines to dry-season, low-water edges. As the water level drops and the lakebed dries, the tracks are preserved as a calendar, revealing which animals were prevalent as the seasons moved from spring through summer and fall. With this record, we can read the timing of specific bird migrations and the changing rhythms of mammals.
The lakebed mud is very fine-grained and leaves extremely sharp and detailed tracks, revealing features that don’t often register in sand or even dust. This mud can capture tracks of the fur between a fox’s or a rabbit’s toes and the pebbly texture of a skunk’s sole. River otter tracks show the small webs between the toes. Raccoon tracks reveal flat-bottomed feet similar to those of wading birds—both evolved for walking in the soft mud of shorelines.
A lot of other animals regularly cross the muddy lake-bottom: coyotes and bobcats, mice and rats, even the occasional ground squirrel. A surprising number of jackrabbits and brush rabbits go back and forth, and opossums are frequent visitors. Bird tracks show species ranging from plovers to sparrows, warblers, ducks, gulls, geese, crows, ravens, hawks and eagles. It is a rich record.
Eager to check such things out, we parked along Point-Reyes Petaluma Road and walked down a small trail through the brush to the shoreline near the dam. Halfway down, we were surprised to find a beautiful four-foot gopher snake lying dead in the trail. It must have been dozing in a warm spot while digesting a morning meal. Its head had been crushed by, we guessed, a hiker walking down the trail earlier that morning. A case of bad luck.
That was odd enough, but looking closer, we saw there was a huge bulge in its belly, about halfway down its length. I couldn’t resist the temptation to see what it was, so I cut the snake open. Slice by slice, through the thin, dry snakeskin, I revealed a large furry body as the group watched, fascinated and a little creeped out.
Finally, I rolled a large Norway rat out of the gopher snake’s body. It had been going down the digestive tract head-first and upside down, with its front paws tucked in under its chin. It was very fresh and healthy looking, with no sign of being digested yet.
Amazed and bemused, we left the rat lying next to the snake and worked our way down the shoreline. We spent a half-hour scoping out tracks. There was little to see—too steep, too rocky and too close to the road—so we decided to move to the south end of the lake, where the exposed lakebed is broad and flat.
On our way back to the road, we stopped to check on the dead snake. To our surprise, the rat was no longer there, and in its place was a neat little pile of intestines. This rat had been eaten twice! In the short time we had been down by the water, some other animal had found it and eaten it, but left the snake alone. This was mid-morning on a Sunday with a fair amount of traffic on the road, and the band of brush was only about 30 feet wide. Nevertheless, someone had found this treasure that quickly—an astounding indication of nature’s lively web of awareness. The gut pile was neat and precise, just like the ones our housecats leave on our doormats from their mouse or gopher hunting.
We speculated that a bobcat had done it. But would a bobcat eat dead prey? If fresh enough, probably so. There are a couple of homes far up some nearby driveways, so a housecat was a possibility, but a rat that size would likely be too big a meal for a cat to have finished so quickly. Coyotes will sometimes dissect and discard specific organs of a rodent—I’ve seen them do it—but not as neatly as a cat. A hawk, at least a large one such as a redtail, would have probably carried the whole rat away to a safer spot. Both the rat and snake carcasses were probably too fresh to have attracted a vulture.
How surprising to think that a bobcat may have been lurking in those very bushes we had walked through. How surprising to see how quickly the opportunity was seized. And if it was a bobcat, we just had to wonder: was it there the whole time? Had it already found the snake and we interrupted it? Had we made a convenient gift out of the situation? Was the bobcat grateful? And what other animals were lurking in the brush, invisibly watching as we passed through, as we pass through any wild landscape? A week later, the snake carcass and the rat intestines were gone. That was the slower work of scavengers, leaving nothing to waste.
As is typical, the lake-bottom mud shrinks as it dries. These deep clay silts leave wide cracks up to 12 inches deep. In our late-summer exploration, we found that one pioneering mouse had made it out to an old piece of carpet that had been dropped onto the dried mud, at least 100 yards from the nearest cover. The mouse had built a nest-ball of sandpiper feathers under it, revealing how crucial a simple roof can be—and how quickly wildlife will inhabit new territory.
In an adjoining crack, the mouse had gathered a cache of seedheads from one widely spaced but fast-growing lake-bottom plant. Two weeks later, she had given birth to two lively babies, who were thriving in the mud cracks. This struck me as a hopeful sign, an indication of how quickly nature can respond and adapt to any new possibility.
Richard Vacha is a Point Reyes Station resident. He is the founder of the Point Reyes Tracking School and the Marin Tracking Club.