snakes

Spring is approaching, and with it groundbreaking on a variety of projects. I'm beginning to get requests to visit sites to complete required pre-construction surveys.

One of these sites is in the Sacramento Valley, and it's potential giant garter snake (Thamnophis gigas) habitat. We're not certain if the species actually occurs in the project area, which is currently in rice production, and the nearest documented locality is about six miles away. But it might be there, and as so often happens, it's more efficient to assume presence and mitigate.

There's some controversy about the habitat needs of the species. The agencies generally consider rice fields to be habitat, and it's true that snakes do sometimes enter them. Rice fields are wet in summer, and thus they mimic the presettlement wetlands of parts of the Central Valley which were once fed by now diverted Sierra snowmelt well into the summer. Rice fields also harbor tadpoles... Pacific tree frogs or introduced bullfrogs... and as the fields are drained in late summer, snakes may forage in the shrinking pools of water if there is more permanent vegetated wetland habitat nearby to provide cover and food in other seasons.

Rice fields are also subject to frequent disturbance, and they can concentrate pesticides and herbicides. They are structurally simple. In my opinion, they're marginal habitat for giant garter snakes, at best. They're used only because so little else exists.

Giant garter snakes persist on some of the National Wildlife Refuges in the area, but these tend to be command-and-control facilities driven by pumps, and managed for waterfowl. They are largely dry in the summer months, and thus they differ considerably from the historic condition. Where more permanent water is present, snakes can do well because vegetation is more structurally diverse and food sources more predictable.

It seems at first glance to be easy to restore the requisite habitat. In practice it may not be so easy, because the water control system is so vast. Yet there are certainly at least some areas where restoration is feasible, and indeed it's been done at a few mitigation banks. Overall though, the lack of imagination is striking, when considering this species.

While I'm out on those sites, I'm going to be looking around, getting a better understanding of the landscape, and of the possibilities.