turtles

Today I had a reason to refresh on the Blanding's turtle literature. For the most part what I found online was disappointing, and for the most part it missed key elements of the habitat as well as the biggest threats.

It's easy enough to itemize a list of habitat types, and at first glance it seems to be fairly wide... sedge meadow, marsh, pond, river backwater. But that fails to take into account the fact that these are surprisingly mobile turtles. Saving or restoring one wetland is going to do little good.

In 1997 I had an opportunity to collaborate with the Lake County (Illinois) Forest Preserve District on a Blanding's turtle project. We gathered background information and then surveyed several preserves. Once we'd found one where turtles were relatively easy to find... which meant discarding 10 or 15 snapping turtles and painted turtles from our traps for every Blanding's turtle... we held a couple of individuals long enough for the county to put radio transmitters on them.

One of those animals quickly left the small but deep marsh where we'd captured it and then released it a day later. It walked roughly north for about 800 meters, crossing the state line into Wisconsin in the process. It stayed there, in another marsh, for a few weeks before returning to yet another marsh in Illinois.

This points out several management challenges. The "core habitat," the marshes where the turtle spent days to weeks before moving to the next core, were all of pretty good quality. But it had to cross relatively small areas of less pristine upland habitat to make those moves. Fortunately, in this case, there were no major roads in the way.

Then there were the management unit boundaries. At that time, the species was state listed in Wisconsin but not in Illinois (where it has since been added to the protected list). It crossed not only a state line, but from county land to private land and back again. The original capture location had been less than 100 meters from yet a third unit, a state-owned parcel and for all we knew perhaps it had been there a week earlier. Each unit had different management regimes, different philosophies at work.

Another management challenge, one poorly understood at best in anything I read earlier today is the key set of threats or stressors. There's the usual discussion of habitat loss, fragmentation, and degradation and certainly this does play a role.

But the central issue is neatly summed up in a 1993 paper by Congdon, Dunham, and Loben Sels (in Conservation Biology). They focused on demographics, on the fact that in their Michigan study area juvenile and adult survival is not sufficient to maintain the population of this very long-lived animal, which may not breed until 17 years of age and can live to be at least 60.

Some of the reasons are at least related to habitat. Certainly outright destruction of habitat results in direct and indirect mortality. Perhaps of more importance, when adult turtles need to cross busy highways on those long movements between core wetlands, a certain percentage of them become roadkill. Since adult Blanding's turtles, which can be quite large, apparently have few natural predators, this kind of removal of breeding age animals from the system is a problem.

The authors point out another less obvious problem, one that I saw no references to earlier today despite it being clearly identified 18 years ago; increases in the populations of mid-level predators such as raccoons, foxes, and skunks have led to a substantial increase in egg predation. In the Michigan study, there was no recruitment at all in some years.

There's plentiful indirect evidence of this on some of my Midwestern study sites. Walk certain open, sunlit upland areas in June, and the remains of turtle eggs are all around. Most of these are from more common species, but some of them are Blanding's turtle eggs.

It's challenging enough to put together roadless preserve complexes of sufficient size, with enough core wetlands, to support a Blanding's turtle population of any size. It's even harder to deal with raccoons, which abound for many reasons... fragmentation, edge habitat, loss of larger predators which once kept them in check, the near-demise of the fur trade, and the abundance of suburban garbage cans to help support large populations of omnivores through lean winters.

Head starting alone isn't enough, although it's been successful in some places. It's labor intensive and may require decades of sustained effort. If the preserves are still fragmented, if some of those turtles die on roads, if mid-level predators still are abundant, then it's just treating symptoms and not going after the real problems.  

In this case, some of the answers are clear enough. The question is whether the political will exists to address them.

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.