Modeling Northern Pacific Rattlesnake Connectivity


Last November, I wrote a blog entry describing our project modeling Northern Pacific Rattlesnake (Crotalus oreganus oreganus) connectivity in Washington State. At the end of that entry, I mentioned that the next steps were to conduct a validation study that would rely on field work and genetic samples. We took the first step towards this plan this past May with a month of den surveys across much of eastern Washington. We hoped this effort would allow us to identify new den sites that could be used for future genetic sampling.

So you might guess that we already have quite a few rattlesnake observations across a broad area like Washington, and you’d be right. So why should we bother with the hassle of trying to identify new sites if we can just sample known sites? First, we actually don’t know the true den sites associated with many of our observations, as many are found on roads or hiking trails. But even with the den locations that are certain, many are clustered together because they are the easiest to access or represent a researcher’s specific study area. So there are many blank spots where we aren’t certain that dens exist, but that our computer models tell us is likely to be good den habitat. This is important for animal surveys in general; we have to go to both the known and unknown areas if we want to get a complete picture of what’s happening on the ground!

To carry out the surveys, I had the help of Marisa Ishimatsu and Kyle Finn, our field technicians for the project. Marisa and Kyle drove over 2300 miles across the state of Washington looking for rattlesnake den sites. It wasn’t always the easiest work for them. After all, because I wanted to hit the unknown spots, I used our computer models (described in November, 2012) to choose locations that had a good chance of having snakes. The models are pretty good, but they’re not perfect, and sometimes a designated spot they went to just wasn’t great habitat. Furthermore, just accessing the sites was often challenging. I did filter the sites to occur on public land and near roads, but many times they would run into issues of having to pass through private land to get to public spots, or simply closed or inaccessible roads. All part of the fun of doing field work in fragmented habitats!

But Marisa and Kyle persevered and quickly began finding snakes and likely dens. Then one last roadblock occurred – the weather! As luck would have it, a week into the survey effort, it suddenly warmed up in the area and sent the snakes moving from the den sites faster than we had anticipated. Fortunately, Marisa and Kyle adapted once more and began searching on the shrubby edges of the outcrops and were able to find quite a few snakes. While we have less certainty that those outcrops are den sites, the presence of snakes nearby suggests that they probably are. All told, the team found rattlesnakes at 14 sites across a 20 day period – quite successful in my book, given some of the obstacles they encountered! We’ll now use this information to help plan our future sampling surveys as we start to initiate genetic studies across this landscape.

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