Sunday, November 18, 2012

Rattlesnakes In My Yard: Is Relocation a Death Sentence?


           For many people, finding a rattlesnake in the yard does not present much of a dilemma. They just kill it. But, for those people that appreciate rattlesnakes and don’t want to kill them all, encountering one of these venomous animals near the house raises an important question: What now?

            A rattlesnake around the house is a risk that most people just don’t want to take. And, that’s understandable. Inevitably, the topic of relocation is raised as a humane alternative to killing the animal, which is likely just traveling through or was attracted to an abundance of rodents. But, a letter from a reader summarizes a common concern.

A Timber Rattlesnake Relocated by Gary L.
I live in northeast Alabama outside of Scottsboro at the base of a small mountain ridge.  A rocky ravine runs down the mountain right to my backyard.  When I walk out of my back door I am automatically herping (i.e. finding a lot of amphibians and reptiles).  Occasionally a timber rattler will show up.  Since I have several small dogs and don’t want the snakes so close to the house, I relocate them.  I have a good set of tongs and snake bag and can relatively safely handle the snakes.  Initially I took the snakes to a secluded area about 5 miles away.  My conscience started to bother me because I knew that the snakes would not be able to return to their proven den site.  Since then I have taken several snakes a short distance backup to the top of the mountain ridge and, I’m sure, in range of their den.  Now I’m concerned about the snakes being able to find their way back to my backyard.  My question is: ‘Is it a death sentence for the snake if I move it far enough away from its range that it cannot get back to its den?’   

Thanks,

Gary L.
Alabama

            As Gary notes, rattlesnakes do not just spend their lives randomly crawling across the landscape.  Timber Rattlesnakes (Crotalus horridus) often use den sites throughout their lives. The use of these dens isn’t just a matter of convenience; the rocky and underground caverns are necessary for the snakes to survive the winter in colder climates. These areas provide protection from the cold and from predators. In the fall, females will give birth around their dens and the young benefit from the security of the rocks and also from having a lot of adult rattlesnakes around.

            Timber Rattlesnakes do sometimes disperse from their “home” den and reach other dens to mingle with new snakes, but the point is that there are often unique features of the landscape that are necessary for a snake to survive and these features are well-known by individual snakes that spend their lives in the same general area.

            So, as you might expect, relocating a rattlesnake away from your house isn’t automatically a humane option at all, it may just be dooming that snake to die a slow death in the woods as it crawls around looking for something familiar.

            One short-term option is to relocate snakes only a short distance from your house, perhaps less than 1000 feet (roughly 300 m). This technique moves the snake away from your home but allows the animal to stay within the forest it knows and close enough to its den that it can easily return. As Gary noted, this means that the snake very well could wander back to the house (even if this is unlikely).

            However, most people that go through the trouble of catching and relocating a rattlesnake want a more permanent solution and are interested in moving a snake far enough that it won’t try to return. I’ve written extensively about how living with rattlesnakes is an inseparable part of living in rattlesnake country and the most ecologically-minded (and safest) plan of action when co-existing with rattlesnakes is to take appropriate precautions (like teaching children and dogs about potentially dangerous animals).  Similarly, I never advocate capturing a venomous snake because it is a dangerous activity and runs a high risk of snakebite. I’m going to assume that you know all this but, for whatever reason, you have decided it is still important to move a rattlesnake away from the house.

            To give a relocated snake the best chance of surviving, it should be moved to an area that already has a population of the same species. This is a sure-fire way of knowing that the area is appropriate and the relocated animal can fulfill all of their needs there, which include the ability to find prey, refuge, and mates. If you don’t know for sure that an area has a rattlesnake population, look for habitats that are similar to the area around your home. For Timber Rattlesnakes on the east coast, good habitats would include deciduous forests, ideally with some rocky slopes and mountains. The same is true for another venomous species that shares this habitat, the Copperhead (Agkistrodon contortrix).

            Even when a rattlesnake is moved to a perfect habitat with a resident rattlesnake population, it will still go through an adjustment period. A study conducted in the early 1990’s radio-tracked a number of Timber Rattlesnakes in Pennsylvania to compare behavioral differences between snakes that had always lived in a particular area versus snakes that had been relocated to that area (the relocated snakes had been captured from areas 5-107 miles [8-172 km] away from their new home). I’ll let the original authors (citation at the bottom of this post) describe the take-home message of the study:

Our results clearly indicate that long-distance geographic translocation (i.e., relocation) results in decreased survival and an alteration of the behavior of C. horridus. Specifically, translocated snakes made frequent and extensive movements. The pattern of movements suggested either the snakes were searching for familiar environmental features, or they were exploring the new territory in order to become familiar with the existing conditions. Translocated snakes suffered from higher rates of overwintering mortality, predation, and disease than did residents. Only four snakes out of 11 (36.7%) are known to have survived through two complete active seasons following translocation.”

            This isn’t meant to be all doom and gloom. The authors note that their relocated snakes were able to find denning sites, even if they did die over the winter in higher proportions than resident snakes. In addition, relocated snakes that did survive the first year or so or life in their new home gradually started to exhibit behavior more similar to resident animals. This means that they started to move around less, and shorter movements reduce a rattlesnake’s risk of being found and eaten by a predator (or run over by a car). The authors further note that young snakes may have an easier time adjusting to a new area than the adult snakes that they had moved around.

            A smaller-scale study conducted in South Carolina had slightly more encouraging news. Of four Timber Rattlesnakes relocated from their capture location, none tried to return to their original home and only one had died after a couple of years, when the study concluded. The animals in South Carolina may have fared relatively well because in the southeastern United States, Timber Rattlesnakes do not seem to rely as much on specific denning sites that are used year after year. This may mean southern snakes are more adaptable to changing conditions but more research with more snakes is needed before this can be said with confidence.

            On a very large scale, when confronted with news that an entire Timber Rattlesnake den was going to be destroyed by some highway development in Kansas, a dedicated group of researchers undertook an intensive effort to identify a new suitable home for the snakes that lived there. These researchers looked for new potential sites with limestone caverns (for winter refuge and denning sites) surrounded by large areas of grasslands and fields (Timber Rattlesnakes out west tend to use different habitats than on the east coast) and lots of small mammals to eat. They even made sure that there were appropriate basking areas that faced the sun in the right direction. Finally, and perhaps most importantly, the new habitat would have to be away from too many humans. They found one site that met all of their criteria and moved 29 rattlesnakes from the doomed highway den to this new site. After a couple years of monitoring, it looks like their homework paid off and the relocated rattlesnakes are generally making themselves at home.

            So, is relocating a rattlesnake away from its original habitat a death sentence? Not necessarily. By carefully choosing an appropriate and suitable relocation site, you can give a rattlesnake a reasonable chance of surviving in a new home. Even in seemingly excellent habitats though, relocated rattlesnakes often have a difficult time adjusting and experience a relatively high risk of dying from disease, predators, or exposure.




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            This post is focused primarily on Timber Rattlesnakes and the habitats they use, but the same general concepts are true for all snakes. If you want to move a snake away from your home and give it a good chance of surviving, you must give a lot of thought to that snake’s needs and ensure that the new home meets these needs. If you have a snake you want to relocate and you're not sure what to do, you can ask me.

Want to Learn More? Check Out These Articles:



M. L. Walker, J. A. Dorr, R. J. Benjamin, & G. R. Pisani (2009). Successful relocation of a threatened suburban population of timber rattlesnakes (Crotalus horridus): combining snake ecology, politics, and education IRCF Reptiles and Amphibians, 16 (4), 210-221

Nowak, E.M., Hare, T, & McNally, J (2002). Management of ‘‘nuisance’’ vipers: effects of translocation on western dia- mondback rattlesnakes (Crotalus atrox). Biology of the Vipers, 533-560

J. R. Mohr (2010). Autoecology of the timber rattlesnake (Crotalus horridus) in the South Carolina mountains Dissertation, Clemson University

Reinert, H., & Rupert, R. (1999). Impacts of Translocation on Behavior and Survival of Timber Rattlesnakes, Crotalus horridus Journal of Herpetology, 33 (1) DOI: 10.2307/1565542

Sealy, J. (1997). Short-distance translocations of timber rattlesnakes in a North Carolina state park: a successful conservation and management program. Sonoran Herpetologist, 10, 94-99


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