But the reality of snake migration, especially in North America, is more complicated than it may seem. Whether (and to what extent) it takes place can have significant consequences – not only on snake populations, but also on the humans who encounter them. In the past few years alone, there has been a spike in snakebites concurrent with snake migration in areas ill-equipped to handle them.
Here are some key factors to consider when thinking about the potential (and consequences) of snake migration.
The Pace of Climate Change and Human-Generated Carbon Emissions
Ectotherms (essentially cold-blooded animals, like snakes) have a narrow temperature window in which to accomplish daily tasks of living. Everything from acquiring food and water, reproduction, and establishing territory must be completed in a limited time frame.
Each year, as climate change warms their habitats, that time frame gets smaller and smaller – even with local temperature changes of less than a degree. In many cases, these tightening windows have come on too rapidly for ectotherms to adapt, leading to the extinction of lizard populations in southern California and the potential extinction of other amphibians and Desert Tortoises over the next few decades.
Additionally, some ectotherms, such as turtles and crocodiles, experience the added stressor of altered sex ratios due to different incubation temperatures. It has been shown that humidity and temperature during the incubation period can even impact the size of their young. That said, most snakes (and lizards) won’t encounter the same problems with incubation – leaving them with a better chance at migration and survival.
If temperatures continue increasing we may eventually see larger and more diverse populations of snakes slither up to northern Canada by 2050, an even greater number of species are likely to simply die off, leaving us with diminished species diversity.
Another consideration: despite garnering attention-grabbing headlines, average temperatures are not as important when it comes to ectotherm migration and survival. Instead, measurements of precipitation and temperature extremes tend to be more relevant, as these more directly impact the thermal niche of a given organism.
For instance, Southwestern Speckled Rattlesnakes may encounter even greater temperature extremes as they head northward, so permanent migration seems unlikely for this particular species.
In addition to temperature, changes in annual precipitation along with regularity and severity of individual precipitation events are likely to have unforeseen impacts on snake populations. Changes in, and increased variability of, precipitation events like seasonal monsoons will undoubtedly have trickle-down effects to every member of local environments.
Vagility and Mobility
As Brett Baldwin, Associate Curator of Herpetology at the San Diego Zoo, stated in Newsweek, when it comes to climate change, “birds have an advantage, mammals have an advantage, reptiles have much less advantage.”
That’s largely because reptiles have another limiting factor: vagility, or their ability to move about freely and migrate. In other words, snakes don’t stray too far from where they den. Typically, they are seasonal migrators that move to more suitable habitat after hibernation in dens or hibernacula, but their lack of appendages means they cannot travel quickly.
Take the Western Rattlesnake, for example. Its recent migrations, considered relatively lengthy in comparison to other snakes near the Canadian border, only range from 3−5km (roughly 1.5−3 miles). Meanwhile, several US and Mexican rattlesnake species are restricted to high-elevation mountaintops. It’s highly unlikely that they would be able to traverse the unsuitable lowland habitats in order to find more suitable environs on an adjacent, higher mountain. Species that don’t have such geographically restricted distributions are likely to fare much better (e.g. Prairie Rattlesnakes or Copperheads). However, we are still likely to see changes in the distributions and ranges of such species. Studies utilizing the known environmental niche of a species coupled with IPCC climate projections for the future have predicted dramatic shifts in the distributions of species like the Copperhead, fueled by degrading conditions across much of their native range.
What will compound this issue in the future? Agricultural and urban development which alter natural habitats. By conversion, fragmentation and destruction of areas that might otherwise serve as potential refuges and transit corridors for species seeking escape from environmental change, these anthropogenic, i.e., human-caused, activities can reduce availability and access to suitable habitats. At the same time, such changes can also open novel habitats to species that would otherwise not have been unable to exist there. This could set the stage for a range of human-snake interactions, as well as encounters between snakes and other animals.
An evolving landscape of snake species
Ultimately, climate change may result in a large bifurcation in the effect it has on snake species. In North America, for instance, a new dichotomy could emerge, in which species from the west fare much worse than those along the eastern seaboard due to being generally more range restricted.
Additionally, a species’ response to the warming climate (and the related impact to human interactions) may not be static – that is, some species or individuals may find temporary refuge by migrating to urban areas to escape heat and/or drought, increasing the risk of envenomations. But further down the line, with the continued rise in temperatures, these same species may find that even urban environments become unsuitable, resulting in population declines and a reduction in envenomation risk.
In the long term, climate change will impact the behaviors and populations of all snakes. Some will adapt. Some will migrate. Others will go extinct. But in the short-term, snakebites will likely continue to increase in many previously unaffected regions, underscoring the importance of effective antivenoms.