Fracking and Crotalus horridus (Timber Rattlesnake) Populations in Pennsylvania

“She (the timber rattlesnake) never begins an attack, nor, when once engaged, ever surrenders: she is therefore an emblem of magnanimity and true courage. As if anxious to prevent all pretensions of quarreling with her, the weapons with which nature has furnished her, she conceals in the roof of her mouth, so that, to those who are unacquainted with her, she appears to be a most defenseless animal; and even when those weapons are shown and extended for her defense, they appear weak and contemptible; but their wounds however small, are decisive and fatal. Conscious of this, she never wounds ’till she has generously given notice, even to her enemy, and cautioned him against the danger of treading on her.”

– Benjamin Franklin, Pennsylvania Journal, December, 1775


This paper analyzes the impact of the ongoing fracking of the Marcellus shale deposit in Pennsylvania on Crotalus horridus (timber rattlesnake) populations in the eastern portion of the state, especially the Schuylkill River Valley. First, the ecological role of C. horridus is analyzed, including its population dynamics, density dependent factors to growth, major predators, and resource competition. The ecosystem of the Schuylkill River riparian area is described, and the issue of fracking is presented. Attention is paid to the various harmful ways which fracking, and more importantly, pipeline construction, impacts C. horridus habitat and population resilience, among other factors. An overview of the drastic measures needed to save the species locally and regionally is then presented. The paper employs sources from multiple herpetological journals and scholarly articles reviewing the ecological impact of fracking and new pipelines.


Crotalus horridus (timber rattlesnake), one of the only poisonous snakes found in eastern Pennsylvania, has a range throughout much of the deciduous forests of the eastern United States and Canada (Clark, 2002). Their range has been vastly reduced due to human impacts since colonial times and they are now listed as a candidate species of concern in Pennsylvania (Ulev, 2008). In many neighboring states they are listed as endangered (Ulev, 2008). In eastern Pennsylvania they thrive only in the mountainous, remote state forests of the north-central part of the state (Urban, 2004). While populations do exist within the Schuylkill Valley watershed they are increasingly scarce and fall victim to numerous types of human impacts on the ecosystem (Urban, 2004).

Ecological role

Within the food web, rattlesnakes are significant predators and as thus have been shown to play a vital role in maintaining equilibrium in ecosystems (Reinhart, 2011). The diet of timber rattlers can vary tremendously, as they feed on several different trophic levels, including peromyscus (deer mice), sorex cinereus (masked shrew), sylvilogus floridanus (cottontail rabbit), scirius carolinensis (gray squirrel), and lymantria dispar (gypsy moth pupa) (Reinhart, 2011). They also feed on other snakes, but do not generally eat each other (Reinhart, 2011)

Aside from humans, the chief predators of timber rattlesnakes in eastern Pennsylvania are birds of prey, which exist on the trophic level above rattlesnakes. Much of the diet of rattlesnakes and birds of prey is shared (Alden and Cassie, 2010), but there are not enough rattlesnakes in the ecosystem for their consumption to limit the resource, as per the competitive exclusion principle (Ricklefs and Miller, 2000). A species of interest in the region is the rapidly recovering population of haliaeetus leucocephalus (bald eagle), with nests popping up close to Philadelphia (Alden and Cassie, 2010). Common birds of prey include accipter cooperii (Cooper’s hawk), the even more common buteo jamaicensis (red-tailed hawk), falco peregrinus (peregrine falcon), and cathartes aura (turkey vulture) (Urban, 2004).

Rattlesnakes are distinct in that depending on the time of year, their dispersion is either evenly spaced or clumped (Ricklefs and Miller, 2000). Rattlesnakes usually hibernate communally, especially where there are cold winters (Wittenberg, 2014). Their local populations are then dispersed from the site of their shared subterranean dens (Wittenberg, 2014). However, once active during the warmer months, studies show very limited overlap of activity ranges between rattlesnakes, even those born of the same litter (Howze et al., 2012). The only other causes of intraspecies interaction is to mate or, for males, to fight over a mate, which is a very common practice during mating season (Reinhart et al., 2011).

Rattlesnakes are most active in Pennsylvania from late April through October, and mating usually occurs in July and August (Urban, 2004). Rattlesnakes experience geometric growth because they only reproduce during specific seasons (Ricklefs and Miller, 2000). Their average lifespan is estimated at between 16 and 22 years, with an upper limit of about 30 years (New York State Department of Conservation). Rattlesnakes seem to have high population resilience because they are both smaller-bodied and longer living (Ricklefs and Miller, 2000). Female snakes begin reproducing at about age eight, and fecundity produces litters of five to fifteen snakes (Olson et al, 2015). However, female snakes typically produce only two to three times in their lifespan, and thus populations grow very slowly (Zenuh, 2003). Pregnant snakes, moreover, are mostly inactive in their dens during the latter stages of their pregnancy, and thus populations are extremely sensitive to human encroachment and predation on den areas (Wittenberg et al, 2014).

One of the most important features of the Delaware River ecosystem for rattlesnakes is hibernacula (Howze et al., 2012). Because winters are cold, all timber rattlesnakes hibernate in Pennsylvania, and they do so communally, sometimes even with other species (Bushar et al, 2015). Habitat destruction – specifically, hibernacula destruction – is therefore the most significant density dependent factor regulating timber rattlesnake populations (Ricklefs and Miller, 2000).

The Schuylkill River Valley

The headwaters of the Schuylkill River are about 135 miles west of Philadelphia (Alden and Cassie, 2010). The river traces through Berks, Chester, and Montgomery counties before emptying into the Delaware River in south Philadelphia. The riparian ecosystem is densely populated by humans, but thins significantly farther upstream. Despite significant development the riparian area surrounding the river is largely intact, and there is even extensive protected green space on its banks and on its smaller tributaries in the city of Philadelphia itself. Given the significant ecological disturbance incurred by the densely populated urban and suburban area surrounding the river, this is remarkable, and provides hope for ultimately reconciling development with increased biodiversity in the region.

The Delaware Valley is a deciduous forest biome that comprises much of the eastern half of the United States (Ricklefs and Miller, 2000). The region typically experiences four distinct seasons, a cold winter, a moderate spring and fall, and a hot summer (Alden and Cassie, 2010). Temperatures reach an average high of 30 degrees Celsius in July, and an average low of -3.6 in January (Climate Pennsylvania, 2016).

Fracking and the Marcellus shale

Hydraulic fracturing is the process of blasting water and chemicals deep into the earth to “fracture” rock so that natural gas may be extracted (Hollecheck et al., 2014). In Pennsylvania, the fracking debate centers around the Marcellus Shale, a 600-mile long stretch of sedimentary rock which was not believed to contain significant deposits of accessible natural gas until 2008 (Hollecheck et al., 2014). Some geologists believe the Marcellus to contain enough natural gas to radically affect the national and even international market (Wilber, 2012). The Marcellus location in the Appalachian Basin places it in close proximity to major eastern seaboard markets like Philadelphia and New York City. This is important because the oil must only travel a short distance via pipelines, and also because these industrial cities have the infrastructure for large refineries to handle a significant load of natural gas.

Because of this, the impact of Marcellus drilling is not limited to the actual range of the shale itself, which only borders the Delaware River Valley. Pipelines snake out from the heart of drilling territory and pass through Chester and Montgomery counties, and proposed projects could bring several more pipelines into the Schuylkill River riparian area (Landscape2, 2016). Marcus Hook, a booming refinery port on the Delaware just south of the Schuylkill, is the destination for many of these pipelines, and they pass through C. horridus habitat already heavily impacted by development. Sunoco’s Mariner East 2 Pipeline, which is 300 miles long and bisects the region, is slated to begin construction in the summer of 2016 (Landscape2, 2016). More controversial is the Penneast Pipeline, a 108-mile project which has not yet been approved (Landscape2, 2016). As fracking continues to grow, even more pipelines are likely. Pipelines destroy and disturb habitat when they are laid, and often leave a permanent ecological impact behind (Service, 2012). There is also the ever-present risk of an accident, which could cause irreparable environmental damage.

Fracking has ecological impacts which extend beyond what drilling and laying pipelines does to the physical environment. The EPA recently issued a report which stated that fracking has reduced carbon emissions and is thus mitigating climate change (EPA, 2016), as compared to our progression toward climate change under a coal-centric energy plan. Critics find this to be misleading, however, because fracking reduces climate change only to the extent that it replaces the coal infrastructure (McKibben, 2016). Fracking may represent a small improvement over coal in the short term in terms of contribution to climate change, but it’s still contributing (McKibben, 2016). Studies such as the EPA’s, environmentalists argue, detract from the focus on the permanent solution – renewable energy – by justifying a slightly less harmful method of natural gas production in the short term.

Physiological effect on C. horridus

Because the Schuylkill River Valley and its tributaries only border fracking sites, limited attention will be paid to damage incurred by the process of fracking itself. However, the contamination of fluids into the air and the ground may lead to negative effects on a regional level (Bamberger and Oswald, 2012). Exposure to fracking fluids has been linked to immediate fatalities to some wildlife and in certain situations has been connected to long-lasting negative health effects in organisms for miles (Bamberger and Oswald, 2012). Some effects observed in a diversity of wildlife have been reproductive complications, breathing problems, growth issues, and pneumonia (Bamberger and Oswald, 2012). Significant mortality rates of multiple species have been noted in the area of drilling sites, as well; in one case, deer population dropped by 45 percent (Bamberger and Oswald, 2012).

Moreover, the increased drilling leads to a greater probability of oil spills which can significantly harm species in environments that are downstream of the spill (Service et al, 2012). For the rattlesnake, contamination from chemicals or oil could lead directly to mortality or a reduction in its food supply via the mortality of its prey populations. It should be noted, however, that there are no studies tying rattlesnake health specifically to the exposure of fracking contaminants to the environment.

Energy flow

The impact of pipelines upon rattlesnakes is both more immediately relevant to the Schuylkill River area and is more conclusively proven. The disturbed strips and ecotones created by pipelines changes the species composition of the ecosystem and thus alters energy flow in the system (Silverman et al, 2008). To the extent that plant density is reduced by the clearing required for pipeline construction, the total amount of energy entering the system will drop (Ricklefs and Miller, 2000). The total amount of detritus correspondingly produced by plants will also drop (Ricklefs and Miller, 2000). This will in turn reduce the amount of total energy reaching each trophic level and limit the productivity of the entire ecosystem (Ricklefs and Miller, 2000).

The ultimate impact of rattlesnakes upon trophic levels can be difficult to tell because they feed infrequently and when they do, they completely digest their prey (Reinert et al, 2011). In Pennsylvania, rattlesnakes rely directly on small herbivores as a keystone of their diet, which represent the next trophic level above plants (Clark, 2002). Common herbivores like peromyscus (deer mice), sorex cinereus (masked shrew), and sylvilogus floridanus (cottontail rabbit) are less likely to be common in denuded pipeline corridors where they have less to eat (Alden and Cassie, 2010), and it follows that as plant density drops for these small mammals, their numbers would drop, and so too would rattlesnake numbers. Even if the disturbed energy flow did not significantly alter prey density for rattlesnakes, they would likely find no opportunities for hunting where a pipeline had been placed because they rely on fallen logs and trees to use as ambush points (Reinert et al, 2011).

Furthermore, studies show that the species which thrive in dense forest adjacent to a new pipeline are completely absent from the liminal area and from the corridor of the pipeline itself, meaning that for those species, the pipeline and its entire corridor represents destroyed habitat (Silverman et al, 2008). Near the Schuylkill River, species which disproportionately thrive in liminal areas like Odocoileus virginianus (white-tailed deer) would increase (Alden and Cassie, 2010). White-tailed deer are tied directly to the spread of invasive species and the loss of native vegetation (Sterba, 2012) which only further begets the cycle of energy loss, habitat loss, and scarcity of predators that is so harmful to C. horridus populations.

Pipelines and population resilience

In similar environments to the Schuylkill River, construction of pipelines has been shown to fragment habitat and radically displace species composition within the ecosystem (Silverman et al, 2008). Pipelines through forests create “disturbed” strips and ecotones, something which rattlesnakes do not like (Urban, 2004). Because the forest along the Schuylkill is already so disturbed, additional fragmentation would further limit and separate habitat into “islands” which rattlesnakes will either struggle to or be unable to repopulate (Clark et al, 2010). Rattlesnakes often will not cross roads or other human constructions, isolating habitats and preventing a metapopulation from taking hold (Bushar et al, 2010). As each population shrinks its likelihood of complete extinction grows (Ricklefs and Miller, 2000). In this way, pipelines significantly reduce resilience of timber rattlesnakes.

Human persecution has historically been a leading cause of snake mortality, and that is a trend that has continued to present day (Olson et al., 2015). Crews at drilling sites and those laying new pipelines in Pennsylvania increasingly employ “wranglers” to capture and remove snakes from the area from work is taking place (Detrow, 2012). While the snakes are usually relocated, there are still mortalities, and the first instinct of a worker who encounters a rattlesnake is often to kill it, not avoid it (Detrow, 2012). Even where snakes are captured and “resettled” elsewhere, the removal could have a negative impact on the remaining population, especially if it is small (Ricklefs and Miller, 2000).

Climate change and fracking

While a controversial study by the Environmental Protection Agency suggests that fracking may limit climate change (US EPA, 2016), detractors have noted that this is true only to the extent that it replaces coal and that fracking still releases methane and still contributes to global warming (McKibben, 2016). Ultimately, any energy infrastructure which does anything other than radically reverse climate change is probably bad news for the timber rattlesnake and its habitat in the United States (Lawing and Polly, 2011). Despite the fact that snakes in general have thrived because of their adaptability (Olson et al., 2015), what remains of their habitat is probably changing too quickly for them to adapt (Lawing and Polly, 2011). Projected increases in global climate would drastically reduce the entire range of the timber rattlesnake in the eastern United States by 2100 (Lawing et al., 2011). Only a small area on the border of North Carolina and Tennessee will be appropriate habitat for the snakes if temperatures increase at that rate (Lawing et al., 2011). Indirectly, then, as new pipelines in Pennsylvania and around the nation promote and enable more fracking, pipelines contribute toward a mass extinction.

Nutrient cycling

Pipelines remove vegetation to clear a corridor to lay down the pipe and thus construction automatically leads to some level of reduction of photosynthesis. Therefore, less nutrients and less energy would be moving through the system (Ricklefs and Miller, 2000). As plant density is decreased, so too will overall herbivory be reduced. Herbivory is one of the most important ways which carbon is moved between “compartments” in the ecosystem (Ricklefs and Miller, 2000).

Images of the proposed Mariner East 2 pipeline in Chester and Delaware counties, via Landscapes2.

Sunoco’s proposed Mariner East 2 pipeline will pass over several streams including the Brandywine Creek, just below the Schuylkill in Chester County (Lansdcapes2, 2016). Pipeline construction through streams can cause significant sedimentation, both during construction and long after (Mason, 2015). Long term bank destabilization and erosion can also result from careless installation, which intensifies sedimentation (Mason, 2015).  Sedimentation can displace nutrient balance in the system which has negative effects for the riparian area by disrupting the food chain (Mason, 2015). This

Resolution and the future of conservation

Timber rattlesnakes are undoubtedly hurtling toward extinction in Pennsylvania and are in dire straits throughout much of their range in the United States, especially in eastern Pennsylvania and the Schuylkill River Valley. Unfortunately, some kinds of reconciliation ecology are of little help for rattlesnakes because the presence of humans in any form is usually bad news for their population. Furthermore, in southeastern Pennsylvania’s dense suburbia, landowners are unlikely to come across rattlesnakes on their property unless they live on a farm or in a rare secluded area. Therefore, projects like the National Wildlife Federation’s backyard habitat initiative make little difference for the rattlesnake, at least in the Schuylkill River Valley. It should be noted that this is not necessarily the case for the wilder sections of Pennsylvania where there is less development and significantly higher numbers of snakes (Urban, 2004).

By far the most important step that can be taken in improving rattlesnake numbers and saving the species from local extinction is providing more wild habitat. Rattlesnakes need significant blocs of land that are uninterrupted by roads, homes, shopping malls, and other concrete jungles (Clark et al., 2010). Fractured patches of habitats, or “islands,” are very rapidly created by human development and have a nearly immediate impact upon snakes (Clark et al., 2010). In addition to lowering genetic diversity and destroying hibernacula, seasonal migration is also limited (Clark et al., 2010). Because there is almost no “wild” land in southeastern Pennsylvania, efforts should be made to eliminate roads in state and county parks and state game lands where possible (Ricklefs and Miller, 2000). The challenge in a small area with so many people is that most open space exists for heavy recreational use, and thus roads and even cement trails – which would have the same effect as a road – are popular for frequent access. The degree to which changes in the management policy of state and county-owned land can influence rattlesnake habitat is limited.

Organizations like the Open Land Conservancy of Chester County and the Natural Lands Trust might be the best hope for timber rattlesnakes in the region because wildlife-centric edicts are in their charters and there are no roads that bisect their lands. In combination with habitat corridors to public lands and efforts to eliminate roads in certain areas, significant stretches of ideal rattlesnake habitat remain feasible. This would be especially true on the immediate banks of the Schuylkill, most of which remains undeveloped in Chester and Montgomery County. Similar efforts could be undergone on the banks of small nearby tributaries like the Skippack Creek and the Perkiomen Creek. The Schuylkill, Skippack, and Perkiomen are also each connected to large preserved areas, including Valley Forge National Park, Evansburg State Park, making corridors even more sustainable. According to several studies, including Clark et al. and Lawing and Polly, habitat corridors are the first suggestion to help improve population.

Once successful habitat has been established, rattlesnakes could be relocated to help bolster the local population (Di Silvestro, 2012).  Outreach and education will remain incredibly important. Communities in rural Pennsylvania which are already accustomed to rattlesnakes still react out of fear and lack of knowledge, and the mindset is often that every rattlesnake they come across must be killed (Detrow, 2012). Rattlesnake “roundups” are frequent and have been declared as animal abuse by the Humane Society of the United States (Humane Society, 2016). Therefore residents of the Schuylkill River Valley must be exposed to the many benefits of timber rattlesnakes. To begin with, they may reduce the spread of lyme disease by preying on species like mice that are carriers (Kabay and Caruso, 2013). As predators, they naturally bring equilibrium to a system. They do not deserve the fearsome reputation that has been foisted upon them simply because they are poisonous; as Benjamin Franklin notes, timber rattlesnakes almost never attack unless threatened (Alden and Cassie, 2010). Aside from Franklin’s romantic overtures about rattlesnakes, they also serve as prey to another American symbol with a threatened but recovering population in southeastern Pennsylvania, the bald eagle (Alden and Cassie, 2010). There is a significant base from which to launch a compelling outreach campaign for rattlesnakes. It’s still not too late to be cautiously optimistic about their return to prominence.

Reference List

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Clark, R, Brown, W, Stechert, R, Zamudio, K. 2010. Roads, Interrupted Dispersal, and Genetic Diversity in Timber Rattlesnakes. Conservation Biology: The Journal of the Society for Conservation Biology 4:1059-69.

Clark, R. 2002: Diet of the Timber Rattlesnake, Crotalus horridus. Journal of Herpetology 36:494-499.

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Kabay, E, Caruso, N. 2013. Timber rattlesnakes may reduce incident of Lyme disease in the northeastern United States. Proceedings of the 98th Annual Meeting of the Ecological Society of America; Minneapolis MN.

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Ricklefs, R, Miller, G. 2000. Ecology. W.H. Freeman and Company: New York.

Service, C, Nelson, T, Paquet, P, McInnes, W, Darimont, C. 2012. Pipelines and Parks: Evaluating External Risks to Protected Areas from the Proposed Northern Gateway Oil Transport Project. Natural Areas Journal 32:367-376.

Sterba, Jim. 2012: Nature Wars: The Incredible Story of How Wildlife Comebacks

Turned Backyards into Battlegrounds, pages 86-117. Crown Publishers: New York.

Urban, Christopher. 2004. The Timber Rattlesnake: Pennsylvania’s Uncanny Mountain Denizen. Pennsylvania Fish and Boat Commission. Accessed from

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Wilber, Tom. 2012. Under the Surface: Fracking, Fortunes, and the Fate of the Marcellus Shale. Cornell University Press.

Wittenberg, Rod, Beaupre, S. 2014. Growth of Timber Rattlesnakes (Crotalus horridus) in an Agriculturally Fragmented and a Contiguously Forested Habitat. Herpetlogica 70:171-183.


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