The Scoop On Snakes!
Snakes are at risk, not just locally, but globally as well. Here we outline many of the dangers these species face. We outline the global threats to these species, but keep in mind that many of these threats are the same at the local level. To find out more about threats at the local level, visit the 'Fun Facts' page.
Top Threats Against Snakes
Road Mortality
One of the biggest threats to snakes around the world is being run over by vehicles on the road and also by other vehicles involved in farming or lawn care. For instance, up to 10,000 red-sided garter snakes are killed each year in Manitoba due to the 3.2km Provincial Truck Highway 17 (Seburn and Seburn 2000). Roads not only reduce population sizes, but can reduce snake populations to become population sinks (Seburn and Seburn 2000). Roads that run through wetlands can also have devastating effects on reptiles. For example, more than 7,500 reptiles and amphibians are killed each year because of a road near Lake Erie in southern Ontario (Seburn and Seburn 2000). It seems that as roads and traffic increase, reptiles decrease.
Road mortality increases as urbanization increases and more roads are being built. Urbanization also causes an increase in habitat fragmentation, impacting the ability of snakes to successfully travel across habitats that are interrupted by roads. This leads to decreased survival, from both being run over and decreased habitat available to them.
Habitat fragmentation and Loss
Land use and urbanization has lead to habitat fragmentation. Habitat loss may decrease the availability of suitable habitats for these species. In other words, loss of habitat decreases the amount of resources, water, protection, and marshland available to snakes. For example, in southern Carolina, 90% of the coastal wetlands has been altered or eliminated, and this has affected the homes of black swamp snakes (Seminatrix pygaea), eastern green water snakes (Nerodia floridana), and chicken turtles (Deirochelys reticularia) (Gibbons et al 2000). Even if enough wetland habitat is protected, this protection would not cover the terrestrial habitats needed by some reptiles for nesting and hibernation. In Canada,
it is estimated that up to 50% of historical wetlands have been drained for agricutlural uses (Seburn and Seburn 2000). Seventy percent of the wetlands have been drained in the prairies and 90% in southwestern Ontario (Seburn and Seburn 2000). The loss of wetlands in Ontario is of the most concern, since about half of the amphibian and reptile species that are at risk are found in this area (Seburn and Seburn 2000).
Moreover, habitat fragmentation has lead to smaller population sizes due to isolating populations from each other, causing increased genetic drift (i.e. changes in random gene frequencies in a population due to chance), increasing inbreeding probability and stochastic variation. The issue of isolated populations is important because many reptile and amphibian species are interconnected with other sub-populations for breeding purposes (Seburn and Seburn 2000). If a stochastic event should occur, these populations can persist by
re-colonizing with other sub-populations (Seburn and Seburn 2000). When habitat fragmenation or loss occurs, re-colonization cannot occur, which results in a higher risk of extinction.
In additon, habitat fragmentation also can lead to a variety of dispersal effects (i.e. effects on distribution and movements in and out of populations). More specifically, habitat fragmentation and degradation can lead to changes in immigration and emigration between populations (Row et al 2010).
Habitat isolation can lead to various impacts on the foraging ability of snakes. There are many species of snakes that are specialists, which means that they require specific types of habitats, with specific conditions and prey, to ensure their survival. Therefore, it may be difficult for these species to adapt to the different environments that habitat degradation may force them into.
With habitat fragmentation there is less area to forage for prey as well as a decreased availability of prey species, increasing competition, and decreasing overall population.
Over Collecting (Laidlaw 2005)
The market for exotic pets is very lucrative all across the world. In particular, there are many species of reptiles that are exported annually from Canada worldwide. Many reptiles are being bred in captivity,
however, many are still being taken from the wild and this is having a detrimental effect on wild reptile populations. Moreover, breeders believe that as long as the reptiles are alive, it is okay and that it gives them an exuse for treating reptiles with cruelty. The reptile pet trade market is growing in Canada and this over collecting is projected to increase as more and more reptiles are being sold in pet stores and through private breeders.
Additionally, the global illegal pet trade and harvesting has grown to be worth billions annually. People are trading snakes for their skins, food, and some are used in traditional medicines (Schlaepfer et al 2005). Many species, such as boas and pythons, have declined because of the harvesting of their skins. For instance, female timber rattlesnakes (Crotalus horridus) take approximately 9 years to reach maturity and only reproduces about a dozen young every 3 years (Gibbons et al 2000). If these snakes continue to be collected, they will dwindle down to nothing
because of their life history traits. It has become unsustainable, often leading to a variety of invasive species being imported into countries like Canada. Rare and endangered species can often garner high prices in the illegal trade market and are valuable to collectors and exotic animal enthusiasts.
In a statement made by the Michigan Department of Natural Resources in 1993, it states that "there is convincing evidence that many populations of these species [reptiles and amphibians] are being decimated by the commercial pet trade". Many organizations keep records to monitor the trading, like the Convention on International Trade in Endangered Species or Wild Fauna and Flora (Schlepfer et al 2005). However, the data is very skewed and inaccurate because most of the time it is not entered properly. This may cause problems with identifying if the trade in reptiles is a problem for certain declining species. Unidentified 'cargo' taken from the wild have the potential to deplete populations of species before declines are even observed! (Schlaepfer et al 2005).
Over collecting of individuals is not just a problem for snakes, but for many other reptiles in North America. In an article by Reptiles Magazine written about North American reptiles, the authors write that while predation and vehicular mortality have a large effect on reptiles such as snakes and turtles, "many populations have been eradicated by collecting alone". Some species congregate in areas for breeding or hibernation, and this behaviour may cause them to be more vulnerable to intensive collecting (Schlaepfer et al 2005).
Invasive Species
Due to things such as pet trading and the transfer of individuals from different areas, there continues to be an increase in the potential for problematic species to be introduced into environments. These invasives may decimate and out-compete native species, including the snakes that are being focused on this site.
For example, it has been observed that within the Western Indies alone, there have been a minimum of 7-12 extinctions and 12-13 local extirpations of reptiles and amphibians in the past 150 years due to non-native predator introductions (Henderson 1992).Invasive species have continued to play large roles in counteracting successful conservation efforts of native species, as often they can grow uncontrollably in a specific habitat and succeed in using all of the resources available in an area. This leaves nothing for the native populations.
An example of the negative impact of invasive species on snake populations can be seen in the case of the introduction of the toxic cane toad (Bufo marinus) in Australia, which has induced a decline in native predator species, including elapid snake populations. When these toads were introduced to the area they became a new prey species for many native species of snakes, lizards, freshwater crocodiles, and marsupials. However, through the consumption of these toxic toads, populations of native predators have been observed to decline since their arrival (Phillips et al 2003).
Direct Persecution
Finally, snake populations have experienced marked declines due to the direct killing of individuals by humans out of fear or because some species are being mistaken for a more dangerous species. Also, many people have intentionally killed snakes and other reptiles by running them over. Biologists have observed cars that swerve to the side of the road to hit these reptile species (Seburn and Seburn 2000). They have observed that some reptiles are being shot for sport, which has a detrimental effect to the continuity of these species, especially ones with long life history traits (Seburn and Seburn 2000).
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You may have heard about the Eastern Massasauga Rattlesnake which has recently been listed as "threatened" on the Species at Risk Act in Canada. The Eastern Massasauga Rattlesnake (the only venomous snake in Canada) is native to southern Ontario and the northern United States, and in recent years has become threatened mainly due to habitat degradation and because of direct killing by people. They are often killed in and around campsites, homes, and industrial areas. Research has suggested that the Massasauga Rattlesnake may have increased survival if proper habitat management is put in place and in areas where there is less infrastructure and human persecution (Baily et al 2011).
As occurrences between humans and snakes continue to increase, more snake populations may experience intense declines because of persecution. In some instances, it may be understandable, in terms of the well-being of humans and
pets. However, species like the Eastern Ratsnake, which are non-venomous, often have been mistaken for more aggressive and dangerous species, such as the Eastern Massasauga Rattlesnake, and are killed whenever they are sighted. Therefore, it is important to learn to recognize which species may be harmless and which may not, in order to decrease the impact that direct persecution is having on populations of native species.