Prairie Rattlesnake populations in Alberta appear to be limited in distribution and number by several factors, including the presence of suitable
hibernacula, and the availability of summer foraging areas and birthing rookeries. These habitat requirements, in conjunction with climate and slow population growth, are "natural" limiting factors, and may further magnify the impact of human-related influences on Prairie Rattlesnake populations. Human activities that appear to have the greatest influence on Prairie Rattlesnake numbers and distribution include
road and pipeline construction, agricultural
activities, and intentional persecution.
Persecution: Traditionally, rattlesnakes have been viewed negatively by the public. However, recent reports in Alberta indicate that the attitude of the public towards rattlesnakes is improving. Rattlesnakes are thought to play an important role in regulating local rodent populations, and reports indicate that some ranchers in Alberta and Saskatchewan are very protective of Prairie Rattlesnakes and their dens because of their perceived role in rodent control. However, intentional killing and den vandalism are still known to occur in western Canada. Rattlesnake aggregations at hibernacula, as well as their conspicuous behaviour (rattling), increases the vulnerability of this species to malicious acts.
Den vandalism is of special concern, as rattlesnakes appear to exhibit high fidelity to den sites, and damage to hibernacula may result in high mortality if rattlesnakes fail to find alternate overwintering locations. Suitable hibernation sites may be limited even in areas with superficial appearance of abundance.
Roads and Pipeline
Construction: Road and pipeline
construction, as well as traffic along roadways, also appear to be important sources of mortality for Prairie Rattlesnakes. Furthermore, improvements to roadways, such as paving, may be increasing road mortality in the province by promoting higher vehicle speeds and allowing easier detection of snakes on pavement for those intent on killing snakes. In the past, there was significant mortality of snakes that fell into pipeline trenches, as these excavations were simply filled in after pipelines were laid. Today, companies such as Express Pipeline Ltd. have started to monitor and remove rattlesnakes from trenches. This practice should greatly reduce the mortality of rattlesnakes associated with pipeline construction.
Activities: A short growing season is characteristic of the semi-arid climate in the mixed grassland region of Alberta. This abbreviated season means that there is relatively little time for rattlesnakes to migrate to and from foraging sites where they accumulate reserves for winter
hibernation. Availability of suitable foraging sites within reasonable distances from den sites is therefore expected to be of great importance for high-latitude populations such as those in Alberta.
The intensification of agriculture within the range of the Prairie Rattlesnake may be reducing the availability of foraging habitat. For example, approximately 23 % of the uncultivated mixed prairie that existed in 1956 had been plowed under by 1981, and much of the remaining rangeland has been subjected to increased grazing pressure. The quality of remaining native grasslands might also be reduced by rodent-control programs, which reduce numbers of prey available to rattlesnakes.
Overall, the impacts of anthropogenic influences on populations of Prairie Rattlesnakes are currently not well known. It has been suggested, however, that habitat reduction and disturbance through agricultural influences may have contributed significantly to the apparent decrease in Prairie Rattlesnake numbers in Canada. Further investigations may reveal whether the same influences are responsible for recent changes in the abundance and distribution of this species in Alberta.
Reprinted from Alberta Wildlife Status Report No. 6
with permission from Alberta
Sustainable Resource Development.