Home: Species at Risk: Hognose Snake

Western Hognose Snake

Limiting Factors

There are a number of natural factors that limit the distribution of the Plains Hognose Snake in Alberta. Whereas the Plains Hognose Snake has demonstrated some adaptability to lightly or moderately impacted prairie habitat types in southeastern Alberta, it is known to be limited on the eastern extremities of its range to areas of sandy substrate.  The Plains Hognose Snake may also be dependent on the burrows of Northern Pocket Gophers for hibernacula. The availability of habitat may be only a minor limiting factor to Plains Hognose Snakes in Alberta at present, as the known range falls within an area that still contains adequate tracts of near "natural" grassland to support healthy populations of other prairie snake species. What may be more important to the Plains Hognose Snake is the quality of available habitat as factors such as Agricultural Activities, Roads, Oil and Gas Activity and Intentional Persecution greatly impact the day to day lives of these snakes. 

Agricultural Activities:  The full effects of agricultural activities on hognose snakes are poorly understood. Cultivation of the prairie renders it largely or completely unsuitable for snake habitat. Today, 68% of Alberta's prairie is cultivated, although the percentage is likely lower in the extreme southeast part of the province. Taking these factors into account, it is likely that cultivation is the single greatest limiting factor for the Plains Hognose Snake in Alberta. Although there is evidence to suggest that this species, being relatively sedentary, can persist on fairly small parcels of suitable habitat, cultivation likely represents a barrier to dispersal, ultimately affecting genetic integrity. Furthermore, the breaking of new sod by the plow may kill most individuals outright, with further individuals being claimed by machinery at harvest time. It is possible that ditches and right-of-ways are important as dispersal corridors, and may even support populations of Hognose Snakes if rodents are abundant. However, no work has been done in Alberta to support this theory.

Insecticides may be of concern as a limiting factor for the Plains Hognose Snake. Grasshoppers have been found in the stomachs of hatchlings, so mortality may occur as a result of ingestion of insecticides. Insecticides may also act indirectly as a limiting factor by reducing the available prey-base for Hognose Snakes. They may also inhibit or prevent successful breeding.

Roads: Roads are likely second in importance as a limiting factor on the Plains Hognose Snake in Alberta. On the otherwise protected Suffield National Wildlife Area, natural gas exploration and extraction activities create heavy vehicular traffic, and snakes, including the Plains Hognose Snake, are probably the only wildlife species present which suffer appreciable road kills.  Plains Hognose Snakes appear especially vulnerable during the morning when they are regularly encountered on heavily traveled access routes. Mortalities from vehicles are likely of most significance to populations in close proximity to roads.

Oil and Gas Activity:  The primary impact of oil and gas activity on Plains Hognose Snakes is likely from vehicular traffic on existing roads and on roads created during well and pipeline construction services. However, trenching during pipeline construction can also cause mortality of snakes. Due to the short duration in which pipeline trenches remain open, and because the Plains Hognose Snake does not appear to be a highly migratory species, mortality from falling into trenches is likely of minor impact on this snake. However, Prairie Rattlesnakes and Bullsnakes are regularly found trapped in trenches, especially in the spring and fall, and therefore it seems probable that hognose snakes may also become trapped (especially in prime habitat). 

Intentional Persecution:  Plains Hognose Snakes are of small size, cryptic colouration, reclusive behavior, remote habitat, and do not make themselves especially vulnerable by denning communally. For these reasons, they likely do not often fall victim to intentional persecution. Nevertheless, this species, like the Bullsnake, are probably killed occasionally as a result of being mistaken for the Prairie Rattlesnake, which is often killed on sight due to its venomous nature, or as a result of the general prejudice which exists against all snakes. 

Reprinted from Alberta Wildlife Status Report No. 15  (1998), with permission from Alberta Sustainable Resource Development.

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