A report of unusual aggregation behaviour in Bullsnakes (Pituophis catenifer sayi) near a nest site in Saskatchewan


  • Noah B. Johnson University of Regina
  • Jenna L. Van Parys University of Regina
  • Christopher M. Somers University of Regina
  • Ray G. Poulin Royal Saskatchewan Museum




Bullsnake, Pituophis catenifer sayi, aggregation behaviour, nesting, herpetology


We describe an unusual aggregation of Bullsnakes (Pituophis catenifer sayi) near a nest site in Saskatchewan. Bullsnake is a wide-ranging oviparous colubrid that reaches the northern tip of its continental range on the prairies and badlands of Canada. At that location, it is considered a species of Special Concern, but, until recently, has been the subject of relatively few natural history reports. This is significant, because, at the northern edge of their range, Bullsnakes may behave differently than elsewhere due to thermal limitations experienced at high latitudes. On 29 June 2019, we observed a mass of five adult Bullsnakes in a Silver Sagebrush (Artemisia cana) shrub on a slope in southwestern Saskatchewan. Aggregations of Bullsnakes are known to occur at hibernacula, during mating, and inside nest chambers before and after oviposition. However, we are unaware of the occurrence of surface aggregations in any other situation. We suggest that these Bullsnakes may have been exhibiting communal gestation, a behaviour thought to be rare in oviparous snakes whereby gravid females congregate before parturition or oviposition for thermal stability or protection from predators.

Author Biographies

Christopher M. Somers, University of Regina

Department of Biology, Professor

Ray G. Poulin, Royal Saskatchewan Museum

Head of Research and Collections