How does roadside foraging behavior develop?

Records of automobile-inflicted grizzly deaths in the GYE (Table 1; 7 of 11 vehicle-felled grizzlies were cubs, yearlings or subadults), as well as roadside activity data and sitings [2,18], strongly suggest that developmental stage is a crucial variable in assessing an individual's likelihood of road use. In other words, this behavior probably requires some degree of naivety regarding the threat of humans, as younger bears are thought to be wary of all perceived threats-- thus, while human-conditioned mother grizzlies might be said to exhibit a 'bold' behavioral compromise in choosing to forage near roads, their young are most likely naive to the risk associated with their behavior [1], which could explain why older bears, conditioned to the threat of humans and more capable of defense against conspecifics, avoid roads [6].





Grizzly Development Summary

[AGE TERMINOLOGY clarified: cub, 0 to 1 yr; yearling, 1 to 2 yrs; subadult, 2 to 5 or 6 yrs; sexually mature adult, 5 or 6+ yrs]


  • Adult females will tend to mate around June or July, and give birth to their young between January and March [21]. Depending on her body mass, a mother can produce up to four cubs per litter [13].
  • In their first year, altricial grizzly cubs require intensive motherly care and will stay close to their mothers until until they reach about 2.5 or 3.5 years of age [15], at which point mothers and subadults disperse.
  • Subadults begin their own solitary lives several years before reaching sexual and physical maturity [12,13].