Bottom-up, trophic mechanism impairs caribou pregnancy in Canada’s oil sands

Background/Question/Methods

Wildlife populations are simultaneously regulated by a number of ecological processes, including forage availability, competition, and predation. These mechanisms commonly interact. Thus, scientific or management approaches that emphasize a single process can lead to misinformation and undesired outcomes. The situation in the Canadian oil sands is a prime example. This area represents the second largest source of oil in the world and overlaps the ranges of endangered caribou. Management has prioritized wolf removal as a necessary solution to recover endangered caribou despite limited data on the relative impacts of predation, nutrition and human activity on caribou reproduction and population growth. Sound information on caribou mortality and population trends do not yet exist for the region.

We surveyed the landscape for the distribution of caribou forage species and used detection dogs to acquire fecal samples on a temporal scale that corresponded to changes in human activity.  Fecal samples provided data on caribou diet, as well as endocrine measures of nutritional and reproductive condition over time. We related a glucocorticoid indicator of nutrition to diet composition, associated progesterone to the distribution of caribou forages on the landscape and examined their interactions with temporal measures of human use.

Results/Conclusions

Results show that lichen provides an important source of glucose during fetal development that has direct impacts on caribou reproductive capacity. Lichens comprise a predominant winter forage species that is rare and unequally distributed across our study area. Limited access to lichens significantly reduced lichen in the diet as well as increased glucocorticoid and decreased progesterone concentrations of female caribou during gestation. These results identify new management options for recovering endangered caribou in Canada’s oil sands that provide viable alternatives to wolf removal. We recommend that lichen-rich areas be identified as critical caribou habitat under Canada’s Species at Risk Act and discuss ways to increase caribou access to this limited resource during the winter gestation perio