The efficacy of conifer seeds as major food resources to deer mice (Peromyscus maniculatus) and southern red-backed voles (Myodes gapperi)

Conifer seeds are a component of the diet of many rodents, but it is not known whether these seeds can be used as a major food source by rodents. Investigating this is critical to understanding how individual rodents utilize conifer seeds, and how their populations interact with seed production by coniferous trees. We examined the effects of conifer seed-diets on survival, body condition, food consumption, and gut morphology of deer mice (Peromyscus maniculatus) and southern red-backed voles (Myodes gapperi) in the laboratory. Experiments were conducted for 14 days using control food (laboratory rodent chow) and lodgepole pine (Pinus contorta), white spruce (Picea glauca), and subalpine fir (Abies lasiocarpa) seeds. The nutritional compositions of these seeds were also analyzed. Subalpine fir seeds contained the lowest crude protein content and highest fibre content relative to the other seeds. 60% of voles fed subalpine fir seeds were euthanized prior to the end of the experiment after losing greater than 25% of their initial body mass, whereas all mice survived to the end of the experiment in each group. Body masses of mice fed subalpine fir seeds were lower than those fed control food early in the experiment, but they compensated for this by increasing seed intake over the remainder of the experiment. They also retained more digesta in the caecum, which could increase digestion efficiency of the low-quality seeds. On the other hand, voles did not compensate for the low quality of subalpine fir seeds behaviourally (food intake) or morphologically (gut dimensions), and decreased in body mass dramatically. They also decreased in body mass in the long-term on white spruce seed-diets. It is likely that plant secondary metabolites played a major role in the deterioration of body condition of voles fed subalpine fir and white spruce seeds. These results indicate that conifer seeds are a sufficient food resource for mice, but cannot be used by primarily herbivorous voles as a major/sole food source.