Seasonal changes in the rumen morphology of Himalayan tahr (Hemitragus jemlahicus) in the Two Thumb Range, South Island, New Zealand

Male and female Himalayan tahr Hemitragus jemlahicus exhibit extreme sexual size dimorphism and are spatially segregated outside the winter mating sea son. Segregation results in a greater change in both habitat selection and diet of males relative to females. Since the structure of the ruminant dige stive tract is closely related to feeding habit, the rumen morphology of ma le and female tahr should reflect these apparently important seasonal chang es. We therefore hypothesized that the rumen morphology of male tahr would undergo greater change between winter (when the sexes are aggregated) and s ummer (when the sexes are segregated) compared to females. Samples of rumen wall mucosa were cut from the dorsal rumen wall, atrium ruminis, caudo-ven tral blindsac, and the ventral rumen wall of tahr collected during winter ( eight male, 10 female) and summer (11 male, 10 female) from the Two Thumb R ange, South Island, New Zealand. Although we recorded a significant seasona l increase in the mean surface enlargement factor (SEF) from winter to summ er for both sexes, the SEF of females and males were not significantly diff erent in winter (3.88+/-0.55, se, and 4.95+/-0.61, respectively) or summer (7.71+/-0.55 and 6.86+/-0.52). We conclude that the effects of inter-sexual differences in habitat selection and diet on rumen morphology were insigni ficant relative to the extreme seasonal changes in forage quality and quant ity that occur in the Two Thumb Range.