Abstract

The South American field mouse Abrothrix andinus (Rodentia: Cricetidae) is a small mammal active throughout the year in the Andes, despite substantial seasonal environmental changes. Body mass exhibited a significant decrease during winter, and maximum metabolic rate for thermoregulation increased by 36.6%. In absolute terms, the maximum thermal differential between body and environmental temperatures increased 44-degrees-C during winter. On the other hand, body temperature and thermal conductance did not show significant changes throughout the year; however, mass-independent conductance decreased in winter. Parallel to these changes, the length and dry mass of the total digestive tract changed significantly with winter-time; at the same time the length and mass of the small intestine and the length of the large intestine also showed significance. Significant differences in gastrointestinal morphology between males and females were found only during the reproductive season (summer).