SZAFRANSKA, Paulina A.*; ZUB, Karol; KONARZEWSKI, Marek; SPEAKMAN, John R.; Mammal Research Institute Polish Academy of Sciences; Mammal Research Institute Polish Academy of Sciences; University of Bialystok; University of Aberdeen: A positive association between resting and field metabolic rates in weasels

A positive association between resting (RMR) and field metabolic rate (FMR) is one of the most important notions of mammalian energetics. It has not, however, been convincingly demonstrated, especially on intra-specific level. To test this, we measured RMR and FMR in male weasels Mustela nivalis. These small predators are characterized by a considerable variation in body mass (range 40g � 150g) and high metabolic rates. Their FMRs (measured by doubly labelled water technique) were strongly depended on daily activity time (estimated by radiotracking), and significantly varied among seasons. Weasels had highest body mass-corrected FMR in spring, intermediate in summer, and lowest in winter. The pattern of annual changes of mass-specific RMR was similar. In consequence, we found a high, positive correlation between mass-specific FMR and RMR. Furthermore, we also demonstrated a high within-individual repeatability of body mass-corrected RMR in an annual cycle. We suggest that an increase of the activity time during reproductive season (spring and summer) was reflected by an increase of FMR, which in turn incurred an increase of RMR. In winter, weasels restricted their energy expenditures by minimizing hunting time and staying in well insulated nests. This type of behavior allowed them to maintain low RMR.