Aquatic thermoregulation in the muskrat (Ondatra zibethicus): energy demands of swimming and diving

Muskrats experienced a steady decline in abdominal and subcutaneous body temperature (ΔTh) during unrestrained dives of 0.5- to 4-min duration. Extent of body cooling, postdive O2 consumption [Formula: see text], and metabolic recovery time increased both with time submerged and declining water temperature (3 – 30 °C). For each additional minute that a muskrat remained submerged, cost increased by 99 mL O2∙kg−1 in 3 °C, compared with 71 and 43 mL O2∙kg−1 in 20 and 30 °C water, respectively. Postdive [Formula: see text] correlated strongly with ΔTh incurred during diving. Mean [Formula: see text], during spontaneous activity in water, when animals were free to swim, dive, or float quietly on the surface, varied inversely with water temperature and directly with ΔTh. Temporal decline in Th during 25-min immersion was matched by a concurrent reduction in voluntary dive time. Mean [Formula: see text], immediately following withdrawal from water exceeded that during an equivalent period of immersion.