DIURNAL FLUCTUATION IN URINE CONCENTRATION IN THE LITTLE BROWN BAT, MYOTIS-LUCIFUGUS, IN A NATURAL ROOST

1. 1. Urine collected periodically from naturally roosting Myotis lucifugus on a rainy, overcast day and on a successive sunny, warm day showed no differences in concentration between sexes, age groups, or activity level (torpid or active). 2. 2. Time of day at which samples were collected and the day of collection both showed significant effects on urine concentration. 3. 3. Urine concentration dropped progressively on the rainy day from 2750 mOsm/kg at predawn to 1890 mOsm/kg at sunset. 4. 4. On the sunny day, midday samples were not different from the previous day; however, samples collected at dusk (2640 mOsm/kg) were significantly more concentrated. 5. 5. Naturally roosting M. lucifugus excreted urine that was 275 mOsm/kg below their mean maximum urine concentration. © 1979.