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1. Bound and total corticosteroid concentrations of yellow-bellied marmots (Marmota flaviventris) were lowest in May after emergence from hibernation and peaked in August prior to immergence. 2. Total corticosteroids were affected by age but not by sex or reproductive status. 3. There was no consistent relationship between measures of population density and concentrations of corticosteroids; when a significant relationship occurred, only 22-34% of the variation was explained. 4. Social status and social behavior were the major factors affecting corticosteroid concentrations.

1. Hemoglobin, packed cell volume, erythrocytes, leucocytes, MCV, MCH and MCHC were determined for a population of Marmota flaviventris over a period of seven years. 2. There was no significant difference in hematology among years, between sexes, or between seasons for adults and yearlings. 3. Early season juveniles had significantly lower PCV, Hb and erythrocyte counts than did late season juveniles. There were no significant differences in hematological values among adults, yearlings and late season juveniles. 4. Juveniles had significantly lower leucocycte counts than adults and yearlings. 5. PCV of marmots responds to acclimatization. 6. Hematological values of scuirids are adaptive to environmental factors such as hypoxia of burrows and high altitude, temperature and metabolic rate. 7. PCV of yellow-bellied marmots evidences an adaptive response to high altitude when compared to the closely-related woodchuck, M. monax.