Date of Award


Document Type


Degree Name

Master of Science (MS)




The hibernacula, overwintering cycles, extent of return to the hibernacula, and associated movements of three species of snakes were studied near Itasca State Park in northwestern Minnesota. Red-bellied snakes (Storeria occipitomacula), smooth green snakes (Opheodrys vernalis), and young eastern gartersnakes (Thamnophis sirtalis) were collected at enclosed hibernacula and marked by scale clipping. Inactive ant mounds built by Formica ulkei were utilised extensively as hibernacula by these snakes. During two winters, eleven mounds yielded 2260 Storeria, 409 Opheodrys, and 182 Thamnophis. Temperatures near overwintering snakes in five hibernacula ranged from 0-5 C. Mortality occurred in one mound where snakes were exposed to -1 C for a six-week period. Arrival in the fall and emergence in the spring were correlated with seasonal temperature changes. Emergence began immediately after the ground thawed. Differences in the time of arrival and emergence were evident with respect to species, age classes, and sexes.

A majority of the snakes returned eyarly to the same mound. Interchange and mis-mounding occurred to a limited extent among mounds. Ninety Storeria moved distances of 100-2750 feet between hibernacula and summer capture points. No movements of Opheodrys or Thamnophis were recorded. The snakes appeared to be selective in their choice of hibernacula. Thirteen Storeria returned over distances of 500-2350 feet to two mounds. An inter-demic system of selection dependent on reproductively isolated mound populations and maintained by differential mortality between mounds is suggested.