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Structure.| Class | Month | % males in population | Factors causing change in the sex ratio |
| Juvenile (1 mo.) | June | 50 | . |
| Juvenile (3 mo.) | August | 50 | . |
| Yearling (11 mo.) | early April | 30 | Juvenile males enter hibernation in fall about 1 mo. later than females, and are thus exposed to mortality (especially predation) factors. Juvenile males emerge from hibernation 2 weeks earlier than females -- a time of food shortage and exposure to snow, cold, and flooding. |
| Yearling (12 mo.) | early May | 11 | Many males present in early April are driven away be females and dominant males when breeding season begins in mid-April. These animals disappear completely and presumably die in nonhabitats. |
Return to Lecture Notes VI: Population
Structure. 
Updated 05 August 1996