Seasonal range selection in bighorn sheep: conflicts between forage quality, forage quantity, and predator avoidance

Area of Science:

• Wildlife Ecology
• Behavioral Ecology
• Mammalian Ecology

Background:

• Bighorn ewes (Ovis canadensis) exhibit complex migratory behaviors.
• Seasonal range selection is influenced by factors like nutrition and predation risk.

Purpose of the Study:

• To investigate the relationship between forage quality and seasonal range selection in bighorn ewes.
• To test the hypothesis that forage quality dictates migratory patterns.

Main Methods:

• Individually marking bighorn ewes for behavioral tracking.
• Analyzing fecal crude protein to assess forage quality.
• Comparing forage quality and availability across different elevations and seasons.

Main Results:

• Pregnant ewes migrated to higher elevations with lower forage quality, prioritizing lamb safety over nutrition.
• Forage quality at higher elevations improved later in the season, but availability remained lower.
• Non-pregnant and yearling ewes displayed different migratory strategies, balancing nutritional needs and predator avoidance.

Conclusions:

• Seasonal range selection in bighorn ewes is a result of both nutritional requirements and antipredator strategies.
• The need to protect vulnerable young can compel ewes to forgo optimal foraging areas.
• Bighorn ewe behavior demonstrates a complex interplay between resource availability and survival pressures.