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Related Experiment Video

Updated: Nov 25, 2025

Protocol for Assessing the Relative Effects of Environment and Genetics on Antler and Body Growth for a Long-lived Cervid

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Linking population performance to nutritional condition in an alpine ungulate.

Thomas R Stephenson¹, David W German¹, E Frances Cassirer²

¹Sierra Nevada Bighorn Sheep Recovery Program, California Department of Fish and Wildlife, Bishop, CA, USA.

Journal of Mammalogy

|December 18, 2020

Summary

Bighorn sheep rely on body fat reserves for survival in harsh environments. Higher fat levels in autumn correlate with increased pregnancy rates, overwinter survival, and population growth.

Keywords:

Sierra Nevada adipose tissue body composition energetics lambda vital rates

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Instrumentation of Near-term Fetal Sheep for Multivariate Chronic Non-anesthetized Recordings

Instrumentation of Near-term Fetal Sheep for Multivariate Chronic Non-anesthetized Recordings

Published on: October 25, 2015

Area of Science:

Wildlife ecology
Animal physiology
Conservation biology

Background:

Bighorn sheep (Ovis canadensis) inhabit environments with seasonal forage scarcity.
Body fat is crucial for meeting metabolic demands during periods of low food availability.
Understanding nutritional condition is key to bighorn sheep population dynamics.

Purpose of the Study:

To develop equations for predicting ingesta-free body fat in bighorn sheep.
To investigate the relationship between body fat, pregnancy, survival, and population growth.
To assess the role of nutritional condition in bighorn sheep demography.

Main Methods:

Developed predictive equations for body fat using ultrasonography and condition scores in vivo and postmortem.
Applied in vivo equations to free-ranging bighorn sheep in California and Nevada.
Analyzed relationships between body fat percentages and demographic parameters.

Main Results:

Established thresholds for body fat predicting high pregnancy (>7.7% in January) and overwinter survival (>13.5% in autumn).
Found a positive association between autumn body fat in lactating females and subsequent population growth (λ).
Demonstrated that bighorn sheep with 26% autumn body fat can sustain resting metabolism for 83 days on fat reserves alone.

Conclusions:

Nutritional condition, particularly body fat reserves, is a critical factor influencing bighorn sheep demography.
Body fat levels reflect habitat quality and the nutritional status of bighorn sheep populations.
Bighorn sheep are capital survivors and breeders, with fat reserves being essential for their persistence in challenging environments.