Food Management by Eastern Woodrats: Behavior and Physiology

Abstract of a Dissertation

Rebecca S. Burton, 1996

The eastern woodrat (Neotoma floridana) apparently decreases its food intake and metabolic rate in winter as a food conservation strategy. Woodrats captured when at low body mass and provided with plentiful food showed different patterns of body mass change depending on their food regime. Those animals provided with a large cache ("control") maintained a steady low mass, while those that were not allowed to accumulate a cache ("no-cache") gained mass. The control animals had a significant decrease in serum triiodothyronine (T3) level when their weights were low, suggesting a reduced metabolic rate. These animals also suffered humoral immune system depression in comparison with no-cache animals. This decrease could have been a result of malnutrition or low metabolic rate. There was no evidence of infection in the immunosuppressed animals. Woodrats may reduce maintenance costs by supporting less tissue and reducing the rate at which their remaining tissue uses energy.

Further experiments indicated that the animals may have adjusted their consumption as a theft-deterrence mechanism. Animals from which food was removed tended toward higher masses than animals allowed to accumulate excess food, even when food itself was not limiting. Storing food as fat protects it from theft, but may not be as efficient as fasting due to the metabolic cost of maintaining the fat and possible loss of nitrogen.

Avoidance of fouled food did not appear to be a valid explanation for fasting. Woodrats presented with food that was either unsoiled, soiled by themselves, or soiled by conspecifics did not exhibit a preference for any of the treatments.

Together, these data suggest that several factors influence woodrat food management. During winter, fasting and decreased metabolic rate may occur even if food is readily available, resulting in an adaptive loss of body mass. Fasting may not occur if animals are not able to defend their stored food. Fasting and metabolic down-regulation may lead to immunosuppression. Possible advantages to conserving food stores include decreased cost during the food gathering period, retention of food for use during or just prior to the breeding season, and insurance against particularly poor environmental conditions.

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Last update Sept. 30, 1997 by RSB