Seasonal variation in hematology, body composition, and food caches of eastern woodrats (Neotoma Floridana)

Abstract

Winter is a critical time for any small mammal in a seasonal environment due to the increased energy demands for thermo regulation and decreased food availability. Small mammals make behavioral and physiological adjustments in order to survive the winter. One such behavioral adjustment is that of a larder hoarder that stores a centrally located food cache, which serves as an energy supply during times of resource scarcity. Small mammals have been shown to make hematological adjustments to increase oxygen carrying capacity in the winter as well. I studied seasonal changes in the hematology (including serum chemistry), body composition, and food caches of eastern woodrats (Neotoma floridana) in east-central Kansas from October 1999 to August 2000. I also evaluated the use of total body electrical conductivity (TOBEC) as a method for estimating lean and lipid mass in eastern woodrats. Hematological analysis showed that packed cell volume (PCV) and red blood cell (RBC) counts were highest in the winter and lowest in the summer, which was consistent with patterns that had been observed previously in other small mammals. However, hemoglobin (HB) levels were lowest in the winter, which was suggestive of iron-deficiency anemia. Plasma lipid levels were lowest in the winter and plasma protein concentrations were constant throughout the seasons studied. Percent body fat was lowest in the winter and highest in the spring and the total energy of food caches was highest in the winter and lowest in the spring. Fall and spring showed intermediate levels in hematological values. The increased PCV and RBC count of wintering eastern woodrats was likely in response to increased metabolic activity for thermo regulation. Eastern woodrats also showed a relationship between energy stored as fat (internal stores) and energy stored as food (external stores). Internal stores were lowest in the winter, which corresponded to the highest levels of external stores. Internal stores were highest in the spring when external stores had been depleted, a strategy that would provide a large amount of internal energy available for reproduction in the spring. Plasma lipid levels also showed that lipids were being conserved during the winter. Two-stage TOBEC models were accurate at predicting lean mass, however they performed poorly at predicting lipid mass. Direct models, in which lipid mass was predicted directly from body mass and TOBEC, predicted lipid mass more accurately in eastern woodrats than did two-stage models. Eastern woodrats showed definite seasonal changes in hematology, body composition, and food caches and TOBEC showed potential for estimating lipid mass of eastern woodrats.