AN APPRAISAL OF OPERATIVE TEMPERATURE MOUNTS AS TOOLS FOR STUDIES OF ECOLOGICAL ENERGETICS

Taxidermic mounts are frequently used to quantify the operative temper ature or standard operative temperature or standard operative temperat ure of complex natural environments. These thermal indices are subsequ ently used to estimate the metabolic heat production of free-living an imals. Such use has often entailed violation of two standards for biol ogical data collection: that multiple samples be analyzed and that ins truments be calibrated under the range of conditions used in empirical analysis. To explore the consequences of these practices, we compared the responses of both heated and unheated taxidermic mounts with thos e of live animals when exposed to combinations of wind and radiation t hat normally could be experienced in nature. Two mammals, the rock squ irrel Spermophilus variegatus and the golden-mantled ground squirrel S permophilus lateralis, as well as a bird, the verdin, Auriparus flavic eps, were studied. For all species, there was substantial individual v ariation in mount responses. Under a single set of environmental condi tions, coefficients of variance for mont response were as high as 71%, and the range of values between mounts typically equaled the change i n the group's average standard operative temperature that was produced by two- to fourfold increases in wind speed. For predicting physiolog ical responses of animals, the adequacy of taxidermic mounts varied wi dely with species, type of mount, and environmental conditions. In som e cases, predictions closely matched animal responses. In other cases, predictions using data from mounts produced errors of up to 28.5 degr ees C in the estimate of standard operative temperature. The types of error observed, combined with the extensive investment of time and res ources required to construct and determine the utility of mounts as op erative temperature thermometers for a particular species, greatly red uces the attractiveness of this technique for quantifying the thermal environments of animals in nature.