Figure 6.—Relationship between body temperature and chamber air temperature in summer (panel A), and winter (panel B): captive females, open circles and solid lines; captive males, solid circles and dashed lines. Solid vertical lines represent lower critical temperatures.
Table 5.—Regression equations describing oxygen consumption (mL O2·g-1·h-1) of Procyon lotor at temperatures below their lower critical temperature (I = x-intercept (°C), n = number of observations, R2 = coefficient of determination, SEE = standard error of estimate for the y-intercept (a) and slope (b), X = chamber temperature (°C), and Y = oxygen consumption).
| Season and sex | Equation | (n) | R2 | SEE | I | |
|---|---|---|---|---|---|---|
| a | b | |||||
| Summer | ||||||
| Trapped male | Y = 1.09 - 0.0281·X | (30) | 0.64 | 0.0353 | 0.0040 | 38.8 |
| Captive male | Y = 0.97 - 0.0258·X | (12) | 0.91 | 0.0235 | 0.0025 | 37.6 |
| Captive female | Y = 1.04 - 0.0251·X | (29) | 0.78 | 0.0288 | 0.0026 | 41.1 |
| Winter | ||||||
| Captive, both sexes | Y = 0.68 - 0.0193·X | (36) | 0.68 | 0.0157 | 0.0023 | 35.2 |
Summer
During summer, Tlc for male raccoons was 20°C, whereas for females it was 25°C ([Figure 2]). Regression equations calculated to describe oxygen consumption at Ta's below Tlc are presented in [Table 5]. For three groups of summer animals, slopes of regressions are identical. This indicates that minimum conductances of these three groups were equivalent. Intercepts of these equations are different, which suggests a difference in metabolic cost of thermoregulation between these groups ([Figure 2]); captive males had a lower intercept than either trapped males (p<0.005) or captive females (p<0.05), but there was no difference in intercepts of captive females and trapped males. These regression equations, therefore, also were derived using values of oxygen consumption expressed in terms of metabolic body mass (Mellen, 1963). Relationships between intercepts of these equations are different than those for regressions in [Table 5]. Intercept for females was intermediate to, and not different from, those of the two groups of males. However, captive males still had a lower intercept than trapped males (p<0.025). Thus, in summer, thermoregulatory metabolism was less expensive for captive than for trapped males, and in spite of a 5°C difference in their Tlc's ([Figure 2]), captive males and females had similar thermoregulatory costs.
Regression lines for three groups of animals in summer extrapolate to zero metabolism at values equivalent to, or greater than, normal Tb; 38.8°C for trapped males, 37.6°C for captive males, and 41.1°C for captive females ([Table 5]). Thus, all three groups had minimized thermal conductance at Ta's below Tlc (Scholander et al., 1950b; McNab, 1980b). Minimum wet thermal conductance calculated for raccoons in summer with [Eq. 4] ([Table 3]) is numerically similar to these "slope" values ([Table 5]), and it was, therefore, considered to be the best estimate of Cmw for Procyon lotor during that season (0.0256 mL O2·g-1·h-1·°C-1).