Metabolic Adaptation to Climate and Distribution of the Raccoon Procyon Lotor and Other Procyonidae

by John N. Mugaas; Kathleen P. Mahlke-Johnson; John Seidensticker

Captive versus Wild Raccoons

Male raccoons trapped in summer had higher Ḣ_b's than our captive animals in any season ([Table 2]). The higher rate of metabolism of these trapped males could have been due to the stress of captivity or to the fact that "wild" animals actually may have higher metabolic rates than those that have adjusted to captivity. If the latter is true, then our data for captive animals underestimated the actual energy cost of maintenance metabolism for Procyon lotor in the wild. At present, we have no way of determining which of these alternatives is true.

Seasonal Metabolism of Raccoons

In some temperate-zone mammals, Ḣ_b is elevated in winter, which presumably increases their "cold-hardiness." Conversely, lower summer metabolism is considered to be a mechanism that reduces the potential for heat stress. Such seasonal variation in Ḣ_b has been found in several species: collard peccary, Tayassu tajacu (Zervanos, 1975); antelope jackrabbit, Lepus alleni (Hinds, 1977); desert cottontail, Sylvilagus audubonii (Hinds, 1973); and, perhaps, cold-acclimatized rat, Rattus norvegicus (Hart and Heroux, 1963). Unlike these species, our captive raccoons showed no seasonal variation in Ḣ_b ([Table 2]). Instead, raccoons achieved "cold-hardiness" in winter and reduced their potential for heat stress in summer with a large seasonal change in thermal conductance ([Table 3]).

Table 7.—Metabolic characteristics of several procyonid species.

Species	Body Mass (g)		Basal[a] metabolism			Minimum[] conductance			Tb[c]			Tn[d]			References
			Meas	Hbr		Meas	Cmwr		α	ρ		Tlc	Tuc
Bassariscus astutus	865		0.43	0.68		0.0288[e]	0.85		37.6	23		35.5			Chevalier (1985)
Procyon cancrivorus	1160		0.40	0.69		0.0368[e]	1.25					26			Scholander et al. (1950b, c)
Potos flavus	2030		0.36	0.51											McNab (1978a)
Potos flavus	2400		0.32	0.65					38.1	36.0		23	30		Müller and Kulzer (1977)
Potos flavus	2600		0.34	0.71		0.0200[f]	1.02					23	33		Müller and Rost (1983)
Nasua nasua	3850		0.26	0.60		0.0200[f]	1.24		38.3	36.4		25	33		Chevillard-Hugot et al. (1980)
Nasua nasua	4847		0.33	0.79		0.0238[e]	1.65		39.1	37.9		30	35		Mugaas et al. (in prep.)
Nasua narica	5554		0.25	0.62		0.0208[e]	1.55		38.9	37.4		25	35
Nasua narica	4150		0.42	1.20		0.0341[e]	2.20								Scholander et al. (1950b, c)
						0.0224[g]	1.45
Procyon lotor															This study
Summer
Trapped male	4400		0.54	1.28								20
Captive male	4790		0.46	1.07		0.0256[f]	1.77		38.4	37.5		20
Captive female	4670		0.42	1.02		0.0256[f]	1.79		38.2	37.6		25
Winter
Captive male	5340		0.47	1.17					38.6	38.6		11
Captive female	4490		0.46	1.10		0.0172[f]	1.15		38.3	37.3		11

[a] Meas is measured basal metabolism (mL O₂·g^-1·h^-1). H_br is the ratio of measured to predicted basal metabolism where the predicted value is calculated from Ḣ_b = 3.42·m^-.25 (Kleiber, 1932, 1961:206) and m is body mass in grams.
[] Meas is measured minimum thermal conductance (mL O₂·g^-1·h^-1·°C^-1). C_mwr is the ratio of measured to predicted minimum thermal conductance where the predicted value is calculated from C_m = 1.0·m^-0.5 (McNab and Morrison, 1963; Herreid and Kessel, 1967), and m is body mass in grams.
[c] T_b is body temperature during the active (α) and rest (ρ) phases of the daily cycle (°C).
[d] T_n is the thermoneutral zone as defined by the lower (T_lc) and upper (T_uc) critical temperatures (°C).
[e] Conductance calculated as the slope of the line describing oxygen consumption at temperatures below the lower critical temperature.
[f] Conductance calculated from C_mw = Ḣ_r/(T_b - T_a), where Ḣ_r is resting metabolic rate at temperatures below T_lc, and other symbols are as described elsewhere.
[g] Inactive-phase thermal conductance: estimated from Scholander et al. (1950b), assuming that active-phase thermal conductance is 52% higher than values determined during the inactive phase (Aschoff, 1981).