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SMITHSONIAN INSTITUTION PRESS
Washington, D.C.
1993

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Mugaas, J. N., J. Seidensticker, and K. Mahlke-Johnson. Metabolic Adaptation to Climate andDistribution of the Raccoon Procyon lotor and Other Procyonidae. Smithsonian Contributionsto Zoology, number 542, 34 pages, 8 figures, 12 tables, 1993.—Although the familyProcyonidae is largely a Neotropical group, the North American raccoon, Procyon lotor, is moreversatile in its use of climate, and it is found in nearly every habitat from Panama to 60°N inCanada. We hypothesized that most contemporary procyonids have remained in tropic andsubtropic climates because they have retained the metabolic characteristics of theirwarm-adapted ancestors, whereas Procyon lotor evolved a different set of adaptations that haveenabled it to generalize its use of habitats and climates. To test this hypothesis we comparedProcyon lotor with several other procyonids (Bassariscus astutus, Nasua nasua, Nasua narica,Procyon cancrivorus, and Potos flavus) with respect to (1) basal metabolic rate (Ḣ_b), (2)minimum wet thermal conductance (C_mw), (3) diversity of diet (D_d), (4) intrinsic rate of naturalincrease (r_max), and, where possible, (5) capacity for evaporative cooling (E_c). We measuredbasal and thermoregulatory metabolism, evaporative water loss, and body temperature of bothsexes of Procyon lotor from north central Virginia, in summer and winter. Metabolic data forother procyonids were from literature, as were dietary and reproductive data for all species.

Procyon lotor differed from other procyonids in all five variables. (1) Procyon lotor's massspecific Ḣ_b (0.46 mL O₂·g^-1·h^-1) was 1.45 to 1.86 times greater than values for other procyonids.(2) Because of its annual molt, Procyon lotor's C_mw was about 49% higher in summer thanwinter, 0.0256 and 0.0172 mL O₂·g^-1·h^-1·°C^-1, respectively. The ratio of measured to predictedC_mw for Procyon lotor in winter (1.15) was similar to values calculated for Potos flavus (1.02)and Procyon cancrivorus (1.25). Values for other procyonids were higher than this, but less thanthe value for Procyon lotor (1.76) in summer. On a mass specific basis, Bassariscus astutus hadthe lowest C_mw with a ratio of 0.85. (3) Procyon lotor utilized three times as many foodcategories as Procyon cancrivorus, Nasua nasua, and Bassariscus astutus; about two times asmany as Nasua narica; and nine times as many as Potos flavus. (4) Intrinsic rate of naturalincrease correlated positively with Ḣ_b. Procyon