_Nasua narica_ and _Nasua nasua_ have tropical and subtropical distributions and they are the only procyonids that are diurnal (Kaufmann, 1962:103-105, 1982, 1987). Because they are active during the day they experience a more extreme thermal environment (higher T_{ a}'s and solar radiation) than their nocturnal cousins. Values of C_{ mwr} for _Nasua narica_ (1.45 and 1.55) and _Nasua nasua_ (1.24 and 1.65) are higher than those for _Procyon cancrivorus_ or _Potos flavus_ (Table 7). Thus, these coatis have higher mass specific C_{ mw}'s than their nocturnal tropical cousins. A high C_{ mw} reduces the cost of thermoregulation in hot environments because it increases an animal's ability to lose excess heat passively. The higher C_{ mw}'s of these coatis serve as an adaptation that contributes to the success of their diurnal life style as well as their ability to expand their habitat use to areas with less thermal stability, such as oak and pine woodlands and deserts.
_Bassariscus astutus._--This species has the lowest mass specific C_{ mw} of these procyonids (C_{ mwr} = 0.85; Table 7), which indicates that its pelt has a greater insulative value than the coats of _Potos flavus_, _Procyon cancrivorus_, _Nasua nasua_, or _Nasua narica_. This, coupled with a lower than predicted [.H]_{ b}, allows _Bassariscus astutus_ to maintain T_{ b} with less energy expenditure than is possible for any other procyonid of comparable size; and this combination of adaptations provides _Bassariscus astutus_ with a distinct energy advantage in environments that have low productivity (Wang et al., 1973). The evolution of a pelt that provides better insulation must be considered an important contributing factor for the spread of this species into desert regions of the western United States.
THERMOREGULATION AND USE OF STORED FAT AT LOW TEMPERATURES
THERMOREGULATION.--At temperatures below a mammal's T_{ n}, heat loss exceeds [.H]_{ b}. To maintain T_{ b} under these conditions, metabolic rate must be increased (Eq. 4). _Procyon lotor_ in summer during its annual molt (Table 5; Figure 2), _Bassariscus astutus_ (Chevalier, 1985), _Nasua nasua_ (Chevillard-Hugot et al., 1980; Mugaas et al., in prep.), _Nasua narica_ (Scholander et al., 1950b; Mugaas et al., in prep.), and _Potos flavus_ (Müller and Kulzer, 1977; Müller and Rost, 1983) all are able to elevate their metabolic rates by 130% above basal when they are exposed to T_{ a} = 0°C. _Procyon cancrivorus_ responds to 0°C with an increase in metabolic rate of 257% above basal (Scholander et al., 1950b). All animals listed have about the same T_{ lc} and T_{ b}, so the temperature differential producing this response is about the same for each species. Metabolic ability to defend body temperature against low ambient temperatures, therefore, is well developed in these procyonids. Such large increases in metabolic rate are energetically expensive, and if these animals were routinely exposed to T_{ a} = 0°C, it would be difficult for them to acquire enough food each day to maintain endothermy. Raccoons in winter pelage, however, need only elevate their metabolic rate by 47% above basal to maintain endothermy at T_{ a} = 0°C (Table 5; Figure 3). Each year at the completion of its molt, the raccoon's highly insulative pelt is renewed. This lowers their T_{ lc} by 9°C to 15°C below that measured for them in summer (Figure 3) and decreases their cost of thermoregulation at low temperatures. The increased insulative capacity of their pelt is one of the primary adaptations that has allowed _Procyon lotor_ to extend its distribution into cold climates.