David A. Zegers

SEASONAL THERMOGENESIS OF SOUTHERN FLYING SQUIRRELS (GLAUCOMYS VOLANS)

Abstract Southern flying squirrels (Glaucomys volans) are small sciurid rodents that reside in deciduous forests of eastern North America. G. volans consumes primarily seeds and fruits, and is active year-round. During winter when food is sparse, flying squirrels conserve energy by forming aggregations in nest-lined cavities of trees. We compared seasonal changes in resting metabolic rate (RMR), nonshivering thermogenesis (NST), body temperature, and body mass of G. volans nesting communally residing in an outdoor enclosure to squirrels nesting singly housed in an outdoor laboratory. Flying squirrels were tested monthly from November 1997 to November 1998. Average RMR was highest in winter (1.14 ml O2 g−1 h−1) and lowest in summer (0.73 ml O2 g−1 h−1); minimal differences occurred among group and solitary nesters. Average RMR ranged from 33% (single) to 38% (communal) lower than predicted by body mass. Average NST was lowest in summer (1.62 ml O2 g−1 h−1) and peaked in winter (4.70 ml O2 g−1 h−1), demonstrating an inverse correlation with minimum ambient temperature. Squirrels nesting singly experienced a longer period of elevated NST in winter and higher mean NST year-round than did squirrels nesting communally. Average body mass ranged from a low of 66.9 g in September for both groups to a high of 76.4 g in communal nesters in December and 79.3 g for single nesters in March; average body temperature ranged from 36.3 to 38.9°C (communal nesters, December and May, respectively).

Adaptations of Peromyscus for Winter Survival in an Appalachian Montane Forest

Both Peromyscus leucopus and P. maniculatus had slightly higher body mass in spring and summer than in autumn and winter. Mean resting metabolic rates of both species were highest in September and November. For both species, maximum nonshivering thermogenesis following norepinephrine dosage increased markedly in early autumn, declined in October and January following unseasonably warm periods, peaked in February during the coldest portion of the winter, and declined throughout the spring. Neither length of photoperiod nor minimum ambient temperature correlated with the variation in resting metabolic rates; however, both environmental factors correlated strongly with capacity for nonshivering thermogenesis.

LONG-TERM PATTERNS OF BOTFLY PARASITISM IN PEROMYSCUS MANICULATUS, P. LEUCOPUS, AND TAMIAS STRIATUS

Abstract We used data collected from 1979 to 1998 at Powdermill Biological Station in southwestern Pennsylvania to explore the relationship between Cuterebra (botfly) and white-footed mice (Peromyscus leucopus), deer mice (Peromyscus maniculatus), and eastern chipmunks (Tamias striatus). Overall, P. leucopus and P. maniculatus exhibited similar levels of botfly infestation (as measured by prevalence), while T. striatus showed greater prevalence than the mice. Adult P. leucopus and T. striatus exhibited greater prevalence than juveniles, and adult and juvenile P. maniculatus showed similar prevalence levels. Male and female prevalence was similar in each species. Botfly-infested individuals tended to remain significantly longer in the trapping area than noninfested individuals and were more likely to meet our criteria for “residents” than were noninfested individuals. We question the relative impact of botflies on individual survival in these species.

Maximizing survivorship in cold: Thermogenic profiles of non-hibernating mammals

Winter-active small mammals residing in seasonal environments employ many different behavioral, anatomical and physiological mechanisms to cope with cold. Herein we review research on survival mechanisms in cold employed by small mammals with emphasis on the families Soricidae, Muridae and Sciuridae. The focus of this review is on research delineating the role of seasonal changes in resting metabolic rate (RMR), nonshivering thermogenesis (NST), body mass, and communal nesting in enhancing winter survivorship of six species of small mammals (masked shrewSorex cinereus, short-tailed shrewBlarina brevicauda, southern red-backed voleClethrionomys gapperi, white-footed mousePeromyscus leucopus, deer mouseP. maniculatus, and southern flying squirrelGlaucomys volans) residing in the Appalachian Mountains of Pennsylvania, USA. Each species shows good over-winter survivorship but exhibits a different suite of mechanisms to maximize survival in cold.B. brevicauda, S. cinereus, andG. volans show slight increases in RMR during winter, whereasPeromyscus andC. gapperi exhibit decreased RMR overwinter. All six species experience elevated NST in winter. The comparatively low RMR and NST ofG. volans during winter was attributable to a decreased energy expenditure due to a larger body mass, coupled with communal nesting in cavities of trees that provided insulation from low ambient temperatures. Squirrels nesting singly experienced a longer period of elevated NST in winter and higher mean NST year-round than did squirrels nesting communally. Energy conservation in the form of growth retardation in winter was exhibited byC. gapperi andS. cinereus but not the other species.

Social thermoregulation in least shrews, Cryptotis parva

Abstract Cryptotis parva exhibits a geographic range and ecological requirements unique among North American soricines: it possesses a latitudinal distribution, metabolism and communal nesting pattern more like the crocidurines of the eastern hemisphere. We utilized oxygen consumption (VO2) techniques to examine metabolic shifts and video to document activity patterns and dynamics of solitary and group nesting C. parva. Between ambient temperatures of 4°C and 34°C, solitary C. parva demonstrated an inverse relationship between ambient temperature (Ta) and resting metabolic rate (RMR); thermal neutral zone (TNZ) was very narrow, between a Ta of 34°C and 36°C. VO2 was measured in groups ranging in size from one to eight at Tas of 4°C, 14°C, 24°C and 34°C. The group size had a significant effect on the median RMR and median predicted Kleiber value and was more effective at reducing metabolic cost at a lower Ta. In a second experiment designed to assess the effects of huddling group size and incubator Ta on the Ta of the nest chamber, both had significant effects. Group size had significant effects on the Ta of the nest chamber at incubator temperatures of 5°C, 10°C, 15°C and 32°C, but not at 25°C. We found no behavioral or physiologic evidence of heterothermy.