Joseph F. Merritt

Winter Survival Adaptations of the Short-Tailed Shrew (Blarina brevicauda) in an Appalachian Montane Forest

The short-tailed shrew ( Blarina brevicauda ) is a very common small mammal in eastern deciduous forests of North America. Survivorship of this winter-active soricid during the winter is good. This study examined seasonal changes in body mass, resting metabolic rate (RMR), and non-shivering thermogenesis (NST) of live-trapped B. brevicauda as important adaptations which enhance over-winter survival. Body mass of shrews captured in April increased 39% over average body mass of September-captured shrews. RMR in January represented a 38% increase in metabolic rate relative to August, and NST increased by 54% in January as compared to August. Monthly RMR and NST values showed an inverse relationship to minimum environmental temperature of the capture site. A general “adaptive winter profile” for B. brevicauda incorporates many behavioral, physiological and anatomical adaptations including: utilization of elaborate nests, food hoarding, reliance on abundant, energy-rich prey, winter foraging confined to a stable thermal regime, reduced activity during periods of cold, and increased thermogenic capacity in winter due to NST with resultant hypertrophy of interscapular brown adipose tissue.

Population Ecology and Energy Relationships of Clethrionomys gapperi in a Colorado Subalpine Forest

Small mammals were live-trapped on a 12 by 12 study grid (1.2 ha) located in a subalpine forest on the eastern slope of the Colorado Front Range at an elevation of 3,120 m. The area was characterized by a continental climate, and snow covered the ground for about 7½ months of the year. Subnivean activity of Clethrionomys gapperi was monitored by use of live-traps located within trap chimneys. The population was monitored at 2-week intervals from January 1974 to September 1975. Population density of mice increased during summer, peaked in late November and then gradually declined to a low in May during spring thaw. Two periods of hardship existed for red-backed voles in the study area—the autumn freeze and spring thaw. The autumn freeze occurred before snow accumulation, which reduced survival. The spring thaw produced extensive flooding, which caused high mortality. Red-backed voles commenced breeding in late March below a continuous snow cover (150 to 200 cm deep). The breeding season lasted about 7½ months. Pregnant females caught in June produced another litter that summer. Voles concluded breeding in September and lactating females were caught in October. Winter-caught red-backed voles weighed significantly less and also showed a lower per gram metabolic rate than the larger summer mice. Winter weight loss seemed advantageous in reducing food requirements as verified by metabolic studies. Small mammals in the subalpine forest ecosystem are not simply primary consumers, their role is complex and derived from numerous “strategies” adaptive in coping with the harsh subalpine environment.

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).

Seasonal thermogenesis and changes in body mass of masked shrews, Sorex cinereus

Masked shrews (Sorex cinereus) are the most widely distributed shrews in North America, occurring from Alaska and Canada south into the northern one-half of the United States. Favorable winter survivorship of S. cinereus is reported from the Appalachian Mountains of Pennsylvania. In the present study, I examined the role of seasonal changes in resting metabolic rate, nonshivering thermogenesis, thermal conductance, and body mass of live-trapped shrews as mechanisms that enhance overwinter survivorship. Shrews were captured monthly from April 1992 to April 1993 in southwestern Pennsylvania. Temperatures at the ground surface ranged from -7 to 22°C, in February and April, respectively, and snow occurred from November to March. Mean resting metabolic rate for shrews was highest in autumn (8.30 ml O 2 g -1 h -1 ) and lowest in spring (5.75 ml O 2 g -1 h -1 ). Body temperature of shrews averaged 38.7°C. Thermal conductance averaged 0.79, ranging from a low in spring to a high in autumn. Mean nonshivering thermogenesis was lowest in summer (8.02 ml O 2 g -1 h -1 ), and peaked in winter (14.60 ml O 2 g -1 h -1 ). Capacity for nonshivering heat production in winter was almost twice that of summer. Nonshivering thermogenesis showed an inverse relationship to minimum ambient, ground surface, and subsurface temperatures. Body mass averaged 4.15 g and declined 53% from summer to winter. The favorable overwinter survivorship of S. cinereus is due in part to the ability of this species to increase thermogenic capacity by means of nonshivering thermogenesis coupled with energy conservation in the form of a decline in mass during winter.

Shrews — Small Insectivores with Polyphasic Patterns

Daily activity patterns of shrews are controlled by metabolic requirements commensurate with their diminutive body mass and resultant high surfaceto-mass ratios: they must forage often to avoid exhaustion of their energy stores. To remain homeothermic, shrews must partition a 24-h period into multiple bouts of foraging, rest, and sleep.

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.

LUNG PARASITES OF SHREWS FROM PENNSYLVANIA

We examined lung parasites of three species of soricids, Sorex cinereus (n = 58), Sorex fumeus (n = 23) and Blarina brevicauda (n = 45) collected from Pennsylvania (USA), from 1990 to 1995. Yeast-like cells of Histoplasma capsulatum var. capsulatum were found in lung sections stained with Grocott s modification of Gomori s methenamine silver, periodic acid-Schiff, Giemsa, and hematoxylin-eosin in two (3%) S. cinereus, eight (35%) S. fumeus and two (4%) B. brevicauda. The number of spores of H. capsulatum in the lungs was low and no inflammatory reaction was evident. The infection was not disseminated to other organs. This is the first report of H. capsulatum infection in any species of shrews of the genus Sorex and the prevalence in S. fumeus was remarkably high compared to those reported for other wild mammals. A nematode, possibly Angiostrongylus michiganensis, was found in the lungs of one S. fumeus on necropsy and in a stained lung section of one S. cinereus. In both cases the host was also infected with the fungus. Pneumocystis carinii, which is the most common lung parasite in Sorex araneus (the numerically dominant Eurasian species of shrew), was not found in any of the North American species of shrew examined in this study.

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.