Three species of western chipmunks, Tamias senex, T. siskiyou, and T. ochrogenys, were removed from T. townsendii because discrete character variation, especially of genitalic morphology, suggested lack of intergradation and species-level distinction. Two of these species, T. senex and T. siskiyou, show substantial geographic variation in cranial morphology and pelage characteristics across their ranges, from humid coastal forests to the relatively arid Sierra Nevada and Cascade ranges in northern California. In both species, specimens from inland localities are paler and smaller than those collected near the Pacific coast. This also is true for another species in Oregon and Washington, where coastal T. t. townsendii is replaced by inland T. t. cooperi. Interspecific convergence in pelage and external variation is so strong that inland T. senex and T. siskiyou resemble each other more strongly than either resembles conspecifics from coastal forests, and vice versa. In spite of this convergence, genital bones confirm the specific identity of inland and coastal specimens. Because both T. senex and T. siskiyou were originally described from inland localities, the novel patterns of color and size described here provide the basis for naming the coastal forms as new subspecies.

Mechanisms of chromosomal change, distribution patterns, extent of genotypic, phenotypic and ecological divergence, and nature and degree of reproductive isolation were reviewed in 10 chromosomally variable southern African rodent species and species complexes. Genetically similar peripatric or parapatric chromosome races freely interbreed (striped mice, Rhabdomys pumilio; vlei rats, Otomys irroratus), while genotypically or phenotypically divergent, sympatric sibling species (multimammate mice, Mastomys natalensis–M. coucha; tree rats, Thallomys paedulcus–T. nigricauda; red veld rats, Aethomys chrysophilus–A. ineptus) appear reproductively isolated, suggesting a correlation between genetic distance and onset of reproductive isolation. The allopatric gerbil species pair, Tatera brantsii–T. afra, shows little or no prezygotic reproductive isolation despite well-developed male-biased postzygotic isolation (i.e., Haldane effect) that may be associated with a rearrangement on the Y chromosome. Within the actively speciating vlei rat, Otomys irroratus, complex, despite widespread laboratory interbreeding between chromosome races, postzygotic isolation (virtual hybrid sterility) was demonstrated due to fixation of a tandem fusion rearrangement in the high-altitude (>1,400 m) A1 race. Both post- and prezygotic isolation have developed in the absence of significant measurable genotypic divergence at either the gene or the DNA level. Acquisition of reproductive isolation and incipient speciation in the vlei rat complex appears to be mediated by both chromosomal (postzygotic) and nonchromosomal (prezygotic) processes.

Phylogenetic relationships among 8 subspecies of Sigmodon hispidus from North, Central, and South America were examined using DNA-sequence data from the mitochondrial cytochrome-b gene. The magnitude of DNA-sequence variation detected among these subspecies, in some cases, exceeded levels of interspecific variation observed among currently recognized species of Sigmodon. These data suggest that S. hispidus is paraphyletic and that a minimum of 3 species exist within the currently recognized taxon. Consequently, the taxonomy should be revised to recognize the following samples as distinct species: those from the United States and north-central Mexico, those from southern Mexico, and those from Central and South America.

The Bering Land Bridge was the intermittent connection that allowed exchange of mammals between Asia and North America. Because some mammalian genera are widely distributed on both continents, recovery of phylogenetic histories of species within these genera may help reconstruct the sequence of intercontinental exchanges. We tested phylogenetic and biogeographic hypotheses in the widespread genus Microtus through parsimony and likelihood analysis of mtDNA-sequence data. The extant species of Microtus in North America are thought to be derived from multiple invasions from Asia or, alternatively, as a single invasion followed by autochthonous speciation. Mitochondrial cytochrome-b gene sequences were obtained for 78 individuals representing 24 species of Microtus. Data supported 1 clade of taiga voles (M. pennsylvanicus, M. montanus, M. townsendii, and M. canicaudus), a clade of Asian species (M. kikuchii, M. fortis, M. montebelli, and M. middendorffi), plus the Holarctic M. oeconomus and several other previously identified clades. M. gregalis also was found to be distant from M. abbreviatus and M. miurus, thus contradicting monophyly of the subgenus Stenocranius. Monophyly of North American species was supported, albeit weakly. Basal relationships were not robust, reflecting a single pulse of diversification about 1.3 × 10⁶ years ago. This pulse mirrors the fossil record and may be partially responsible for the unstable taxonomic history.

Craniodental form and function were evaluated in the 2 extant, parapatric species of dermopterans (Dermoptera: Cynocephalidae). The level of morphological distinction between the 2 taxa was such that were they known as fossils; most taxonomists would not contest their genus-level distinction as indicative of adaptive differentiation. In fact, these taxa exemplify the widely employed but implicit morphological distance-based standards used for delineating mammalian genera in the paleontological literature. Appropriate names for these 2 taxa are Cynocephalus volans for the Philippine flying lemur and Galeopterus variegatus for the heterogeneous populations of the Sundaic flying lemurs. Cynocephalus probably has a hypertrophied version of the ancestral cynocephalid molar complex and modified incisor and canine morphology. The hypertrophied metaconules of cynocephalids occlude with an expanded paracristid and a cusplike shelf, the distocuspid. Cynocephalus also has a broader rostrum, a greater degree of postorbital constriction, and enhanced ectocranial ridges associated with a more robust masticatory musculature than Galeopterus. Cynocephalus appears adapted to a diet that requires a greater degree of shearing by the anterior dentition and crushing by the molariform dentition. These anterior shearing teeth (I3, C1, P3, c1, p3) are larger and more bladelike than those of Galeopterus, and the bite force is more anteriorly directed. Angle of the mandible is ventrally expanded in Cynocephalus, facilitating enhanced chewing force for the postcanine dentition while maintaining orientation of the temporalis muscle. Dwarfed forms of Galeopterus are found on many of the smaller islands of the Sunda Shelf and in central Laos. They are not morphologically distinguishable from larger members of this species, other than in size, and do not warrant specific distinction. However, it may be desirable to designate 4 subspecies of G. variegatus: G. v. variegatus from Java, G. v. temminckii from Sumatra, G. v. borneanus from Borneo, and G. v. peninsulae from the Malay Peninsula and mainland Southeast Asia. Separate species rank for each of the dwarfed populations should not be recognized. Phylogenetic relationships of Dermoptera are discussed in light of the morphological differences of the 2 genera.

Little is known about geographic variation in the local composition of South American assemblages of mammals or the factors that may produce such variation. This is particularly unfortunate in Paraguay because it occurs at the interface of a number of phytogeographic regions (e.g., Cerrado, Chaco, Interior Atlantic Rainforest, and Pantanal) and is the point at which many temperate species reach their northern limits or at which tropical species reach their southern limits. Based on 2 years of intensive fieldwork, we documented the species and familial composition of bat assemblages at 25 sites throughout the country. We also estimated similarity among sites based on indices sensitive to presence or absence of species (Ochiai's index), to rank abundance of species (rank correlation index), or to relative abundance of species (Euclidean index). Geographic distance between sites accounted for little variation in composition based on presence–absence or rank abundances of species but accounted significantly for variation related to both identity and relative frequency of species. Distinct assemblages of species do not correspond to the 7 distinct biomes of the country; rather, strong differences exist between sites east (mesic) and west (xeric) of the Río Paraguay. For the most part, these differences are related to dominance by molossids (e.g., Eumops patagonicus, Molossops temminckii, and Molossus molossus) and vespertilionids (e.g., Lasiurus ega, Myotis albescens, and M. nigricans) in dry regions versus phyllostomids (e.g., Artibeus fimbriatus, A. lituratus, and Sturnira lilium) in mesic regions. As a consequence, classification of sites into 2 broad biogeographic regions based on bat familial composition generally is concordant with that based on plants.

We surveyed 10 bridges hourly 1 night/month, April–September 1996, and another 50 bridges on 2 occasions on each of 2 nights, July–September 1996, to assess nocturnal use of bridges by bats in the central Oregon Coast Range. We also collected guano monthly from 28 bridges, April 1996–November 1997, to evaluate temporal patterns of use. Eight species of bats were observed using bridges as night roosts. Bats roosted under cast-in-place concrete bridges in larger concentrations than under other types of bridges and roosted more frequently in end chambers than in center chambers of concrete cast-in-place bridges. Greatest use occurred between 0300 and 0430 h and in June–September, although some bridges were used year-round. We observed females of all reproductive stages, males, and volant juveniles night-roosting under bridges. Our data suggest that size and thermal characteristics of bridges influence use of bridges as night roosts. Further research on use of night roosts by bats would be valuable to more fully understand the ecology of bats.

Southern blossom bats, Syconycteris australis (Pteropodidae), were followed by radiotelemetry in lowland rainforest in Kau Wildlife Area, Madang Province, Papua New Guinea. Eleven individuals were monitored ≤31 days. Based on 706 radiotelemetry positions, home ranges of 11 bats were 2.7–13.6 ha. There were no significant differences in home-range sizes between sex or age classes, but there was individual overlap of the home ranges of these bats. Long axes of home ranges were 263–725 m. During each night, bats visited most parts of their home ranges; however, activity was concentrated in core-use areas representing 19–33% of the home range and containing ≥1 food patches. During the day, S. australis roosted in the foliage of trees. Bats showed fidelity to a day-roost area (0.4–10.8% of home range) but not to a single roost tree. Day-roost areas monitored within a given year showed virtually no overlap.

“Chirp” calls of adult white-nosed coatis (Nasua narica) were measured and compared to determine form and function of these frequently emitted vocalizations. Behavioral contexts during vocalizations were documented, and chirp calls were tape recorded and analyzed using a digital spectrograph. Also, a bat detector was used to determine whether ultrasonic frequencies were emitted in chirps. Duration of the chirp calls was 0.146–0.202 s. Spectrogram analyses revealed that the lowest frequencies of the chirps averaged 4.66–11.83 kHz and that the highest frequencies averaged 1417.66 kHz. Ultrasonic frequencies (30–55 kHz) also were detected in chirp calls. Chirps differed among individuals regarding the differential frequency between the 1st and 2nd resonance bars (P ≤ 0.01). Chirps seem to function as contact calls for this social mammal because they were emitted only while coatis were moving. The short duration and high frequency of the calls may allow for contact with nearby group members while minimizing auditory detection by predators. Unique features of each coati's chirp also may allow individual recognition.

A new middle Pleistocene record of Mustela nigripes is reported from Cathedral Cave, White Pine County, Nevada. The specimen dates to 750,000–850,000 years ago and represents one of the oldest remains recovered of the black-footed ferret. Forty-two percent of fossil faunas known to contain M. nigripes do not contain Cynomys, the common prey of black-footed ferrets in historic times. Consideration of dietary information and habitat requirements of M. nigripes and its sister taxon, M. eversmanni (steppe ferret), reveals ancestral behavioral repertoires for ferrets. We suggest that the historically documented “obligate” predator–prey relationship between M. nigripes and Cynomys was a secondary effect of colonization by black-footed ferrets of Cynomys-dominated habitats sometime in the past 800,000 years. A phylogenetic perspective on the behavior of ferrets combined with paleontological data indicates a broader range of possibilities for conservation of the black-footed ferret.

Niche differentiation occurred on 3 dimensions in a size-structured guild of marsupial carnivores (Marsupialia: Dasyuridae) that included the Tasmanian devil (Sarcophilus laniarius), spotted-tailed quoll (Dasyurus maculatus), and eastern quoll (D. viverrinus). Diet was partitioned on a body size–prey size axis, but substantial overlap occurred between adjacent species. Complementary niche differentiation also occurred on horizontal (vegetation type and structure) and vertical (arboreal) habitat dimensions. Eastern quolls separated completely by using grasslands more than the other 2 species. Spotted-tailed quolls were distinguished by a greater degree of arboreal activity that reflected a large proportion of arboreal prey species in their diet. A strong relationship was found between body size, arboreal activity, and morphologic adaptations for climbing between predators and prey. Coevolution in phenotype among predators and prey and consequent constraint on performance in different habitat types were the most easily measured explanations for habitat differentiation among these species, particularly between spotted-tailed quolls and devils. The “ghost of competition past” is an alternative and nonexclusive explanation that can equally explain arboreal habitat use by spotted-tailed quolls and separation between the eastern quoll and the spotted-tailed quoll. Risk of predation and prey availability also may be important factors.

Habitat use and separation between 2 sympatric species, the giant panda (Ailuropoda melanoleuca) and the red panda (Ailurus fulgens), were studied in Yele Natural Reserve, Mianning County of Sichuan Province, China, to elucidate the coexistence of these specialized carnivores. Nineteen variables describing proximate habitat structure were measured at each fecal-group site. We tested if habitat structure differed between pandas and examined habitat separation between the species. Habitats used by each species differed significantly. The 2 pandas exhibited different patterns in microhabitat use, although their habitats overlapped in the study area. The giant panda occurred at sites on gentle slopes with lower density of fallen logs, shrubs, and bamboo culms. Sites also were close to trees and far from fallen logs, shrubs, and tree stumps. The red panda occurred at sites on steeper slopes with higher density of fallen logs, shrubs, and bamboo culms. Sites also were close to fallen logs, shrubs, and tree stumps. We conclude that microhabitat separation contributes to coexistence of giant and red pandas in areas of sympatry.

Kit foxes (Vulpes macrotis) are nocturnal, monogamous, and territorial. We used telemetry to monitor nocturnal interactions of pair members with each other and neighboring foxes in central California during 1989–1991. Observed distances between mated foxes consistently were closer than expected by chance. This positive association probably resulted from a tendency for foxes to move around common den or foraging sites; mates did not exhibit concordant movement patterns. Nocturnal encounters probably are not necessary to maintain pair bonds because mates regularly share dens during the day throughout the year. Encounters may be more important during pair formation because members of recently formed pairs encountered each other more frequently (>16% of locations) than did established pairs (<13% of locations). Observed distances between neighboring foxes were not consistently closer or further apart than expected by chance, and encounters were rare (<2% of locations). Hence, direct interactions between neighboring foxes may be relatively unimportant for maintaining established territories. However, 2 male mated kit foxes trespassed into neighboring territories during the breeding season, probably in search of extra-pair copulations.

Predation on mule deer (Odocoileus hemionus) by mountain lions (Puma concolor) and coyotes (Canis latrans) was examined to test effects of hunting style and body size, and for mountain lions reproductive status, on selection of prey. Mountain lions, which hunt by stalking, selected ≤1-year-old mule deer as prey. Body condition of mule deer did not affect prey selection by coyotes or mountain lions, and both predators preyed upon females and older adult deer more often than expected based on the percentage of these groups in the population. Female mountain lions selected female deer, but male mountain lions did not. Female mountain lions without offspring, however, did not differ from male mountain lions in prey selection. Coyotes did not select for young deer. Female mountain lions with kittens were selective for young deer in late summer.

Why do sexes of polygynous ruminants segregate spatially outside the mating season? Existing hypotheses for differences in niche partitioning among species are not sufficient to explain temporal patterns of segregation and aggregation between sexes. Moreover, other hypotheses, including risk of predation, do not explain why females of some species inhabit sites with higher-quality forage while segregated from males, although competitive exclusion of males by females has been proposed. We offer a new hypothesis to explain this conundrum in sexually dimorphic deer (Cervidae) based on an allometric model of metabolic requirements, minimal food quality, and digestive retention. The model predicts that male deer consume abundant forages high in fiber because ruminal capacity prolongs retention and permits greater use of fiber for energy than in nonpregnant females. Low density of animals, high abundance of food, and adaptations of ruminal microflora keep large males on fibrous forages until quantity of food declines. Compared with males, smaller-bodied females are better suited to postruminal digestion of food, especially when intakes increase concomitantly with requirements for energy and protein during reproduction. High demands for absorption of nutrients during lactation and growth stimulate investment in intestinal and hepatic tissue in females, increasing the cost of maintenance and reinforcing differential use of habitats and forages when sexes are segregated. This new model explains sexual segregation without invoking predation or competitive exclusion of males by females.

We present a synthesis of diet information for all 78 species of extant African Bovidae (excluding goats and sheep), based on an extensive survey of the literature. We compiled data on food types (percentages of fruits, dicotelydons, and monocotyledons), seasonal and geographic variability, and body mass. Information reported in the literature was evaluated critically to assess its reliability. We performed cluster analyses to identify 6 discrete dietary strategies: frugivores, browsers, generalists, browser–grazer intermediates, variable grazers, and obligate grazers. We identified a positive correlation between an increase in the proportion of monocots in the diet and body mass, and a negative correlation between increases in proportions of dicots and fruits and body mass. We found some degree of correspondence between taxonomic groupings and dietary strategies. Species in the tribes Alcelaphini, Hippotragini, and Reduncini have high proportions of monocots in their diets. Cephalophini, with the exception of Sylvicapra, are frugivores. Tragelaphini and Neotragini, with the exception of Ourebia, have diets that include high proportions of dicots.

We studied effects of forest fragmentation on 15 species of small mammals, including 6 species of forest-dwelling granivorous rodents, in the Indian Pine watershed of west-central Indiana. Presence–absence and population densities of small mammals were assessed in spring in 35 woodlots of various sizes (0.1–150 ha) and 2 continuous forest sites (>1,000 ha) using live traps in 1992–1996. Presence–absence and population density were related to landscape attributes using logistic and multiple linear regression models, respectively. Species richness of forest-dwelling small mammals increased with area and was highest in continuous forest sites. Nested subsets of the full complement of species were found in smaller woodlots. White-footed mice (Peromyscus leucopus) were ubiquitous, and eastern chipmunks (Tamias striatus) were nearly ubiquitous across the landscape; densities of both species were related inversely to forested area. Fox squirrels (Sciurus niger) were found at 84% of study sites, and they did not respond negatively to isolation of forest patches. Red squirrels (Tamiasciurus hudsonicus) were unevenly distributed across the landscape and were found most often in woodlots with large core areas and simple shapes, possibly indicating sensitivity to edge. Southern flying squirrels (Glaucomys volans) and gray squirrels (S. carolinensis) were restricted to continuous forest sites and >4.6-ha woodlots adjacent to other wooded habitat. Species of small mammals differ appreciably in their sensitivities to agriculturally induced fragmentation of forests. Interspecific differences within this assemblage were not due solely, or even primarily, to body size. Rather, differential responses of species to fragmentation likely resulted from variation in habitat breadth and ability to move through an agricultural matrix.

Coarse woody debris, which includes fallen logs, snags, and stumps, may be an important habitat component for many mammals. I examined use of woody debris by the cotton mouse (Peromyscus gossypinus) with radiotelemetry and fluorescent-powder tracking in a managed loblolly pine (Pinus taeda) forest. Most day refuges of cotton mice were associated with woody debris, including refuges in rotting stumps (69%), under upturned root boles (14%), and under fallen logs and brush (9%). Stumps used by cotton mice were larger in diameter (P < 0.05) and more highly decomposed (P < 0.001) than stumps randomly selected at the study area. Nighttime telemetry locations of 4 of 8 cotton mice were closer to large (10 cm diameter) fallen logs than expected by chance (P < 0.05), whereas locations of no mice were farther from logs than expected. Pathways of cotton mice crossed woody debris (including logs of all sizes) for a greater distance than random transects at the study area (P < 0.05). Logs used by powder-tracked mice were longer than randomly selected logs (P < 0.01). Extensive and selective use suggests that woody debris, particularly in the form of large logs and stumps, is an important habitat component for the cotton mouse in southeastern pine forests.

We used mark–recapture and removal trapping during 37 months to examine structure of small-mammal assemblages in agricultural and pastoral areas on the western llanos of Venezuela. Among 34 sites sampled, species richness, diversity, population densities, and relative contribution to the assemblage by 10 rodent and 3 marsupial species varied by habitat or land-use category, major vegetative formation, and (within agricultural systems) crop species. Most habitat types, especially relatively uniform areas of mechanized agriculture, were numerically dominated by 2 rodents, Sigmodon alstoni and Zygodontomys brevicauda. Subsistence agriculture plots were more variable and had the highest species richness and diversity. Peridomestic habitats were dominated by Rattus rattus. In contrast to findings in agroecosystems in the United States and Argentina, relative densities were not lower in crop fields than in adjacent borders nor were there differences in the structure of the rodent assemblages. Captures of Heteromys anomalus, Oecomys speciosus, and Oecomys trinitatus document range extensions for these species on the western llanos.

We used cafeteria-style feeding trials with 8 types of mast in various combinations to examine differences in resource selection among 5 syntopic species of granivorous forest rodents in west-central Indiana. Patterns of resource selection corresponded to differences in phylogeny and body size of granivores, with greatest similarities among closely related species of similar body size. Breadth of resource use varied inversely with body size in our trials. Resource selection by Sciurus carolinensis, S. niger, and Tamiasciurus hudsonicus was correlated positively with caloric and lipid content of mast and its size, whereas selection by Glaucomys volans was correlated negatively with the percentage of protective tissue associated with seeds. Laboratory trials indicated that T. hudsonicus and G. volans discriminate among mast of comparable physical and chemical composition on the basis of size, with a preference for larger seeds. Contrary to our expectations, T. hudsonicus, a recent immigrant from the boreal forest, did not exhibit a preference for seeds of red pine (Pinus resinosa) relative to mast of hardwood species. G. volans and Peromyscus leucopus tended to consume perishable white oak acorns immediately and to cache a substantial portion of less perishable seeds of nonpreferred species. Our results demonstrate the potential for considerable overlap in resource use among members of this guild. Guild members also seem to be affected differentially by physical and chemical properties of mast, and patterns of resource selection reflect contrasting foraging constraints under which these animals operate.

Fecal pellets collected from 10 small-mammal species captured in a Panamanian cloud forest were examined for presence of spores of arbuscular mycorrhizal fungi. Fifty-two percent of the 94 fecal samples examined contained spores of ≥1 of 6 arbuscular mycorrhizal fungi species, including Sclerocystis coremioides, Glomus fasciculatum, G. rubiforme, G. geosporum, and 2 unidentified Glomus species. G. fasciculatum was the most frequently encountered species, occurring in 87% of the fecal samples that contained spores and occurring in diets of 7 small-mammal species occupying terrestrial and arboreal habitats. Peromyscus mexicanus and Oryzomys devius frequently consumed arbuscular mycorrhizal fungi and may be important spore dispersers in terrestrial habitats. Arbuscular mycorrhizal fungal spores also were common in diets of the primarily arboreal rodent Reithrodontomys mexicanus, suggesting a potentially important role of this species in the dispersal of arbuscular mycorrhizal fungal spores to epiphytes of Neotropical cloud forests.

Timing of activity, seasonal changes in food availability, environmental fluctuations, and costs of reproduction are important determinants of an animal's life history. In mountain ground squirrels (Spermophilus), the shortness of the active season influences how they time their activities. I studied timing of the active season, reproduction, and weight loss during hibernation in Columbian ground squirrels (S. columbianus) in Alberta, Canada, from the summer of 1994 to the spring of 1998. Entry into hibernation and emergence from hibernation the following year were earlier for females that did not wean a litter compared with those that did. The active season was shorter and hibernation longer for unsuccessful females than for successful females. Molt of females was earlier when they did not wean a litter than when they did. Date of mating had no influence on success in weaning a litter, but juveniles surviving to yearling age came from litters born earlier than juveniles that did not survive to yearling age. In successfully reproducing females, early entry into hibernation was associated with early mating. Daily and total weight loss during hibernation was higher in females that weaned young than in females that did not wean young.

The American shrew-mole (Neurotrichus gibbsii) seems to occupy an ecological and evolutionary position intermediate to that of shrews and fully fossorial moles. However, because little is known regarding their physiology, we examined the metabolic rate and thermoregulatory competence of 6 shrew-moles exposed to ambient temperatures ranging from 3 to 34°C with flow-through respirometry. The basal rate of metabolism of N. gibbsii (3.94 ml O₂ g⁻¹ h⁻¹; 77.90 J g⁻¹ h⁻¹) was 2.32 times greater than predicted for similar-sized placental mammals and close to that of soricine shrews of comparable mass (10–12 g). Over the entire range of test temperatures, mean body temperature (38.4 ± 0.2°C SE) of this small semiterrestrial talpid was higher and more labile than that of other North American moles but within the range typical for north-temperate soricids. With declining ambient temperatures, shrew-moles exhibited gradual reductions in body temperature and minimal whole-body thermal conductance. In 2 instances, shrew-moles were observed to enter an apparent state of hypometabolism. Whether the observed reductions in body temperature and metabolic rate of Neurotrichus exposed to low ambient temperatures are adaptive energy-conservation mechanisms exhibited during periods of prolonged cool wet weather and food deficits in nature, or simply reflect an inability to proficiently thermoregulate after an extended fast, is currently unknown.

Small mammals in the tropics and subtropics usually rely opportunistically on favorable environmental conditions for breeding rather than base their breeding decision on prediction from photoperiodic cues as most high-latitude species do. Species producing precocial young may be more likely to reproduce aseasonally than species with altricial young. For female wild guinea pigs (Cavia aperea) from Argentina (35°S) that produce extremely precocial young, these hypotheses would predict moderate responsiveness of female reproduction to photoperiod. These predictions were tested in a series of laboratory experiments. Guinea pigs reproduced aseasonally when kept under natural photoperiod and temperatures at Bielefeld (52°01′N, 8°32′E). When given short days (9L:15D) and long days (14L:10D) under indoor temperature conditions (20–23°C), no effect of photoperiod on female reproduction was noted. A shift from long day length (14L:10D) to short day length (9L:15D) did not stop reproduction. Increasing energy expenditure for thermoregulation at low temperature (5°C) under long-day (14L:10D) conditions also did not inhibit reproduction. Wild guinea pigs thus reproduce throughout the year without respect to photoperiod as long as food and temperature conditions allow reproduction.

Previous descriptions of the daily pattern of activity of the unstriped Nile grass rat (Arvicanthis niloticus) conflict. Researchers have described this species as diurnal, nocturnal, or crepuscular. In our laboratory colony, some animals are diurnal and others are nocturnal in running wheels. We systematically examined activity patterns of free-living grass rats in the Masai Mara National Reserve, Kenya, where the animals in our lab originated. Sherman traps were set at dawn or dusk near animal burrow entrances, and the time of capture was recorded for each animal. Seventy-seven A. niloticus were captured 287 times at 20 different sites. Captures occurred almost exclusively during daylight. In contrast, other small mammals that were trapped on 49 occasions were caught exclusively at night. The temporal pattern of capture of A. niloticus did not vary as a function of age or sex. The diurnal pattern of activity we observed in A. niloticus is unusual among small rodents.

Paternal behavior of the volcano mouse (Neotomodon alstoni) was studied and its role in the care of young compared with that of the female. Paternal behavior of this rodent under laboratory conditions consisted of direct and indirect activities, such as huddling, grooming, sniffing, and retrieving young as well as maintenance and vigilance of the nest. The male volcano mouse exhibited all components of parental behavior displayed by mothers, except suckling. However, the male participated significantly more than the female in huddling, grooming, and sniffing. The existence of paternal behavior in this rodent suggests that under natural conditions this species exhibits a monogamous mating system because monogamy in rodents is often associated with paternal care.

The lesser white-toothed shrew (Crocidura suaveolens) is a common but infrequently studied small insectivore. Because of difficulty in conducting direct observations in nature on the social behavior of this species, we designed a laboratory study to evaluate its social organization. We conducted encounters between strange pairs of shrews, simulating such interactions in the wild, in neutral sites, or between “resident” and “intruder” shrews. The effect of familiarity was tested by observing encounters between the same pairs immediately after the encounter and 24 h later. Sexual conflict was observed between male and female shrews, with males trying to mount females during the initial encounters and intensive female agonistic behavior toward the males. In addition, whereas males were equally aggressive to both sexes, female aggression toward another female was rarely observed. Familiarity between the pair resulted in decreased levels of aggression and increased tendency to spend time with the opponent regardless of its sex. We suggest that sexual differences in behavior of shrews result from differences in breeding strategies: males attempt to mate with the maximum number of females, and females try to establish long-term relationships with specific males. Long-term familiarity maximizes the pair bond, maximizes the female's reproductive success, and may allow free access of females to food resources in stable overlapping home ranges of males prior to parturition.