We documented the breeding frequency of 25 wild female short-beaked echidnas, Tachyglossus aculeatus multiaculeatus, fate of young, and recruitment of subadults into a population over a 7-year period. Echidnas had 1 annual breeding period with courtship lasting 7–37 days. Females monitored were observed to mate only once per breeding season with 1 male. All females that mated produced a single fertile egg 23 days ± 1 SE after mating. Frequency of reproduction differed among individuals and years. Number of young hatched each season varied between 1 and 9. A total of 22 hatchlings was produced by 17 different females between 1990 and 1996. Seven young died before weaning, 8 were known to survive to weaning, and the fates of the remaining 7 were unknown. Number of new subadults found in the study site was comparable with the number of young known to have been produced each year.

A new species (Muridae, Sigmodontinae, Phyllotini), belonging to a new genus, is described on the basis of 2 specimens from 1 locality in the mountain forests of southeastern Bolivia. Diagnostic features are posteriorly divergent edges of supraorbital region, large and hypsodont molar teeth with somewhat prismatic pattern, and anterior zygomatic process not projecting as an overhanging point. The diploid chromosome number is 56 and the fundamental number is 76. Other external, cranial, dental, and karyologic characters in the tribe and new taxon are described, illustrated, and discussed. The hypothesized phylogenetic placement of the new genus based on gene-sequence, chromosomal, and morphologic data is presented relative to evolutionary relationships of selected phyllotine taxa.

We describe an extinct murid, assigned to the tribe Phyllotini, from the late Pleistocene (Tafí del Valle Formation) of La Angostura (26°55′30″S, 65°41′50″W; 1,900 m elevation) in northwestern Tucumán Province, Argentina. The new genus is characterized by very hypsodont molars with flat crowns and simplified occlusal structure, upper incisors with a mediolateral groove, a straight premaxillary–maxillary suture, and high zygomatic plate with a small spine on its anterodorsal edge. Phylogenetic analyses including fossil and living members of the Reithrodon group show that the new genus is the sister taxon to the Reithrodon–Neotomys–Euneomys clade. The paleoenvironmental and paleogeographic significance of the new genus is discussed within the context of the climatic changes that occurred during the late Pleistocene in southern South America. The new phyllotine would have lived in high-elevation grasslands, which today occur >1,000 m higher under cold and dry climatic conditions than those of the last glacial maximum.

We provide new data on the karyologic patterns of the Andean rodents Aepeomys and Thomasomys, including the 1st karyotypic description of A. lugens and T. vestitus. Two differentiated chromosomal formulae were found for Aepeomys in Venezuela; they are a diploid chromosome number (2n) = 28, fundamental number (FN) = 48 karyotype corresponding to A. lugens and a 2n = 44; FN = 46 karyotype for an unnamed population (Aepeomys sp.). According to the structure of these 2 karyotypes and the distribution of constitutive heterochromatin (scarce and restricted to a few chromosomes in A. lugens versus abundant and scattered among chromosomes in Aepeomys sp.), we suggest that Aepeomys sp. is a more primitive form than A. lugens. T. laniger and T. vestitus showed karyotypes of 2n = 42, FN = 40 and 2n = 44, FN = 42, respectively; the latter has an additional pair of small-sized metacentric chromosomes and an acrocentric X chromosome (metacentric in T. laniger). Our results suggest that Aepeomys and Thomasomys are closely related taxa in terms of their karyologic patterns.

From September 1996 to May 1997, 187 wild house mice (Mus domesticus) were fitted with radiotransmitters at an agricultural site in the wheatlands of northwestern Victoria, Australia, to examine movements and social organization. Males had slightly larger home-range areas than females. Home-range size was highly variable (0.0002–8.024 ha) but could not be predicted from body size or body condition in males and females, or by whether females were breeding. Mice were site-attached during the breeding season, with extensive intersexual overlap of home ranges but variable intrasexual overlap. Home ranges were significantly larger during the nonbreeding season compared with the breeding season. Evidence existed for exclusive home-range use by females at all densities of mice, low to moderate home-range overlap for males when densities were low and increasing, and an apparent switch to a more gregarious phase in male mice when the breeding season ceased and densities were high. Nonbreeding mice seemed to be nomadic when densities were low, which is consistent with an earlier study of home ranges and social organization of mice on the Darling Downs, Queensland.

We studied microhabitat use by Proechimys semispinosus (Central American spiny rat) by livetrapping along transects in 5 forested sites in central Panama. Microhabitat was quantified by measuring 14 variables at each sampling station. Relative abundance of P. semispinosus was 1.86 individuals/100 station-nights, which was typical of abundances of this species and other members of the genus. Spiny rats were distributed throughout sampled microhabitat space defined by factor analysis of 14 variables. We used logistic regression analysis to relate presence–absence at trap stations to microhabitat structure. Variables describing disturbed and younger forest were strong predictors of presence at trap stations. Associations of P. semispinosus with younger forest (smaller trees and lianas and lower canopies) and treefall gaps within older forest may have implications for regeneration of local forest patches through the activities of these rodents as seed predators and dispersers of seeds and arbuscular mycorrhizal fungi spores.

This study reports results of a 14-month live-trap study of small-rodent communities in 2 habitats, cloud forest and disturbed areas, at Las Joyas Scientific Station of the Sierra de Manantlán Biosphere Reserve, western Mexico. Seven taxa of 2 families (Muridae, Heteromyidae) of small rodents were captured (Hodomys alleni, Liomys pictus, Oryzomys couesi, Peromyscus aztecus, Reithrodontomys fulvescens, R. sumichrasti, and Sigmodon alleni). Information about age structure, population dynamics, biomass, and reproduction were obtained with mark–recapture techniques for the most abundant species (P. aztecus and R. fulvescens) in both habitats. These species comprised 80.3% of the 707 captures in the cloud forest (P. aztecus, 51.2%; R. fulvescens, 29.1%), whereas, in the disturbed areas, R. fulvescens represented 81.7% of the 916 captures. Species varied in population density, relative abundance, and timing of reproduction, which was seasonal. Reproductive activity for P. aztecus peaked in the middle of the wet season (September 1995) in the cloud forest and in the wet season and middle of the dry-cold season (January 1996) in the disturbed areas. R. fulvescens showed reproductive activity in the wet season (July–October 1995) in both habitats. Density fluctuated annually for P. aztecus in both habitats, with a peak in January and February 1996; R. fulvescens showed the same patterns of density in both habitats with the highest values at the end of the wet season.

The plains pocket gopher (Geomys bursarius) is a fossorial rodent noted for having a wide range of pelage colors that tend to match the color of soil in which it lives. This phenomenon is considered adaptive as concealing coloration. If being well camouflaged is advantageous, then natural selection should favor a pelage color that specifically matches the color of soil that surrounds pocket gophers when they are most often exposed to the surface. We tested the hypothesis that dorsal coloration of G. bursarius matches color of moist, freshly excavated soil from its burrow more closely than color of drier soils that surround newly formed mounds. Our study examined 5 subspecies that live in soils having different colors (black, dark brown, reddish brown, yellowish brown, and white). The degree of cryptic coloration was quantified using methods that do not reflect biases of color perception by humans. At all locations, color of the pocket gophers' heads was closer to color of dark moist soil than to the color of pale dry soil. The same was true for their backs, except for a brown individual from the black soils of Illinois.

Diversity of species in communities of heteromyid rodents presents a classic problem to ecologists, because species are similar ecologically and share a limiting seed resource. Mechanisms of coexistence considered to date have focused on interspecific variation in ability to exploit heterogeneity in resources caused by environmental factors. An unexplored possibility is that coexistence is promoted by heterogeneity among species in seed-caching behavior. To begin evaluating this possibility, we asked whether coexisting species differ in their propensity to cache and in types of caches made. In an indoor arena, we presented millet seeds to 8 species of kangaroo rats (Dipodomys) and pocket mice (Perognathus and Chaetodipus) from 2 communities, 1 in California and 1 in Arizona. Species within communities differed in amounts of seed consumed and cached per night. Both consumption and caching increased with body mass in a manner similar to whole-animal metabolic rate, suggesting that energetics underlie food storage behaviors. Species also differed significantly in propensity to cache in the home burrow (larderhoard) versus in small depots outside the burrow (scatterhoard); scatterhoarding increased with body mass. Kangaroo rats scatterhoarded proportionally more than sympatric pocket mice, and species from California tended to scatterhoard more than those of similar body size from Arizona. These interspecific differences are consistent with the possibility that caching promotes coexistence. Our results appear to contradict those from a similar study of heteromyid caching behavior that used a different protocol for presenting seeds. This discrepancy underscores the importance of understanding the extent to which caching behavior is sensitive to details of experimental protocol or animal state and of moving experimental caching studies into more natural situations.

Fossils of the Heteromyidae usually are distinguished using quantitative dental characters because of a lack of diagnostic qualitative characters. However, utility of these characters in addressing taxonomic questions is unclear. Teeth of 19 extant species of kangaroo rats (Dipodomys) were measured to determine if quantitative characters provided reliable separation of taxa and to what extent morphometric analyses revealed meaningful higher level relationships. A discriminant analysis correctly allocated >70% of specimens to their a priori species groups. Dimensions that were best able to separate taxa, as judged from a canonical variate analysis, were lengths of premolars and 1st lower molar. Squared Mahalanobis distances, canonical variate analysis, principal component analysis, cluster analysis, and minimum spanning trees supported morphological groupings including: D. nelsoni and D. spectabilis; D. compactus and D. ordii; D. merriami and D. nitratoides; and the 5 species D. agilis, D. heermanni, D. panamintinus, D. simulans, and D. stephensi. D. deserti and D. elator differed in their dental morphology from all other taxa. Overall, results closely paralleled those of previous workers, suggesting that quantitative dental characters can reliably distinguish heteromyid taxa and perhaps help elucidate higher level taxonomic relationships.

Archaeocete whales of the subfamily Dorudontinae (Cetacea, Basilosauridae) show strong evidence of having replaced upper and lower 1st deciduous premolars with permanent teeth late in their dental eruption sequence. This situation is rare in modern mammals, many of which have no teeth in the 1st premolar position or which retain a deciduous tooth in the 1st premolar position that is not replaced. Evidence for replacement of deciduous 1st premolars in dorudontine archaeocetes comes from both juvenile and adult specimens of Dorudon atrox from Egypt and Zygorhiza kochii from North America. Replacement of deciduous 1st premolars by permanent teeth may have been precipitated by a general delay in skeletal maturation found in cetaceans, which allowed dental development to proceed for a longer period of time than is generally available for most mammals.

Bacula are relatively small in terrestrially mating species of pinnipeds (otariids and elephant seals, Mirounga), perhaps reflecting adaptive size reduction to minimize bacular fracture. Fur seals and sea lions (Otariidae) are a good group with which to investigate this question, because most species copulate solely on land and body size varies interspecifically. We studied bacular size and relative growth in the largest extant otariid, the Steller sea lion (Eumetopias jubatus). Bacula roughly tripled in length and increased 30-fold in mass between 1 and 8 years of age. Allometric relationships changed over development; bacular length and mass changed from being initially positively allometric to body length to negatively allometric and isometric, respectively; bacular mass and thickness were positively allometric to body length throughout life, and apical growth was isometric then was positively allometric to bacular length. In adults (>7 years of age), bacula averaged 18.1 cm length (6.2% of body length), 36.7 g mass, and 2.02 g/cm density (mass : length). The baculum of Eumetopias is about the same length relative to body length as in other adult male otariids but is about twice the density, presumably to increase strength. Information on small or aquatically mating species of otariid are needed to extend our findings and interpretations.

Univariate and multivariate statistical methods were used to examine geographic variation in skull and horn characters of 694 bighorn sheep (Ovis canadensis) specimens from the Great Basin north to British Columbia and Alberta to test previous taxonomic hypotheses. Substantially more morphometric variation in skull and horn size and shape was found west of the Rocky Mountains than within the Rocky Mountains. Our results did not support the recognition of Audubon's bighorn sheep (O. c. auduboni) as a subspecies separate from Rocky Mountain bighorn sheep (O. c. canadensis). California bighorn sheep (O. c. californiana) from Washington and British Columbia were not distinguishable from Rocky Mountain bighorn sheep but differed notably from populations in the Sierra Nevada considered part of that subspecies. Extirpated native populations from northeastern California, Oregon, and southwestern Idaho, also considered to be O. c. californiana, shared with Nelson bighorn sheep (O. c. nelsoni) from the Great Basin desert a horn-related character that distinguished them from Rocky Mountain bighorn sheep. Bighorn sheep from the Sierra Nevada were found to be distinguishable from those of the adjacent Great Basin region. Our morphometric results were concordant in geographic patterns with mtDNA data. We synonymize O. c. auduboni with O. c. canadensis. We also assign extant and extinct native populations of O. c. californiana from British Columbia and Washington to O. c. canadensis. Finally, we assign the extinct native populations of O. c. californiana from Oregon, southwestern Idaho, northern Nevada, and northeastern California to the Great Basin Desert form of O. c. nelsoni, recognizing that some transition to Rocky Mountain bighorn sheep probably occurred along that northern boundary. With these taxonomic revisions, the range of O. c. californiana includes only the central and southern Sierra Nevada.

We studied survival of 220 calves of radiocollared moose (Alces alces) from parturition to the end of July in southcentral Alaska from 1994 to 1997. Prior studies established that predation by brown bears (Ursus arctos) was the primary cause of mortality of moose calves in the region. Our objectives were to characterize vulnerability of moose calves to predation as influenced by age, date, snow depths, and previous reproductive success of the mother. We also tested the hypothesis that survival of twin moose calves was independent and identical to that of single calves. Survival of moose calves from parturition through July was 0.27 ± 0.03 SE, and their daily rate of mortality declined at a near constant rate with age in that period. Mean annual survival was 0.22 ± 0.03 SE. Previous winter's snow depths or survival of the mother's previous calf was not related to neonatal survival. Selection for early parturition was evidenced in the 4 years of study by a 6.3% increase in the hazard of death with each daily increase in parturition date. Although there was no significant difference in survival of twin and single moose calves, most twins that died disappeared together during the first 15 days after birth and independently thereafter, suggesting that predators usually killed both when encountered up to that age.

Temporal distributions of matings and births were studied in a feral population of Bizet sheep (Ovis aries) introduced to Ile Longue in the subantarctic Kerguelen Archipelago. Two rutting peaks occurred each year, in summer and winter. Most births occurred in winter, a period that was not favorable for the survival of young. Lambs born in midsummer also were born too late with regard to the most favorable period in spring. Individual ewes did not consistently breed in 1 season but switched from summer to winter breeding. Regardless of whether they were lactating or nonlactating in summer, almost 70% of females gave birth the subsequent winter. Only 25% of females observed in winter (lactating or nonlactating) also lactated in summer. Differential fertility and reproductive success may be due to seasonal variation in body mass. Females were heavier in summer than winter. The biannual reproductive cycle also may result from the early reproductive history of ewes. Sexual maturity occurred earlier for the winter compared with the summer cohort. Therefore, most females of both cohorts gave birth for the first time in winter. Our results reveal that feral domestic animals will not always quickly adapt to different environmental conditions.

We examined genetic variability and spatial heterogeneity of maternally (mtDNA) and biparentally (allozymes) inherited genes for a large, widely distributed mammal. White-tailed deer (Odocoileus virginianus) in 6 populations from the coastal plain in Georgia and South Carolina showed high levels of variability and spatial heterogeneity for mtDNA and allozymes. There was little sharing of mtDNA variants among samples separated by 30 to 100 km, and 12 of 13 allozyme loci showed significant differentiation among populations. Spatial genetic heterogeneity was positively correlated with geographical distance as predicted in Wright's isolation by distance model. High spatial heterogeneity is surprising considering the species' physical capacity for moving great distances. Dispersal must be limited, but more so in females because they accounted for only an estimated 13% of total dispersal. Social factors must strongly limit dispersal in white-tailed deer and probably many other mammals.

Because of anthropogenic factors in the early 1900s that caused populations to decline dramatically, wolverines (Gulo gulo) currently are designated as endangered in eastern Canada and classified as vulnerable throughout the Holarctic Region by the International Union for Conservation of Nature and Natural Resources. Although numerous examples exist that illustrate the utility of genetic data for development of conservation plans, no study has investigated the genetic structure of natural populations of wolverines. We assessed allozymic and mitochondrial DNA (mtDNA) variability of wolverines within and among 5 sites from the Northwest Territories, Canada. Five of 46 presumptive allozyme loci were polymorphic. Estimates of heterozygosity (2.6%) and polymorphism (11.6%) were lower than values reported for most mammals but were within the range reported for Carnivora. To evaluate levels of variation in mtDNA, we sequenced the left domain of the control region. Six variable nucleotide sites were observed, resulting in 9 haplotypes of mtDNA. Within-site diversity of haplotypes (h) was high, but within-site diversity of nucleotides (π) was low, indicating little sequence divergence among the 9 haplotypes. Sequence data for mtDNA revealed considerably more genetic partitioning among sites (ϕ_ST = 0.536) than did allozyme data (F_ST = 0.076). Based on fixation indices, gene flow estimates (Nm) were moderate for nuclear markers but low for mtDNA loci. These findings suggest that, although wolverines maintain large home ranges, they exhibit fidelity to discrete areas, gene flow is predominantly male-mediated, and most sites in the Northwest Territories are genetically independent and thus represent populations. Therefore, any conservation plan for wolverines in the Northwest Territories must consider preservation of populations if genetic diversity of this taxon is to be maintained.

Relationships of wolves (Canis lupus) and ungulates were studied in the Polish part of Białowieża Primeval Forest with high densities of prey. The number of wolves ranged from 7 to 19, and the number of packs ranged from 2 to 4. Average densities were 2.3 wolves/100 km². Red deer (Cervus elaphus) was the main prey of wolves. Roe deer (Capreolus capreolus), wild boar (Sus scrofa), moose (Alces alces), and European bison (Bison bonasus) were hunted less than expected based on their abundance. Mean mass of ungulates killed by wolves was 55 kg. Prey were consumed quickly, with 57% of kills completely eaten on the 1st day after killing. Average killing rate by wolves was 0.78 ungulate per wolf pack per day (0.14 prey item per wolf per day). Results of this study combined with the data obtained in the Belarussian part of Białowieża Primeval Forest in 1946–1985 allowed for analysis of dietary response of wolves to changes in densities of ungulates. Wolves showed a response to abundance of red deer. The amount of other ungulates in their diet depended on the densities of red deer. From 1991 to 1996, wolves annually removed 57–105 red deer, 19–38 wild boar, 19–25 roe deer, and 0–2 moose per 100 km². Those amounts were equivalent to 9–13% of spring–summer densities of red deer, 4–8% of wild boar, 3–4% of roe deer, and 0–29% of moose. Additionally, hunters annually harvested 131–140 red deer, 44–114 roe deer, 1–7 moose, and 45–142 wild boar per 100 km². Effects of predation and harvest by hunters on ungulate mortality were likely additive and caused declines in ungulate populations during our study.

We investigated dispersal patterns of San Joaquin kit foxes (Vulpes macrotis mutica) on the Naval Petroleum Reserves, California. Of 209 juvenile kit foxes monitored during 1980–1996, 33% dispersed from their natal territory. Significantly more males (49.4%) than females (23.8%) dispersed, and dispersal peaked in July. Dispersing males tended to be heavier than philopatric males; philopatric females were significantly heavier than dispersing females. Expressed as a percentage of all juveniles monitored, annual dispersal ranged from 0% to 79% for males, 0% to 50% for females, and 0% to 52% for all foxes. Percentage of male dispersal was related weakly to mean annual litter size (r² = 0.27), and percentage of female dispersal was weakly and inversely related to annual indices of small-mammal abundance (r² = 0.46). Most (65.2%) dispersing juveniles died within ≤10 days of leaving their natal range. Survival tended to be higher for dispersing males than for philopatric males but was similar between dispersing and philopatric females. Sixty percent of all foxes that survived to breeding age reproduced except among dispersing females, none of which reproduced. Alloparental care did not account for sex-biased dispersal in kit foxes. Auxiliary adults were observed occasionally with mated pairs, but helping behavior was not observed. Dispersal patterns of kit foxes may be a function of innate sex-biased dispersal altered by physical and biological pressures.

We studied social organization and behavior of arctic foxes (Alopex lagopus) in 3 adjacent territories from 1988 to 1995 in central Norway, where the major rodent prey were cyclic. Twenty-five foxes were equipped with radiotransmitters and several other individuals could be recognized visually. Paired adult foxes and their cubs had home ranges that overlapped more with each other than with neighboring foxes (37% versus 2.9%) and therefore seemed to be territorial. Family composition varied from monogamous pairs, to pairs with additional adults, to an example with 2 reproducing females and 1 male in the same den. Presence of additional family members was independent of the state of the rodent cycle and the reproductive state of the breeding pair. Additional family members contributed only 2% of the food provided to young pups and were therefore not regarded as true helpers. Breeding adults remained resident within the same territory even in years with low abundance of rodents, when they did not breed. All pups left their natal territory by 6 months of age, although some subsequently returned to their natal range or one of the adjacent dens.

Little information is available on growth rates and reproductive effort in microchiropteran bats that breed in temperate areas, are not colonial, and do not hibernate. We measured growth in individual young of the hoary bat, Lasiurus cinereus, a solitary, foliage-roosting, migratory species, and assessed growth rate using changes in forearm length. We tested the prediction that growth is slower in this than in other species because of the less stable thermal environment that adults and juveniles experience. Forearm length and mass of 1-day-old young (X̄ ± SE) were 19.11 ± 0.30 mm and 4.73 ± 0.20 g, respectively. Over 3 years, growth rate of young differed, with young growing slowest (1.14 mm/day) during the coldest year and fastest (1.45 mm/day) during the warmest year. Young were not weaned until 7 weeks of age and nearly 3 weeks after fledging and continued to gain mass over winter. Unlike other species, lactating females did not lose mass through the breeding season. Based on a Levenberg-Marquardt algorithm for nonlinear regression, the growth constant of young hoary bats (0.083 in females) is less than that documented for most other species breeding in temperate North America. Migratory habits of L. cinereus allow adults and young of the year to forage throughout winter and may be associated with slow growth in this species and production of relatively large litters in species of Lasiurus in general.

Discriminant function analysis has been used to assess morphological distinctiveness of putatively different taxa. We used randomizations of previously published morphological data for 2 subspecies of the coyote, Canis latrans frustror and C. l. thamnos, to quantify a recognized but previously unexamined bias in discriminant-function analyses that use resubstitution classification. This bias results in overestimates of intertaxon distinctiveness and is exacerbated when sample sizes are small. An alternative classification technique, jackknife sampling, is relatively unbiased.

Wild-caught deer mice (Peromyscus maniculatus) may harbor the highly pathogenic Sin Nombre hantavirus. Founding of new colonies of deer mice and use of the species indoors require that they first be shown to be free of the virus. We developed a safe and inexpensive outdoor facility for extended quarantine of deer mice. It consists of 34 self-enclosed artificial burrows (nest boxes) contained within a fenced enclosure (20 by 20 m). The nest box used in this study allowed us to maintain juvenile and adult wild-caught Peromyscus successfully for extended periods (≤18 weeks) through fluctuating weather, including heavy rains, snow, and ambient temperatures of −7.6–41.1°C. Nest boxes were effective for protection against predators, and rodents were unable to escape. Outdoor standards for safe handling of wild hantavirus-infected rodents are applicable in this setting rather than those applying to laboratories intended for high-level biological containment. Use of such enclosures should facilitate the use of deer mice as experimental models in general and allow Peromyscus infected with Sin Nombre virus to be experimentally manipulated outside of a biological containment laboratory.

Recent advances in systematics have resulted in the development of statistical approaches to phylogeny estimation and hypothesis testing. We present this emerging statistical perspective, distinguish it from the nonstatistical approach as commonly practiced, and demonstrate its application to 2 systematic proposals from the recent literature on rodents: Mares and Braun's (1996) retention of Andalgalomys contra Steppan (1995) and the conclusion of Engel et al. (1998) that Calomys is a multitribal composite taxon. Systematic arguments and recommendations by Mares and Braun are critiqued in detail. We argue that the statistical approach provides a more objective and powerful basis for evaluating alternative phylogenetic hypotheses and a more stable foundation for nomenclatural decisions.

We respond to Steppan and Sullivan's (2000) critique of the systematic arguments and recommendations presented by Mares and Braun (1996). We argue that a “nonstatistical” approach still has a place in systematics as it is currently practiced. Although useful for hypothesis testing, Steppan and Sullivan's (2000) statistical approach should be used with caution when proposing changes in classification.