This commentary is the text of an oral presentation delivered at the 88th Annual Meeting of the American Society of Mammalogists in Brookings, South Dakota, on 22 June 2008 to recognize receipt of the Joseph Grinnell Award for Excellence in Education in Mammalogy. Much has been written by previous recipients of the Joseph Grinnell Award about the declining interest in natural history and organismic biology in academia and in society in general. In the course of 40 years of university teaching and student advising, as well as field research with students on 5 continents, I too have witnessed this increasing abandonment of the natural world. This phenomenon seems to stem from changes in the early experiences of children and young people over the past 40 years and, thus, I would advance the premise that mammalogy and other branches of natural history begin at home. Three types of learning seem important to the developing mind. First is the time and opportunity for unstructured, unforced exploration of the local environment—time to develop from the inside out rather than merely as a shell coated with a number of intellectual veneers. Second is learning from the example and caring instruction of enthusiastic parents, teachers, and mentors. Third is the transfer of information—from personal experience, reading, teaching, and selectively from a vast array of electronic sources—once again with time for synthesis and contemplation. All 3 types of learning appear to be critical to an appreciation of the natural world. Unfortunately, these processes have been grossly distorted by the loss of outdoor experience, by parental fears and ambitions, and by a kind of electronic idolatry associated with constant entertainment, instant gratification, and virtual relationships. Such an upbringing may affect not only a child's physical and mental health, but his or her future commitment to preserving the natural world as an adult. Published studies of “nature deficit disorder” and “videophilia” now describe this phenomenon and challenge families, schools, and scientific organizations to respond in a timely way.

The substantial body of research on Holarctic ground squirrels amassed over the past century documents considerable variability in morphological, cytogenetic, ecological, and behavioral attributes in the genus Spermophilus F. Cuvier, 1825. Recent molecular phylogenetic studies suggest that the traditionally recognized genera Marmota Blumenbach, 1779 (marmots), Cynomys Rafinesque, 1817 (prairie dogs), and Ammospermophilus Merriam, 1892 (antelope ground squirrels) render Spermophilus paraphyletic, potentially suggesting that multiple generic-level lineages should be credited within Spermophilus. Herein, we recognize 8 genera formerly subsumed in Spermophilus, each of which is morphologically diagnosable, craniometrically distinctive, and recovered as a monophyletic clade in phylogenetic analyses utilizing the mitochondrial gene cytochrome b. Generic-level names are available for each of these ground squirrel assemblages, most of which are exclusively or predominantly North American in distribution (Notocitellus A. H. Howell, 1938; Otospermophilus Brandt, 1844; Callospermophilus Merriam, 1897; Ictidomys J. A. Allen, 1877; Poliocitellus A. H. Howell, 1938; Xerospermophilus Merriam, 1892; and Urocitellus Obolenskij, 1927). Only Spermophilus sensu stricto is restricted to Eurasia. Generic subdivision of Spermophilus more aptly illuminates the taxonomic relationships, ecomorphological disparity, and biogeographic history of Holarctic ground squirrels.

The desert pocket mouse (Chaetodipus penicillatus) comprises 6 nominate subspecies that occupy warm, sandy desert-scrub habitats across the Mojave and Sonoran deserts. The most thorough morphological assessment within the species noted variable levels of distinctiveness, leading to uncertainty regarding the geographic distributions of subspecies. Subsequent genetic assessments using chromosomal, allozymic, and mitochondrial DNA (mtDNA) sequence data detected a general east–west divergence centered on the Colorado River, but few locations were included in these assessments. We investigated phylogeographic structure in C. penicillatus by sequencing regions of mtDNA for 220 individuals from 51 locations representing all continental subspecies. We identify 2 major monophyletic mtDNA lineages (clades) roughly centered in the Mojave and Sonoran deserts. These clades broadly overlap along the Lower Colorado River valley and adjacent desert regions across most of the range of C. p. penicillatus. Outside this zone of mtDNA clade overlap, Sonoran clade haplotypes occur in populations from across the range of C. p. pricei and extend to the northwestern edge of the Sonoran Desert within the southern range of C. p. angustirostris. Northern clade haplotypes occur in populations within the ranges of C. p. sobrinus and C. p. stephensi and in populations from the western Mojave Desert in the northern range of C. p. angustirostris. Based on rough estimates for rates of sequence evolution, divergence among the major clades appears to have occurred during the Pleistocene, but well before the latest glacial maximum. The secondary contact among the major clades appears to have some longevity, with little evidence of recent, postglacial range expansion. We develop ecological niche models (EMNs) for the major lineages of C. penicillatus, and project these models onto reconstructions of climatic conditions during the latest glacial maximum (LGM; 18,000–21,000 years ago). The ENMs for each clade indicate differences in predicted current geographic distributions as well as distributions during the LGM. Models for the LGM indicate broad retention of potential habitat within the area of contact among the major clades. Furthermore, the ENM for the Mojave clade in particular indicates retention of suitable habitat during the LGM in small isolated patches within northern areas, consistent with the haplotype network that supports the perspective that some populations from the Mojave clade were isolated within northern refugia during the last glacial period.

A new genus and 2 new species of erinaceomorph insectivores from the Eocene of Utah are named and described. Both come from Member B of the Uinta Formation, which consists of terrestrially deposited rocks of Early Uintan age. The best specimen consists of dentaries, a few teeth, and several associated elements of the postcranial skeleton; additional dental and postcranial remains also have been recovered. Dentally, the new genus resembles the smaller erinaceomorphs known from earlier in the Rocky Mountain region of North America rather than the contemporary large ones from southern California, indicating that large body size and omnivory evolved independently in different regions of North America during the Eocene. The new genus is primitive in lacking many specializations of the ankle seen in extant erinaceids and other Eocene insectivores. The morphology of the forelimb suggests some digging behavior in having an expanded entepicondyle and the presence of distinct tubercles for insertion of the extensor carpi radialis on the bases of metacarpals II and III. The hind limb exhibits a mosaic of features typical of terrestrial runners, such as anteroposteriorly deep femoral condyles and a deep patellar groove, along with features seen in arboreal climbers, such as a medially and plantarly inflected calcaneal heel. We conclude that the new genus was terrestrial, perhaps moving rapidly over an uneven substrate such as a littered forest floor, but it could probably dig and climb as well.

Colostrum is a special type of milk produced in eutherian mammals during the end of pregnancy and during the 1st few days after birth. It supplies passive immunity to the offspring. The composition of colostrum and mature milk is compared in this study. In species with prenatal passive immunization (humans, baboons, and rabbits), immunoglobulin transfer via colostrum is of little importance and the difference in relative protein concentration between colostrum and mature milk can be small. In ungulates, on the other hand, colostrum has to supply the offspring postnatally with passive immunity and colostrum is relatively rich in immunoglobulin. Large differences between relative protein concentration in colostrum and milk can be observed in ungulates. Compositions of colostrum and milk thus reflect differences in immunoglobulin transfer.

Long-beaked echidnas (Zaglossus), which are endemic to New Guinea, are the largest and least-studied of the 3 extant genera of monotremes. Zaglossus is listed as endangered by the World Conservation Union and data regarding the natural history of long-beaked echidnas are critical to efforts to protect these animals. However, no detailed studies of the ecology of this genus have been published. From 2000 to 2005, I captured 22 Zaglossus bartoni in the Crater Mountain Wildlife Management Area in Simbu Province, Papua New Guinea. Mean body masses for these animals were 6.5 kg ± 1.4 SD (n = 15, range: 4.2–9.1 kg) for adults and 4.3 ± 7.4 kg (n = 6, range: 3.2–5.1 kg) for juveniles. Eleven of the adults captured were followed via radiotelemetry for 1–12 months. The home ranges for these individuals varied in size from 10 to 168 ha. Home-range size was not correlated with body mass, age, or sex. Long-beaked echidna dens were most commonly located in underground burrows, although individual echidnas favored different types of den sites. Mean burrow length was 2.7 m ± 1.8 SD (n = 5, range: 1.3–4.9 m) and mean den depth was 0.48 m ± 7.8 SD (n = 5, range: 0.42–0.57 m) below the soil surface. Animals were never found foraging in daylight. Although no animals were found with eggs or young in the pouch, 1 individual was lactating when captured in April 2002 and again in April 2005. The data generated by this study provide valuable insights into echidna biology that will facilitate efforts to conserve populations of these unusual mammals.

Comparative analyses of the biology of insular and mainland populations of mammals have demonstrated a number of behavioral differences. Individuals from island populations generally have reduced home-range sizes, increased territory overlaps, and reduced aggressiveness with neighbors in comparison to mainland counterparts. We tested the hypothesis that island and mainland populations of the swamp antechinus (Antechinus minimus maritimus), an insectivorous marsupial, will differ in their use of space. We predicted that the home ranges of individuals on an offshore island are smaller and their territory overlaps greater compared to those of antechinus at an adjacent mainland site in southeastern Australia. We used radiotelemetry to measure home-range areas and overlaps, as well as the temporal activity patterns of 40 individuals in the nonbreeding and breeding seasons at island and mainland sites. These dasyurid marsupials were social animals and nested together at both sites, and a high degree of spatial overlap was recorded in both populations. Island individuals occupied significantly smaller home ranges and were mainly nocturnal, whereas mainland individuals were diurnal and had large home ranges. The small home ranges of island individuals may have been in response to increased food resources, resulting from large allochthonous inputs from seabirds. The nocturnality of island animals was likely a predator-avoidance mechanism to evade diurnal raptors in the open tussock grassland.

Nine-banded armadillos (Dasypus novemcinctus) have undergone a dramatic range expansion within the last 150 years, yet few quantitative data are available describing their habitat selection patterns, and only a single population has received the vast majority of research attention in general. Because armadillos may negatively impact native fauna, improved knowledge of their habitat selection patterns is needed to better understand their ecology and improve estimates of their future distribution. We used radiotelemetry to monitor 31 armadillos at a site in southwestern Georgia during 2005–2006. Males and females selected habitats similarly. Armadillos were located farther than expected from mature pine habitats within their home ranges, but individual variation in this measure was high, which we suspect may be a fire-dependent response. Armadillos did not prefer hardwood hammocks, as has been reported for other populations, and we suspect this surprising result may have gone undetected had we not used radiotelemetry. Overall, armadillos did not exhibit much evidence of habitat selection at all. It therefore appears that factors other than habitat type, such as temperature and precipitation, may be more important in determining future armadillo distributions and negative impacts may be more widespread than previously thought.

Multiple factors likely influence natal dispersal behavior of juvenile mammals, which is typically male-biased. Because of their small body size and specific habitat requirements, pygmy rabbits (Brachylagus idahoensis) are expected to exhibit limited dispersal. We predicted that dispersal would be male-biased, that juveniles born later in the year would disperse farther, and that juveniles would be more likely to disperse away from areas of higher habitat saturation. We used radiotelemetry to study dispersal of 61 juvenile pygmy rabbits (31 males and 30 females) from shortly after emergence from natal burrows (April–July) to the beginning of the next breeding season (mid-March) during 2004–2006. Juveniles dispersed before 12 weeks of age, and typically completed dispersal movements within 1 week. Both sexes exhibited a high rate of dispersal (males = 90%; females = 80%); however, juvenile females settled more than 3 times farther from their natal areas than males. Median natal dispersal distances for males and females were 1.0 km (range = 0.03–6.5 km) and 2.9 km (range = 0.02–11.9 km), respectively. Dispersing juveniles crossed gravel roads and perennial streams; however, rabbits tended to initiate dispersal movements away from nearby streams. Mortality rates for male and female juvenile rabbits were 69.2% and 88.5%, respectively, and were highest during the first 2 months after emergence from the natal burrow. We found no evidence that date of emergence, body condition, or habitat saturation influenced dispersal frequency or distance in juvenile pygmy rabbits. Results indicate that pygmy rabbits are capable of dispersing long distances and suggest that their conservation will require land management at broader spatial extents.

Mating behavior and social structure can influence genetic structure within and between populations, yet most studies focus on highly kin-structured, polygynous species. The North American beaver (Castor canadensis) is socially monogamous; however, examination of recent genetic data suggests that this species may be opportunistically promiscuous. We used 7 microsatellite loci to quantify genetic structure within and between 2 beaver populations in Illinois. An analysis of molecular variance revealed significant genetic subdivision among breeding groups in southern Illinois (F_ST = 0.086, P < 0.001), whereas regional genetic subdivision was evident in central Illinois (F_ST = 0.037, P < 0.001). Overall F_ST between populations also was significant (0.068 ± 0.012 SE, P < 0.001). Bayesian clustering assigned individuals from the 2 geographic sampling regions into 2 distinct genetic clusters with 70% of individuals assigned to 1 of the 2 clusters. Migration between populations was low at 0.16 individuals/generation (confidence interval = 0.0079–0.33). Estimates of population subdivision, cluster analysis, and dispersal indicate that these populations are genetically distinct, but are connected by infrequent dispersal.

Using a long-term study of black-tailed prairie dogs (Cynomys ludovicianus), we asked whether subdivision of a subpopulation (colony) into social breeding groups (coteries) influenced gene dynamics. We measured gene dynamics with common statistical tools, F-statistics and effective population size (N_e), but at a finer scale to account for coteries. We used 2 methods of estimating the gene dynamics of subgroups, and determined if these methods produced similar results that were congruent with an empirical measure of the observed effective population size (N_eO). Modified F-statistics were estimated from pre- and postdispersal data from pedigrees and allozymes. Both indicated significant genetic substructuring of the colony subpopulation into coterie breeding groups. The rate of inbreeding of individuals relative to the coterie lineage indicated lower than expected inbreeding at the coterie level. Inbreeding of individuals relative to the colony was consistent with random mating. Asymptotic effective size estimates varied substantially. Chesser's method produced estimates of 77 (range 69–90, pedigree) and 86 (range 70–111, allozyme) individuals consistent with the N_eO of 76 and previous empirical estimates of the instantaneous asymptotic effective size from pedigrees (92.9). Nunney's method produced much lower estimates of approximately one-half the N_eO. Social subdivisions of the colony into coteries clearly influenced gene dynamics. Only the Chesser method accounted for genetic structure introduced by genealogy, both from polygynous mating and matrilines of philopatric females. This may prove important when estimating the rate of loss of genetic variation in highly social mammals.

Characterizing habitat associations of species is fundamental to understanding the mechanistic basis of community organization. Typically, investigators estimate microhabitat characteristics that account for significant amounts of variation in species composition. Nonetheless, highly resolved microhabitat characteristics may account for no more variation in species composition than coarse macrohabitat distinctions, particularly in heterogeneous environments. We describe micro- and macrohabitat associations of 13 species of nocturnal rodents distributed across 31 communities within the Mojave Desert. Rodent species composition, biomass of 81 perennial plant species, representation of 9 soil and rock classes, and the percent cover of annuals and grasses were quantified. Communities also were assigned to macrohabitats based on qualitative characteristics. Multivariate analysis of variance indicated highly significant community-wide differences among macrohabitats and species-specific analyses of variance substantiated differences for all but 1 species analyzed. Microhabitat characteristics accounted for approximately 55% of the variation in rodent species composition. Moreover, microhabitat characteristics accounted for 17% variation in rodent species composition over and beyond that shared with macrohabitat distinctions. Micro- and macrohabitat perspectives provide complimentary insights into species composition of rodent communities. Edaphic features in particular represented important environmental heterogeneity that likely acts both directly on rodent species composition and indirectly through influencing variation in plant species composition. Indeed, the Mojave Desert is represented by a spatial mosaic of species-rich and compositionally dynamic rodent communities that will provide many insights into the coexistence of species at regional spatial scales.

We tested the hypothesis that microhabitat variables, abundance of terrestrial rodents, and microhabitat selection patterns of terrestrial rodents vary between the cool-dry and warm-wet season in the Atlantic forest of Brazil. We selected variables associated with ecological factors potentially important to terrestrial rodents (physical structure of litter and woody debris, and arthropod availability) and established 25 small, independent sampling units covering 36 ha of a homogenous, mature Atlantic forest patch. Litter humidity and height, amount of small woody debris, arthropod availability, and terrestrial rodent abundance increased, whereas the quantity of large woody debris decreased in the warm-wet season. Greater spatial segregation among terrestrial rodents also was observed in this season, especially between morphologically similar species. The distribution of 3 of the 4 most common terrestrial rodents was influenced by microhabitat variables in at least 1 of the seasons, and these species also differed in their pattern of microhabitat selection between seasons. In general, the amount of small woody debris and litter humidity were more important for the microscale distribution of terrestrial rodents in the cool-dry season, whereas in the mild warm-wet season species distributions were associated with food availability or were not clearly influenced by the measured variables. The patterns of microhabitat selection by 3 common terrestrial rodents, which were associated with features that characterize old-growth forest, may be responsible for their vulnerability to forest fragmentation.

The effects of food availability on immune function of gray red-backed voles (Myodes rufocanus) exposed to low temperature (5°C) were examined under a short photoperiod (10L:14D). Twenty-seven voles, caught in the wild, were evenly divided into 3 groups adjusted for sample size, body mass, and sex ratio. Among the 3 food-manipulation groups (food control, food addition, and food restriction), the food-added group displayed enhanced immune response. In contrast, the food-restricted group displayed weakened immune response and the lowest body mass. Kidneys, hearts, and livers of food-restricted voles were significantly hypertrophied in comparison with food-control voles and food-added voles. Therefore, food limitation (quality and quantity) may cause a reduction in immune function and body mass at low temperature on short photoperiods because of maximum expenditure of acquired resources for thermoregulation and maintenance of body condition and, consequently, may induce higher mortality during cold and long winters.

Female and male cervids often use different habitats, and patterns of habitat selection and space use by the sexes may be influenced in part by selection of different forage resources. We tested the hypothesis that female and male ruminants select habitats that differ with respect to quality and abundance of forage by evaluating sex-specific responses of North American elk (Cervus elaphus) to an experimental fuels-reduction program at the Starkey Experimental Forest and Range (Starkey) in northeastern Oregon. From 2001 to 2003, 26 stands of true fir (Abies) and Douglas-fir (Pseudotsuga menziesii) were mechanically thinned and burned, whereas 27 similar stands were left untreated to serve as controls. We used measured differences in forage quality and quantity to predict sex-specific responses to this habitat manipulation. We compared seasonal patterns of habitat selection between the sexes using locations from 48 female and 14 male elk collected during daily periods of peak foraging activity during spring and summer of 2005 and 2006. During spring, females selected 4-year-old burns and used 2- and 3-year-old burns in proportion to their availability, whereas males avoided all fire-treated stands. In addition, control stands were avoided by females but selected by males during spring. During summer, control stands were selected and treatment stands either were avoided or used in proportion to their availability by the sexes. Use of treated stands by female and male elk was influenced by different environmental variables across seasons, but mean overlap of utilization distributions between the sexes was higher in summer than spring. These results indicate that although fuels-reduction treatments at Starkey may have increased foraging opportunities for female elk in spring, those treatments likely were of little benefit to male elk.

Knowledge of seasonal movements by pronghorns (Antilocapra americana) within the easternmost extension of sagebrush-steppe communities is limited. Current hypotheses regarding movement patterns suggest that pronghorns initiate seasonal movements in response to severe winter weather, snowfall patterns, spatial and temporal variation in forage abundance, and availability of water. From January 2002 to August 2005, we monitored movements of 76 adult (≥1.5 years) female pronghorns on 2 study areas (Harding and Fall River counties) in western South Dakota. We collected 8,750 visual locations, calculated 204 home ranges, and documented 17 seasonal movements. Eighty-four percent (n = 55) of pronghorns were nonmigratory and 10% (n = 6) were conditional migrators. Mean distance between summer and winter range was 23.1 km (SE = 2.8 km, n = 13). Five adult pronghorns (8%) dispersed a mean distance of 37.6 km (SE = 12.4 km); of which 1 female moved a straight-line distance of 75.0 km. Winter and summer home-range size varied (P < 0.0001) between study sites. Mean 95% adaptive kernel winter and summer home-range size of pronghorns was 55.5 and 19.7 km², respectively, in Harding County and 127.2 and 65.9 km², respectively, in Fall River County. Nonmigratory behavior exhibited by pronghorns was likely associated with minimal snow cover and moderate temperatures during winter 2002–2004. Variation in size of adult seasonal home ranges between sites was likely associated with differences in forage distribution and availability between regions.

Individual differences in body mass exert a major influence on several life-history traits of mammals. We investigated the factors influencing variation in body mass of calves of migratory caribou (Rangifer tarandus) at birth (June, 19 years of data) and in autumn (October, 15 years of data) in the Rivière-aux-Feuilles (Feuilles, 1991–2003) herd and the Rivière-George (George, 1978–2003) herd in Québec and Labrador, Canada. Mass at birth (hereafter, birth mass) did not differ between herds, possibly because part of their winter ranges overlapped. However, Feuilles calves were smaller in autumn than George calves, possibly reflecting differences in summer ranges. The birth mass of calves also varied with year, likely as the outcome of both intrinsic and extrinsic factors. Birth and autumn body mass were influenced positively by habitat quality in June, estimated by the normalized difference vegetation index. The North Atlantic Oscillation of the previous winter was positively correlated with autumn mass of the George calves. Previous winter snowfall was negatively related to the mass of George calves, and daily movement rates in summer were negatively correlated with the mass of calves of both herds in autumn. Birth mass was positively related with productivity in October in the George herd and also with productivity 3 and 4 years later, which corresponds to the beginning of reproduction of females. We suggest that a mechanism of delayed quality effect of the calves could have been involved in the decrease of fall productivity and population size of the George herd.

Parents often face a trade-off between allocating resources to many young with lower survival, or fewer young with higher survival. To examine trade-offs in litter size and juvenile survival in mule deer, and how survival was influenced by the nutritional condition of the female, we compared the survival of 30 twin and singleton mule deer (Odocoileus hemionus) fawns during their 1st summer in eastern Washington. Overall fawn mortality was high (51.6%), especially during the 1st half of the summer (61.3%). Coyote predation caused 58.3% of all identified fawn mortalities. Twin fawns had a risk of dying 2.6 times higher than single fawns, and the difference between twin and singleton survival was most drastic during the first 1.5 months of life. Body fat of females during their last trimester of pregnancy predicted the number of fetuses they were carrying and whether they had at least 1 fawn surviving until the fall, but not the number of fawns surviving. Under these conditions, a litter size of 2 would be considered optimal because mothers giving birth to twins produced an average of 0.92 fawns by fall, whereas mothers producing singles ended up with only 0.75 fawns. However, our model suggested that a population producing only twins would be expected to increase only 4% faster than one producing only singletons.

Large carnivores play a key role in the structuring and dynamics of many ecosystems, yet the factors influencing dynamics of carnivore populations themselves are often poorly understood. Spotted hyenas (Crocuta crocuta) are the most abundant large carnivores in many African ecosystems. We describe demographic patterns in a population of spotted hyenas observed continuously for 15.5 years, and assess the effects of per capita prey availability, interspecific competition, rainfall, anthropogenic disturbance, and disease on 2 key determinants of population dynamics: reproduction and survival. Annual reproduction, survival of juveniles (i.e., recruitment to adulthood), and mortality of adults varied among years of the study. Per capita prey availability and group size both had positive effects on reproduction, whereas interspecific competition with lions had a negative effect. Competition with lions and rainfall both had negative effects on survival of juveniles. We suggest that the negative effect of rainfall on survival may be mediated by increased rates of human–carnivore conflict during periods of heavy rain, although human population size did not influence survival or reproduction directly. Disease had no substantial effect on this hyena population, despite occurrence of at least 2 disease outbreaks among sympatric carnivores during the study. By focusing on demographic processes that determine population growth (i.e., survival and reproduction), this study highlights the importance of both top-down and bottom-up forces acting on populations of large carnivores. These findings also add to a growing literature suggesting that interspecific competition may be more important than previously recognized in the dynamics of populations of large carnivores.

Tigers (Panthera tigris) are endangered wild felids whose elusive nature and naturally low densities make them notoriously difficult to count. We present 7 years of camera trapping, tracking, and observational data on a local tiger population in Chitwan National Park, Nepal, to quantify changes in abundance of demographic groups and to identify underlying causes. Mean abundance in the 100-km² study area was 18 tigers, but there was high variance among years. Transients were generally recorded at low levels, but there were large oscillations in numbers of tiger offspring, driven by infanticide perpetrated by male tigers taking over territories. The number of breeding animals in the study area remained relatively stable, with about 6 breeding females and 1 or 2 breeding males. The high density of breeding adults in Chitwan National Park highlights the region as a potential stronghold for tigers. Concentrating on counting breeding animals increases the power of monitoring programs to detect change over time. An alternative approach is to carry out surveys on a scale large enough to encompass sufficient territories to compensate for the local impacts of periodic turnover of adult males on total abundance.

Crab-eating foxes (Cerdocyon thous) and pampas foxes (Lycalopex gymnocercus) are very similar in body size and food habits, with distributional ranges that overlap extensively in South America. We used camera-trap records of both species obtained at the Iberá Nature Reserve (INR), northeastern Argentina, to test the hypothesis that, when living in sympatry, they reduce competition by using different habitats and by being active at different times. Camera-trap records obtained at 2 additional sites inhabited by only 1 of these species, the Atlantic Forest of Misiones (AF) and Lihué Calel National Park (LCNP), were used to determine the activity patterns of these foxes when living alone. At INR, we set 41 camera-trap stations in 2 habitats (shrubland forest and flooded grassland), and in 2 treatments per habitat (with or without cattle). Three stations also were set in gallery forests. We obtained 540 photographs of crab-eating foxes (289 records) and 175 photographs of pampas foxes (115 records) in 1,521 camera-trap days. At LCNP, 27 camera-trap stations (1,002 camera-trap days) provided 109 records of pampas foxes. At AF, 195 camera-trap stations (11,689 camera-trap days) provided 103 records of crab-eating foxes. At INR, crab-eating foxes were more frequently recorded in forest habitats, whereas pampas foxes preferred opened grasslands. However, both species were found in all habitats and their recording rates were not negatively correlated. At INR, crab-eating foxes were nocturnal, with peaks of activity after dusk and before dawn, a pattern similar to that observed at AF and elsewhere. At INR, pampas foxes showed a peak of activity between 0000 and 0400 h and another between 1000 and 1300 h, a pattern that differed from that observed at LCNP and other places, where the species is mostly nocturnal. At INR, pampas foxes reduced their activity at times when activity of presumably dominant crab-eating foxes was high, which may facilitate their coexistence.

We investigated molar-crown–size variation, sexual dimorphism, and allometry in the black bear (Ursus americanus), using hunter-shot specimens (n = 429) from the island of Newfoundland, and museum specimens from elsewhere in Canada and the continental United States (n = 502). We predicted higher variation in and weaker correlations among molar size in this omnivorous species than in other species of Carnivora with dentition more specialized for carnivory, because of relatively weak normalizing selection on food-processing mechanisms in U. americanus. Molar-size variation in Newfoundland bears (mean coefficient of variation ∼ 5.6%) was intermediate between species of Carnivora with simpler (e.g., pinnipeds) and more complex (e.g., canids) postcanine dentition. There was negligible size variation within the molar teeth, unlike some mammals. Bilateral symmetry was strong, especially in mandibular length (r ∼ 1.0 between left and right sides; r ∼ 0.95 for other mandibular and maxillary variables and molar size); symmetry in molar size was higher than in phocid seals. Size was positively correlated across molars, especially between adjacent (but not occluding) molars; patterns were similar between sexes and geographic regions, and correlation levels did not differ from other species of Carnivora. We also predicted (and found) smaller sexual differences (= 100[(male/female) − 1]) in molar size than in body size, because definitive molar size is attained early in life: differences in molar size averaged ∼5.5% in Newfoundland (higher in continental subsamples), which is less than differences in cranial size (7–9%) or body mass^1/3 (21%). Sexes did not differ in relative molar size. Molar size was mainly isometric or positively allometric to adult body size (using mandibular and maxillary size as proxies).

Brachydelphis mazeasi Muizon, 1988a, from the Pisco Formation (middle Miocene, Peru), is an odontocete originally known from 2 incomplete skulls and a few associated postcranial elements, assigned to the family Pontoporiidae, and to the subfamily Brachydelphininae (= Brachydelphinae) created to include this genus. The holotype is considered here as a juvenile because it has no alveolar septa and presents wide-open cranial sutures. Consequently, some of the diagnostic features actually correspond to juvenile features and are not taxonomically significant. Here we offer a more comprehensive view of the morphology and variation of this taxon with new specimens from both Pisco and Bahía Inglesa formations (late Miocene, Chile). A revision of the original description of the genus, compared to other taxa of the Inioidea clade is provided. Additionally, a comparison by morphometric analysis (geometric and traditional) to Pontoporia blainvillei (living Pontoporiidae) is given. The shape variation of fetal, young, and adult specimens of P. blainvillei was compared to specimens of juvenile and adult B. mazeasi to evaluate ontogenetic, individual, and interspecific variation.