Black bears (Ursus americanus) forage selectively in natural environments. To determine if bears also forage selectively for anthropogenic resources we analyzed data on vehicles broken into by bears from Yosemite National Park, California. We classified vehicles into 9 categories based on their make and model and collected data on use (2001–2007) and availability (2004–2005). From 2001 to 2007 bears broke into 908 vehicles at the following rates: minivan (26.0%), sport–utility vehicle (22.5%), small car (17.1%), sedan (13.7%), truck (11.9%), van (4.2%), sports car (1.7%), coupe (1.7%), and station wagon (1.4%). Only use of minivans (29%) during 2004–2005 was significantly higher than expected (7%). We discuss several competing hypotheses about why bears selected minivans.

An understanding of how top mammalian carnivores respond to urbanization is important for conservation and management of human–wildlife conflicts. Coyotes (Canis latrans) have recently become more prevalent in many metropolitan areas; however, their apparent success is poorly understood. We estimated home-range size and selection of land-use types for coyotes in a heavily urbanized landscape, with a particular focus on responses of coyotes to those parts of the urban landscape with high levels of human development or activity. Mean (± SE) annual home ranges of transient coyotes (X¯  =  26.80 ± 2.95 km²) were larger than those of resident coyotes (X¯  =  4.95 ± 0.34 km²), and home-range size for resident coyotes did not vary among seasons or between age and sex classes. Although most home ranges were associated with natural patches of habitat, there was considerable variation among coyotes, with some home ranges entirely lacking patches of natural habitat. Within home ranges, coyotes typically avoided land-use types associated with human activity (i.e., Residential, Urban Grass, and Urban Land) regardless of coyote characteristics, seasons, and activity periods. Few coyotes were nuisances, and conflicts occurred when coyotes were sick or exposed to wildlife feeding by humans. We found little evidence that coyotes were attracted to areas associated with human activity, despite at times having home ranges located in heavily developed areas.

The competitive dynamics between domestic and native carnivores are poorly studied. We examined competition for food between sympatric populations of free-ranging dogs (Canis familiaris) and Indian foxes (Vulpes bengalensis) through dietary analysis in a protected, dry grassland habitat in central India. We expected significant dietary overlap between dogs and foxes because of clear evidence of interference competition between dogs and foxes in this area. However, dogs subsisted largely on human-derived foods (HDFs) from direct feeding, and scavenging on garbage, crop residue, and livestock carcasses (83% relative occurrence [RO]). Wild-caught foods constituted only 11% RO of the diet of dogs. The majority of the diet of Indian foxes consisted of invertebrates (33% RO), rodents (20% RO), and fruits of Zizyphus (18.5% RO). Indian foxes did not consume HDF, nor did they scavenge from large-mammal carcasses, and included only a small portion of agricultural produce in their diet. The low contribution of HDF and agricultural food sources to the diet of Indian foxes was surprising because this species is a generalist omnivore. Dogs may be preventing foxes from accessing agricultural lands and human-associated foods by interference competition.

The contemporary genetic structure of animal populations is sculpted by past events, including demographic bottlenecks and expansions and movement of animals by humans. In an analysis of microsatellite DNA of black bears (Ursus americanus; n  =  540) across California, we discovered distinct population structure and genetic evidence of 2 historic colonization events. First, genotypes of bears sampled in southern California are most related to those from the Yosemite National Park region and not with spatially intervening populations. Historical records recount the translocation of 28 black bears from the Yosemite National Park area of the central Sierra Nevada to the San Bernardino Mountains in southern California in the 1930s. Second, before colonization of California by Europeans, the Central Coast region was inhabited by the now extinct California grizzly bear (Ursus arctos californiensis), but not black bears. Following an apparent competitive release and range expansion during the past century, black bears now inhabit the Central Coast region of California. Black bears in California's Central Coast display lower genetic diversity (founder effect) and a genetic signature most closely allied with black bears from the southern Sierra Nevada. In both these cases, molecular genetic techniques allowed historical reconstruction of anthropogenic events leading to changes in animal distributions.

The American black bear (Ursus americanus) experienced a significant range contraction during the 19th and 20th centuries due to a variety of anthropogenic factors. Although previous molecular studies of black bears provided insight into historic and contemporary forces shaping phylogeographic patterns, none included black bears from the central part of the species distribution. Understanding the historical aspects of the connectivity and genetic differentiation of black bears in this region is important for proper management and conservation programs, but this understanding is confounded by poorly documented translocation efforts and population expansion. To address these issues, we generated mitochondrial DNA sequence data for 409 black bears from 15 populations in North America. Two sampling localities (Manitoba, Canada, and Minnesota) were source populations for translocation into western Arkansas and Louisiana. Major conclusions from our study include: black bears in western Arkansas were affected genetically by the translocation program; eastern Oklahoma has been repopulated by westward expansion of bears from Arkansas with a mixture of translocated bears and remnant individuals; black bears in Louisiana were not affected genetically by the translocation program; black bears in western Texas and northern Mexico dispersed there from the southeastern United States; and bears in White River National Wildlife Refuge (eastern Arkansas) share closer genetic affinities with U. a. luteolus than they do with the widespread U. a. americanus.

In this report, we provide the 1st phylogenetic assessment of the evolutionary relationships of Platacanthomyidae. This enigmatic family of rodents comprises 2 genera, Platacanthomys and Typhlomys, that are distributed disjunctly in western India and southern Asia, respectively. We analyze sequence data from the nuclear genes encoding the interphotoreceptor retinoid-binding protein (IRBP) and the growth-hormone receptor (GHR) to address the relationships of Typhlomys cinereus to other rodents, with a particular focus on testing whether its evolutionary affinities lie with glirids or muroids. Our results provide compelling evidence that Typhlomys is a muroid and that it represents the earliest split within this clade. We use the resulting phylogeny to explore the origin and evolutionary history of muroid rodents. We conclude that both Myodonta and Muroidea originated in Eurasia and that the 3 earliest divergences within Muroidea were restricted to the Eurasian supercontinent. Moreover, our analyses support the view that global muroid diversity resulted from independent radiations in separate continental regions.

A new species of shrew tenrec (Microgale) is described from the central western and southwestern portion of Madagascar. Based on pelage, morphology, and DNA sequence data, this new species can be readily distinguished from its sister taxon, M. brevicaudata. Mitochondrial DNA (mtDNA) divergences between the 2 species are on par with those observed in other closely related shrew tenrecs, and both taxa are recovered as reciprocally monophyletic haplotype clades. Furthermore, mtDNA sequence obtained from the holotype of Paramicrogale occidentalis confirms that the name occidentalis cannot be assigned to the new taxon and is a junior synonym of M. brevicaudata. Microgale new species and M. brevicaudata have latitudinally overlapping distributions, and although they are not known to occur in direct sympatry, specimens of both species have recently been collected at sites within 50 km of each other on opposite sides of the Soahany River in central western Madagascar. However, the respective distributions of these 2 species, among the most diminutive of Madagascar's endemic terrestrial mammal fauna, suggest that rivers do not serve as significant barriers to dispersal. Historical demographic analysis under a coalescence framework suggests that the northerly distributed M. brevicaudata has experienced a recent population expansion, whereas the new species described herein has undergone a population decline. Little is known about the ecology of Microgale new species, but it lives in dry forest formations. This species is known from sites within several protected areas (Bemaraha and Namoroka), as well as forest parcels currently proposed as new conservation zones. However, toward the southern limit of its known distribution, at the north bank of the Onilahy River, there is continued extensive anthropogenic habitat loss that may warrant future monitoring.

Small mammals are rarely reported from subfossil sites in Madagascar despite their importance for paleoenvironmental reconstruction, especially as it relates to recent ecological changes on the island. We describe the uniquely rich subfossil small mammal fauna from Ankilitelo Cave, southwestern Madagascar. The Ankilitelo fauna is dated to the late Holocene (∼500 years ago), documenting the youngest appearances of the extinct giant lemur taxa Palaeopropithecus, Megaladapis, and Archaeolemur, in association with abundant remains of small vertebrates, including bats, tenrecs, carnivorans, rodents, and primates. The Ankilitelo fauna is composed of 34 mammalian species, making it one of the most diverse Holocene assemblages in Madagascar. The fauna comprises the 1st report of the short-tailed shrew tenrec (Microgale brevicaudata) and the ring-tailed mongoose (Galidia elegans) in southwestern Madagascar. Further, Ankilitelo documents the presence of southwestern species that are rare or that have greatly restricted ranges today, such as Nasolo's shrew tenrec (M. nasoloi), Grandidier's mongoose (Galidictis grandidieri), the narrow-striped mongoose (Mungotictis decemlineata), and the giant jumping rat (Hypogeomys antimena). A simple cause for the unusual small mammal occurrences at Ankilitelo is not obvious. Synergistic interactions between climate change, recent fragmentation and human-initiated degradation of forested habitats, and community-level processes, such as predation, most likely explain the disjunct distributions of the small mammals documented at Ankilitelo.

Ranchers have observed that residual hemorrhage decreases after livestock suffer repeated bites from common vampire bats (Desmodus rotundus). We hypothesized that repeated exposure to the anticoagulants in the bats' saliva generated an immune response. We compared clotting time of blood mixed with Desmodus saliva between individuals of several species of livestock that were regularly exposed to vampire bats (“bat-attacked”) and individuals living where bat predation was not observed (“bat-naïve”). We also compared the bleeding times of domestic sheep following a single defensive bite from a bat, before and after subjecting the animals to a series of feeding bites by Desmodus. Clotting time was significantly shorter in bat-attacked than in bat-naïve livestock. Bleeding time after a provoked defensive bat bite was significantly shorter after sheep were exposed to a series of feeding bites from Desmodus. Bat predation induced increased resistance by the prey against the anticoagulants, suggesting an immune response.

Adult males of the long-nosed bat (Leptonycteris curasoae) produce odoriferous “sebaceous” secretions in the interscapular region (dorsal patch), exclusively during the mating season (November–December). These dorsal patches might play a role in mate selection by L. curasoae in northern Venezuela. We evaluated differences between body traits of males with and without dorsal patches to determine whether these structures could be used by females as indicators of male quality, examined whether the size of the dorsal patch shows a relationship with other body traits during the mating season, and investigated the physical and behavioral development of dorsal patches. Thirty-seven percent of all males sampled (n  =  99) showed conspicuous dorsal patches during the mating season in November and December. Males with conspicuous dorsal patches had larger testes, smaller body masses, lower body condition indices, and lower ectoparasite loads than males without dorsal patches. Larger testes and lower ectoparasite loads suggest that the dorsal patch could be signaling male quality and readiness for mating. A typical dorsal patch covered approximately 1.7 cm² of a male's interscapular region, but size of this structure did not vary with any of the body traits examined. We describe a novel, stereotypic behavior performed by male L. curasoae, which we call “smearing behavior,” and suggest that this is associated with development of the dorsal patch because males appear to smear different body fluids onto this patch. We further suggest that sebaceous secretions in the interscapular region would not be the determining factor in dorsal patch development.

Biologists routinely punch the flight membranes of bats to collect tissue for molecular analyses, or to mark animals in the field, or both. The current standard is to biopsy the wing membrane (chiropatagium) because it is easy to access and is less vascularized, and thus bleeds less, than the tail membrane (uropatagium). Although flight membrane biopsies are assumed not to affect the bat's ability to fly or capture prey, almost nothing is known about wound healing times and the optimal punch size or location for tissue excision. We measured wound healing in the wing and tail membrane of 32 big brown bats (Eptesicus fuscus) biopsied with 2 circular punch tool sizes, and quantified the concentration of DNA extracted from the excised tissue. Our results show that tail wounds healed significantly faster than wing wounds for both 4-mm- and 8-mm-diameter biopsy wounds. We also were able to extract significantly more DNA from tail biopsies than from wing biopsies of the same size. The newly healed tissue remains unpigmented for considerable time after wound closure, and this allows identification of individuals for an extended period. We hypothesize that the increased vasculature in the uropatagium contributes to faster healing times compared to the chiropatagium. Examination of our data indicates that tissue biopsy for molecular analyses in bats should be taken from the tail membrane, although biopsies of the wing membrane are useful for marking associated with recapture programs because the wound and scar will persist longer.

Foraging plasticity that includes facultative nectarivory is extremely rare in temperate insectivorous bats. We investigated flower-visiting behavior of pallid bats (Antrozous pallidus, Vespertilionidae) to bat-adapted flowers of cardon cacti (Pachycereus pringlei) to determine whether pallid bats consume floral nectar or visit flowers to opportunistically glean insects attracted to flowers. In 2007 and 2008, we recorded flower-visiting behavior of bats using infrared videography on 143 cactus-nights across 14 sites in Baja California, Mexico. Pallid bats were regular visitors to cardon flowers and consumed floral nectar by plunging their faces into the corolla to lap pooled nectar. We recorded 1,198 flower visits by A. pallidus, which accounted for 10% of visits to flowers by all bats. Pallid bats visited flowers on 57% of cactus-night observations (n  =  81/143) and 52% (n  =  28/54) of captured bats had visible pollen loads. Flower-visiting activity by A. pallidus was concentrated early in the evening where nectarivorous Mexican lesser long-nosed bats (Leptonycteris yerbabuenae [ =  curasoae], Phyllostomidae) were present, but more evenly distributed throughout the night at sites without L. yerbabuenae, suggesting potential competitive exclusion among these nocturnal chiropteran pollinators.

Prescribed fire is becoming a common management tool for restoring forests of North America; however, effects of prescribed fire on forest-dwelling bats remain unclear. During 2006 and 2007, we monitored prey availability, diet, foraging behavior, and roost selection of adult female northern bats (Myotis septentrionalis) before and after 2 prescribed fires in dissected terrain of the Red River Gorge on the Daniel Boone National Forest in eastern Kentucky. Size of home ranges and core areas did not vary between bats radiotracked before and after fires. Bats foraged more often in the vicinity of pine stands than hardwood or mixed stands, and along ridges and midslopes than lower slopes, regardless of burn condition. Home ranges were closer to burned habitats following fires than to unburned habitats. Abundance of coleopterans, dipterans, and all insects combined captured in blacklight traps increased following prescribed fires. Fecal samples of bats demonstrated lepidopterans, coleopterans, and dipterans to be the 3 most important groups of insect prey, with consumption of dipterans increasing after burning. Bats chose roosts that were taller in height and in earlier stages of decay than random snags, and after prescribed fires chose roosts in trees with a greater number of cavities and a higher percentage of bark coverage. More roosts were observed in burned habitats (74.3%; n  =  26) after fires than in unburned habitats (25.7%; n  =  9). The results of this work suggest that northern bats are tolerant to prescribed fire on the landscape pattern and scale observed in this study. Northern bats responded to habitat alterations resulting from prescribed fires through shifts in the location of foraging areas as bats tracked changes in insect availability, and through shifts in the selection of roost trees by occupying trees and snags possessing more potential roosting microsites.

Characterizing circadian activity patterns is one of the essential steps to understanding how a species interacts with its environment. This study documented activity patterns of pygmy rabbits (Brachylagus idahoensis) in free-ranging populations at 5 sites in Nevada and California. Infrared-triggered camera systems were placed within areas occupied by populations of pygmy rabbits and operated for 1 year. The number of photographs obtained per hour was used as an index of aboveground activity. Activity was analyzed for diel and seasonal patterns as well as for differences among populations. All populations showed a bimodal diel activity pattern with most activity occurring at dawn and at dusk during all seasons. Greatest activity occurred at dawn except during winter. Four of the 5 study sites showed similar levels of activity. The atypical site was located 550 m higher in elevation at a locality known for extreme weather; activity levels were twice as high at that site. Activity patterns of pygmy rabbits likely reflect a combination of predation pressures as well as metabolic energy demands.

The date that yellow-bellied marmots (Marmota flaviventris) emerge at a site in Colorado has been used as evidence that climate is affecting hibernating species. Over 6 springs, and at 16 marmot groups, the date of 1st emergence of males, females, and the group as a whole was recorded. Emergence date of males was a function of the number of males in a group (a metric of reproductive competition) and the date that 50% of the ground was snow free in the marmot group (a metric of climatic variation). The number of adult males explained no variation in the date that the 1st adult female was detected, or the date by which one-half of the group emerged, but the 1st female was sighted earlier in groups with more females. Thus, to understand climatic effects on the phenology of social species, researchers must consider the potential for reproductive competition as well as climatic factors such as the timing of snow melt.

The Active Territorial Defense Hypothesis (ATDH) and Passive Range Exclusion Hypothesis (PREH) are contrasted as possible explanations for patterns of latrine use in a high-density population of the European badger (Meles meles) in the United Kingdom. Using bait-marking techniques, temporal patterns in latrine use by individuals and social groups were investigated to test for any systematic marking behavior, especially whether coordination of individual actions might be involved in the group territorial marking strategy. Latrine use by 4 groups was concentrated primarily along territory boundaries and particularly along parts of the boundary closer to that group's sett, rather than closer to active feeding areas. Boundary latrines were used to a similar extent by each group, with a consistent percentage (but differing subset) of a group's boundary latrines used daily. Individually, badgers preferentially used certain latrines and male badgers, in particular, showed a tendency to deposit more feces in latrines closer to their group sett. Our results indicate that badgers partition the collective responsibility of marking their territories, with the result that their entire boundaries are marked regularly and consistently, regardless of where focal individuals may be feeding. Individuals did not simply defecate at the section of boundary closest to where they happened to be active, but rather according to a pattern resulting in comprehensive, regular group coverage of the border. The patterns of latrine use accorded more closely with the ATDH than the PREH. This study provides evidence that badgers may cooperate systematically to defend their territories.

The white-lipped peccary (Tayassu pecari) is a neotropical ungulate that forms some of the largest groups living in dense tropical forest. Populations of this species have declined throughout Mesoamerica during the last 50 years at alarming rates. Home-range and habitat preferences of this species have been documented in Brazil and Costa Rica for humid tropical forest. Here we studied home-range features and habitat preferences of white-lipped peccaries for a seasonally dry tropical forest of the Yucatan Peninsula—the Calakmul Biosphere Reserve—where water and food can be temporarily scarce or even absent. By using radiotelemetry and direct observations for 18 months of individuals in 4 groups, we documented some of the largest home ranges reported for some of the smallest group sizes documented for this species. Dry-season home ranges were constrained to the close vicinity of a few available water sources, whereas during the rainy season peccary groups were more mobile and traversed long distances. Compositional analyses of habitat preferences indicated that groups preferred ponds and Medium Sub-Perennial Forest in combination with Low Flooded Forest, whereas the least preferred was the Dry Forest. Apparently, the combination of ranging over large areas to access widely dispersed resources while living in smaller groups and sharing space allows white-lipped peccaries to survive in Calakmul.

It is often difficult to test hypotheses about how and why animal movement responds to environmental conditions, and at what spatial scales movement decisions are made, all of which are critical for sound management. We used fractal dimension (D) as a measure of tortuosity because it described animal movement patterns and was useful for testing hypotheses about effects of sex, home-range size, monthly rainfall, and reproductive phase on movement paths and for detecting changes in movement patterns of animals across a range of movement distances. We captured and fitted 33 (18 females and 15 males) white-tailed deer (Odocoileus virginianus) with global positioning system collars. We found that females moved more tortuously (D  =  1.75 ± 0.035 SE) than males (D  =  1.549 ± 0.025). These differences in movement were related to home-range size of females but not of males. Rainfall predicted D for females; thus, females may have been able to forage more intensively in a smaller area due to increased forage availability. Fractal D of females was greatest during the parturition period (1.468 ± 0.02), likely due to restricted movements in smaller areas or increased foraging. Home-range size of males was similar in spring and rut, but D was lower during rut, indicating that deer changed movement patterns within previously established home ranges. Movement patterns were similar at path lengths related to foraging patches and home ranges, whereas movement patterns changed as path length approximated the size of habitat patches.

Maternal investment plays a critical role in neonate survival, and adults can improve survival of offspring by defending them against predators. However, limited information exists documenting ungulate aggression toward humans in defense of neonates. During captures of neonates in spring 2007 and 2008 in north-central South Dakota, we documented 24 aggressive encounters by adult female and yearling male and female white-tailed deer (Odocoileus virginianus) defending neonates. Eleven (45.8%) aggressive encounters included yearlings accompanying adult females. Mean ages and weights of neonates that were aggressively defended were greater (P < 0.0001) than ages and weights of those that were not; adults began protecting neonates at approximately 4 days of age. Male fawns were more likely (P  =  0.013) to be defended than female fawns. Examination of our data suggests that sex- and age-biased maternal defensive behavior exists in white-tailed deer, and that deer biased maternal investment toward older, male neonates.

Life-history theory predicts that within a species, reproduction and survival rates will differ among populations that differ in resource availability or predation rates through phenotypic plasticity. When populations are near carrying capacity (K) or when they are declining due to reduced prey resources, the average age at 1st reproduction (average AFR) is predicted to be older than in populations below K. Differences between the trajectories of northern sea otter (Enhydra lutris kenyoni) populations in Alaska provides an opportunity to examine phenotypic plasticity. Using premolar teeth or reproductive tracts, we estimated average AFR from demographically distinct populations of sea otters in Alaska. We obtained samples from 2 populations near K, Prince William Sound (PWS) and the Aleutian Archipelago (archived samples), and from 2 populations below K, the Kodiak Archipelago and Sitka. The average AFR was lower in populations below K (3.60 years ± 0.16 SD) compared to those near K (4.21 ± 0.13 years, P < 0.001), and differed among all populations, with the Aleutian population possessing the oldest average AFR (4.29 ± 0.09 years) followed by PWS (4.05 ± 0.24 years), Sitka (3.80 ± 0.21 years), and Kodiak (3.19 ± 0.37 years). The difference in average AFR among populations supports life-history theory and provides evidence of phenotypic plasticity in sea otters. Our findings highlight the value of using average AFR as a tool for monitoring mammalian populations.

Mammalian reproductive biology is modified consistently across pinnipeds to achieve a synchronous and seasonal reproductive pattern. This synchrony relies on an embryonic diapause and ensures optimal conditions for offspring survival. Behavioral observations on Galapagos sea lions (Zalophus wollebaeki) indicate little synchrony and variable breeding seasons, making this species unique among otariids. We studied the reproductive physiology of wild female Galapagos sea lions in 2 months in contrasting seasons, March 2005 (n  =  11) and August 2006 (n  =  12) by examining progesterone and estrogen concentrations in serum and plasma. We provide physiological evidence for remarkably low synchrony and minor seasonality in the breeding cycle of Galapagos sea lions. Specifically, we found females in intermediate or advanced pregnancy during both seasons, as determined by high progesterone concentrations coupled with physical examination. Possible causes for this low synchrony are absence of strong photoperiodic change throughout the year, thought to regulate embryonic diapause, or adaptation to an environment with variable productivity and prey availability, or both.

Island mammals often differ behaviorally, demographically, and morphologically from their mainland conspecifics. A comparison of the water flux (WF, ml/day), daily energy expenditure (DEE, kJ/day), activity budgets, body mass, and diets of female swamp antechinuses (Antechinus minimus maritimus) from island and mainland habitats was undertaken to determine whether features associated with the island habitat influenced their physiological ecology. WF differed significantly between the 2 populations, with mainland animals having a WF 36% greater than island animals. However, there was no significant difference in DEE between individuals in different habitats (island versus mainland), although they exhibited markedly divergent behavioral patterns. Differences in diet and availability of free water for drinking may have caused the divergence in the WF values between mainland and island individuals. Although energy requirements play a key role in the spatial ecology of small mammals, other factors such as social interactions could cause observed differences in spatial organization between female A. minimus on the island and mainland.

Many long-term studies of wildlife populations rely on individual identification based on natural markings or genetic profiling, or both. However, only rarely are these 2 independent data sets systematically compared with each other to estimate the error rates inherent in these studies. Here, >25 years of photo-identification data on the endangered North Atlantic right whale (Eubalaena glacialis) were compared with high-resolution genetic profiles, available for >75% of the individuals in the photo-identification catalog, in order to identify sources and rates of errors associated with both methods of individual identification. The resulting estimates were 0.0308 errors/identification for the photo-identification data, and 0.00121 errors/locus and 0.0327 errors/multilocus profile for the genetic data. These are among the lowest error rates yet reported, and indicate that the approaches used provide reliable means of individual identification for this species. However, despite these low error rates, the large size of the data sets results in a nonnegligible estimated number of errors, indicating that the potential for these errors needs to be incorporated into other analyses that are based on these data. A similar situation likely exists in other long-term studies where, although error rates are assumed to be low, the size of the data set results in a large number of errors that will influence subsequent analyses. Regularly conducting and reporting extensive database comparisons such as this is invaluable for maintaining the integrity of long-term data sets by identifying where sources of error are occurring and how protocols can be improved to lower error rates in the future.

Distinct annuli in cementum, a mineralized tissue surrounding the root of mammalian teeth, are used to estimate age in wildlife. Life-history information may be recorded in cementum patterns but interpretation is complicated by variation in cementum width between individuals, among their teeth, and around the surface of the root. First premolar teeth from polar bears (Ursus maritimus) were evaluated. We identified sources of variation in cementum growth and methods are presented that reduce error and permit comparisons within and between individuals. A minimum of 10 measurements from 1 aspect was required to produce precise estimates of cementum growth layer group (GLG) width. Variance component analysis revealed that comparisons between distal and mesial aspects of the root introduced the greatest variation among bears. Controlling for aspect, variance was partitioned differently between the mesial and distal surfaces. Comparisons between maxillary and mandibular premolars from the same bear indicated that data from these teeth should not be pooled; data collected from left and right lower premolars may be combined. Indices to represent adjusted GLG widths are described that reduce age and allometric effects, allowing life-history or environmental factors to be compared.