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The social behavior of the smaller fox species is poorly known compared with that of larger and more gregarious canids that can be directly observed. We studied social relationships and reproductive behavior of island foxes (Urocyon littoralis) on San Clemente Island (SCI) and San Miguel Island (SMI), off the coast of Southern California, using proximity logging collars. On both islands, pair members interacted more frequently and spent more time together than other types of dyads. On SCI, a high contact rate identified the same 10 mated pairs that were identified by a high degree of home-range overlap. A high contact rate also identified 3 mated pairs on SMI, 2 of which were associated with large pups 9–10 months old. On SMI, the number of contacts and amount of time that mates spent together per day varied across months and peaked in February, when most conceptions occur. Mates spent much less time together in April to June, the pup-rearing season. More unpaired male–female and male–male dyads interacted during January and February than in subsequent months. Paired males appeared to guard their mate during the period when she was receptive. The average duration of estrus was approximately 40 h. Paired females were in contact with other males in addition to their mate near the time they were presumably in estrus, and paired males were in contact with other females in addition to their mate. The relatively short duration of estrus, combined with asynchrony of estrus among females, enabled paired males to leave their mate and seek extrapair copulations without risk of cuckoldry. Proximity logging collars provide a new opportunity to learn about these temporal aspects of social and reproductive behavior in canids.
Forests in the Sierra Nevada, similar to those across the continent, have been substantially altered by logging, fire exclusion, and other human activities. Current forest management emphasizes maintenance or restoration of resiliency in the face of contemporary disturbance factors that include wildfire, climate change, continued urbanization, and invasive species. We evaluated responses of small mammals to forest management by monitoring a series of 12 replicate trapping grids in compositionally homogeneous forest over 8 years, and implemented 2 levels of canopy thinning. Livetrapping efforts (119,712 trap-nights) yielded 15,613 captures of 2,305 individuals of 13 species, and although forest structure was significantly influenced by canopy treatments, small mammal numbers and assemblage composition were not. To better understand this we assessed habitat associations of small mammals at 599 census points on 75 transects established in a stratified random manner throughout Plumas National Forest. We analyzed these data with 2 complementary forms of constrained ordination (canonical correspondence and canonical correlation) that extract major gradients in 1 data set (e.g., distribution of small mammal captures) and explain these in terms of measured variables from a 2nd data set (e.g., habitat and environmental measurements). Over 3 years and 57,504 trap-nights of effort we captured 1,367 individuals of 11 species. Both forms of ordination exposed significant associations between small mammals and underlying habitat metrics, but they explained remarkably little variation in these data, suggesting that small mammals are responding only modestly to habitat variation as expressed by the available environmental variables measured at each plot. We followed this with stepwise multiple Poisson regression to build models of habitat associations of these species. We applied model-averaging and employed Akaike's information criterion corrected for small sample size (AICc) to evaluate candidate models. Reflecting ordination results, competitive models (e.g., those with Akaike differences [ΔAICc] < 2.0) cumulatively explained little variation (12–36%) and regression coefficients were very low. Hence, both ordination and Poisson multiple regression suggest that the limited response by small mammals to canopy thinning primarily reflects the generalist habits of the common species in this forest. We propose that anthropogenic influences have led to structural homogenization of these forests, even across > 800 m of elevation, such that habitat specialists (e.g., old-forest–dependent species such as Myodes [Clethrionomys] californicus and Glaucomys sabrinus) have become less common due to the lack of suitable habitat. Further efforts should target nonforested habitats (meadows and riparian corridors), but results presented here suggest that managers should strive to increase heterogeneity at large spatial scales and especially to promote the development of mature forest structure.
Investigating social learning in free-ranging mammals is gaining popularity among researchers. Natural experiments are ideal for studying social learning, but are rare compared to captive studies because of practical limitations and ethical concerns. Such experiments are often restricted or forbidden because they require manipulation of the environment, ecology, or behavior of free-ranging species. As a result, developing new methods to investigate social learning in the field is essential. The main goal of this study was to use genetic data and a new testing framework to determine if social learning from mothers to their offspring is at least partly responsible for free-ranging black bears foraging on human foods in Yosemite National Park. I estimated a relatedness coefficient and the most probable relationship for all combinations of 2 bears (n = 150) sampled in 2004–2007. I then grouped these pairs by their foraging behavior to test predictions deduced from asocial learning, transmission, genetic inheritance, and social learning hypotheses. Results from both analyses suggest that mother–offspring social learning is the primary mechanism responsible for black bears foraging on human food in Yosemite. In addition, results also suggest that some bears are innovators, learning to forage on human food as independents. I found no support for the genetic inheritance hypothesis.
The gray wolf (Canis lupus) exhibits both genetic and morphologic clinal variation across North America. Although shape variation in wolf populations has been documented, no study has been made to exhaustively quantify it, or to correlate morphologic variation with environmental variables. This study utilizes a large historical database of wolf skull linear measurements to analyze shape, and attempts to correlate it with wolf ecology. A variety of statistical tests are employed; size and shape are examined through a principal component analysis and a calculation of allometry vectors. Multiple regression analysis (both global and stepwise) are then used to test the resulting principal components against various biotic and abiotic factors. In addition, the effects of sexual dimorphism and taxonomy on morphology are explored through 1-way analysis of variance and canonical variates analysis, respectively. Several patterns are revealed, including size increase with latitude in accord with Bergmann's rule. Static allometry is significant, the fundamental pattern being a decrease in the robusticity of the basicranium relative to the viscerocranium. Sexual dimorphism, allometry, and a correlation with precipitation are other key factors driving morphological variation. Examination of these patterns has allowed us to make conclusions about the direct and indirect ways the environment has affected clinal variation in wolves.
For many herbivorous mammal species across the world, geophagy, the consumption of soil, is an important method for obtaining minerals, especially sodium. However, this behavior has not been recorded in marsupials. The eastern grey kangaroo (Macropus giganteus), an intensively studied macropod species, is known to use physiological and micromorphological adaptations to conserve sodium. We present results of another adaptation, the use of natural licks, by this species and 3 other macropod species at Sundown National Park, Australia. Natural licks had significantly higher levels of sodium, magnesium, and sulfur than surrounding soils. We examined patterns of lick use by kangaroos to test 3 possible proximate causes of geophagy: whether lick use was affected by dietary mineral content, life-history stage, and thermoregulation. The number of kangaroos visiting the licks increased with temperature and mean cloud cover, varied among months, and was marginally significantly influenced by dietary mineral content. Visit durations to one lick increased with temperature and were influenced by month and life-history stage; females with high lactation demand and large males spent the most time at the lick. The proportion of time spent in geophagy when at a focal lick varied with month and reproductive state. Therefore geophagy is not restricted to eutherian mammals, and kangaroos, like many eutherian species, appear to adjust this behavior in response to their mineral demand. Geophagy in kangaroos is facultative, rather than obligative, and has not been detected in other intensively studied populations. In areas of Australia with low levels of sodium, high temperatures, and suitable lick sites, geophagy may play a key role in marsupial ecology.
We used carbon and nitrogen isotopes measured in hair to compare the diets of 2 sympatric species of wild mice, Peromyscus californicus and P. boylii, in Santa Cruz County, California. The ability of these 2 Peromyscus species to coexist is thought to be the result of spatial partitioning through canopy plant associations as well as possible dietary niche partitioning. We used stable isotope analysis to determine the trophic level at which each species is feeding and stable isotope mixing models to estimate dietary contributions of various arthropod and plant-derived food sources. We found P. californicus to be omnivorous, specializing mainly on arthropods and consistently feeding at a higher trophic level than P. boylii. P. boylii is omnivorous as well, but specializes mainly on tanoak (Notholithocarpus densiflorus) acorns. Dietary niche partitioning appears to be seasonal; in the fall, partitioning breaks down to some degree, likely because food is so abundantly available, and both species consume a larger, overlapping array of acorns and arthropods. These findings coupled with other studies on habitat niche partitioning present a clearer picture of how these 2 sympatric species can coexist.