Biotic factors influencing the unexpected distribution of a Humboldt marten (Martes caurina humboldtensis) population in a young coastal forest

The origin, connectivity, and individual specialization of island wolves after deer extirpation

Wolves are assumed to be ungulate obligates, however, a recently described pack on Pleasant Island, Alaska USA, is persisting on sea otters and other marine resources without ungulate prey, violating this long-held assumption. We address questions about these wolves regarding their origin and fate, degree of isolation, risk of inbreeding depression, and diet specialization by individual and sex. We applied DNA metabarcoding and genotyping by amplicon sequencing using 957 scats collected from 2016 to 2022, and reduced representation sequencing of tissue samples to establish a detailed understanding of Pleasant Island wolf ecology and compare them with adjacent mainland wolves. Dietary overlap was higher among individual wolves on Pleasant Island (Pianka's index mean 0.95 ± 0.03) compared to mainland wolves (0.70 ± 0.21). The individual diets of island wolves were dominated by sea otter, ranging from 40.6% to 63.2% weighted percent of occurrence (wPOO) (mean 55.5 ± 8.7). In contrast, individual mainland wolves primarily fed on ungulates (42.2 ± 21.3) or voles during a population outbreak (31.2 ± 23.2). We traced the origin of the Pleasant Island pack to a mainland pair that colonized around 2013 and produced several litters. After this breeding pair was killed, their female offspring and an immigrant male became the new breeders in 2019. We detected 20 individuals of which 8 (40%) were trapped and killed while two died of natural causes during the 6-year study. Except for the new breeding male, the pedigree analysis and genotype results showed no additional movement to or from the island, indicating limited dispersal but no evidence of inbreeding. Our findings suggest wolves exhibit more flexible foraging behavior than previously believed, and hunting strategies can substantially differ between individuals within or between packs. Nevertheless, anthropogenic and natural mortality combined with limited connectivity to the mainland may inhibit the continued persistence of Pleasant Island wolves.

American marten occupancy and activity patterns at the southern extent of their range in the eastern United States

The relatively recent rediscovery of an American marten (Martes americana) population that was reintroduced over 30 years ago in southern Vermont provides an opportunity to investigate the relative importance of other mesocarnivores, and forest stand (e.g., DBH, downed logs, vertical structure) and habitat variables to their presence on the Green Mountain National Forest. Marten are state-listed as an endangered species in Vermont and occur there at the southern extent of their range in the eastern United States. We collected detection data from camera surveys in 5 km2 units between 2019 and 2021 (December-April; n = 40 units, 238 cameras). We examined activity patterns and applied an occupancy modeling framework to the detection data to assess the relative importance of covariates at unit and camera levels and assess interactions of marten with other mesocarnivores. We did not find any unit-level occupancy models with significant covariates that were better supported than the base model in the single-season unit-level analysis. Distance to the nearest release site was the covariate most supported for detectability at both spatial scales, and marten occupancy at the camera level was positively influenced by the amount of canopy cover. Two species interaction models did not indicate any positive or negative association beyond random with other mesocarnivores and activity patterns among mesocarnivores had substantial overlap. Marten recovery since the time of the reintroduction appears slow, and even 30 years later, the marten distribution is limited and suggests that dispersal is restricted at some level. We recommend a further investigation of the possible impact of other mesocarnivores to juvenile survival or other vital demographic rate (e.g., recruitment) in marten that were not explicitly measured in this study.

Limitations of current knowledge about the ecology of Grey Foxes hamper conservation efforts

Species-specific conservation is important for maintaining the integrity of ecological communities but is dependent on sufficiently understanding multiple aspects of a species’ ecology. Species-specific data are commonly lacking for species in geographic areas with little research and species perceived to have insufficient charisma or economic importance. Despite their widespread distribution across central and North America and status as a furbearing mammal, little is known about the ecology of Grey Foxes Urocyon cinereoargenteus compared to other species of furbearing mammals. To understand what is known about this species, especially factors affecting population dynamics, we performed a systematic review of the scientific literature. We found 234 studies about Grey Foxes, with studies increasing substantially over time but with geographic gaps in the Great Plains and most of Mexico and central America. Most studies we reviewed examined relative abundance or occupancy (n= 35), habitat associations (n= 30), primarily as part of larger mammalian community studies, or spatiotemporal effects of other mammalian carnivores (n= 19), predominately Coyote Canis latrans. Grey Foxes were primarily forest-associated although associations with specific forest communities or anthropogenically disturbed habitats varied among studies. Multiple studies across ecoregions reported this fox as among both the most- and least-abundant mammalian carnivore. The inter-specific effects of Coyote were often, but not exclusively, negative and were likely mediated by landscape composition and human development. Importantly, very few studies examined population-effects of coyotes on Grey Foxes. Studies of population trends, demographics, and space use of Grey Foxes were comparatively rare and small inter- and intra-study sample sizes limited our ability to infer broader patterns. We suggest multiple avenues for future research to better understand the population status of this species throughout their range. 

Predicted distribution of a rare and understudied forest carnivore: Humboldt marten (Martes caurina humboldtensis)

BACKGROUND

Many mammalian species have experienced range contractions. Following a reduction in distribution that has resulted in apparently small and disjunct populations, the Humboldt marten (Martes caurina humboldtensis) was recently designated as federally Threatened and state Endangered. This subspecies of Pacific marten occurring in coastal Oregon and northern California, also known as coastal martens, appear unlike martens that occur in snow-associated regions in that vegetation associations appear to differ widely between Humboldt marten populations. We expected current distributions represent realized niches, but estimating factors associated with long-term occurrence was challenging for this rare and little-known species. Here, we assessed the predicted contemporary distribution of Humboldt martens and interpret our findings as hypotheses correlated with the subspecies' niche to inform strategic conservation actions.

METHODS

We modeled Humboldt marten distribution using a maximum entropy (Maxent) approach. We spatially-thinned 10,229 marten locations collected from 1996-2020 by applying a minimum distance of 500-m between locations, resulting in 384 locations used to assess correlations of marten occurrence with biotic and abiotic variables. We independently optimized the spatial scale of each variable and focused development of model variables on biotic associations (e.g., hypothesized relationships with forest conditions), given that abiotic factors such as precipitation are largely static and not alterable within a management context.

RESULTS

Humboldt marten locations were positively associated with increased shrub cover (salal (Gautheria shallon)), mast producing trees (e.g., tanoak, Notholithocarpus densiflorus), increased pine (Pinus sp.) proportion of total basal area, annual precipitation at home-range spatial scales, low and high amounts of canopy cover and slope, and cooler August temperatures. Unlike other recent literature, we found little evidence that Humboldt martens were associated with old-growth structural indices. This case study provides an example of how limited information on rare or lesser-known species can lead to differing interpretations, emphasizing the need for study-level replication in ecology. Humboldt marten conservation would benefit from continued survey effort to clarify range extent, population sizes, and fine-scale habitat use.

The Rapid Rise of Next-Generation Natural History

Many ecologists have lamented the demise of natural history and have attributed this decline to a misguided view that natural history is outdated and unscientific. Although there is a perception that the focus in ecology and conservation have shifted away from descriptive natural history research and training toward hypothetico-deductive research, we argue that natural history has entered a new phase that we call “next-generation natural history.” This renaissance of natural history is characterized by technological and statistical advances that aid in collecting detailed observations systematically over broad spatial and temporal extents. The technological advances that have increased exponentially in the last decade include electronic sensors such as camera-traps and acoustic recorders, aircraft- and satellite-based remote sensing, animal-borne biologgers, genetics and genomics methods, and community science programs. Advances in statistics and computation have aided in analyzing a growing quantity of observations to reveal patterns in nature. These robust next-generation natural history datasets have transformed the anecdotal perception of natural history observations into systematically collected observations that collectively constitute the foundation for hypothetico-deductive research and can be leveraged and applied to conservation and management. These advances are encouraging scientists to conduct and embrace detailed descriptions of nature that remain a critically important component of the scientific endeavor. Finally, these next-generation natural history observations are engaging scientists and non-scientists alike with new documentations of the wonders of nature. Thus, we celebrate next-generation natural history for encouraging people to experience nature directly.

Spatial and temporal variability in the diet of Pacific marten (Martes caurina) on Haida Gwaii: an apex predator in a highly modified ecosystem

Knowledge of the diet ecology of apex predators in insular island ecosystems has direct applications to the conservation of endemic species at risk of extinction. We used stable isotopes of carbon and nitrogen to infer resource-use strategies of an indigenous predator, the Pacific marten (Martes caurina (Merriam, 1890)), in a highly modified ecosystem on Haida Gwaii, British Columbia, Canada. We used Bayesian isotopic mixing models to estimate the relative contributions of different food sources to marten diet across seasons and during overall lifetime, and to determine how diet varied with different levels of access to marine resources. Isotopes of carbon and nitrogen measured in hair and muscle tissue suggested that marten consumed salmon (3%–17%) and berries (25%–37%) seasonally; these diet groups were relatively minor components of the lifetime diet. Analysis of bone collagen suggested that terrestrial fauna — including birds, deer, small mammals, and invertebrates — contributed the most to diet (41%–55%), and marine invertebrates (38%–48%), not salmon (0%–3%), were the main allochthonous marine nutrient subsidy to lifetime diet. Plasticity in foraging ecology, combined with a broad dietary niche, introduced prey, notably the invasive Sitka black-tailed deer (Odocoileus hemionus sitkensis Merriam, 1898), as well as abundant marine resources, may allow marten to outcompete other indigenous and endemic carnivores on Haida Gwaii.

Evaluating livetrapping and camera-based indices of small-mammal density

Density estimates are integral to wildlife management, but they can be costly to obtain. Indices of density may provide efficient alternatives, but calibration is needed to ensure the indices accurately reflect density. We evaluated several indices of small-mammal density using livetrapping and motion-activated cameras in the Cascade Mountains of Washington (USA). We used linear regression to compare spatially explicit capture–recapture density estimates of mice (genus Peromyscus Gloger, 1841), voles (genera Microtus Schrank, 1798 and Myodes Pallas, 1811), and chipmunks (genus Neotamias A.H. Howell, 1929) with four indices. Two indices were based on livetrapping (minimum number alive (MNA) and number of captures per 100 trap-nights) and two indices were based on photos from motion-activated cameras (proportion of cameras detecting a species and number of independent detections). We evaluated how the accuracy of trap-based indices increased with trapping effort using subsets of the full dataset (n = 7 capture occasions per site). Most indices provided reliable indicators of small-mammal density, and livetrapping indices (R2 = 0.64–0.98) outperformed camera-based indices (R2 = 0.24–0.86). All indices performed better for more abundant species. The effort required to estimate each index varied and indices that required more effort performed better. These findings should help managers, conservation practitioners, and researchers select small-mammal monitoring methods that best fit their needs.