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.

Identifying resting locations of a small elusive forest carnivore using a two-stage model accounting for GPS measurement error and hidden behavioral states.

BACKGROUND: Studies of animal movement using location data are often faced with two challenges. First, time series of animal locations are likely to arise from multiple behavioral states (e.g., directed movement, resting) that cannot be observed directly. Second, location data can be affected by measurement error, including failed location fixes. Simultaneously addressing both problems in a single statistical model is analytically and computationally challenging. To both separate behavioral states and account for measurement error, we used a two-stage modeling approach to identify resting locations of fishers (Pekania pennanti) based on GPS and accelerometer data. METHODS: We developed a two-stage modelling approach to estimate when and where GPS-collared fishers were resting for 21 separate collar deployments on 9 individuals in southern Oregon. For each deployment, we first fit independent hidden Markov models (HMMs) to the time series of accelerometer-derived activity measurements and apparent step lengths to identify periods of movement and resting. Treating the state assignments as given, we next fit a set of linear Gaussian state space models (SSMs) to estimate the location of each resting event. RESULTS: Parameter estimates were similar across collar deployments. The HMMs successfully identified periods of resting and movement with posterior state assignment probabilities greater than 0.95 for 97% of all observations. On average, fishers were in the resting state 63% of the time. Rest events averaged 5 h (4.3 SD) and occurred most often at night. The SSMs allowed us to estimate the 95% credible ellipses with a median area of 0.12 ha for 3772 unique rest events. We identified 1176 geographically distinct rest locations; 13% of locations were used on > 1 occasion and 5% were used by > 1 fisher. Females and males traveled an average of 6.7 (3.5 SD) and 7.7 (6.8 SD) km/day, respectively. CONCLUSIONS: We demonstrated that if auxiliary data are available (e.g., accelerometer data), a two-stage approach can successfully resolve both problems of latent behavioral states and GPS measurement error. Our relatively simple two-stage method is repeatable, computationally efficient, and yields directly interpretable estimates of resting site locations that can be used to guide conservation decisions.

Pliocene-Early Pleistocene Geological Events Structure Pacific Martens (Martes caurina).

The complex topography, climate, and geological history of Western North America have shaped contemporary patterns of biodiversity and species distributions in the region. Pacific martens (Martes caurina) are distributed along the northern Pacific Coast of North America with disjunct populations found throughout the Northwestern Forested Mountains and Marine West Coast Forest ecoregions of the West Coast. Martes in this region have been classified into subspecies; however, the subspecific designation has been extensively debated. In this study, we use genomic data to delineate conservation units of Pacific marten in the Sierra-Cascade-Coastal montane belt in the western United States. We analyzed the mitochondrial genome for 94 individuals to evaluate the spatial distribution and divergence times of major lineages. We further genotyped 401 individuals at 13 microsatellite loci to investigate major patterns of population structure. Both nuclear and mitochondrial DNA suggest substantial genetic substructure concordant with historical subspecies designations. Our results revealed that the region contains 2 distinct mitochondrial lineages: a Cascades/Sierra lineage that diverged from the Cascades/coastal lineage 2.23 (1.48-3.14 mya), consistent with orogeny of the Cascade Mountain chain. Interestingly, Pacific Martes share phylogeographic patterns similar with other sympatric taxa, suggesting that the complex geological history has shaped the biota of this region. The information is critical for conservation and management efforts, and further investigation of adaptive diversity is warranted following appropriate revision of conservation management designations.

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

Pacific martens (Martes caurina) are often associated with mature forests with complex structure for denning, resting, and efficient hunting. Nonetheless, a small isolated population of the Humboldt subspecies of Pacific martens (Martes caurina humboldtensis) occupies a narrow strip of young, coastal forest (< 70 years old) but not inland mature forest in the central Oregon Coast Range. We examined factors contributing to this unexpected distribution of martens by 1) analyzing marten diets using DNA metabarcoding to assess 90 scats, 2) using camera traps to assess differences in the relative abundances of prey, competitors, and predators across a coastal to inland gradient of vegetation types, and 3) quantifying differences in extent of fruit-producing shrubs and vegetation structure within vegetation types. Diets of martens were diverse (12, 10, and 3 species of birds, mammals, and amphibians respectively), and most fall and winter scats contained fruit. Voles, mice, and varied thrushes (Ixoreus naevius) were dominant prey items. Voles, mice, and most birds, but not varied thrushes, were more commonly observed in the coastal shrub-dominated forest than in inland forest. The coastal shrub-dominated forest had the highest diversity of vertebrates and potential prey overall. Bobcats (Lynx rufus), a key potential predator, were more commonly detected in inland forest. Of potential competitors, western spotted skunks (Spilogale gracilis) were more commonly detected in inland forest, with gray foxes (Urocyon cinereoargenteus) and raccoons (Procyon lotor) detected almost exclusively in coastal forests. Vegetation in coastal forests appears to provide, at least seasonally, more prey and fruit, and more overhead shrub cover compared with inland forest. Remaining plausible hypotheses for the restricted distribution of marten to coastal forests include increased prey, fruit, and overhead cover, and reduced predation risk from bobcats.

Describing vegetation characteristics used by two rare forest-dwelling species: Will established reserves provide for coastal marten in Oregon?

Forest management guidelines for rare or declining species in the Pacific Northwest, USA, include both late successional reserves and specific vegetation management criteria. However, whether current management practices for well-studied species such as northern spotted owls (Strix occidentallis caurina) can aid in conserving a lesser known subspecies-Humboldt martens (Martes caurina humboldtensis)-is unclear. To address the lack of information for martens in coastal Oregon, USA, we quantified vegetation characteristics at locations used by Humboldt martens and spotted owls in two regions (central and southern coast) and at two spatial scales (the site level summarizing extensive vegetation surveys and regionally using remotely sensed vegetation and estimated habitat models). We estimated amount of predicted habitat for both species in established reserves. If predicted overlap in established reserves was low, then we reported vegetation characteristics to inform potential locations for reserves or management opportunities. In the Central Coast, very little overlap existed in vegetation characteristics between Humboldt martens and spotted owls at either the site or regional level. Humboldt martens occurred in young forests composed of small diameter trees with few snags or downed logs. Humboldt martens were also found in areas with very dense vegetation when overstory canopy and shrub cover percentages were combined. In the South Coast, Humboldt martens occurred in forests with smaller diameter trees than spotted owl sites on average. Coastal Humboldt martens may use stands of predicted high quality spotted owl habitat in the Pacific Northwest. Nonetheless, our observations suggest that coastal Humboldt martens exist in areas that include a much higher diversity of conifer size classes as long as extensive dense shrub cover, predominantly in the form of high salal and evergreen huckleberry, are available. We suggest that managers consider how structural characteristics (e.g., downed logs, shrub cover, patch size), are associated with long-term species persistence rather than relying on reserves based on broad cover types. Describing vegetation may partially describe suitability, but available prey or predation risk ultimately influence likelihood of individual Humboldt marten use. Guidelines for diversifying vegetation management, and retaining or restoring appropriate habitat conditions at both the stand level and regionally, may increase management flexibility and identify forest conditions that support both spotted owls and Humboldt martens.

Ketamine and midazolam anesthesia in Pacific martens (Martes caurina).

Abstract The use of midazolam as a tranquilizer for anesthesia in mustelids in conjunction with the cyclohexamine ketamine is not well documented. Because midazolam is fast acting, inexpensive, and quickly metabolized, it may serve as a good alternative to other more commonly used tranquilizers. We trapped and anesthetized 27 Pacific martens (Martes caurina) in Lassen National Forest (northern California, US) August 2010-April 2013. We assessed anesthesia with ketamine at 18 and 25 mg/kg combined with 0.2 mg/kg of midazolam by comparing mean times of induction, return to consciousness, and recovery, plus physiologic parameters. No reversal was used for the midazolam portion of the anesthetic. Mean (±SD) induction for both ketamine dosages was 1.7±0.5 and 1.8±1.0 min, respectively. Return to consciousness mean times were 8.0 min longer (P<0.001) for martens receiving a 25 mg/kg ketamine dosage. Mean recoveries were 15.1 min longer (P<0.003) for the 25 mg/kg ketamine dosage. Physiologic parameter means were similar for both ketamine dosages with no statistically significant differences. Body temperatures and heart and respiratory rates were generally stable, but percentage of oxygen saturation and end tidal carbon dioxide values were below those seen in previous mustelid studies. The combination of ketamine, at both dosages, and midazolam provided reliable field anesthesia for Pacific martens, and supplemental oxygen is recommended as needed.