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.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Energetic balance is central to the survival and persistence of free‐ranging animals. Quantifying expenditures and identifying factors that drive energetics informs our understanding of species' ...ecology and their responses to shifting environmental conditions. Approaches used to estimate energetic expenditures of free‐ranging species, such as doubly‐labelled water (DLW), are precise but difficult to implement. Global positioning system (GPS) collars and accelerometers have emerged as alternatives for estimating expenditures, but these techniques have few applications in terrestrial species and no applications in small‐bodied (<5 kg) terrestrial animals. Here, we estimated movement characteristics and field metabolic rates (FMR) of Pacific martens Martes caurina, a small‐bodied carnivore with relatively high energetic costs, in a heterogeneous landscape to explore the role of movement and landscape characteristics in energetics. We concurrently used DLW and GPS collars to investigate the relationship between movement characteristics and FMR. Movement velocity explained the greatest amount of variation in mass‐specific FMR and we used this relationship to predict expenditures of previously collared martens. We found that predicted mass‐specific FMR was highest among males and increased in open patches primarily as a result of increased velocity and more erratic movements. Additionally, martens moving through deep snow also exhibited increased FMR. Our work shows movement metrics can effectively explain variation in FMR and identify landscape features, like forest structure and snow depth, that influence movements with cascading effects on energetics for free‐ranging mammals in rapidly changing systems.
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.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Niche conservatism—the retention of ecological traits across space and time—is an emerging topic of interest because it can predict responses to global change. The conservation of Grinnellian niche ...characteristics, like species‐habitat associations, has received widespread attention, but the conservation of Eltonian traits such as consumer–resource interactions remains poorly understood.
The inability to quantify Eltonian niches through space and time has historically limited the assessment of Eltonian niche conservatism and the dynamics of foraging across populations. Consequently, the relative influence of endogenous factors like phylogeny versus exogenous features like environmental context has rarely been addressed.
We tested Eltonian niche conservatism using a paired design to compare foraging among four populations of American martens Martes americana and Pacific martens Martes caurina, morphologically and ecologically similar sister taxa that are allopatrically distributed throughout western North America. We developed a three‐stage isotopic framework and then quantified dietary niche overlap between the sister species and paired island‐mainland sites to assess the relative influence of endogenous (i.e., species) versus exogenous (i.e., environment) factors on Eltonian niches. First, we calculated pairwise dietary overlap in scaled δ‐space using standard ellipses. We then estimated proportional diets (“p‐space”) for individuals using isotopic mixing models and developed a novel utilization distribution overlap approach to quantify proportional dietary overlap. Lastly, we estimated population‐level proportional diets and quantified the differential use of functional prey groups across sites.
We detected no pairwise overlap of dietary niches in δ‐space, and distributions of individual diets in p‐space revealed little overlap in core diets across populations. All pairwise comparisons of individuals revealed significant differences in diet, and population‐level comparisons detected contrasting use of functional prey groups.
We developed a multi‐faceted isotopic framework to quantify Eltonian niches and found limited evidence of Eltonian niche conservatism across carnivore populations. Our findings are consistent with the growing recognition of dietary plasticity in consumers and suggest that consumer–resource dynamics are largely driven by exogenous environmental factors like land cover and community composition. These results illustrate the context‐dependent nature of foraging and indicate consumer functionality can be dynamic.
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Simplifying stand structure to reduce fuel density is a high priority for forest managers; however, affects to Pacific marten (Martes caurina) movement and connectivity are unknown. We evaluated ...whether thinning forests to reduce fuels influenced movements of Pacific marten. We collected movement paths from 22 martens using global positioning system telemetry to evaluate habitat selection and describe movement patterns. We quantified motion variance, speed, and path sinuosity in 3 stand types that differed in structural complexity (i.e., complex dense, simple thinned, and open). We hypothesized marten movement would differ between stand types and predicted that 1) martens would select stand types with increased structural complexity (complex > simple > open); 2) movements would increase in complexity (sinuosity, motion variance) and decrease in speed when martens traveled through stands with increased structural complexity; 3) speeds would increase during summer, indicating increased movement during the breeding season; and 4) males would move more rapidly because of their larger home ranges. Martens traveled 0.5–27.2 km/day and an average (SD) of 1.4 (0.4) km/hour. Martens selected home ranges with fewer openings compared to the study area overall. Within home ranges, martens strongly selected complex stands over simple stands and openings. Speed and movement complexity were most consistent over time and movements were more sinuous and slower in complex stand types compared with openings and simple stands. Movement was erratic and more linear in openings than in both complex and simple stands. In simple stands, movement patterns were intermediate between complex stands and openings. Females generally moved more slowly, sinuously, and less variably compared to males. Martens moved more quickly, less sinuously, and more variably during winter compared to summer. However, martens avoided stands with simplified structure, and the altered patterns of movement we observed in those stands suggested that such treatments may negatively affect the ability of martens to forage without increased risk of prédation. Fuel treatments that simplify stand structure negatively affected marten movements and habitat connectivity. Given these risks, and because treating fuels is less justified in high elevation forests, the risks can be minimized by applying treatments below the elevations where martens typically occur.
Guidelines suggest using a regurgitant fraction of 50% and regurgitant volume of 60 ml for determination of severe mitral insufficiency. Recent MRI data has suggested that a regurgitant fraction of ...40% defines severe primary mitral insufficiency. We sought to determine whether there were gender differences in primary mitral regurgitant volumes for regurgitant fractions of 40% and 50%. A database search identified 394 patients that had MRI with a mitral regurgitant volume ≥ 10 ml or a study indication of mitral insufficiency. Chart review identified 97 patients with primary mitral insufficiency. Of these patients, 53 (54%) were women. Men had significantly larger left ventricular volumes, myocardial mass, stroke volumes and mitral regurgitant volumes (37 ± 25 ml vs. 24 ± 12 ml). The difference in regurgitant fraction between genders was not significant (27 ± 14% vs. 24 ± 11%;
p-value
=
0.24
). Regurgitant fraction and regurgitant volume had a strong linear correlation in both men (r = .95) and women (r = .92). Despite similar linear correlations, the slope-intercept equations differed significantly between men and women (p < .001). A regurgitant fraction of 40% correlated with a regurgitant volume of 59 ml in men and 39.5 ml in women, while a regurgitant fraction of 50% correlated with a regurgitant volume of 76.2 ml in men and 49.6 ml in women. Regurgitant fraction, determined by cardiac MRI, provides a gender independent assessment of primary mitral insufficiency, and suggests that regurgitant volume thresholds for severe primary mitral insufficiency may be lower in women.
When wildlife species exhibit unexpected associations with vegetation, replication of studies in different locales can illuminate whether patterns of use are consistent or divergent. Our objective ...was to describe fine‐scale forest conditions used by Pacific martens (Martes caurina) at 2 study sites in northern California that differed in forest composition and past timber harvest. We identified denning and resting locations of radio‐marked martens and sampled structure‐ and plot‐level vegetation using standardized forest inventory methods between 2009–2021. Woody structures used by martens were significantly larger than randomly available structures across types (e.g., live tree, snag, log) and at both study sites. Den and rest structures occurred in areas characterized by higher numbers of logs and snags, lower numbers of live trees and stumps, larger diameter live trees and logs, and greater variation in live tree and log diameter. Features of denning and resting locations were largely consistent across study sites and were generally representative of fine‐scale forest heterogeneity and increased structural complexity, conditions that martens have been widely associated with at broader spatial scales (i.e., home range or landscape). The spatial occurrence of denning and resting locations may indicate that fine‐scale structural complexity facilitates marten foraging while reducing predation risk. Our work offers timely and directed information that can guide forest management in the context of increased landscape change.
We characterized forest conditions used at fine spatial scales by Pacific martens at 2 study sites in northern California over a 12‐year time period (2009−2021). Woody structures (e.g., live and dead trees) used by martens were significantly larger diameter than randomly available structures and consistently occurred in heterogeneous and physically complex forest stands across study sites, despite the sites differing in past land use practices (e.g., timber harvest intensity) and forest composition. Focused retention of such conditions during management activities could benefit martens and a suite of other forest‐dependent wildlife species.
Holarctic martens (genus Martes) are small carnivores that are considered functionally solitary, with both resource scarcity and martens' inability to store energetic reserves posited as precluding ...social behavior. Interactions between martens are expected to be largely agonistic with the exception of mating and rearing of kits by adult females. Nonetheless, we documented multiple instances of conspecific tolerance by Pacific martens (M. caurina) during long-term monitoring of radio-marked animals in 2 study populations. Observations from radio-tracking and remotely triggered camera trap photographs suggested that pairs of martens traveled, foraged, and rested together. Presumed marten associations occurred both inter- and intrasexually and often, but not exclusively, consisted of younger (i.e., juvenile and subadult) individuals. Although social interactions between martens appeared to be highly uncommon, our work nonetheless supports mounting evidence that carnivore social systems are more nuanced than presumed. We briefly explore mechanisms that could allow for plasticity in marten sociality and offer suggestions on how future efforts can continue to elucidate behavioral phenomena that may be rare and difficult to document. Las martas holárticas (género Martes) son pequeños carnívoros considerados funcionalmente solitarios, y se postula que la escasez de recursos y la incapacidad de almacenar reservas energéticas impiden su comportamiento social. Se espera que las interacciones entre martas sean en gran medida agonísticas, con la excepción del apareamiento y cuidado de las crías por parte de las hembras adultas. No obstante, hemos documentado múltiples casos de tolerancia conespecífica por parte de martas del Pacífico (M. caurina) durante el monitoreo a largo plazo de animales marcados por radio en dos poblaciones de estudio. Las observaciones realizadas a partir del monitoreo por radio y de fotografías tomadas con cámaras trampa disparadas a distancia, sugieren que las parejas de martas viajaban, buscaban comida y descansaban juntas. Las presuntas asociaciones de martas se produjeron tanto intersexualmente como intrasexualmente y a menudo, aunque no exclusivamente, estaban formadas por individuos jóvenes (i.e., juveniles y subadultos). Aunque las interacciones sociales entre martas parecen poco frecuentes, nuestro trabajo apoya la creciente evidencia de que los sistemas sociales de los carnívoros tienen más matices de lo que se presume. En este trabajo, exploramos brevemente los mecanismos que podrían permitir la plasticidad en el comportamiento social de la marta y ofrecemos sugerencias sobre cómo futuros esfuerzos pueden continuar para dilucidar fenómenos de comportamiento que pueden ser raros y difíciles de documentar.
Celotno besedilo
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Quantifying the demography of wildlife populations is imperative to evaluating population trends. Understanding patterns of influential demographic parameters often requires investigation of ...mechanisms influencing demography, which can be difficult to determine for cryptic species. We radio‐tracked Pacific martens (Martes caurina), a small‐bodied and elusive mesocarnivore, to estimate survival, determine causes of mortality, and assess co‐occurring pathological conditions. We tracked 18 female and 33 male martens for an average (±SD, range) of 16.35 months (±8.7, 1–41) from 2009–2013 and 2015–2017 in northern California. Annual survival rates were 0.81 (95% CI = 0.66–0.95) and 0.68 (95% CI = 0.57–0.79) for female and male martens, respectively. We documented 16 marten mortalities, 13 of which were suspected predation events. Seven mortalities were empirically linked to predation via clinical forensic evidence, with bobcats (Lynx rufus; n = 5) representing the majority of predator species identified. The proximate cause of mortality for 1 marten was attributed to toxicosis from anticoagulant rodenticide exposure, which has not been previously reported in free‐ranging martens. Our findings suggest the timing of marten mortality aligned with reproductive periods that incurred increased energetic requirements, which may result in increased predation risk. We propose continued pairing of field and clinical assessments to better substantiate mortality sources of wildlife, elucidate underlying pathology, and identify novel stressors.
Our study revealed Pacific marten mortalities aligned with reproductive periods that incur increased energetic demands, which may result in increased predation risk. Further, we documented the first known occurrence of anticoagulant rodenticides in free‐ranging, North American martens. We propose pairing of field and laboratory clinical assessments to better substantiate mortality sources of wildlife, elucidate underlying pathology, and understanding how pathology and toxicants affect individual and population‐level fitness.
Occupancy‐based monitoring has become an important tool in wildlife conservation and management. Nonetheless, meeting occupancy modeling assumptions and providing biologically accurate information ...are difficult tasks over long time periods, large areas, or when monitoring multiple species. In occupancy modeling frameworks, derived grids are commonly used to divide landscapes into discrete units. Grid sizes that match the home range size of the species of interest are considered optimal, but this practice is complicated as home range size may vary by sex, habitat quality, or among species. Additionally, studies often assume their survey methods sample an entire grid cell when the actual effective sampling area may be much smaller. The effect of reduced effective sampling area on occupancy estimation has received little attention to date, despite being flagged as a critical issue. In this study, we assessed (1) how the relationship between effective area, home range size, and grid size affects power to detect trends in occupancy; (2) how varying the sampling design factors of effective area, duration, detection probability, and resurvey interval influence monitoring efficiency; and (3) determine whether a single sampling design can simultaneously detect declines in two species with different home range sizes. We used a spatially explicit simulation framework to create biologically realistic declining populations over 10 yr and assessed statistical power to detect known declines using occupancy modeling. We found that effective area and detection probability had the greatest influence on statistical power. We could not reliably detect declines when detection probability was low or when effective sampling area was <1/4 cell. We conclude that failing to account for effective area less than the cell size will result in overestimation of statistical power. Our simulations suggest occupancy models can detect declines for two species with different home range sizes using the same grid cell size under certain conditions, for instance, surveying >25% of the landscape, ≥25% effective area, and fixed sampling locations. Further, increasing resampling interval greatly increased monitoring efficiency. Our results show monitoring planning requires explicit consideration of effective sampling area and methods with sufficient detectability to detect population declines.
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