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Carnivores play critical roles in ecosystems, yet many species are declining worldwide. The Sierra Nevada Red Fox (Vulpes vulpes necator ; SNRF) is a rare and endangered subspecies of red fox limited to upper montane forests, subalpine, and alpine environments of California and Oregon, United States. Having experienced significant distribution contractions and population declines in the last century, the subspecies is listed as at-risk by relevant federal and state agencies. Updated information on its contemporary distribution and density is needed to guide and evaluate conservation and management actions. We combined 12 years (2009–2020) of detection and nondetection data collected throughout California and Oregon to model the potential distribution and density of SNRFs throughout their historical and contemporary ranges. We used an integrated species distribution and density modeling approach, which predicted SNRF density in sampled locations based on observed relationships between environmental covariates and detection frequencies, and then projected those predictions to unsampled locations based on the estimated correlations with environmental covariates. This approach provided predictions that serve as density estimates in sampled regions and projections in unsampled areas. Our model predicted a density of 1.06 (95% credible interval = 0.8–1.36) foxes per 100 km2 distributed throughout 22,926 km2 in three distinct regions of California and Oregon–Sierra Nevada, Lassen Peak, and Oregon Cascades. SNRFs were most likely to be found in areas with low minimum temperatures and high snow water equivalent. Our results provide a contemporary baseline to inform the development and evaluation of conservation and management actions, and guide future survey efforts. [ABSTRACT FROM AUTHOR]

Context: A central problem in road ecology is the need to minimise roadkill without exacerbating fragmentation. The best current solution to this problem is wildlife-exclusion fencing combined with crossing structures. However, because species vary in their propensity to use crossing structures, optimising their design for a suite of species remains a challenge. Aims: We investigated medium- and large-mammal use of undercrossings along Highway 101 in the Central Coast of California. Specifically, we quantified how undercrossing size, surrounding habitat, and the presence of a wildlife-exclusion fence, influenced overall species richness, as well as use by black bear, mule deer, puma, and bobcat. Methods: Using wildlife cameras, we documented mammal use at 11 undercrossings in our study area. We calculated the openness index of each undercrossing and remotely measured habitat features, such as percentage tree cover, and distance to nearest stream. We determined the relative importance of these factors on overall species richness, and the activity of focal species, using generalised linear mixed models in an information-theoretic framework. Key results: Mesocarnivores used a wider variety of undercrossings, and used them more frequently, than did larger mammals. Species richness and bear activity were greater closer to streams, and there was more bear activity at undercrossings within the wildlife-exclusion fence zone than outside it. Deer activity was strongly and positively related to undercrossing openness. Our puma and bobcat analyses were uninformative, likely because we detected puma too infrequently, and because bobcats showed little variation in use across sites. Conclusions: Our results support previous research highlighting natural travel corridors (e.g. riparian areas) as important places for wildlife crossings, both for a diversity of medium–large mammals and a low-density large carnivore. Ungulates may be the most selective taxa in respect to undercrossing use. Implications: Large, open undercrossings along natural travel routes accommodate the greatest diversity of medium–large mammal species. Designing wildlife crossing structures for a suite of species remains a challenge. We monitored 11 crossings along a major highway in California from 2012 to 2017 and found that mammal species richness and black bear use were greater closer to streams, whereas mule deer almost exclusively used large undercrossings. Large undercrossings associated with natural corridors are likely to promote connectivity for the most species of medium–large mammals. Photograph by the authors. [ABSTRACT FROM AUTHOR]

Microplastics are persistent environmental contaminants that to date have been studied primarily in aquatic systems, but few studies have examined their prevalence or impact in terrestrial trophic networks. A recent study documented microplastics in the gastrointestinal (GI) tracts of terrestrial raptors in central Florida. We used protocols based on that study to develop a baseline dataset of microplastics in the GI tracts of terrestrial raptors on the central coast of California. In 2021, Pacific Wildlife Care, a wildlife rehabilitation center in Morro Bay, CA, provided 16 raptor carcasses: three red-tailed hawks (Buteo jamaicensis), four red-shouldered hawks (Buteo lineatus), two great horned owls (Bubo virginianus), and seven barn owls (Tyto alba). We found microplastics in the GI tracts of all 16 birds, with a mean (± SE) of 12.25 (± 1.89) microplastic particles per bird. Of the 196 microplastic particles we observed, microfibers were the most abundant (58%), followed by microbeads (34%), and microfragments (8%). However, microbeads were the most prevalent, found in all 16 birds, followed by microfibers (15 birds), and microfragments (6 birds). The chemical composition and source of these contaminants remains unclear, along with the physiological and ecological implications to raptor populations and their ecosystems, and the extent to which microplastics occur in other terrestrial species and regions in California. [ABSTRACT FROM AUTHOR]

Fossil, archaeological, and morphometric data suggest that indigenous red foxes in North America were derived from vicariance in two disjunct refugia during the last glaciation: one in Beringia and one in the contiguous USA. To test this hypothesis, we conducted a phylogeographical analysis of the North American red fox within its presettlement range. We sequenced portions of the mitochondrial cytochrome b (354 bp) gene and D-loop (342 bp) from 220 historical red fox specimens. Phylogenetic analysis of the cytochrome b gene produced two clades that diverged c. 400 000 years before present (bp): a Holarctic and a Nearctic clade. D-loop analyses of the Nearctic clade indicated three distinct subclades (≥ 99% Bayesian posterior probability); two that were more recently derived (rho estimate c. 20 000bp) and were restricted to the southwestern mountains and the eastern portion of North America, and one that was older (rho estimate c. 45 000bp) and more widespread in North America. Populations that migrated north from the southern refugium following deglaciation were derived from the colonization of North America during or prior to the Illinoian glaciation (300 000–130 000bp), whereas populations that migrated south from the northern refugium represent a more recent colonization event during the Wisconsin glaciation (100 000–10 000bp). Our findings indicate that Nearctic clade red foxes are phylogenetically distinct from their Holarctic counterparts, and reflect long-term isolation in two disjunct forest refugia during the Pleistocene. The montane lineage, which includes endangered populations, may be ecologically and evolutionarily distinct. [ABSTRACT FROM AUTHOR]

The extinction of California's flightless duck, Chendytes lawi, stands out in the faunal history of North America because it involved a marine animal that disappeared in the late Holocene, not in the terminal Pleistocene when humans arrived from Asia, nor with the more recent entry of Europeans and associated resource exploitation. Here we evaluate the duck's ecology by combining a stable isotopic evaluation of its feeding niche with records of human predation and climatic variation to evaluate (1) alternative influences on the duck's extinction and (2) possible ecological consequences of its disappearance. Results indicate that a mid-late Holocene increase in human population density coincided with a decrease in mean sea surface temperatures (SST) and an increase in SST variance, all of which were contemporaneous with the demise of the flightless duck ca. 2500 cal BP. Climate appears to be a main exogenous driver of this extinction event by not only negatively impacting flightless duck food availability, but positively impacting one of the duck's main predators: humans. Isotopic findings indicate the duck had a unique feeding ecology that overlapped equally with analog species reliant mostly on marine invertebrates (sea otters [ Enhydra lutris ]) and on fish (harbor seals [ Phoca vitulina ]). This dietary niche overlap suggests the duck's extinction could have opened foraging opportunities for harbor seals and sea otters. Otter numbers appear to have increased coincident with the duck's decline which also correlates with a decrease in size and abundance of red abalone (Haliotis rufescens), one of the otter's preferred prey. These correlations suggest that new feeding opportunities may have emerged for otters in the face of the duck's extinction, encouraging an increase in otter populations, which then had negative impacts on abalone that also were targeted by humans. Overall findings suggest the possibility of an unanticipated prehistoric precursor to the historic baseline of this nearshore ecosystem. • Pre-contact Holocene extinction of California's flightless duck was highly unusual. • Duck's stable isotopic profile suggests feeding niche unlike any living duck. • Isotope profile suggests feeding ecology akin to sea otters and harbor seals. • Time series comparisons suggest extinction influenced by human predation and climate. • Duck's disappearance may have affected changes in nearshore ecology. [ABSTRACT FROM AUTHOR]