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Cinereus shrew
Cinereus shrew
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Cinereus shrew[1]
Secure
Secure  (NatureServe)[3]
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Eulipotyphla
Family: Soricidae
Genus: Sorex
Species:
S. cinereus
Binomial name
Sorex cinereus
Kerr, 1792
Cinereus shrew range

The cinereus shrew or masked shrew (Sorex cinereus) is a small shrew found in Alaska, Canada, and the northern United States.[2] This is the most widely distributed shrew in North America, where it is also known as the common shrew.

Description

[edit]

It is grey-brown in colour with a light grey underside and a pointed snout. It has a long tail that is brown on top and pale underneath with a dark tip. Its body is about 9 cm (3.5 in) in length including a 4 cm (1.6 in) long tail. It weighs about 5 g (0.18 oz). It has darker colouring than other shrews. Masked shrews can live up to two years, but, on average, only survive eighteen months.

In a long-term study done in Alaska, Yom-Tov and colleagues (2005) found that the masked shrew's body size contradicts Bergmann's rule.[4] The study, done on 650 specimens and spanning from 1950 to 2003, examined body size in relation to ambient temperature. Measurements of body weight and the length of the tail, ear, hind foot, and body were taken. Results yielded that the masked shrew's body size decreased with high latitudes and with lower mean January temperatures, a trend that opposed Bergmann's Rule. It was suggested that this may be a coping mechanism to limit total energy requirements due to decreased food availability in winter months. Additionally, it was shown that body and tail length increased with rising temperatures during the second half of the twentieth century. This may be due to higher temperatures increasing the availability of the shrew's main diet.

Distribution

[edit]

The masked shrew is the most widely distributed shrew.[5] Its range covers most of northern North America extending south as far down to Maryland, along the Rocky Mountains in the west, and to the Appalachians in the east. This species was introduced into Newfoundland in the late 1950s. It can be found in many types of habitat like arid grasslands, moist areas, woodland, and tundra. The masked shrew mostly lives in humid areas and with high levels of vegetation to hide in. Moisture determines the abundance of this shrew.

Predation and parasitism

[edit]

Predators include larger shrews, hawks, owls, shrikes, snakes, herons, foxes, leopard frogs, bluebirds, brown trout, and weasels. Masked shrews are susceptible to many types of parasites, like fleas and tapeworms.[6] Cowan and colleagues (2007) found that the high volume of food masked shrews consume causes them to be more susceptible to parasitism. Since males have larger ranges, they have a higher exposure to parasites.[6]

Diet and prey

[edit]

Masked shrews are opportunistic generalists. They eat insects, worms, snails, small rodents, salamanders, and seeds. Due to its high metabolism, the masked shrew can eat three times its weight a day.[7] The shrew has to eat almost constantly, because they can only survive a few hours without food.[7] Their metabolism drops when they are at rest.

McCay and colleagues (1997) found a higher abundance of masked shrews in non-irrigated forests due to a higher availability of larval insects, which is the preferred food source of the masked shrew. Masked shrews chose Lepidoptera larva over other food sources.[8]

Behavior

[edit]

This animal is active day and night year-round. Masked shrews can be nocturnal or diurnal depending on the weather. Doucet and colleagues (1974) showed that rain increases the nocturnal activity of the masked shrew, while cloud cover increases day and night activity.[9] It digs tunnels but also uses tunnels created by other small mammals. It uses dry grass to make nests in these tunnels. It can make high frequency pulses and has lateral scent glands. The home range of the masked shrew depends on availability of food, but it is on average 0.55 hectare. It has a low tolerance for other shrews in its home range. Merritt and colleagues (1995) found that its mass declined by half from summer to winter and non-shivering heat production, energy conservation, and reduced body mass.[5]

Reproduction

[edit]
A litter of four newborn masked shrews

Masked shrews living at high latitudes are born in late spring and summer, reach adult size by the time they leave their nests, and complete their life cycle within a year.[4] They are born during spring or summer, remain immature in winter, and breed the following spring.[5] Masked shrews breed from May to September. Females have one litter of 6 to 7 young during the breeding season. The young are born hairless and clawless and have translucent abdominal walls.[7] Body mass increases and peaks at twenty days, then decreases when the young leave the nest after about 27 days. Masked shrews have a high chance of mortality during their first two months of life and most die during the first year. Masked shrews become sexually mature at two months, but wait until their first spring to breed.

References

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Sources

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Cinereus shrew

View on Grokipedia
from Grokipedia
The cinereus shrew (Sorex cinereus), also known as the masked shrew, is a small insectivorous belonging to the Soricidae, recognized as the most widely distributed species in . It features brown fur on its dorsal side and grayish-white fur on its ventral side, which darkens slightly in winter, with a total body length of about 99 mm, including a tail of roughly 40 mm, and weighs 3–6 grams in adulthood, showing no significant . This shrew is characterized by its high metabolic rate, requiring it to consume more than its body weight in food daily, primarily , spiders, and other . Native to , most of , and the —from the Atlantic to Pacific coasts and northward to the edge of the but absent from extreme regions and certain islands like —the cinereus shrew occupies diverse habitats including moist forests, meadows, riverbanks, willow thickets, and edges of woodlands. It is solitary and active year-round. Reproduction occurs from to , with females typically producing 1–2 litters per season of 5–8 young each, born after a 18–22 day ; newborns weigh 0.2–0.3 g and open their eyes at 17–18 days, by 20–21 days and reaching at approximately 5 months, though breeding often begins the following spring. The average lifespan is 1–2 years in the wild, with most individuals dying before adulthood due to their intense metabolic demands and environmental pressures. Classified as Least Concern by the as of , the is common and stable across its range, facing no major threats but potentially impacted locally by habitat loss from development, , or .

Taxonomy

Classification

The cinereus shrew, scientifically known as Sorex cinereus, was formally described under its by Kerr in 1792, drawing from earlier observations by of similar North American shrew specimens. This naming established it as a distinct within the diverse shrew lineage, commonly referred to as the masked shrew or cinereous shrew. In the taxonomic hierarchy, S. cinereus is classified under Kingdom Animalia, Phylum Chordata, Class Mammalia, Order , Family Soricidae, Subfamily Soricinae, Genus Sorex, and Species S. cinereus. Within the Soricidae family, it belongs to the red-toothed shrews of the Soricinae subfamily, characterized by reddish pigmentation on the tips of their teeth due to iron deposits in the enamel, which likely enhances tooth durability. The genus Sorex encompasses approximately 88 species distributed across and , representing one of the most speciose genera in the family. Evolutionarily, S. cinereus is part of the Soricinae, with the genus Sorex having a record extending to the epoch, approximately 11.6 to 5.3 million years ago, based on dental remains from n and n sites. This placement highlights its ancient origins within the radiation, with Soricinae lineages colonizing during the middle through multiple dispersals from .

Subspecies and recent revisions

Historically, the cinereus shrew (Sorex cinereus) was recognized with several subspecies, distinguished primarily by geographic variations in pelage coloration and cranial morphology across its North American range. Prominent examples include S. c. cinereus, which occurs in northern populations from Alaska to the northeastern United States, and S. c. haydeni (now recognized as the distinct species S. haydeni), associated with the Rocky Mountains and characterized by paler pelage and specific dental traits. Other historically noted subspecies encompass S. c. acadicus, S. c. hollisteri, S. c. lesueurii, S. c. miscix, S. c. ohionensis, and S. c. streatori, each tied to regional differences in habitat and morphology. A major taxonomic revision in 2025 by Victor E. Diersing elevated Sorex fontinalis—previously treated as a of S. cinereus and known as the —to full status. This change was supported by analyses of morphological traits (including dental and cranial features), parapatric distributions in and adjacent states, and genetic data indicating no intergradation between S. fontinalis and S. cinereus. The revision narrows the eastern U.S. range of S. cinereus by reassigning populations in mesic forests and wetlands previously identified as S. c. fontinalis. Additionally, in 2024, Diersing recognized S. c. nigriculus (Tuckahoe masked shrew) as a distinct based on morphological evidence. Taxonomic revisions such as this rely on criteria like distinct dental morphology (e.g., tooth row length and shape), pelage color variations (darker in S. cinereus versus grayer in related forms), and habitat specificity (e.g., upland versus lowland preferences). Ongoing debates center on integrative approaches, balancing morphological evidence with molecular phylogenies that suggest S. cinereus may encompass additional cryptic within the diverse Sorex genus. Following the 2025 split of S. fontinalis and accounting for prior elevations like S. haydeni, approximately 8 subspecies of S. cinereus are currently recognized.

Description

Physical characteristics

The cinereus shrew (Sorex cinereus), also known as the masked shrew, possesses a small, cylindrical body with a long, pointed snout, tiny eyes, small ears largely hidden in the fur, and five-toed feet adapted for terrestrial movement. The tail is bicolored—darker above and paler below—with a slightly darker tip, and it comprises roughly half the head-body length, averaging about 4 cm in length. Adult individuals typically measure 7–10 cm in head-body length, with a tail of 2–5 cm and a weight of 2.5–6 g, though measurements can vary slightly with latitude. The dorsal pelage is grey-brown, contrasting with the lighter ventral , creating a "masked" appearance due to a darker patch around the eyes and face. The exhibits subtle bicoloration, and the overall is dense, providing insulation. Cranially, the features a long rostrum and a narrow braincase, with an average condylobasal length of 15.22 mm and cranial breadth of 7.48 mm. Dentally, it has 32 teeth following the formula I 3/1, C 1/1, P 3/1, M 3/3, including several unicuspid teeth with characteristic reddish tips typical of the family Soricidae. Sensory adaptations include poor vision due to small eyes, compensated by an acute for detecting prey and an enhanced sense of hearing, potentially aided by echolocation-like pulses in the 30–60 kHz range; long vibrissae () further assist in through dense .

Seasonal variations

The masked shrew (Sorex cinereus) undergoes pronounced physiological adaptations to seasonal changes, particularly in response to winter conditions, as part of Dehnel's phenomenon—a reversible reduction in body size observed in several species. Body mass typically decreases substantially from summer to winter, with reductions up to 50% reported in northern populations to minimize energy expenditure and heat loss in cold environments. A 2025 study on southern masked shrews documented an average 13% decrease in body mass during winter, alongside reductions in skeletal dimensions like braincase height and length, highlighting the plasticity of this adaptation even in milder climates. This seasonal shrinkage extends to the , where volume decreases by approximately 9% through water loss rather than neuronal , allowing for rapid regrowth in spring. The mechanism involves shifts that enhance dehydration tolerance in neural tissues, as evidenced by a 2025 eLife study on common shrews (Sorex araneus), which shares this trait with the masked shrew. Concurrently, the winter pelage becomes thicker and denser, with length increasing from 3.6 mm in summer to 4.4 mm and density rising to 8100 hairs per mg from 7767, providing improved insulation against low temperatures. Metabolic adjustments further support winter survival, with seasonal increases in mass-specific resting metabolic rate (from 5.75 ml O₂ g⁻¹ h⁻¹ in spring to 8.30 ml O₂ g⁻¹ h⁻¹ in autumn) and enhanced nonshivering thermogenesis capacity (peaking at nearly twice summer levels in winter), facilitating enhanced nonshivering thermogenesis to maintain body temperature despite the overall smaller body size. This counters expectations from Bergmann's rule, under which larger body sizes are predicted in colder regions; instead, masked shrew body size decreases with latitude, a pattern linked to elevated metabolic demands in warmer southern areas where prey is more abundant year-round. Data spanning 1950-2003 from Alaskan populations confirmed this trend. These adaptations contribute to a typical lifespan of 12-18 months in the wild, where high overall mortality rates are offset by improved overwinter survivorship for individuals that successfully shrink and endure food scarcity.

Distribution and habitat

Geographic range

The cinereus shrew (Sorex cinereus), also known as the masked shrew, has the broadest distribution of any shrew species in North America. Its native range spans Alaska and most of Canada, including all provinces and territories, extending southward into the northern United States from Washington state eastward to Maine. In the U.S., the species occurs along the Pacific Northwest coast through Idaho and Montana, reaches the Rocky Mountains down to New Mexico and Colorado, and extends across the northern Great Plains into states such as Wyoming, Nebraska, Iowa, Illinois, Indiana, and Ohio. Further east, it inhabits the northern Appalachian Mountains from New York to Pennsylvania and northward, while populations in the mid-Atlantic region (southeastern Pennsylvania to northern Virginia, including the Atlantic coastal plain to northern Maryland and New Jersey) and parts of the southern Appalachians are now recognized as the separate species S. fontinalis. The ' range covers more than 2,500,000 km², making it the most widespread in , with an altitudinal distribution from near to elevations of 3,625 m in mountainous regions. It is absent from arid regions of the , such as much of the desert Southwest, and the southern prairies, where drier conditions limit its occurrence; near its southern boundaries, populations are typically confined to higher elevations. Historically, the cinereus shrew was intentionally introduced to Newfoundland in 1958 from to control outbreaks; by 1973, it had become established across the island, with no other known translocations outside its native range. Regarding , the nominate S. c. cinereus occupies much of the boreal forest zones across its distribution, while western montane populations were formerly assigned to S. c. haydeni; however, recent taxonomic revisions as of 2025 have elevated the eastern S. fontinalis (formerly a ), which occupies the mid-Atlantic region from southeastern south to , including the , to full status, affecting delineations in the Appalachian and mid-Atlantic portions of the range.

Habitat preferences

The cinereus shrew (Sorex cinereus) prefers moist ecosystems such as , coniferous, or mixed forests, wetlands, bogs, swamps, and meadows with dense vegetation, while generally avoiding arid open grasslands and deserts. These habitats provide the necessary cover and resources, with population densities peaking in areas of high moisture availability. Within these ecosystems, the favors microhabitats featuring leaf litter, -covered logs, rocks, and stream banks that offer concealment and maintain elevated levels. It requires environments with high , often exceeding 50-60% in litter layers, and moderate temperatures typical of cool, mesic conditions to support its high metabolic rate. Nesting occurs in shallow self-dug burrows or commandeered tunnels, as well as surface nests constructed from woven grass and (typically 4-6 cm in diameter) under logs or in concavities with multiple exit tunnels; home ranges average 0.2-1 , varying with population density. The species demonstrates considerable adaptability, tolerating disturbed sites like post-logging clearcuts or old fields provided regrowth restores cover and . It occupies an elevational gradient from lowlands to subalpine zones up to 3,600 m, with higher abundances in , moister upland forests near range limits. In areas of , such as with the smoky shrew (S. fumeus), S. cinereus partitions microhabitats by slightly drier or less log-dense mesic sites, reducing competition through fine-scale preferences for and cover.

Behavior and ecology

Activity patterns

The masked shrew (Sorex cinereus) displays a polyphasic , remaining active day and night year-round with frequent bouts averaging 19 periods totaling about 217 minutes over 24 hours and cycles roughly every 1.5 hours. Its activity pattern is bimodal and predominantly , featuring peaks around midnight, particularly between 01:00 and 02:00, though diurnal activity occurs as well; this shifts toward greater during rainy or cloudy conditions, where activity intensifies, while overall levels rise with warmer temperatures unless overridden by . As solitary and territorial animals, masked shrews maintain exclusive home ranges averaging 0.55 ha for males—typically larger than those of females—with minimal overlap indicating low tolerance for conspecifics outside brief aggregations in shared systems. Males expand their ranges during the breeding season, and individuals navigate their territories using surface runways along logs and leaf litter, as well as tunnels created by moles or voles. They produce high-frequency squeaks and ultrasonic vocalizations that aid in , functioning in a manner akin to crude echolocation for detecting obstacles and features at close range. Masked shrews do not hibernate but enter short torpor bouts during rest periods in extreme cold, characterized by depressed metabolic rates that conserve energy without prolonged dormancy. Additionally, they exhibit Dehnel's phenomenon, involving a seasonal reduction in body size and mass during winter to further aid energy conservation; a 2025 study documented decreases of 13% in body mass, 11.5% in braincase height, and 8.7% in femur length in southern populations at 35.7° N latitude. Their average lifespan is about 18 months, rarely exceeding 24 months, with high mortality driven largely by predation risk; population dynamics exhibit marked fluctuations linked to weather variations, such as increased abundance following favorable moist conditions that boost activity and survival.

Diet and foraging

The Cinereus shrew (Sorex cinereus) exhibits opportunistic insectivory, with comprising the majority of its diet, approximately 80% by volume across studied populations. Primary prey includes larvae, which form a dominant component and elicit a in consumption rates tied to their availability; other key items are beetles (both adults and larvae), earthworms, snails, , spiders, and fly larvae. Juveniles show a heightened preference for larvae compared to adults, reflecting seasonal abundance peaks and recruitment patterns observed in forests from 1983 to 1985. Diet composition varies geographically—for instance, constitute up to 50% of intake in , while insect larvae predominate in —but consistently outnumber other categories. Vertebrates such as small and salamanders, along with occasional plant matter like seeds and fungi, account for the remainder, typically less than 20% combined. High metabolic demands drive the shrew's foraging intensity, with an average resting of 780 beats per minute and oxygen consumption rates reaching 30.0 ml O₂ g⁻¹ h⁻¹, among the highest recorded for mammals of comparable size. To meet these needs, individuals consume 1.25–3.3 times their body weight daily, equivalent to about 11.7 g for a 3.6 g adult, often in frequent bouts totaling around 217 minutes of activity per day. Excess food is cached in burrows, enhancing during brief periods, as shrews can only endure 3–4 hours without eating due to their elevated . Foraging occurs primarily on the , where the probes moist soil and leaf litter with its elongated to detect prey via touch and olfaction, supplemented by potential echolocation for locating hidden in low light. Activity peaks nocturnally in summer (up to 85% of foraging between 01:00 and 02:00), shifting toward diurnal patterns in winter to align with under-snow prey availability and milder midday temperatures. run swiftly, jump 10–15 cm to pursue mobile prey, and climb low vegetation when necessary, destroying far more potential food than consumed—up to 833 larch eonymphs daily per individual when abundant. Seasonal shifts in diet reflect prey scarcity, with increased reliance on plant material such as and subterranean fungi during winter when availability declines. Studies from 1997–2004 in irrigated boreal forests confirmed persistent preference in summer but noted broader selectivity in leaner seasons, with no significant methodological updates evident by 2025. As a trophic generalist, the Cinereus shrew plays a key role in controlling forest populations, reducing densities of pests like caterpillars and sawflies through predation disproportionate to its biomass.

Predators and parasites

The cinereous shrew (Sorex cinereus), due to its small size and frequent surface activity, is highly vulnerable to predation by a variety of avian and mammalian carnivores. Primary avian predators include hawks, , and shrikes, which detect the shrew's movements in open habitats. Mammalian predators such as foxes, weasels, and larger species like the short-tailed shrew (Blarina brevicauda) also frequently prey upon it, often ambushing individuals in dense cover. Snakes, including garter snakes and other small reptiles, contribute to predation, particularly in warmer months when shrews are more active above ground. To mitigate these risks, cinereous shrews employ anti-predator strategies such as remaining concealed under leaf litter and during the day, exhibiting primarily nocturnal activity patterns, and relying on rapid dashes or freezing behaviors when threatened. Predation imposes significant pressure, with annual mortality rates approaching 90% in some populations, largely attributable to predator encounters rather than other factors. The cinereous shrew hosts a diverse array of ecto- and , reflecting its role in food webs and exposure during foraging. Ectoparasites commonly include fleas, ticks such as Ixodes species, and mites, which attach to the shrew's fur and ; these are particularly prevalent in moist, vegetated habitats where vectors thrive. encompass nematodes (e.g., Liniscus spp. in the and Angiostrongylus michiganensis in the lungs) and cestodes like tapeworms, with gastrointestinal helminths reported in up to 96% of examined individuals in regional surveys. Males typically exhibit higher parasite loads than females, linked to their larger home ranges and increased encounters with infected hosts or vectors during the breeding season. Lung infections, such as yeast-like , occur infrequently but can coincide with nematode presence, though without evident inflammatory responses in most cases. Parasitic infestations can impact shrew populations through direct effects like reduced fitness and secondary disease transmission, with ectoparasites serving as vectors for pathogens. Notably, ticks infesting cinereous shrews transmit Borrelia burgdorferi, the causative agent of , positioning the shrew as a competent reservoir host that infects up to 50% of feeding larvae in endemic areas. Heavy parasite burdens may exacerbate mortality in humid environments, where and densities peak, contributing to fluctuations in shrew abundance; however, no shrew-specific pathogens dominate, and infestations rarely cause epizootics.

Reproduction

Breeding season

The breeding season of the cinereus shrew (Sorex cinereus) typically begins in late or May and extends through August or across much of its range, with pregnant and lactating females observed during this period and males exhibiting reproductive activity into early October. In northern populations, the season is more restricted to May through , primarily triggered by lengthening photoperiods and increasing temperatures that signal favorable conditions for reproduction. Southern populations may experience extended breeding, potentially into November or sporadically year-round if food remains abundant, though mid-winter births are rare and documented only in specific locales like . These temporal patterns align with seasonal physiological changes, such as gonadal enlargement, that prepare individuals for . The is polygynous, characterized by males roaming widely to access multiple females, often forming small aggregations that facilitate encounters and vocalizing behaviors. Males expand their activity ranges during this time, utilizing lateral to mark territories and burrows, which helps locate receptive females through olfactory cues. Male adaptations include significant enlargement of the testes in spring, leading to swollen inguinal regions, alongside heightened that peaks during the breeding period to compete for mates. Gestation lasts approximately 17–25 days, after which females produce 1–4 litters per , with an average litter size of 6–7 young (ranging from 3 to 10). Although occurs in some soricid populations to delay implantation, it is not prominently reported for S. cinereus. Breeding success is influenced by environmental factors, including availability and conditions; abundant resources can prolong the , while cold springs or adverse may delay onset and reduce reproductive output. Moisture levels in habitats also play a key role, with drier conditions suppressing breeding activity.

Life cycle

The young of the cinereus shrew (Sorex cinereus) are altricial, born hairless and blind within grass-lined nests constructed by the female. Newborns weigh approximately 0.28 g and measure 12–14 mm from crown to rump. Ears open between 14 and 17 days, while eyes open at 17–18 days; occurs between 20 and 27 days, after which the young begin independent foraging. Body mass increases rapidly during this period, peaking at around 3.5 g by 20 days before a temporary decline prior to nest departure at approximately 27 days. Growth continues post-weaning, with individuals attaining adult size by about 2 months of age and reaching at 2–3 months. However, most delay first breeding until the following spring, exhibiting a semelparity-like pattern where reproduction occurs primarily in the second year. Juveniles leave the nest at 3–4 weeks and disperse shortly thereafter to establish home ranges, typically averaging 0.55 ha, though specific dispersal distances vary with local conditions and density. Mortality is exceptionally high during early life, with approximately 80% of individuals dying before , and the greatest losses occurring in the first two months due to and predation. Of those that survive initial vulnerability, about 50% succumb within the next five months. The life cycle includes a juvenile phase from birth to 6 months and an adult phase from 6 to 18 months, with few exceeding 16 months in the wild and a maximum recorded lifespan of 24–30 months; overwinter survival for summer-born cohorts is low, enabling only a subset to breed the following year. No evidence of is observed, consistent with the species' short lifespan and high metabolic demands. Studies from the early 2000s confirm these developmental and reproductive patterns.

Conservation

Status

The cinereus shrew (Sorex cinereus) is assessed as Least Concern on the , a status assigned in 2008 and unchanged as of 2025, owing to its extensive geographic range across and lack of evidence for population declines. NatureServe assigns it a global rank of G5 (secure), with subnational ranks of S5 (secure) in most U.S. states and Canadian provinces where it occurs; following the 2025 taxonomic recognition of Sorex fontinalis as a distinct , while the species overall is secure, the subspecies S. c. nigriculus is listed as T1 (critically imperiled) by NatureServe. The species is considered abundant, with population densities typically ranging from 5 to 20 individuals per in suitable habitats. Ongoing monitoring through trapping surveys indicates no significant population declines, as confirmed by a 2024 report documenting its security across diverse habitats. No specific legal protections are required for the cinereus shrew, as it is not listed under the U.S. Endangered Species Act or Appendix I, II, or III. The cinereous shrew faces minor threats primarily from associated with and , which can disrupt connectivity and reduce available cover, though the species demonstrates resilience through its broad adaptability across moist woodlands and edges. applications in agricultural and forested areas further pose risks by diminishing prey availability, as evidenced by shifts in diet and reduced lepidopteran larvae consumption following exposure in jack pine plantations. Climate change presents potential challenges, including northward range shifts driven by warming temperatures that favor expansion into previously unsuitable northern habitats, such as Alaskan tundra margins. Warmer winters may disrupt seasonal adaptations like Dehnel's phenomenon, where body size reduction aids overwinter survival, but such impacts remain unconfirmed by studies through 2025. Population trends for the cinereous shrew are stable overall, with the species classified as Least Concern globally due to its widespread distribution and abundance exceeding 25,000 individuals in regions like . However, populations exhibit cyclic fluctuations on 3- to 5-year intervals, often linked to variations in food resources and parasite loads, as observed in boreal forest monitoring. Recent long-term studies highlight resilience in mixed forest ecosystems, where abundance varies seasonally but rebounds effectively despite environmental pressures. The 2025 taxonomic recognition of Sorex fontinalis as a distinct , previously subsumed under S. cinereus, primarily affects eastern populations formerly classified as the fontinalis , potentially leading to localized declines in fragmented Appalachian habitats if moisture-dependent preferences differ from core ranges. No broad population impacts have been documented from this split, as the core cinereus range remains unaffected. Conservation needs are minimal given the species' secure status, with recommendations focused on ongoing monitoring of climate-induced range dynamics rather than active intervention programs as of 2025.

References

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