Mearns's squirrel (''Tamiasciurus douglasii mearnsi'') is a

subspecies In Taxonomy (biology), biological classification, subspecies (: subspecies) is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (Morphology (biology), morpholog ...

of the

Douglas squirrel The Douglas squirrel (''Tamiasciurus douglasii'') is a pine squirrel found in western North America, from the Pacific Northwest (including the northwestern coastal states of the United States as well as the southwestern coast of British Columb ...

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

. It is

endangered An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching, inv ...

and occurs in low densities, and is threatened by

habitat loss Habitat destruction (also termed habitat loss or habitat reduction) occurs when a natural habitat is no longer able to support its native species. The organisms once living there have either moved elsewhere, or are dead, leading to a decrease ...

.Koprowski, Ramos, Pasch & Zugmeyer (2006)
Observation on the ecology of the endemic Mearn's Squirrel (''Tamiasciurus mearnsi'').
''The Southwestern Naturalist'' 51(3): 426-430. It is possibly also threatened by competition from the eastern gray squirrel, which was introduced to the range of Mearns's squirrel in 1946, but may not be present anymore. It is closely related to other subspecies of the Douglas squirrel, but far less is known about its behavior, which was first studied in detail in 2004. It is named for the 19th-century American naturalist Edgar Mearns.

Taxonomy

Although formerly considered a distinct species due to its isolated habitat, phylogenetic evidence indicates that it has little genetic differentiation from the Douglas squirrel, and that the clades comprising the

are

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

with respect to it, and due to this it was reclassified as a subspecies of the Douglas squirrel. Despite this, it is very different from any other member of ''Tamiasciurus'' in habitat and behavior, and thus it is thought to be of major conservation value.

Description

Mearns's squirrel is a relatively small

tree squirrel Tree squirrels are the members of the squirrel Family (biology), family (Sciuridae) commonly just referred to as "squirrels". They include more than 100 arboreal species native to all continents except Antarctica and Oceania. They do not form a ...

, with an average head-body length of , and weighing about . They have soft, dense, fur, which is grey-brown on the upper body and white with yellow patches on the underparts. There is a stripe of solid black fur on each flank, and a narrow band of reddish-yellow fur runs down the middle of the back. The tail is bushy, with darker fur than the body, but fringed with white and yellow. The fur on the head is mostly grey, becoming yellowish towards the snout, and with dark ears and clear rings of white fur around the eyes.

Distribution and habitat

Mearns's squirrel is known from only three sites in the

Sierra de San Pedro Mártir Sierra de San Pedro Mártir ( Kiliwa: ʔxaal haq, ) is a mountain range located within southern Ensenada Municipality and southern Baja California state, of northwestern Mexico. It is a major mountain range in the long Peninsular Ranges System, ...

Baja California Baja California, officially the Free and Sovereign State of Baja California, is a state in Mexico. It is the northwesternmost of the 32 federal entities of Mexico. Before becoming a state in 1952, the area was known as the North Territory of B ...

. The region is surrounded by areas of chaparral and desert, isolating the tree squirrel from its closest relatives elsewhere, and indicating that it is likely a

relict A relict is a surviving remnant of a natural phenomenon. Biology A relict (or relic) is an organism that at an earlier time was abundant in a large area but now occurs at only one or a few small areas. Geology and geomorphology In geology, a r ...

population isolated by forest fragmentation during the

Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

. The three sites all consist of

pine A pine is any conifer tree or shrub in the genus ''Pinus'' () of the family Pinaceae. ''Pinus'' is the sole genus in the subfamily Pinoideae. ''World Flora Online'' accepts 134 species-rank taxa (119 species and 15 nothospecies) of pines as cu ...

and

fir Firs are evergreen coniferous trees belonging to the genus ''Abies'' () in the family Pinaceae. There are approximately 48–65 extant species, found on mountains throughout much of North and Central America, Eurasia, and North Africa. The genu ...

forests at altitudes of , and cover an area of no more than .

Biology and behavior

Mearns's squirrel is diurnal and

herbivorous A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat n ...

, feeding mainly on the seeds of fir and pine trees. Unlike its closest relatives, such as the Douglas squirrel, it does not hoard food for future use, and it rests in cavities in trees, rather than constructing nests from leaves. The squirrels do not appear to be territorial, and two individuals may sometimes share the same resting cavity. Vocalizations are known to include a high-pitched "rattle", a chirp, and a barking sound. The mating season lasts from around February to August, with one or two litters of two to five young being born each year.

References

{{Taxonbar, from=Q1762156 Endemic mammals of Mexico Tamiasciurus Subspecies Mammals described in 1897 Taxonomy articles created by Polbot Endemic fauna of the Baja California Peninsula