Yes, some species of squirrels are definitely endangered, while other species definitely are not. Habitat loss is perhaps the most important factor contributing to the decline of squirrel populations around the world. Forests and grasslands are disappearing to make way for farming, grazing, and human development. Although some species of squirrels have proven adept at living alongside humans, many squirrels will not be able to survive in this altered environment. The following example demonstrates that the situation may be exceedingly complex.
Vancouver Island marmots are one of the most endangered mammals on the planet. Endemic to Vancouver Island in British Columbia, there are only 35 still living in the wild and a further 93 marmots in captivity. These marmots live at elevations of 1,000 meters (3,281 feet) or higher and depend on treeless meadows and good soil for burrowing. The causes for the decline of the Vancouver Island marmot are multiple and include human disturbance, weather, predation, disease, and hunting. In the 1960s and 1970s areas of Vancouver Island were logged extensively. These logging activities cleared land and created artificial meadows that seemed to benefit the Vancouver Island marmot. Since marmot numbers peaked at 350 animals in the 1980s, however, they have declined. Studies have shown that marmots living in these clear-cut habitats produce fewer dispersing young than those marmots that live in natural meadows. Because fewer young are dispersing, the numbers of marmots living in a small area within and around these habitats are larger, thus increasing the risk for severe weather or predation to wipe out a large number of marmots at one time. In addition logging roads increase the ease with which predators can travel from place to place.
Table 10.1. Endangered and threatened squirrel species
Red List—International Union for Conservation of Nature and Natural Resources (IUCN)
• Critically endangered
Namdapha flying squirrel (Biswamoyopterus biswasi), Southeast Asia
Sumatran flying squirrel (Hylopetes winstoni), Southeast Asia
Northern Idaho ground squirrel (Spermophilus brunneus brunneus), North America
New Mexico least chipmunk (Tamias minimus atristriatus), North Americaa
Hidden forest chipmunk (Tamias umbrinus sedulus), North America
Mount Graham red squirrel (Tamiasciurus hudsonicus grahamensis), North America
Vincent’s bush squirrel (Paraxerus vincenti), Africa
• Endangered
Nelson’s antelope ground squirrel (Ammosphermophilus nelsoni), North America
Mexican prairie dog (Cynomys mexicanus), North America
Woolly flying squirrel (Eupetaurus cinereus), South Asia
Particolored flying squirrel (Hylopetes alboniger), South Asia
Sipora flying squirrel (Hylopetes sipora), Southeast Asia
Vancouver Island marmot (Marmota vancouverensis), North America
Northern Palawan tree squirrel (Sundasciurus juvencus), Southeast Asia
Complex toothed flying squirrel (Trogopterus xanthipes), North Asia
Prince of Wales flying squirrel (Glaucomys sabrinus griseifrons), North America
Idaho ground squirrel (Spermophilus brunneus), North America
• Vulnerable
Irrawady squirrel (Callosciurus pygerythrus), Southeast Asia
Anderson’s squirrel (Callosciurus quinquestriatus), Southeast Asia
Carruther’s mountain squirrel (Funisciurus carruthersi), Africa
Carolina northern flying squirrel (Glaucomys sabrinus coloratus), North America
Virginia northern flying squirrel (Glaucomys sabrinus fuscus), North America
Montane long-nosed squirrel (Hyosciurus heinrichi), Southeast Asia
Lowland long-nosed squirrel (Hyosciurus ileile), Southeast Asia
Mentawi flying squirrel (Iomys sipora), Southeast Asia
Four-striped ground squirrel (Lariscus hosei), Southeast Asia
Menzbier’s marmot (Marmota menzbieri), North Asia
African pygmy squirrel (Myosciurus pumilio), Africa
Cooper’s mountain squirrel (Paraxerus cooperi), Africa
Red bush squirrel (Paraxerus palliatus), Africa
Swynnerton’s bush squirrel (Paraxerus vexillarius), Africa
Small Travancore flying squirrel (Petinomys fuscocapillus fuscocapillus), South Asia
Secretive dwarf squirrel (Prosciurillus abstrusus), Southeast Asia
Indian giant squirrel (Ratufa indica), South Asia
Grizzled giant squirrel (Ratufa macroura), South Asia
Forrest’s rock squirrel (Sciurotamias forresti), South Asia
Southern Idaho ground squirrel (Spermophilus brunneus endemicus), North America
European ground squirrel (Spermophilus citellus), Europe
Franklin’s ground squirrel (Spermophilus franklinii), North America
Mohave ground squirrel (Spermophilus mohavensis), North America
Speckled ground squirrel (Spermophilus suslicus), Europe
Washington ground squirrel (Spermophilus washingtoni), North America
Jentink’s squirrel (Sundasciurus jentinki), Southeast Asia
Palawan montane squirrel (Sundasciurus rabori), Southeast Asia
Samar squirrel (Sundasciurus samarensis), Southeast Asia
Selkirk least chipmunk (Tamias minimus selkirki), North America
Palmer’s chipmunk (Tamias palmeri), North America
Organ Mountains chipmunk (Tamias quadrivittatus australis), North America
United States Fish and Wildlife Service Endangered Species Listings
• Endangered
Carolina northern flying squirrel (Glaucomys sabrinus coloratus)
Virginia northern flying squirrel (Glaucomys sabrinus fuscus)
Delmarva Peninsula fox squirrel (Sciurus niger cinerus)
Mount Graham red squirrel (Tamiasciurus hudsonicus grahamensis)
• Threatened
Northern Idaho ground squirrel (Spermophilus brunneus brunneus)
Utah prairie dog (Cynomys parvidens)
• Candidates for listing
Palm Springs round-tailed ground squirrel (Spermophilus tereticaudus chlorus)
Southern Idaho ground squirrel (Spermophilus brunneus endemicus)
Washington ground squirrel (Spermophilus washingtoni)
The Canadian government has taken action to protect the Vancouver Island marmot, first listing it as threatened in 1979. A recovery team was established in 1988, and an official recovery program was started in 1993. The recovery of the Vancouver Island marmot is a multilayered process that includes captive breeding programs, reintroductions, population monitoring, ongoing research, habitat protection and manipulation, contingency plans (in case of environmental catastrophe), fundraising, and public communication. The Canadian government even named May 1, “Marmot Day,” with the idea that the endangered marmot is yelling, “Mayday! Mayday!” or to French Canadians, “M’aidez! M’aidez!” At this time, recovery efforts appear to be successful. Andrew Bryant, a senior researcher for the Marmot Recovery Program, stated that in 2005 the total number of Vancouver Island marmots has reached 120 marmots for the first time since 1998.
A female Vancouver Island marmot (Marmota vancouverensis) named Oprah interacts with her young at Haley Lake Ecological Preserve on Vancouver Island. She was first captured and marked in 1987 as a 2-year-old. When this photo was taken, she was 8 years old and had just had her third litter of pups. Her pup in this picture is probably 5–6 weeks old. Oprah lived to age 9, which is the maximum age so far recorded for a Vancouver Island marmot wild female. Photo © Andrew A. Bryant
Another big obstacle facing the conservation of squirrel populations is the enormous lack of data on many species of squirrels, in particular, squirrels living in remote areas, such as the Himalayas or in the forests of Southeast Asia. Regrettably, habitat destruction is outpacing data collection in many of these areas, and is severe in parts of Southeast Asia. One of our colleagues, Illar Muul, spent many years in Southeast Asia, where he collected squirrels for epidemiological studies. He found a rare species of pygmy flying squirrel, Petaurillus kinlochii, in one site in Selangor, the only state in Malaysia where this squirrel has been found. Upon returning to the site in 2004, he discovered the forest had been cut down. Whether or not Petaurillus kinlochii still exists anywhere is not known. Similarly, in many other areas, squirrels may be threatened but we do not have enough information to know.
Two other very significant factors affecting squirrel populations are climate change and invasive species. We treat these next as separate questions.
Yes, squirrels will be affected by climate change, as will almost all other animals and plants. Change has been a consistent theme throughout the earth’s history. Over the course of millions of years, land masses have come together and split apart, mountains have formed and been eroded away, seas have been created and then disappeared, and glaciers have advanced and retreated. As the geography changed so too did the earth’s climate, and these variations in geography and climate have fueled the evolution and extinction of species.
Global warming is an increase in earth’s average temperature, which causes many other changes in the earth’s climate. We know that throughout the earth’s history the planet’s average temperature has increased at various times and decreased at others. The current trend in global warming is extraordinary, however, because it is happening as the direct result of human actions—namely, our increased emissions of gases such as carbon dioxide— and it is occurring much more rapidly than global warming in the past. Scientists do not know what the end effect of global warming will be; yet biologists conducting long-term field studies are already noticing behavioral and other changes in species that seem to result from global warming.
(Left) A female Vancouver Island marmot at Haley Lake Ecological Preserve on Vancouver Island. This female was 4 years old when the photo was taken and lived for at least two more years, after which she disappeared. Her colony became extinct in 1998, but in 2004 captive-bred marmots were introduced to the site. Photo © Andrew A. Bryant (Right) A museum specimen of the Selangor pygmy flying squirrel (Petaurillus kinlochii) from Southeast Asia.
David Inouye, of the University of Maryland, has been doing research at the Rocky Mountain Biological Laboratory in Crested Butte, Colorado, for 33 years. When Inouye and his colleagues looked at some of the long-term data, they saw that yellow-bellied marmots (Marmota flaviventris) at the site are emerging from hibernation 38 days earlier than they were 23 years ago. They hypothesize that this earlier emergence is due to warmer spring air temperatures.
Denis Reale, of McGill University, Stan Boutin, of the University of Alberta, and their colleagues noticed similar behavioral changes in a North American red squirrel (Tamiasciurus hudsonicus) population in the southwest Yukon. Average spring temperatures in that area have increased 2°C (4°F) over the past 27 years, and in response to this the local population is now breeding 18 days earlier than 10 years ago. The warmer temperatures have also increased the spruce cone crops, which North American red squirrels feed on, increasing food abundance over the animal’s lifetime.
Both of these populations of squirrels are robust, and it seems that they are adapting to the changing temperatures. It is unclear what effect global warming may have on endangered and threatened populations of squirrels. One example is the Mount Graham red squirrel (Tamiasciurus hudsonicus grahamensis), which is restricted to elevations above 3,200 m in the Pinaleño Mountains in Arizona. Between 1986 and 2001, the population of these squirrels never exceeded 580 individuals. During the last glacial period the Mount Graham red squirrel had a much larger range because of the pervasive cool, moist environment and was connected to more northern populations. As the glaciers retreated and the climate warmed and dried, the squirrels retreated up the mountains to find suitable habitat and since have been isolated from other populations of squirrels for about 10,000 years. Continued global warming threatens to eliminate what is left of the cool, moist environment that Mount Graham red squirrels depend on for survival. Many Alpine populations of marmots also face the same risk as temperatures warm and their habitat changes.
Another risk of global warming is disease. New parasites may flourish in a warmer environment, affecting squirrels that have no resistance to them. One potential example of this was examined by Peter Weigl and colleagues at Wake Forest University. He studied the nematode parasite Strongyloides robustus and its effects on populations of northern and southern flying squirrels that co-occur in areas of the Appalachians in North America. Although southern flying squirrels readily carry and transmit Strongyloides robustus, northern flying squirrels are a naïve host—rarely becoming infected. When infected, however, northern flying squirrels often die, and southern flying squirrels rarely suffer any harmful effects. Currently, where northern flying squirrels and Strongyloides co-occur temperatures are unfavorable to the parasite, as it requires more consistent warm temperatures to successfully reproduce in large numbers. This keeps infection rates very low among the northern flying squirrels. If temperatures increase, Strongyloides probably will become more successful and infections among northern flying squirrels will increase. Because northern flying squirrels do not have defenses against the parasite, death rates will probably be high. The result may be a die-off of the northern flying squirrels in this range.
An introduced species is a species not native to the ecosystem, region, or country in which it now resides. Species are introduced either intentionally or unintentionally. These species are sometimes beneficial, sometimes benign, and sometimes have a long-lasting, negative effect on the ecology of their new “home.” These latter, highly successful and prolific introduced species are commonly referred to as invasive species.
The most common introduced squirrel species is the eastern gray squirrel (Sciurus carolinensis). This squirrel species has been introduced to many places across the globe either for novelty or sport, and in some areas it is clearly an invasive species. Perhaps the best documented is its introduction to the United Kingdom from North America in the mid-1880s. The eastern gray squirrel quickly became established across most of the United Kingdom and, in conjunction with deforestation, has been identified as the primary cause of the demise of the native Eurasian red squirrel (Sciurus vulgaris), a smaller species found in the United Kingdom and across most of Eurasia. The reasons why the Eurasian red squirrel is being replaced by the eastern gray squirrel are not completely understood. Luc Wauters, of the University of Insburia, discovered that in areas where Eurasian red and eastern gray squirrels coexist, the Eurasian red squirrel has a lower daily energy intake than in areas where only Eurasian red squirrels exist. This may mean that the eastern gray squirrel is out-competing the Eurasian red squirrel for high-quality food or that the eastern gray squirrel is stealing food from Eurasian red squirrel caches. Disease spread by the eastern gray squirrel also seems to be having a significant impact on the decline of the Eurasian red squirrel, at least in the United Kingdom. Daniel Tompkins, at the University of Stirling, and colleagues have looked at one likely culprit, the parapox virus. This virus, carried by the eastern gray squirrel, spread to the Eurasian red squirrel as the eastern gray squirrel’s range expanded across the United Kingdom. While the eastern gray squirrel is immune to the virus, the Eurasian red squirrel has limited or no immunity to it. The virus, which causes ulcers, skin lesions, and often death, has killed numerous Eurasian red squirrels across the country.
Eastern gray squirrels also have been introduced into other areas. They were introduced into Italy three different times: in 1948 to Piedmont, in 1966 to Genoa, and in 1994 to Trecate. The Trecate population no longer exists, the Genoa population is confined to a relatively small area, but the Piedmont population has expanded to an area of 880 km2 (339.8 square miles). A large-scale plan to eradicate the eastern gray squirrel from Italy was stalled in 1997, and it is feared that the eastern gray squirrel will continue to expand into mainland Europe and the rest of Eurasia, causing devastation to native Eurasian red squirrel populations similar to what has occurred in the United Kingdom.
In 1900 the eastern gray squirrel was brought to Groote Schuur in South Africa, and a population still exists, though it is limited to the western Cape. Eastern gray squirrels also have been introduced to parts of western Canada and the northwestern United States. At one time, a population of introduced eastern gray squirrels existed in Melbourne, Australia, but it has since gone extinct.
Because of its success establishing itself in new environments and the risk it poses to native squirrel species, the eastern gray squirrel has been included on the list of “100 of the World’s Worst Invasive Alien Species” put out by the Invasive Species Specialist Group of the World Conservation Union (www.iucn.org).
Several other squirrel species also have been introduced to new areas, though on much smaller and (so far) less destructive scales than the eastern gray squirrel, so they are not yet considered invasive species. Fox squirrels (Sciurus niger) have been introduced into California, Oregon, Washington, Idaho, and Montana. Finlayson’s squirrels (Callosciurus finlaysonii ), native to Southeast Asia, were introduced to northwest Italy in 1988, and now about 50 individuals are established there. Siberian chipmunks (Tamias sibiricus), native to Scandinavia, western Russia, and Asia, exist in isolated populations in France, Italy, Germany, Netherlands, and Austria—most established by escaped pets. A population of Indian palm squirrels (Funambulus pennanti) exists in Perth, Australia, and the Southeast Asian red-bellied tree squirrel (Callosciurus erythraeus) has been introduced to Japan, France, and Argentina.
Native animals are occasionally reintroduced to areas where they have gone extinct. For example, historical climate change severely shrank the range of the Alpine marmot (Marmota marmota) in Europe. Starting in 1860, reintroduction programs for the Alpine marmot began in the Austrian Alps and in 1948 they began in the French Pyrenees. Thanks to these reintroductions, stable populations of Alpine marmots have successfully re-colonized significant areas of their previous range.
Yes, squirrel hunting is a common practice with a long history. It is hard to imagine any type of hunting more linked with American history and tradition than squirrel hunting. The famous Kentucky long rifle, developed in the early 1700s by German gunsmiths in Pennsylvania, was often referred to by many early pioneers as their “squirrel rifle.” Superbly handmade and extremely functional, the rifles were amazingly accurate in the hands of these early hunters.
Evidence of exactly how capable these master riflemen were was seen later that century when Pennsylvania placed a bounty of three pence each on the common bushytails. Many men simply quit work and went squirrel hunting, and within one year the Pennsylvania treasury was drained of eight thousand pounds sterling.
The guns have changed, but the hunting of squirrels is still common and many states have squirrel seasons and bag limits for hunters. Squirrels are still one of the most popular game animals among hunters in the eastern United States. The United States Fish and Wildlife Association reported that there were 2,119,000 squirrel hunters in 2001 and estimated that the average hunter spends at least $2,000 per season.
Regarding eating squirrels, a search on the Internet for “squirrel recipes” yielded 166,000 hits. Native Americans undoubtedly hunted squirrels and ate them before the colonists arrived. The Hopi and Navajo tribes have recipes for baked prairie dogs. They recommend animals taken in the spring, presumably because prairie dogs put on fat and become excessively greasy later in the year. Because marmots are large, they have also been hunted for food, and they continue to be popular among persons who eat wild game. In Mongolia, tarvaga (Marmota sibirica) hunts are conducted on horseback and are popular pastimes.
In many other countries, hunting of squirrels is determined by the price of shotgun shells relative to the value of bush meat, which usually means that large squirrels are hunted and small species are ignored by hunters, although small squirrels are sometimes hunted by children. In Africa, monkeypox virus occurs most frequently among 5- to 9-year-old children in small villages, because they hunt and eat squirrels.
Yes, they are made from the hairs of the tails of squirrels and the brushes are used in painting and in the application of cosmetics. We are familiar with three different species that are used: the North American red squirrel of Canada (Tamiasciurus hudsonicus), the Eurasian red squirrel (Sciurus vulgaris), and the northern palm squirrel (Funambulus pennanti).
In Rajasthan, India, the northern palm squirrel is captured in the spring of the year, the long lateral hairs on the tail are cut off, and these are used to make brushes for artists. The squirrel is released. The hairs are carefully selected and a small bundle of them are slipped into a thin tube, the ferrule, adjusted so that those hairs protruding form a suitable brush, glued in place, and a handle is attached to the other end of the ferrule to complete the brush.
Most squirrel hair used in art or cosmetic brushes comes from Canadian populations of North American red squirrels and Russian populations of Eurasian red squirrels. Three kinds of hair are recognized among the Russian squirrel-hair brushes. These seem to originate from three different areas in Russia, where the squirrels have different colored hairs. The Talahoutky hairs are brown, Kazan hairs are more brown-black, and Sacamena hairs are blue-black. In contrast, the Canadian squirrel hairs are yellow-brown, with dark tips. Surprisingly, even among the Russian squirrels there are reputed differences in quality of the hairs, and the Sacamena hairs are considered the best for watercolor brushes. The differences seem to relate to the thickness of the hairs and their springiness, which affect how they hold paint and how it flows to the tip of the hairs.
There are at least two answers to this question. First, tree squirrels, when chased by predators, use a strategy of dodging to and fro in an attempt to out-maneuver the predator. When they cross a street and react similarly to the threat of an automobile, a successful strategy quickly becomes a fatal strategy as they dodge directly under a wheel. It is instructive to compare this strategy with the straight-line, mad-dash strategy of cats, which is a far more successful way to avoid automobiles. Young tree squirrels seem particularly vulnerable to automobiles. With age, the squirrels find ways to avoid automobile predation by crossing roads on wires or by other means. Curt Sabrosky, an entomologist and former colleague at the Smithsonian, described the road-crossing technique of a gray squirrel just south of the White House. The squirrel waited on the grass near a crosswalk until people began to cross the street, and then it crossed the street behind them. We must confess that we don’t know if this was an accidental observation or the usual strategy of the squirrel.
In other cases, squirrels are commonly hit by cars because the distribution of resources causes the squirrels to cross roads frequently. The lush median strip covered with grass and clover is a temptation that has lured many a woodchuck to its death on the highway. The presence of a nut-bearing tree on the opposite side of the street from a chipmunk’s burrow will cause the animal to make numerous trips back and forth across the street. It is especially a death trap if nuts fall on the street and the shells are broken open by the tires of automobiles, because the chipmunk will stop to collect all the pieces of the nut meat, right in the path of the next automobile.
