Squirrels: The Animal Answer Guide

12 “Squirrelology”

Which species are best known? A great deal of information is available about the common North American squirrels. The eastern gray squirrel and the eastern fox squirrel are game animals, hunted in many areas, so a large literature exists on both species , dealing with game management. There is a whole book by Durward Allen, Michigan Fox Squirrel Management, for example, and the Journal of Wildlife Management includes many articles about the management of eastern gray squirrel populations. In addition, many biologists have studied them, leading to books like The World of the Gray Squirrel, by Fred Barkalow and Monica Shorten, and North American Tree Squirrels, by Michael Steele and John Koprowski. Squirrels are very poor choices as laboratory animals, so most of the literature deals with studies in the wild. The North American red squirrel (Tamiasciurus hudsonicus) has also been studied extensively—Michael Steele’s review of its biology in 1998 listed three full pages of references to studies of this species. The North American red squirrel has long been known to store food in larders and to defend these aggressively, but until a paper by Fritz Gerhardt was published in 2005, we were unaware how important pilfering is in this species. This should be a lesson to us all that there are probably large gaps in our knowledge , even of the most well-known animals. The Eurasian red squirrel (Sciurus vulgaris) has been the subject of many studies, too, most recently because introductions of the eastern gray squirrel have extirpated the Eurasian red squirrel over large areas (as described in our question about invasive species). John Gurnell’s book, The Natural Chapter 12 “Squirrelology” History of Squirrels, is a good introduction to the basic biology and ecology of the species. The North American ground squirrels also are well known. Because many species of these ground squirrels are social, their wild, social colonies are popular study sites. For example, there is a book called The Black-Tailed Prairie Dog by John Hoogland, another entitled Marmots: Social Behavior and Ecology by David Barash, an extensive series of papers on the yellow-bellied marmot by Ken Armitage, and many studies on Richardson’s ground squirrels , Columbian ground squirrels, Belding’s ground squirrels, and eastern chipmunks by diverse authors. Because North American ground squirrels hibernate, several species have been maintained in laboratories and studied intensively. Accordingly, we know much more about ground squirrel physiology than that of tree squirrels. Some African and Southeast Asian squirrels have been well studied. The giant tree squirrels of southern Asia have been the subjects of extended studies by biologists Junaidi (formerly John) Payne in Malaysia (Ratufa bicolor and R. affinis) and Renee Borges in India (Ratufa indica). Smithsonian researcher Louise Emmons conducted an extensive study of nine species of squirrels from five genera in Gabon, Africa (Protoxerus, Epixerus, Heliosciurus , Paraxerus, and Funisciurus), and University of Pretoria professor San Viljoen studied species of Paraxerus and Funisciurus in southern Africa . Currently, Jane Waterman, of the University of Central Florida, is conducting long-term studies of the South African ground squirrel (Xerus inauris) and its remarkable social system. The anatomy of squirrels is fairly well documented, initially by an excellent nineteenth-century German monograph on the anatomy of the Eurasian red squirrel. The North American squirrels—their bones and musA yellow-bellied marmot (Marmota flaviventris). Photo © National Park Service “Squirrelology” 153 154 Squirrels: The Animal Answer Guide cles—were studied in detail by Monroe Bryant (1945), and a survey of the cranial osteology of all genera of squirrels was conducted by Joseph Moore (1959). A book on the anatomy of the woodchuck by Abraham Bezuidenhout and Howard Evans (2005) appeared recently. A series of shorter papers has supplemented this information in more recent years, on myology, brain size, osteology, and other features, but there is still much to be studied. Which species are least known? Flying squirrels are surely the least known squirrels, because they are active at night, they can move considerable distances, quickly and silently, and most species occur in Southeast Asia. The two North American species (Glaucomys volans and Glaucomys sabrinus), the Eurasian species (Pteromys volans), and the Japanese giant flying squirrel (Petaurista leucogenys) are the best known, but we have only tantalizing tidbits of knowledge about most others. Many of the Southeast Asian flying squirrels are known only from museum studies of skins and skeletal material. A wide variety of tantalizing questions remain...