1. Tupai:
An Introduction
Treeshrews
[1] I use the single word treeshrew, rather than tree shrew or tree-shrew, to distinguish these animals as clearly as possible from genuine shrews of the order Insectivora (longtailed shrew, pygmy shrew, etc.).
suffer from chronic mistaken identity: first, they are not shrews; second, most are not found in trees; and third, what they really are (among mammalian orders) has never been agreed on. The first treeshrew recorded by a Western naturalist was collected in 1780 by William Ellis, surgeon to Captain Cook's expedition (Lyon 1913). He thought it was a squirrel. Indeed, at first glance, treeshrews are so much like squirrels that people who live where they occur often confuse the two, and they are known by the same common name, tupai, in the Malay/Indonesian language. This local name was the basis for the first treeshrew generic name, Tupaia, and its family, Tupaiidae. Forty years passed before taxonomists recognized treeshrews as different from squirrels (Lyon 1913). These animals, which would better have been called squirrelshrews, are in fact like no others.The best-known treeshrews, in the genus Tupaia, are active, alert creatures that border on the neurotic. They are squirrel-sized, brownish mammals with large, dark, lashless eyes; short, bare ears; and a large, wet nosepad like a pencil eraser on the tip of a long muzzle (fig. 1.1). They have squirrel-like feet; soft, dense fur; inconspicuous whiskers; and a long bushy tail that flicks upward. When alarmed, they chatter, whine, or whistle.
Fig. 1.1. A portrait of a Tupaia tana.
WHAT IS A TREESHREW?
The question, What is a treeshrew? has been asked many times, almost always while seeking the answer to the treeshrew's place in evolutionary history. In this book I am mainly concerned with other questions, but because a living animal is a result of its history, I begin with a brief overview of thought on treeshrew taxonomy and phylogeny—the search for their true, but often mistaken, identity.
Before 1900 treeshrews were generally thought to be in the order Insectivora and related to the true shrews, but by the first decade of the twentieth century comparative anatomists separated them from that order and proposed a closer relationship to other groups, especially elephant
This has returned us to perspectives similar to those of 1910 and earlier. Several hypotheses, one more than a century old, have grouped treeshrews with other mammalian orders, primarily Macroscelidea, Dermoptera (flying lemurs), and Lagomorpha (rabbits), and into a superorder with these and/or primates and bats, but there is still no consensus. Clearly, the last ancestor that tupaiids shared with members of other living orders was so long ago that no unambiguous set of morphological characters allies treeshrews more closely with one order than with another. Along with most other mammalogists, I consider treeshrews to belong in their own order,Scandentia Wagner, 1855, and await more robust evidence of their deeper systematic relationships. Treeshrews are treeshrews.
The only complete review of the genera and species of treeshrews was the classic work of Lyon (1913), who reviewed all available forms, named many new ones, and in the process discovered many important physical features (taxonomic characters) useful for classification. Lyon recognized six genera and forty-six species of treeshrews. Since then, many of these have been grouped together as synonyms, especially island populations of the genus Tupaia, to the point that only five genera and sixteen species were recognized (Corbet and Hill 1991, 1992; Honacki, Kinman, and Koeppl 1982). However,Wilson (1993) recently reversed this trend by
WHY STUDY TREESHREWS?
As representatives of one of only twenty-six living orders of mammals, treeshrews are worth studying just to discover the characteristics of a major branch of the Mammalia, but aside from pure curiosity, there are other reasons to find out more about these obscure small animals. Although treeshrews are no longer considered primates, they are thought by some to belong to a group of closely related orders (a grandorder), the Archonta, which besides treeshrews includes the primates, bats, and flying lemurs. In this group treeshrews are the least specialized (most primitive) members. As such, they may still be the most closely related living models of the very earliest primate ancestors of the late Cretaceous period. Their lifestyles can thus provide a window on our earliest antecedents, and perhaps a view of why evolution may have taken the direction it did.
Almost all of the 220 million years of mammalian history are recorded only by fossil bones, more often than not from mere fragments, a teaspoonful of teeth. For the first two-thirds of mammalian history, all mammals were small to tiny carnivores or insectivores (Lillegraven, Kielan-Jaworowska, and Clemens 1979). From these inconspicuous creatures came the great Paleocene evolutionary radiations of mammals, which followed the extinction of the dinosaurs at the end of the Cretaceous period 65 million years ago. We can only guess how these early mammals might have used their habitats. Such guesses are largely built from analogies drawn from living species that have similar morphology: we assume
EARLIER STUDIES
During the half century of treeshrew glory, when treeshrews were considered primates, enormous quantities of research were done on their anatomy and physiology, and also some behavioral work on laboratory colonies. A bibliography of treeshrews published in 1971 contains 1,036 references (Elliot 1971), almost all laboratory or zoo studies of captivebred animals. The subjects of almost all of this work were laboratory stock purportedly of a single species (but perhaps three), Tupaia glis and its related forms belangeri and chinensis, whose origins were usually unknown but who were thought to come from Thailand. These became a mythical entity: “The Treeshrew.”
In a pioneering study at Seewiesen, Germany, where Konrad Lorenz had introduced entirely new approaches to research on animal behavior, Robert D. Martin (1968) conducted the first comprehensive study of treeshrew reproduction and behavior with animals kept under conditions where they behaved normally. This was followed a decade later by the only two detailed field studies of treeshrews before my own, both focused on the Malaysian Tupaia glis. One of these (Langham 1982) was a capture-mark-release study based on trapping only; the other was based on field observation of a population of marked individuals (Kawamichi and Kawamichi 1979, 1982). Both represented significant advances of
I was originally drawn to study treeshrews not only because I am fond of small mammals and these were poorly known but also because they were reported byMartin (1968) to have one of the most enigmatic parental care systems known among mammals. The mother Tupaia births in a nest remote from her own, and, apart from a visit of a couple of minutes once every other day to suckle her young, she seemingly abandons them. Not only that, she was also reported to lack even the rudiments of the behavioral patterns that ordinary mammal mothers need to care for such helpless altricial infants, such as grooming them or rescuing them from danger (Martin 1968).
This, the ultimate in cursory parenting, was known only from captivity, and there was surprisingly little information about the ecology of wild treeshrews that might help us to understand the natural context of this odd behavior; or, therefore, its function. Intrigued, I went to Borneo to learn how treeshrews of several species lived in the wild, both to see if some feature of their lives might give insight into their “absentee” parenting and to try to describe for the first time in detail the natural history of members of this unique order.
In this study I again asked, What is a treeshrew? but with a different subset of questions. I asked, What is a living treeshrew? How does it act in its environment? What does it do, where does it go, what does it eat, where does it sleep? How does it raise its young? Do different species do these things differently? This book describes what I discovered. I show that “The Treeshrew” does not exist, for each of the six species that I followed has a distinct lifestyle, although all the species share many common features.
I had spent many years in the tropical rainforests of Africa and South America, studying mammals of many kinds. One of my personal goals for this study was to see for myself how the forests of Asia were similar to, or different from, those on the other continents and how communities of mammals resembled, or differed from, each other across the globe. Perhaps from this perspective I could gain insight into how all rainforest communities develop and are maintained.