Behavior of North American Mammals

Read an Excerpt

This book attempts to capture and share portions of the rich, dynamic lives of many North American mammals. This is not a replacement for your Peterson Field Guide to Mammals, but a book to complement it. Think of the subtitle for this guide as “The Secret Lives of Mammals.” Our emphasis is on behavior and how mammals survive, reproduce, and interact with other animals and the environment in which they live. This information will not only fascinate and inform, but also leverage your time in the field and allow you to see and know more of what is happening when you watch wild mammals.

WHAT IS A MAMMAL?
Mammals are warm-blooded animals with hair that feed their young with milk produced by the mother. Mammalian bodies regulate their own temperatures, and hair functions in many mammals as insulation and protection against temperature and weather. Lactation—the production of milk in mammary glands—allows mothers to provide sustenance to offspring as they develop outside the womb. These traits have allowed mammals to extend their collective range from pole to pole, to inhabit nearly every aquatic and terrestrial ecological community on earth, and to build incredibly complex societies.

LEARNING ABOUT MAMMAL BEHAVIOR AND NATURAL HISTORY There are three easy ways to increase your knowledge of mammal natural history and behaviors: viewing wildlife, interpreting mammal tracks and signs, and delving into the literature—the books, articles, and other media that record and convey our collective knowledge of mammal life and behavior. Watching animals in the wild requires patience, stealth, and knowledge of where and how to find them. Of course, some species are more easily seen than others, and some places can make wildlife watching seem easy.
  In the Lamar Valley in northern Yellowstone National Park, with some patience and a spotting scope, you can watch wild wolves, coyotes, bison, elk, Brown Bears, Black Bears, ground squirrels, Red Foxes, and others. Atop Mount Evans in central Colorado you can easily observe Yellow-bellied Marmots, American Pikas, Bighorn Sheep, and Mountain Goats. There are plenty of books, websites, and employees of parks and refuges out there expressly to help you find these places. Any opportunity to watch animals move and interact with each other is valuable, and you shouldn’t wait until your next vacation to do so. Animals in zoos and wildlife parks are tremendously educational, and you can learn a lot from watching videos. Opportunities to watch urban and suburban wildlife abound, and even domestic animals provide us some insights into wild animals. Watching domestic cats hunt in the garden teaches us much about their wild counterparts. There is also new technology to help you watch wildlife at night, whether you are awake or not. New night-vision goggles expose nocturnal animals, and inexpensive remote cameras unobtrusively record mammal behaviors throughout the day and night while we are away.
  Learning to interpret wildlife tracks and signs will open a window to the hidden behavior of wild animals. Scratches on the trail are territorial scrapes of coyotes; girdled saplings are sites of feeding Snowshoe Hares. This book doesn’t teach you how to identify tracks and signs, but it supplies the critical knowledge necessary for finding and interpreting them. It will provide the “why” that is so important to understanding the bits and pieces you observe directly and indirectly through tracks and signs in the field. Some excellent field guides to wildlife signs are Mammal Tracks and Sign: A Guide to North American Species (Stackpole Books) and the Peterson Field Guide to Animal Tracks, 3rd ed. (Houghton Mifflin Harcourt).
  There are literally tons of printed material written about mammal behavior and natural history. Information can be found in literary accounts of naturalists; in field guides to mammals, forests, and regions of North America; in magazine articles; and in scientific journals. Every resource has something to offer. At one extreme, scientific publications are frustratingly opaque to most people, but they are the foundation of our knowledge of wildlife behavior. At the other extreme, various Internet sites deliver easily accessible information, but often of unknown accuracy. The species accounts provided by museum and university websites are often quite informative, and Wikipedia, too, provides wonderful accounts for many species. For many mammals, there is also a host of printed books for readers of all backgrounds and interests.
  Your local libraries and universities should have excellent books and journals, as well as special web-based search tools to help you find what you are after. Universities also maintain a staggering number of online subscriptions to the scientific journals that publish the latest research. The help of a librarian will be invaluable in learning to navigate the various different sources of information.

GETTING STARTED Two handy concepts to help understand mammal behavior are niche and fitness. An animal’s niche describes how an animal makes its living, including what it does and where it does it. Wolves are social predators of large ungulates, which they hunt by coursing, or running, in packs. Chipmunks are solitary, seed-hoarding, burrowing rodents. There are more technical definitions of niche, but for now consider it as a snapshot of what a particular animal “is.”
  Fitness, on the other hand, helps us imagine the “why.” Fitness is the quality of success experienced by an animal. In ecology, it is measured by how well one reproduces—the continuation and proliferation of an individual’s genes into the future. Evolution selects for behavior that improves fitness, and keeping this in mind allows us to better interpret behavior. An animal has high fitness when it produces numerous offspring that themselves produce many offspring. Having offspring is not enough to ensure the continuation of one’s genetic heritage. An animal’s offspring need to survive long enough to breed, and their offspring too need to survive. Think of the measure of success as the number of grandchildren an animal has, since having grandchildren indicates successful production of offspring that were, in turn, able to survive and reproduce.
  A species’ niche is strongly influenced by its evolutionary heritage. Scientists use an evolutionary family tree to classify all living things based on how recently they shared a common ancestor. This book is organized phylogenetically, meaning “according to the evolutionary tree.” What this does in a practical sense is group species together in families—the “branches of the tree” that contain closely related, and therefore similar, species.
  You can improve your ability to understand any one species if you know something about the other members of the family. Many behaviors are common to entire families, and since space is limited, you might find an illustration for a behavior in another account in the same family as the one you are reading. That said, we wrote each species account to stand alone. If you are interested only in muskrats, walrus, or moles, you can find the relevant account and read the most economical, readable portrait we have been able to distill.

HOW TO USE THIS BOOK Each species account follows the same organization, with information broken down into eight topical sections: Activity and Movement, Food and Foraging, Habitat and Home Range, Communication, Courtship and Mating, Development and Dispersal of Young, Interactions among the Species (for example, Interactions among Armadillos), and Interactions with Other Species. We begin with a series of brief snapshots of the eight sections, which provide background terminology and useful concepts to interpret and understand the information in the book. Enjoy.

ACTIVITY AND MOVEMENT Activity studies in the field usually rely on animals with telemetry collars (radio and GPS collars) that relay to researchers when an animal is active and how far they travel in a period of time. Daily movement is related to food or reproduction and habits of rest, grooming, and maintenance. If an animal is most active at night, it is called nocturnal, and if active during the day, diurnal. Many animals are crepuscular, which means most active in the twilight hours around dawn and dusk.
  In North America, seasonal changes cause shifts in temperature, precipitation, and food availability and are a major factor in shaping mammalian ecology and behavior. Many behaviors are synchronized with the seasons, and often the length of daylight per day is the trigger. Breeding, migration, and hibernation all depend on changes in photoperiod (the amount of light per day) that trigger hormonal changes. External events also influence behaviors. When winter approaches and days grow shorter, a storm may cause a species migration, while at other times of year a storm will only cause animals to seek cover. With a redundant system, animals are less likely to migrate at the wrong time because of a freak snowstorm in July.

FOOD AND FORAGING Most of a wild animal’s life is dominated by its search for food. Food determines where animals are found, and over time, food selection significantly influences the shape of a mammal’s jaws, teeth, tongue, and digestive system, as well as the manner in which it secures its food.

FORAGING In the interest of survival, animals balance the benefits of a meal with the costs of foraging for it. Most animals maintain stable home ranges, allowing their experience to inform and refine their foraging. Foraging becomes more efficient when future searches are in areas that paid off in the past.
  The theory of optimal foraging predicts that animals make choices that optimize their gain, compared with the costs that they incur while collecting it. Generally speaking, if two types of food are available, a mammal (whether carnivore or herbivore) should always choose the one with the greatest net benefit in terms of energy, or calories. The cost of foraging includes the energy invested in finding and “handling” the food. Handling includes attacking and subduing a source of food, accessing the food (for example, cracking a clamshell), biting, chewing, and digesting. When the calories spent foraging are deducted from the calories gained from the meal, the result is the net energetic value of the food. Of course foraging is more than just counting calories. The dangers posed by competitors and predators; the risks of starvation, illness, and injury; and changing environmental conditions all influence how and where a species forages.

TYPES OF EATERS Different foods require different tools and foraging techniques. Herbivores specialize in eating plant tissues, carnivores eat other animals, and omnivores often eat everything. More specific terms also exist: insectivores eat insects and other invertebrates, piscivores eat fish, granivores eat seeds, and frugivores eat fruits.
  HERBIVORES. For herbivores, catching and “subduing” their food is not much of a challenge. The biggest energetic cost is from digestion, which is impeded by cellulose (fiber), the structural support in plant tissues. Different portions and stages of a plant differ in their fiber content, and most herbivores show some selectivity for foods that are high in essential nutrients and low in fiber. Plant fiber can be broken down, but that requires the right tools and considerable time.
Many plant tissues are also toxic. Plants have a host of defenses, including thorns and spines, but chemical toxins are the most pernicious. Compounds such as tannins inhibit mammalian digestion by binding to enzymes in the mouth and stomach. They also bind to the proteins in the food itself, preventing their absorption. Mammals compensate by either avoiding or overcoming the effects of these compounds.
  CARNIVORES. The term carnivore can be confusing. First, a carnivore is any member of the mammal families grouped together in the order Carnivora. In looser terms, a carnivore is a mammal that eats meat. All members of the order Carnivora eat other animals, but to very different degrees and under different circumstances. They range from the almost strictly meat-eating cats to the largely insectivorous skunks to the omnivorous dogs and raccoons to the largely herbivorous bears.
Meat is nontoxic, comes in nutritionally complete packages, and is comparatively easy to digest. But finding, pursuing, and subduing prey requires a lot of energy and drives numerous morphological and behavioral adaptations. Mammalian carnivores have teeth to hold and kill animals, shear meat, or crack hard-shelled invertebrates. Meat-eaters depend on sometimes taxing and dangerous capture and handling of prey, so they tend to specialize in certain types or sizes of prey to maximize their advantages and avoid competition with each other.
  OMNIVORES. Omnivores can eat almost any type of food, but many of our omnivores in North America are primarily carnivorous or insectivorous. Omnivores take advantage of easily digested plant foods as well as readily available animal foods, but they lack special adaptations for catching, handling, or digesting any one specific kind of food efficiently. Bears and raccoons eat a variety of plant and animal foods, but sleep through the winter when the foods they can catch and digest are in short supply.