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The Gnu's World

The Gnu's World: Serengeti Wildebeest Ecology and Life History

Richard D. Estes
Copyright Date: 2014
Edition: 1
Pages: 368
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  • Book Info
    The Gnu's World
    Book Description:

    This is the first scholarly book on the antelope that dominates the savanna ecosystems of eastern and southern Africa. It presents a synthesis of research conducted over a span of fifty years, mainly on the wildebeest in the Ngorongoro and Serengeti ecosystems, where eighty percent of the world’s wildebeest population lives. Wildebeest and other grazing mammals drive the ecology and evolution of the savanna ecosystem. Richard D. Estes describes this process and also details the wildebeest’s life history, focusing on its social organization and unique reproductive system, which are adapted to the animal’s epic annual migrations. He also examines conservation issues that affect wildebeest, including range-wide population declines.

    eISBN: 978-0-520-95819-7
    Subjects: Ecology & Evolutionary Biology

Table of Contents

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  1. Front Matter
    (pp. i-vi)
  2. Table of Contents
    (pp. vii-xvi)
  3. Introduction: The Author’s Fifty-Year History of Wildebeest Research
    (pp. 1-24)

    My purpose in writing about the natural history of the wildebeest is twofold: to give the antelope that once dominated the plains of eastern and southern Africa a book all to itself and to repay my debt to the animal that I have studied off and on for half a century while privileged to live in World Heritage Sites and International Biosphere Reserves.

    How did I single out the wildebeest from among all the other teeming plains game? I didn’t plan it that way.

    I had dreamed of living among the large mammals on the African savannas from the age...

  4. CHAPTER 1 Africa: The Real Home Where Antelopes Roam
    (pp. 25-44)

    The diversity and abundance of antelopes sets Africa apart from all the other continents. Africa has 72 to 75 different species, and Eurasia has 12; the other continents have none. The American pronghorn, adapting to similar plains habitats, looks a lot like an antelope but actually is so different that it is placed in a family of its own. Then what, exactly, is an antelope?

    Good question. Antelope is the common name for all members of the family Bovidae other than cattle, sheep, or goats, plus a few tribes with no domesticated species (mountain goat and chamois, muskox and takin)...

  5. CHAPTER 2 African Savannas: Understanding the Tropical Climate, Vegetation, and the Gnu’s Ecological Niche
    (pp. 45-64)

    This chapter is intended as a primer on Africa’s climate and vegetation as an aid to understanding the kinds of habitat that constitute the wildebeest’s ecological niche. Inhabitants of the north temperate zone often have little understanding of tropical climates beyond knowing it’s warm there. The position of the sun directly overhead at the equator and between the Tropics of Cancer and Capricorn at 23.5°N and S is the reason this zone is the warmest part of the globe (see map. 2.1, below). Due to the tilt of the earth’s axis, the sun appears to move between the two tropics,...

  6. CHAPTER 3 Introducing the Wildebeest’s Tribe: Similarities and Differences among the Four Genera and Seven Species
    (pp. 65-84)

    The Alcelaphini include seven living species in four genera:

    Alcelaphus buselaphus,hartebeest

    A. lichtensteinii,Lichtenstein’s hartebeest

    Damaliscus lunatus,topi/tsessebe/tiang

    D. dorcas,blesbok/bontebok

    Beatragus hunteri,hirola/Hunter’s antelope

    Connochaetes taurinus,blue/white-bearded wildebeest/gnu

    C. gnou,black wildebeest/white-tailed gnu

    A wholly African tribe or clade ( = branch) of the bovid family tree in origin and distribution, alcelaphines reached their peak two million years ago, when there were over eight genera with at least fifteen species. Though now pared to four genera and seven species, this tribe remains one of the most numerous and widely distributed of African bovids.

    The tribe comprises antelopes of...

  7. CHAPTER 4 Wildebeest Subspecies and Status of Migratory Populations
    (pp. 85-108)

    C. t. taurinus,blue wildebeest or brindled gnu. Namibia and South Africa to Mozambique north of the Orange River, from Mozambique to Zambia south of the Zambezi River, and from southwestern Zambia to eastern and southern Angola. Slate blue coat with conspicuous dark stripes, black beard, and upstanding black mane. Shoulder height (Sh.) males 147 (140–56) cm (58 [55–61] in.), females 135 (129–40) cm (53 [51–55] in.); weight (wt.) males 237, 252 kg (522–56 lb.), females 190–215 kg (418–74 lb.).¹,²

    C. t. cooksoni,Cookson’s wildebeest. Restricted to the Luangwa Valley, Zambia. Vagrants occasionally...

  8. CHAPTER 5 Increase and Protection of the Serengeti Wildebeest Population
    (pp. 109-122)

    The Serengeti ecosystem lies on the high interior plateau of East Africa west of the Gregory Rift Valley. From the heights of the Crater Highlands (3,000 m), the land slopes down to Lake Victoria, at 920 m. The Serengeti plains are situated at an elevation between 1,600 and 1,800 m above sea level, a relatively cool island with daily minimum temperature of 15°C, surrounded by hot and humid lowlands; daily minima are 30°C at the lake.

    The range of the western white-bearded wildebeest defines the Serengeti ecosystem (map 5.1). It is bounded on the east by the western wall of...

  9. CHAPTER 6 Serengeti Grasslands and the Wildebeest Migration
    (pp. 123-142)

    The gnu’s specialization for a particular range of grassland habitats, conveniently identified as acacia savanna, was outlined in chapter 2 and compared in chapter 3 with topi and hartebeest, two members of the same tribe with which it associates in the Serengeti ecosystem. Their numbers and their movements can hardly be compared to the wildebeest’s, whose migration covers the entire Serengeti ecosystem (fig. 6.1; see maps 6.1, 7.1).

    The straight-line distance from end to end of the wildebeest migration, from the Serengeti plains to the Masai Mara, is about 325 km. So a round trip would cover 650 km. But...

  10. CHAPTER 7 Social Organization: Comparison of Migratory and Resident Populations
    (pp. 143-160)

    While serving as resident naturalist at a Masai Mara resort some years ago, I was often asked to explain the erratic, “stupid” behavior of wildebeest at crossing points. They can behave rather mindlessly, I have to admit. Even with no obvious deterrent, like basking crocs (often ignored and nearly stepped on, actually) or a line of cars, a file or column will walk down to the water’s edge, look ready to plunge in, only to turn suddenly and gallop back to the plain. When zebras are present, either leading or following a column of wildebeest, they are more likely to...

  11. CHAPTER 8 Male and Female Life Histories
    (pp. 161-184)

    The natal sex ratio of wildebeest is equal.¹ It remains equal as long as both sexes stay with their mothers and/or in herds of females and young. Calves remain dependent on their dams until weaned by nine months. From then on through the next calving season (February–March), most calves separate from their mothers and associate as a class within aggregations. But some, mostly females, continue to follow their mothers as yearlings through the next calving season.

    Despite minimal sexual dimorphism (fig. 8.1), territorial bulls can readily tell which is which (by scent if not by sight) and routinely evict...

  12. CHAPTER 9 Cooperation and Competition among Twenty-Seven Herbivores That Coexist with the Wildebeest
    (pp. 185-212)

    The Serengeti ecosystem supports twenty-eight ungulates together with ten large carnivores that eat them. This is an extraordinarily rich and diverse ungulate community (fig. 9.1). How can all these species coexist with the wildebeest, which outnumbers them all put together and is so dominant that this one ruminant grazer defines the whole ecosystem? The impact on other grazers that share the savanna is particularly relevant.

    “Under these circumstances,” wrote Fryxell et al. inSerengeti III,¹ “one would normally expect to witness competitive exclusion by the dominant competitor and hence reduced diversity; yet unparalleled diversity is the name of the Serengeti...

  13. CHAPTER 10 The Amazing Migration and Rut of the Serengeti Wildebeest
    (pp. 213-238)

    The rut of the Serengeti wildebeest is like nothing else on earth. Some half a million cows are bred during three weeks of frenzied activity. Yet surprisingly little of the activity actually involves mating. Most of it involves herding, chasing, and fighting among the bulls that are currently holding territories. They herd and chase the cows and fight one another as they compete to collect and hold a group. Success depends not only on their efforts, but on the willingness of the cows to be detained. When there is a general movement, the bulls’ efforts are largely futile. They move...

  14. CHAPTER 11 The Calving Season: Birth and Survival in Small Herds and on Calving Grounds
    (pp. 239-262)

    Eight months after the rut, the cows that became pregnant during the three-week peak produce their calves. Assuming a 95 percent pregnancy rate and that 80 percent of the cows bred during the rut, over 400,000 calves would be expected in a population of 1.3 million wildebeest. Given a carnivore population of about 3,000 spotted hyenas and 2,000 lions, plus a few hundred cheetahs, leopards, and wild dogs—the only predators that actively hunt wildebeest calves—it is obvious that they can only consume a small percentage of the calf crop. Glutting their predators is rightly considered the primary advantage...

  15. CHAPTER 12 Serengeti Shall Not Die? Africa’s Most Iconic World Heritage Site under Siege
    (pp. 263-316)

    That the Serengeti migratory ecosystem remains largely intact would seem to defy the odds, for all other African migratory ecosystems (apart from the floodplains of South Sudan, where the kob and tiang migrations miraculously survived the civil war) have been severely disrupted. Even the Serengeti ecosystem lost an estimated 40 percent of its original area (approx. 30,143 sq. km in 1910) by the 1990s.¹

    I have dwelled on the characteristics that set the Serengeti apart from all other savanna ecosystems in the preceding chapters. In this final chapter I want to enumerate the challenges to survival of this most iconic...

  16. Bibliography
    (pp. 317-338)
  17. Index
    (pp. 339-352)