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The Ostrich Communal Nesting System:

The Ostrich Communal Nesting System:

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    The Ostrich Communal Nesting System:
    Book Description:

    As the study of cooperative breeding systems expands, a number of key species form the examples that underpin our general understanding. The ostrich is increasingly becoming such a textbook species, on the basis of the results obtained in Brian Bertram's study of vigilance and egg discrimination in this extraordinary bird. Here Bertram presents new data on the ostrich communal nesting system, in which several females lay in one female's nest, with only one female and the male doing all the work. The Ostrich Communal Nesting System unravels the basis of the cooperation observed, and explains how a system involving apparent altruism is maintained by natural selection. It is now possible as never before to explain and quantify the effects of the different choices these birds make and to integrate ecological and morphological factors such as predation and size. Based on three seasons of study in Tsavo West National Park in Kenya, this book depended on recognizing individual birds, detecting and monitoring well-concealed nests, determining motherhood of eggs from their surface appearance, and time-lapse photography of nests. Key findings were that females could switch rapidly between reproductive strategies, that a nesting female could recognize her own eggs and when necessary discriminate against those of other females, and that the whiteness of ostrich eggs is an adaptation that protects them against overheating but at the cost of greater vulnerability to predation.

    Originally published in 1992.

    ThePrinceton Legacy Libraryuses the latest print-on-demand technology to again make available previously out-of-print books from the distinguished backlist of Princeton University Press. These paperback editions preserve the original texts of these important books while presenting them in durable paperback editions. The goal of the Princeton Legacy Library is to vastly increase access to the rich scholarly heritage found in the thousands of books published by Princeton University Press since its founding in 1905.

    eISBN: 978-1-4008-6314-3
    Subjects: Ecology & Evolutionary Biology

Table of Contents

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  1. 1 The Ostrich
    (pp. 1-18)

    The ostrich is well known to be the world’s largest living bird. An adult male stands 2.1–2.7m high (Cramp and Simmons, 1980). Females are generally a bit smaller. Information on measured weights of these birds in the wild is characteristically scarce; a small sample (n= 13) from Kenya averaged 111 kg, ranging from 86 to 145 kg (A. V. Milewski, pers. comm.).

    Their size alone would render ostriches incapable of flight. Instead, they are adapted to a walking and running way of life. The very long bare legs carry the large bird economically (Fedak and Seeherman, 1979) and...

  2. 2 Methods
    (pp. 19-32)

    In order to understand in their context the data presented in subsequent chapters, a summary is first provided in this chapter of the environment in which ostriches were studied in Kenya. The methods by which the birds could be observed and recognized individually are outlined, and the kinds of observations that were possible given the birds’ timidity. One of the main limiting factors in the study was the difficulty of finding and observing surviving ostrich nests, and a variety of indirect methods proved to be necessary.

    The fauna and flora of Tsavo West National Park have been described by Cobb...

  3. 3 The Population
    (pp. 33-48)

    In order to investigate the relative breeding success of different ostriches, it was necessary to determine the categories of birds that were distinguishable and the proportions of the population falling into those age and sex categories. The relative advantages of different reproductive strategies depend partly on the sex ratio of breeding birds within the population; biases due to differential conspicuousness and distribution make the sex ratio much more difficult to determine than might at first be imagined with such large birds.

    Breeding success depends also on the male and female being together for at least part of the time, and...

  4. 4 The Breeding System
    (pp. 49-70)

    Having dealt with the adult population in Chapter 3, I now present general observations and data on their nesting. The intention at this stage is to provide a background of information against which later to carry out more detailed analyses of the reproductive options open to different categories of breeding birds. This chapter summarizes when and where ostrich nests in general were started, and by whom; how they grew; how they were attended; what other birds laid in them and when; how large they finally ended up; and how many of those eggs were incubated and by whom. It was...

  5. 5 Ecological Aspects
    (pp. 71-101)

    One of the aims of this study was to quantify the reproductive advantages and disadvantages of different breeding strategies. The benefits are often measured in later chapters in terms of numbers of eggs laid. Set against these, two of the most prevalent costs are the loss of eggs and the death of birds, and in this chapter I endeavour to quantify some of the effects of the natural hazards that ostriches face in Tsavo West National Park.

    Predation on nests was a highly significant hazard. The great majority of ostrich nests did not produce any chicks, mainly because of predation....

  6. 6 Strategies Adopted by Major Females
    (pp. 102-123)

    The factors that determine whether a female ostrich embarks on a major or minor role, and the relative reproductive pay-offs of the two different strategies, are considered in Chapter 7. In this chapter, for major females already having begun a nest, I will consider the options open to them at various stages, and the reproductive consequences of the choices they make. I use and analyse the data in previous chapters and present further more detailed data.

    Major female ostriches were remarkably tolerant of minor females coming to lay in their nests. As described earlier, a major hen would usually rise...

  7. 7 Major and Minor Female Strategies
    (pp. 124-137)

    I have described some of the major female’s main choices and have outlined the reproductive consequences of her decisions at these points. As a result, it is becoming clear why, if she is a major female, an ostrich hen behaves as she does. We must now consider what a minor female’s options are. I examine to what extent the minor hen strategy was consistent and whether there were different categories of minor hens linked with nesting stages. It is possible from the data available to quantify some aspects of the reproductive success of birds using either the major or the...

  8. 8 Male Strategies
    (pp. 138-158)

    During the breeding season, male ostriches presumably have the option of whether to start their own nests. If a male does start a nest and it survives, he goes out of breeding condition at incubation, whereas if he does not have a nest, he remains in breeding condition for longer and continues to mate promiscuously with females who lay in others’ nests. In this chapter, I consider first what proportion of males started nests, and at what stage of the nesting season. In later sections, I consider the costs and reproductive benefits of starting a nest, and examine possible areas...

  9. 9 Discussion: The Evolution and Maintenance of the Communal Nesting System
    (pp. 159-187)

    The breeding system of the ostrich has been shown to be both varied and complex. It is highly unusual among birds. It is therefore worth asking how does it all come about? This Chapter will examine what selective pressures are operating within the ostrich communal nesting system to influence the choices that individual birds make at different stages of their nesting. It is the consequences of those choices that natural selection acts upon: selection will enhance the frequency in future generations of those genes which make individual birds more likely to make choices that on average have beneficial reproductive consequences....