Marler / Slabbekoorn Nature's Music

The Science of Birdsong
1. Auflage 2004
ISBN: 978-0-08-047355-0
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 504 Seiten

The voices of birds have always been a source of fascination. Nature's Music brings together some of the world's experts on birdsong, to review the advances that have taken place in our understanding of how and why birds sing, what their songs and calls mean, and how they have evolved. All contributors have strived to speak, not only to fellow experts, but also to the general reader. The result is a book of readable science, richly illustrated with recordings and pictures of the sounds of birds. Bird song is much more than just one behaviour of a single, particular group of organisms. It is a model for the study of a wide variety of animal behaviour systems, ecological, evolutionary and neurobiological. Bird song sits at the intersection of breeding, social and cognitive behaviour and ecology. As such interest in this book will extend far beyond the purely ornithological - to behavioural ecologists psychologists and neurobiologists of all kinds.* The scoop on local dialects in birdsong* How birdsongs are used for fighting and flirting* The writers are all international authorities on their subject

Autoren/Hrsg.

Marler, Peter R.

Slabbekoorn, Hans

Inhaltsverzeichnis

1;front cover;1
2;copyright;5
3;toc;6
4;front matter;10
5;body;20
6;back matter;407
7;index;484

Leseproben

Chapter 2 Vocal fighting and flirting: the functions of birdsong SARAH. COLLINS INTRODUCTION
Birdsong has long been associated in our minds with mating behavior and male aggression. When males are active in defending territories and attracting mates, we think of springtime and breeding seasons. A large body of research on birdsong confirms that its two main functions are repelling rivals and attracting mates. My aim is to review this evidence and discuss the importance of specific aspects of male song. The aspects of singing behavior that are important for each function vary between species. In a few cases, I will also outline the role that female song may play. One pervasive theme will be how the evolution of song has been driven by the twin selection pressures of female choice and male competition. EVIDENCE THAT SONG IS IMPORTANT
Is song in fact used in male–male competition and female choice and, if so, which aspects of an individual’s song make him more successful when it comes to reproduction? It is possible that individual characteristics are reflected in the song, and individuals who impress with their song may have a greater reproductive success through repelling rivals or attracting females. So a primary question is whether male song does reflect some aspect of male quality and increases the reproductive success of the singer. Some simple experiments show that females do respond to male song, and that males can be intimidated by a rival’s song. If males are removed from their territories and replaced by loudspeakers broadcasting song, the territories remain unoccupied for longer than silent control territories without broadcast song (Krebs 1976; Falls 1988; Nowicki et al. 1998a). Song evidently does repel rivals from intruding into a territory. Females, on the other hand, are more likely to be attracted to nest boxes where males have been removed and replaced with loudspeakers, rather than to silent nest boxes (Eriksson & Wallin 1986; Mountjoy & Lemon 1996; Johnson & Searcy 1996). Females also respond to song by performing copulation solicitation displays (Searcy 1992a), and tend to approach speakers playing male song in the laboratory (Clayton 1988). If song is to serve these dual functions, both sexes will use it to assess the male, as a rival or a potential mate. However, the qualities on which males and females should base their assessment are somewhat different. Females need to find a mate who will maximize their reproductive success. We expect that factors such as the male’s, age, condition, parental ability, and the quality of his territory will affect his attractiveness as a partner. Where male rivalry is concerned, competitors need to know the location of a rival male, who he is, how likely he is to attack, and his fighting ability. In some cases, the same song characteristic may give information to both males and females on aspects of the singer to which they will respond. However, in many cases, the information of interest is quite different and we would therefore expect different song parameters to be used. MALE–MALE COMPETITION: VOCAL FIGHTING
Contests among males may be over mates, a territory, or the resources that attract females, such as a nest or feeding site. So the question is, what kind of song will best prevent a male from trying to take over a rival’s nest box, territory, or female? Why should a male pay attention to the song of his rival? Why not fight and let the winner take the spoils? Of course, if a male territory owner can indicate he is such a superior fighter that, in a combat, the rival would lose, then both males may gain from avoiding a fight. Therefore, any song characteristic that suggests, either honestly or by bluffing, that a male is an excellent fighter, should be produced by the male to cause rivals to withdraw. The outcome of fights is likely to depend on physical strength, fighting skills, and motivation to fight. Factors determining physical strength, such as size, weight, body condition, and energy reserves, become important in the assessment of rivals. Motivation to fight may vary among males, depending on what they have to gain and lose. Males who are more motivated are more willing to escalate a fight and are thus more dangerous opponents (imagine a small dog seeing off a larger one by not giving up, constantly yapping and snapping). Males who have a breeding female on their territory may be more motivated to fight; a male trying to take over a territory may find it easier to move on and try his luck at a new site rather than risk a fight with a highly motivated opponent. However, what is to prevent a male from singing a song that indicates he is a superior fighter, or highly motivated to fight when in fact he is not? If it is possible for inferior males to signal that they are superior or highly motivated, then an intruder should take account of the possibility of deception. Why retreat when you may in fact be stronger than your rival? This conflict is at the heart of the evolution of the signals that occur between rival males. Territory owners should do all they can to repel rivals, but rivals should only withdraw if they can determine that the signal is a true indicator of superior fighting ability or of willingness to escalate the intensity of a fight. There are several possible solutions to the signaling problem. Signals that are costly to produce are likely to be honest (Zahavi 1975, 1977) and the cost itself ensures their honesty. We may assume that an inferior male simply cannot produce a signal as costly as the one that a superior male is able to produce. There may be production costs such as the energy needed to utter a particular signal, and males with higher energy reserves may be able to generate a ‘stronger’ signal than those with lower reserves. This type of cost would lead to a gradual increase in the intensity of a particular song parameter in relation to a male’s condition. If body condition affects fighting ability, as is quite likely, then a song reflecting this characteristic will also indicate a competitor’s strength. Alternatively, costs could be imposed by other individuals. A good analogy may be the way humans use aggressive shouting to intimidate rivals. Aggressive shouting will often cause rivals to withdraw, but it also runs the risk that a particularly strong or aggressive individual, rather than being intimidated, will respond physically. If your signal was all bluff you may get injured in the ensuing fight. Therefore, it is better not to signal that you will act aggressively unless you can follow it up if challenged. Replace shouting with singing in a particular manner and you have a good idea of what may happen in territorial disputes in birds. The cost of cheating, by pretending to be stronger or more aggressive than you are, will be related to the level of probing, or testing, by rivals. Bluffing may occur at some level, and its frequency will be related to the likelihood and cost of being probed. In this scenario, the signal itself need not be costly to produce, but should indicate the likelihood of attacking, level of aggression, or motivation to fight. This kind of signal is known as a ‘conventional signal’ (Guilford & Dawkins 1995), so called because the specific form of the signal is arbitrary and a matter of convention. The definition of a conventional signal is that “the signal is more or less arbitrarily related to the message, many signals can carry the same message” – costs are target receiver dependent, so signals can be cheap to produce” (Guilford & Dawkins 1995). As long as everyone understands what different arbitrary signals mean, the system works. With conventional signals there are more likely to be different signal categories rather than gradual increases in the intensity of the same signal, as is likely to be the case for a physically costly signal. Some signals are affected by physical restrictions and are thus, potentially, indicators of male quality. For example, larger males can produce deeper frequency sounds due to their larger vocal apparatus; a smaller male simply cannot cheat by producing a lower frequency sound. If larger males are better fighters, as is quite likely, then it makes sense to withdraw if you hear a low frequency sound indicating a male is larger than yourself. But this connection is not foolproof. Sometimes physical restrictions can be overcome. In some species the trachea has become elongated so that it is no longer proportional to body size. The frequency of the song, or call, now indicates trachea size and not body size (Fitch 1999). Smaller males can cheat. It would be interesting to see whether the elongated trachea of a large male is still longer that that of a small male. When a cat increases its apparent size by raising its fur on end, a large cat will still look bigger than a small one. Testing the Role of Song in Male Rivalry
Three main methods have been used to address questions about the role of male song in rivalry. The first is observational. Birds are observed and recorded during aggressive encounters, and their song characteristics are compared to nonaggressive interactions. For example, male barn swallows emphasize rattles in the song during aggressive encounters, indicating that rattles are a relevant component of competitive...