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Accueil du site → Doctorat → Allemagne → 2016 → Cooperative breeding and anti-predator strategies of the azure-winged magpie (Cyanopica cyanus Pallas, 1776) in northern Mongolia

Georg-August Universität zu Göttingen (2016)

Cooperative breeding and anti-predator strategies of the azure-winged magpie (Cyanopica cyanus Pallas, 1776) in northern Mongolia

Bayandonoi, Gantulga

Titre : Cooperative breeding and anti-predator strategies of the azure-winged magpie (Cyanopica cyanus Pallas, 1776) in northern Mongolia

Auteur : Bayandonoi, Gantulga

Université de soutenance : Georg-August Universität zu Göttingen

Grade : ’Doctor of Philosophy’ 2016

Résumé partiel
In this study, I investigated the proximate mechanisms underlying an expression of the helping behaviour by examining feeding rate and frequency of helpers under varying food availability and predation risk in different breeding colonies (see chapter 2). Many hypotheses have developed to explain the underlying mechanisms of the cooperative breeding. However, it appears to have no single hypothesis that can explain it, instead several hypotheses can be applied for the evolution of cooperative breeding. The kin-selection, life-history and ecological constraints hypotheses are widely accepted, though none of them can explain the evolution of the cooperative breeding exclusively. The nest predation hypothesis was underlined because the main cause of nest failure among cooperative breeding birds is nest predation (Brown 1987, Stacey and Ligon 1991), suggesting its potential selective factor for evolution of cooperative breeding (Poiani and Pagel 1997). Yet, not much empirical evidence has been found to support it. I could show that both low food availability and high predation risk increase the benefits of helping behaviour, thus they lead to expression of the helping behaviour. Our findings support the nest predation hypothesis that high nest predation pressure over ecological time favours the cooperative breeding (see Poiani and Pagel 1997). However, nest predation hypothesis cannot explain the evolution of cooperative breeding solely, it is one of the selective factors that work in conjunction with other selective factors such as ecological constraints and kin-selection. Helpers at the nest have long been assumed to increase nestling survival through enhancing nestling’s body condition. But in last two decades many studies have documented for some species that helpers at the nest appear to reduce nest predation (e.g. Austad and Rabenold 1985, Emlen and Wrege 1991, Mumme 1992, Schaub et al. 1992, Innes and Johnston 1996, Boland 1998, Valencia et al. 2003, Hatchwell 2004). The data on nestling body mass, nest attentiveness and egg-laying period along with observational records of helpers’ active involvement in nest defense in this study showed that helpers improved nestling condition and reduced chick rearing time period at the nest, which both in turn reduce nest predation (see chapter 2). Therefore, helping behaviour appeared to be an effective anti-predator strategy since it reduces nest predation substantially (see chapter 2 and 3). Besides that, our findings revealed several other anti-predator strategies that azure-winged magpies employ under high predation risk. Greater concealment of the nest, proactive avoidance of the nest location from the predator nest along with involvement of helpers at the nest were the most effective anti-predator strategies in our study (see chapter 3). Although, nest concealment is arguably the widespread anti-predator strategy not only for birds but for many other animal groups, most field studies found no evidence of which nest concealment reduced nest predation (reviewed by Borgmann and Conway 2015). Borgmann and Conway (2015) concluded that lack of evidence of nest-concealment hypothesis, i.e. birds prefer nest sites enclosed by dense foliage to reduce the likelihood of detection by predators and brood parasites (Martin et al. 1988, Martin and Li 1992), in large quantity of studies largely caused by morphological traits and methods used to measure concealment which in turn likely resulted in lack of support. Benefits through nest concealment may be traded-off by consequences associated with greater concealed nest site (Morosinotto et al. 2010, Borgmann and Conway 2015) or compensated by active defense in some bird species (Götmark et al. 1995, Cresswell 1997, Weidinger 2002, Remeš 2005, Fontaine and Martin 2006a)

Mots clés  : Azure-winged magpie ; Cooperative breeding ; Anti-predator strategies ; helping behaviour ; nest concealment ; nest distance ; pair experience ; sub-colony ; nest clustering ; protector species ; nest predation

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Page publiée le 17 janvier 2019