Abstract
Aggressive behaviour plays a fundamental role in the distribution of limiting resources. Thereby, it is expected to have consequences for fitness. Here, we explored the relationship between aggression and fitness in a long-term database collected in a wild population of the collared flycatcher (Ficedula albicollis). We quantified the aggression of males during nest-site defence by conducting simulated territorial intrusions in the courtship period. We estimated the fitness of males based on their pairing success, breeding output and survival to next year. Earlier arriving and older males had a higher probability to establish pair-bond, and males that started to breed earlier fledged more young. Aggression did not predict pairing and breeding performances. However, the probability of a male to return in the next year was significantly related to aggression in an age-dependent manner. Among subadult males, more aggressive individuals had higher chances to return, while among adult males, less aggressive ones did so. This finding is in harmony with our general observation that subadult collared flycatcher males behave more aggressively than adult males when confronted with a conspecific intruder. Subadult males may be socially inexperienced, so they should be more aggressive to be successful. In contrast, if adult males suffer from higher physiological costs, a lower level of aggression may be more advantageous for them. Our study shows that aggressive behaviour can be a fitness-related trait, and to understand its role in determining fitness, age should be taken into account.
Highlights
Behaviours that are directed toward conspecifics involving elements that can intimidate or harm the opponent and are performed with the goal of ensuring the access and maintenance of limited resources are called aggression (Maynard Smith et al 1988)
Given that several hypotheses predict relationship between aggression, reproductive success and survival, we aimed to disentangle the fitness correlates of nest-site defence aggression in an exceptionally long-term database collected in a wild population of collared flycatchers
The collared flycatcher is a small, migratory, insectivorous, primarily monogamous, sexually dichromatic, hole-nesting passerine that breeds in deciduous forests in Europe
Summary
Behaviours that are directed toward conspecifics involving elements that can intimidate or harm the opponent and are performed with the goal of ensuring the access and maintenance of limited resources (such as space, sexual partner and food) are called aggression (Maynard Smith et al 1988). In many songbird species that defend breeding or foraging sites, aggression has been found to be an individualspecific trait, repeatable within individuals during a single or over multiple breeding seasons (collared flycatcher (Ficedula albicollis), Garamszegi et al 2006; dark-eyed junco (Junco hyemalis), Cain et al 2011, Cain and Ketterson 2012; eastern bluebird (Sialia sialis), Burtka and Grindstaff 2013, Harris and Siefferman 2014; tree swallow (Tachycineta bicolor), Rosvall 2008, Betini and Norris 2012; western bluebird (Sialia mexicana), Duckworth 2006; wood warbler (Phylloscopus sibilatrix), Szymkowiak and Kuczyński 2017). Because of its fundamental role in sexual selection, aggression is a relevant behavioural trait for fitness and has either direct or indirect consequences for both reproductive success and survival of the individuals. Patterns of balancing the investment in current reproductive success and future survival may correlate with the expression of aggression
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