Male aggressiveness and risk-taking during reproduction are repeatable but not correlated in a wild bird population

Abstract

The existence of among-individual variation in behaviour within populations is poorly understood. Recent theory suggests that fine-scale individual differences in investment into current versus future reproduction may lead to a ‘slow-fast’-pace-of-life continuum, also referred to as the ‘pace-of-life-syndrome’ (POLS) hypothesis. According to this idea, individuals are predicted to differ in their level of risk-taking, which may drive among-individual variation and covariation of behaviours. Consistent individual differences in aggression, an ecologically relevant and potentially risky behaviour, have been reported across the animal kingdom. Here we test whether such individual differences in aggression are a manifestation of underlying differences in risk-taking. In a wild blue tit (Cyanistes caeruleus) population, we used standard behavioural tests to investigate if male territorial aggressiveness and risk-taking during breeding are positively related. At the start of breeding, we simulated conspecific territorial intrusions to obtain repeated measures of male aggressiveness. Subsequently, we measured male risk-taking as their latency to resume brood provisioning after presenting two different predators at their nest: human and sparrowhawk, a common predator of adult songbirds. First, we found substantial repeatability for male aggressiveness (R = 0.56 ± 0.08 SE). Second, while males took longer to resume provisioning after presentation of a sparrowhawk mount as compared to a human observer, risk-taking was repeatable across these two predator contexts (R = 0.51 ± 0.13 SE). Finally, we found no evidence for a correlation between male aggressiveness and risk-taking, thereby providing little support to a main prediction of the POLS hypothesis. Significance statement Consistent, and often correlated, individual differences in basal behaviours, such as aggression, exploration and sociability, are found across the animal kingdom. Why individuals consistently differ in their behaviour is poorly understood, as behavioural traits would seem inherently flexible. The ‘pace-of-life syndrome’ (POLS) hypothesis proposes observed behavioural variation to reflect differences in risk-taking associated with individual reproductive strategies. We tested this idea in a wild blue tit population by investigating whether individual males that were more aggressive toward territorial intruders also took more risk when provisioning their nestlings under a threat of predation. While we found consistent individual differences in both aggressiveness and risk-taking, these behaviours were not significantly correlated. Therefore, our study demonstrates among-individual variation in ecologically relevant behaviours in wild blue tits but provides little support for the POLS hypothesis.

Untangling behaviours: independent expressions of female–female aggression and snake-like hissing in the blue tit (Cyanistes caeruleus)

“…Indeed, our results are in line with previous results on aggression in female great tits 7 , 19 . Moreover, studies on male aggression during simulated territorial intrusions in another blue tit population reported even higher repeatability (R = 0.56 23 ) compared to our observations in females. Yet another study on blue tits found that the repeatability of female nestling defence and handling aggression to be equal or higher, respectively, to that of males 6 , suggesting potential sex and/or population dependent variability in the repeatability of aggression.…”

“…repeatable) between-individual variation in behaviour is commonly referred to as a personality trait 21 , 22 . Several studies have shown that intrasexual aggression and hissing are repeatable behaviours, with evidence of consistent individual variation in intrasexual aggression observed in various taxa, including a number of songbirds (reviewed in Salazar et al 23 ). While fewer studies have focussed on hissing behaviour, it has also been found to be individually consistent in female great tits, highlighting the recognition of these traits as aspects of animal personality 5 , 19 .…”

“…activity in a novel environment, approaching novel objects) have yielded mixed results, where contextual overlap may enhance likelihood of finding correlations due to the experimental environment affecting measured behaviours in the same way (reviewed in Garamszegi et al 32 ). Few studies have tried to link aggression across a conspecific and predator context 23 , particularly in females (but see Thys, Pinxten, et al 19 and Cain et al 27 ). In female dark-eyed juncos ( Junco hyemalis ), relative levels of aggression towards predators, same- and opposite-sex intruders were found to be correlated, suggesting a potential link between conspecific aggression and anti-predator behaviour 27 .…”

Agonistic song rate positively correlates with male breeding success and avian malaria infection in a promiscuous songbird with female-only parental care

“…However, our study does not indicate that singing effort is related to the studied fitnesstraits in the aquatic warbler. Although in some songbirds it was found that repeatability of the repertoire size is greater than expected by chance (Naguib et al 2019;Salazar et al 2021), future studies on the aquatic warbler should attempt to establish variation in song traits more precisely, e.g. by recording males repeatedly within a season, and to cover more breeding seasons.…”

Agonistic song rate positively correlates with male breeding success and avian malaria infection in a promiscuous songbird with female-only parental care

“…However, our study does not indicate that singing effort is related to the studied tness-and quality-traits in the aquatic warbler. Although in some songbirds it was found that repeatability of the repertoire size is greater than expected by chance (Naguib et al 2019;Salazar et al 2021), future studies on the aquatic warbler should attempt to establish variation in song traits more precisely, e.g. by recording males repeatedly within a season, and to cover more breeding seasons.…”