No abstract

Early-life experience can fundamentally shape individual life-history trajectories. Previous research has suggested that exposure to stress during development causes differences in social behaviour later in life. In captivity, juvenile zebra finches exposed to elevated corticosterone levels were less socially choosy and more central in their social networks when compared to untreated siblings. These differences extended to other aspects of social life, with 'stress-exposed' juveniles switching social learning strategies and juvenile males less faithfully learning their father's song. However, while this body of research suggests that the impacts of early-life stress could be profound, it remains unknown whether such effects are strong enough to be expressed under natural conditions. Here, we collected data on social associations of zebra finches in the Australian desert after experimentally manipulating brood sizes. Juveniles from enlarged broods experienced heightened sibling competition, and we predicted that they would express similar patterns of social associations to stress-treated birds in the captive study by having more, but less differentiated, relationships. We show striking support for the suggested consequences of developmental stress on social network positions, with our data from the wild replicating the same results in 9 out of 10 predictions previously tested in captivity. Chicks raised in enlarged broods foraged with greater numbers of conspecifics but were less 'choosy' and more central in the social network. Our results confirm that the natural range of variation in early-life experience can be sufficient to predict individuals' social trajectories and support theory highlighting the potential importance of developmental conditions on behaviour.

C (2019) High air temperatures induce temporal, spatial and social changes in the foraging behaviour of wild zebra finches. Animal Behaviour, 149. pp. 33-43.

The recent growth of research on animal personality could provide new insights into our understanding of sociality and the structure of animal groups. Although simple assays of the type commonly used to study animal personality have been shown to correlate with social aggressiveness in some bird species, conflicting empirical results do not yet make it clear when such assays, typically using isolated individuals, predict behaviour within social groups. We measured aggressiveness in groups of a very gregarious species, the common waxbill (Estrilda astrild), and performed five commonly used behavioural assays on the same individuals: tonic immobility, mirror test, novel object test, open-field test and a variant of the latter in an enriched environment. We found that larger individuals were more dominant and that differences in aggressiveness were repeatable. None of the traditional behavioural assays were related to aggressiveness or dominance. Standard personality assays may fail to capture individual differences relevant to predict social behaviour, and we discuss biological and methodological explanations for these results, such as social behaviour being in part an emergent property of groups rather than an intrinsic property of individuals, or gregarious species being particularly sensitive to the conditions of standard personality assays that test individuals alone.Ethology 121 (2015) 84-93

Sexual traits (e.g. visual ornaments, acoustic signals, courtship behaviour) are often displayed together as multimodal signals. Some hypotheses predict joint evolution of different sexual signals (e.g. to increase the efficiency of communication) or that different signals trade off with each other (e.g. due to limited resources). Alternatively, multiple signals may evolve independently for different functions, or to communicate different information (multiple message hypothesis). We evaluated these hypotheses with a comparative study in the family Estrildidae, one of the largest songbird radiations, and one that includes many model species for research in sexual selection and communication. We found little evidence for either joint evolution or trade-offs between song and colour ornamentation. Some negative correlations between dance repertoire and song traits may suggest a functional compromise, but generally courtship dance also evolved independently from other signals. Instead of correlated evolution, we found that song, dance and colour are each related to different socio-ecological traits. Song complexity evolved together with ecological generalism, song performance with investment in reproduction, dance with commonness and habitat type, whereas colour ornamentation was shown previously to correlate mostly with gregariousness. We conclude that multimodal signals evolve in response to various socio-ecological traits, suggesting the accumulation of distinct signalling functions.

No abstract

Selection due to social interactions comprises competition over matings (sexual selection stricto sensu) plus other forms of social competition and cooperation. Sexual selection explains sex differences in ornamentation and in various other phenotypes, but does not easily explain cases where those phenotypes are similar in males and females. Understanding such similarities requires knowing how phenotypes influence nonsexual social interactions as well, which can be very important in gregarious animals, but whose role for phenotypic evolution has been overlooked. For example, 'mate choice' experiments often found preferences for ornamentation, but have not assessed whether those are strictly sexual or are general social preferences. Using choice experiments with a gregarious and mutually ornamented finch, the common waxbill (Estrilda astrild), we show that preferences for ornamentation in the opposite-sex also extend to same-sex interactions. Waxbills discriminated between opposite-and same-sex individuals, but most preferences for colour traits were similar when interacting with either sex. Similar preferences in sexual and nonsexual associations may be widespread in nature, either as social adaptations or as by-product of mate preferences. In either case, such preferences may set the stage for the evolution of mutual ornamentation and of various other similarities between the sexes.

Sexual signals can comprise traits with multiple functions, and species with extreme phenotypes offer an opportunity to link function with signal evolution. This is the case in the serin Serinus serinus, a songbird with extremely fast syllable rate compared to related finches, and high sound frequency for its body size. Previous work on receiver responses showed that playback of artificially increased syllable rate is avoided and inhibits vocal responses, suggesting it is perceived as aggressive, while, on the contrary, higher sound frequency appears preferred by females. We tested whether senders also change these traits during aggressive singing, with a field playback experiment. Serin males responding aggressively by approaching the playback loudspeaker also increased syllable rate, while males responding less aggressively did not change syllable rate. Together with work on receiver responses, this suggests that aggressive signalling may have been an important selective pressure for the evolution of extremely fast syllable rate in this species. It is noteworthy that aggressive male serins still increase syllable rate, despite of their already elevated natural syllable rate. We found no changes in sound frequency when singing aggressively, which agrees with previous work that instead showed a female preference for high song frequency. We conclude that the evolution of extreme traits in serin song is best explained by multiple functions.