Elsevier

Animal Behaviour

Volume 150, April 2019, Pages 285-301
Animal Behaviour

Female and male plumage colour signals aggression in a dichromatic tropical songbird

https://doi.org/10.1016/j.anbehav.2019.01.025Get rights and content

Highlights

  • Our understanding of female signals and sex differences is still limited.

  • We used a mirror image test to study whether plumage colour signals aggression.

  • Both sexes were more aggressive to natural, less colourful mirror reflections.

  • Manipulated birds were more aggressive to increased colour reflections.

  • Plumage colour of females and males appears to be used as a competitive signal.

Animal signals of competitive ability allow contests for limited resources to be settled without costly physical fights. Traits indicating competitive ability are diverse and span visual, acoustic or chemical modalities. Although animal signalling has been intensively studied, research has focused mainly on male traits. Little is known about the extent and functionality of competitive signals in females and whether there are sex differences in signal function. We studied whether plumage colour signals competitive ability in female and male lovely fairy-wrens, Malurus amabilis. In this species, both sexes sport elaborate but sexually dichromatic ornamental plumage. Using a mirror image stimulation test, we first assessed the relationship between male and female colour and agonistic behaviour, controlling for other physical, social and ecological variables. We then tested whether colourful plumage influenced aggressive response in both sexes by experimentally manipulating plumage colour and measuring individual responses to their mirror image. Females and males were more aggressive towards naturally less colourful reflections of the cheek patch in the mirror. However, when we manipulated plumage colour, both females and males responded more aggressively to experimentally increased cheek colour reflection in the mirror. Our findings suggest that plumage colour signals competitive ability in an aggressive context in both sexes and raises the possibility that signal reliability may be maintained by social interactions where individuals police and punish dishonest signals.

Section snippets

Study Species and Field Data Collection

The lovely fairy-wren is a small nonmigratory bird, endemic to the wet tropics of Australia that breeds throughout the year, but primarily in the dry season (Leitão et al., 2019). It is a facultative cooperative breeder that forms long-term pair bonds and maintains territories year round. Resident males, females and subordinates engage in coordinated territorial disputes that can escalate to physical aggression between same-sex opponents (Leitão et al., 2019). Adult males and females are

Behavioural Responses to Mirror Image Stimulation

Individuals changed their behaviour when the mirror was exposed, spending less time at intermediate distances and more time close to the mirror (experiments 1 and 2, paired-sample Wilcoxon test: Z = −2.68, N = 106, P < 0.01) as well as far from it (Z = −3.09, N = 106, P < 0.01). Two per cent of females and 17% of males performed displays towards the mirror (feathers erected, wings extended) and 40% of females and 60% of males pecked or swooped at the mirror (physical contact with the mirror; Appendix

Discussion

Using mirror image stimulation to experimentally assess aggressive behaviour in close-range same-sex interactions, we showed that female and male lovely fairy-wrens both reacted more aggressively to their mirror image reflection when they were less ornamented themselves (i.e. less blue or shortwave-rich colours). However, experimental manipulations of the cheek plumage revealed the opposite pattern: individuals with enhanced (richer in shortwaves) cheek colour behaved more aggressively towards

Acknowledgments

We are grateful to R. Shepperd, P. Chaon, G. Marini, Z. Zelazny, L. Nelson and I. Mestre for field assistance and scoring videos over the 2015 and 2016 seasons and B. Venables for his support during field work. We thank M. Elgar for the spectrophotometer and useful feedback on the project, O. Branquinho for helping with the figures, P. De Geest for providing bird photos, the Mulder Lab, K. Meyers and J. Macdonald for helpful discussions that improved this work, and I. Leitão and C. Funghi for

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