Melanin-based plumage ornamentation signals condition and physiological stress in the Black-headed Gull

Piotr Minias,Amelia Chyb,Jacek J Nowakowski,Jarosław Kowalski,Piotr Indykiewicz,Beata Dulisz,Jacek Betleja,Mateusz Ledwoń,Tomasz Janiszewski

doi:10.1007/s10336-019-01690-7

Abstract

There is increasing evidence that melanin-based plumage ornaments play a role in the sexual selection of birds, although there seems to be little consensus on the mechanisms underlying the signalling function of melanin-based plumage. The aim of this study was to assess the potential of a melanin-based plumage ornament (brown hood) to reflect components of individual quality (condition and physiological stress) in a common larid species, the Black-headed Gull Chroicocephalus ridibundus. For this purpose, we measured the size of the hood in over 500 Black-headed Gulls captured in several breeding colonies distributed across Poland. We found that hood size correlated positively with blood haemoglobin concentration, although we found no evidence for a relationship with blood glucose concentration or body mass. There was also a negative relationship between hood size and physiological stress, as assessed by leucocyte profiles (heterophil/lymphocyte ratio). We found this correlation in both sexes, suggesting that hood size may be an honest signal of individual quality in males and females, which implies a mutual mate choice in the Black-headed Gull. Finally, the relationship between hood size and blood haemoglobin concentration was primarily attributed to the parallel variation of these traits among the colonies, suggesting that Black-headed Gulls may settle in colonies in a despotic manner. As far as we are aware, our study is one of the first to show an honest signalling role of melanin-based ornaments in the gull family, Laridae. It remains to be tested whether different melanin-based plumage ornaments in gulls are developmentally and functionally integrated with each other and with carotenoid-based integument coloration.

Highlights

There is increasing interest in the role of melanin-based plumage ornaments in the behavioural ecology and sexual selection of birds
We found no relationships of hood size with body mass and blood glucose concentration (Table S2, S3)
There was a negative relationship between hood size and the level of physiological stress, as assessed by leucocyte profiles (H/L ratio)

Summary

Introduction

There is increasing interest in the role of melanin-based plumage ornaments in the behavioural ecology and sexual selection of birds. Carotenoids play an important role as antioxidants, which generates a serious trade-off between their allocation to plumage expression and an organism’s fight against free radicals [the oxidation handicap hypothesis (Alonso-Alvarez et al 2008)]. This is important with regards to hypotheses on the reliability of carotenoid-based signals, as individuals of high genetic and phenotypic quality should have the capacity to secure more carotenoid-rich food (e.g. through a better ability to forage or higher dominance rank) and, should have brighter and larger carotenoid-based ornaments (Hill 1991; Hill et al 2002). It has been reported that the expression of carotenoid ornaments depends on the current physical state or health of an individual, which is consistent with condition-dependent expression (Johnsen et al 2003; Saks et al 2003) and the viability indicator hypothesis, which assumes that only individuals in superior condition are able to maintain the high expression of secondary sexual traits (Andersson 1994; Svobodová et al 2018)

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