Elsevier

Behavioural Processes

Volume 83, Issue 3, March 2010, Pages 324-330
Behavioural Processes

Condition dependence of iridescent wing flash-marks in two species of dabbling ducks

https://doi.org/10.1016/j.beproc.2010.01.017Get rights and content

Abstract

Growing empirical evidence supports the hypothesis of male mate choice for female ornaments which are thought to reflect individual quality and future breeding ability. While structural colors are clearly used in mate choice and pairing, the condition dependence of such traits is less obvious, particularly in females. We present spectral measurements of wing flash-marks in two species of dabbling ducks during the pairing period and evaluate color and brightness contrasts as seen through the mallard's (Anas platyrhynchos) visual system. We tested for possible relationships between body size (and condition) and feather measurements both on captive and wild individuals. By analyzing reflectance spectra of semi-captive mallards soon after the molting period, we found that brightness was condition related. Color contrast was positively related to body size, but only in females. In wild ducks, color contrast was positively related to body size in the common teal A. crecca only for females. These results suggest that female color traits are likely to be used by males for mate choice, and support the hypothesis that the structural color is condition-dependent. Finally, brightness contrast decreased over time in both duck species. Natural abrasion or the effect of keratinolytic bacteria could explain such pattern.

Introduction

Animal coloration is thought to evolve as a compromise between two antagonistic selection pressures (Endler, 1978): sexual selection that leads signals towards maximal conspicuousness of mates and rivals (Andersson, 1994), and natural selection, through communication with prey (Rohwer and Paulson, 1987) or predators (Baker and Parker, 1979) and selecting for maximal crypsis. Under sexual selection, because females are expected to be the choosy sex, conspicuous plumage coloration is more likely to evolve in males than in females (Andersson, 1994, Hill, 2006a). Courtship and coloration have traditionally been viewed as means for the male to convey information about himself to the female (Hamilton and Zuk, 1982, Andersson, 1994). This may include information on species identity and individual quality. Among birds, ducks (family Anatidae) display some of the most complex behaviours and brightest plumage (Lorenz, 1978), involving both pigments and feather microstructure.

Cues in mate choice such as courtship activity (Bossema and Kruijt, 1982, Holmberg et al., 1989), hormonal status (Sorenson et al., 1997), body condition (Holmberg et al., 1989) and bill or plumage coloration (Holmberg et al., 1989, Omland, 1996a, Omland, 1996b, Peters et al., 2004), have been investigated in ducks. However, as pointed out by Davis (2002), little attention has been paid to female phenotype. While it is well established that females prefer to pair and mate with brighter and/or more colorful males (review by Hill, 2006a), there is also growing evidence that males too make pairing and mating choices, leading to conspicuous female signals at least in some species (review in Amundsen and Pärn, 2006). Even in such highly sexually dichromatic species, both males and females possess wing flash-marks.

The information content of these wing flash-marks is unclear (Omland, 1996a, Omland, 1996b, Sorenson and Derrickson, 1994). The wing flash-marks in dabbling ducks come from iridescent feathers that diffract ambient light and compose a structural color trait (Hill, 2006b). Nutritional condition of an individual during molt might be reflected in the expression of structural coloration (review in Hill, 2006b). Previous studies on mallard and other closely related dabbling duck species have suggested that breeding ability was related with body condition (e.g. Heitmeyer, 1995, Blums et al., 2005). Moreover, nutrient reserves on the wintering grounds affect survival as well as pairing success, hence future reproductive success (e.g. Pawlina et al., 1993, Guillemain et al., 2008). Generally, ducks pair in fall and winter (Hepp and Hair, 1983), which is also when they exhibit courtship behaviours. In ducks, reflectance spectrometry has been used to study bill color in the mallard (Peters et al., 2004) and wing flash-marks in the common eider, Somateria mollissima (Hansen et al., 2006, Hansen et al., 2008), while other male ornaments have only been investigated using human vision (Holmberg et al., 1989, Omland, 1996a, Omland, 1996b). By using recent spectrometry techniques, our aims are twofold:

  • (1)

    With mallards fed ad libitum held in semi-captivity, we investigated reflectance intensity delivered by the flash-marks at the beginning of the pairing period and soon enough after molting to avoid feather degradation after growth. We investigated the possibility of condition dependence of the wing flash-mark coloration and tested the relationships between body size (or condition, two individual phenotypic measures known to modulate breeding performance in Anatidae) and feather reflectance. We expect a positive relationship between body condition and flash-mark reflectance for both sexes.

  • (2)

    Compare the signal obtained when individuals came from natural habitats (killed by hunters in autumn and winter, i.e. during the pairing period of these species; Hepp and Hair, 1983). Same predictions on sex and condition (or size) listed in point 1 are expected for wild individuals. We also expect wild individuals to display lower quality plumage than semi-captive individuals due to a more constraining environment in nature (i.e. less food availability, Hill, 2006b).

Finally, we hypothesize that, overall structural plumage gradually fades due to the abrasion mediated by keratinolytic bacteria (Burtt and Ichida, 1999, Shawkey et al., 2007) or to natural abrasion, and therefore expect a decrease of plumage coloration over time.

All our predictions are tested according to two different measures of the feather reflectance spectra: color and brightness contrasts (see Section 2).

Section snippets

Feather collection and body measurements

We collected one feather from the wing color flash-mark (also termed “speculum”, i.e. the distal side of secondary remiges) of each individual killed by hunters or reared in our laboratory.

In the laboratory, feather collection took place in September for semi-captive mallards (N = 19 female and 23 male mallards) fed ad libitum with a mix of wheat and corn grains. Adult ducks descended from individuals caught in the wild.

We measured body mass, flattened wing length, tail length (length of the

Results

For both species, reflectance spectra of dabbling ducks wing flash-marks showed both a peak in the UV and a peak in the visible wavelengths (Fig. 1). In mallards, the UV peak occurred on average at 346.9 nm ± 25.5 SD for wild (N = 339) and 342.3 nm ± 18.4 SD for captive mallards (N = 42). The blue color peak occurred on average at 463.6 nm ± 9.06 SD for wild individuals and at 470.0 nm ± 8.4 SD for captive ones. In teal (N = 1167), the UV peak occurred on average at 340.8 nm ± 41.8 SD and the green at 547.6 nm ± 48.2

Discussion

Our results revealed that body size (and condition to a lesser extent) and structural signals were related in ducks. This was especially true for semi-captive birds, measured soon after molting. The positive relationships were significant in females but not in males, a result consistent with what was found for wild teal on wing length. Wild birds were less bright and colored than semi-captive birds fed ad libitum. In natura, we first found an age effect indicating that adults were more colored

Conclusion

This study suggests that brightness and color contrasts are involved in different signaling functions. Sexual differences in speculum coloration are related to color contrast while the brightness contrast is more influenced by time. Individuals able to produce more colorful structural feathers, well discriminated at short distance, would be less conspicuous to predators using brightness contrast from a longer range. Mediated by both natural and sexual selection, colorful individuals should be

Acknowledgements

We sincerely thank Franck Latraube and Francois Bourguemestre for their help in collecting feathers in the field. We are grateful to the staff members of the Fédération Départementale des Chasseurs de l’Indre (FDC36), the Association des Chasseurs de Gibiers d’Eau de l’Indre and the Réserve Naturelle de Chérine (especially Jacques Trotignon) for their continuous support. We strongly acknowledge the hunters who provided teal wings to ONCFS, and the valuable help of Vincent Schricke and David

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