The Value of Immaculate Mates: Relationships between Plumage Quality and Breeding Success in Shelducks

Abstract

Immaculateness, a novel measure of bird plumage quality, defined as the regularity of the borders of a coloured patch of feathers, and the uniformity of the colour within the patch, tends to decline as a result of feather wear and damage. If it declines more quickly amongst birds in poor condition, it has the potential to act as an honest signal of individual quality and therefore be subject to social and sexual selection. We scored plumage immaculateness in shelducks Tadorna tadorna, based on the absence of white feathers in the red‐brown chest band and the evenness of the band's border. We monitored body condition and plumage quality in birds at feeding sites in the Severn Estuary (UK) during the early breeding season when females were forming eggs, and later in the season when chicks arrived. Drakes had more immaculate chest bands than ducks. At preferred feeding sites, drakes were more immaculate, and birds of both sexes were in better body condition. Birds with more immaculate plumage tended to mate assortatively at preferred sites and were more likely to produce a brood that survived the journey to the feeding areas. Immaculateness could therefore be an honest signal of parental quality. Although our evidence is only correlational, we suggest that plumage immaculateness indicates the ability to establish and maintain control over the best breeding sites and feeding territories in the face of competition with other shelducks.

Cosmetic Coloration in Birds: Occurrence, Function, and Evolution

“…Hence, a bird choosing a potential mate based on plumage appearance would select not only an individual that was in good condition during molt to produce intensely colored feathers but also an individual of sufficiently high quality to devote much time and energy to preening activities and substances (Walther and Clayton 2005). Indeed, there is evidence that individuals with more intact or less worn plumage are in better condition, are dominant, have higher reproductive success, and are preferred by females (Fitzpatrick and Price 1997;Ferns and Lang 2003;Ferns and Hinsley 2004;Zampiga et al 2004).…”

Effects of the Cardiff Bay tidal barrage on the abundance, ecology and behaviour of shelducks Tadorna tadorna

“…An additional spring count of the shelduck population of the whole of the Welsh shore of the Severn Estuary was (Ferns and Lang, 2003;Ferns et al, 2005). These studies were in turn stimulated by some of the questions raised by the Wildfowl and Wetlands Trust's 1988Trust's , 1989Trust's and 1990 surveys of breeding and moulting shelducks in the Severn Estuary (Fox and Salmon, 1994).…”

“…Body condition (the convexity or concavity of the abdominal profile between the legs and the tail), relative bill knob size (males only) and plumage quality (immaculateness of the chestnut breast band) were recorded on single days with good visibility before and after barrage closure, using the criteria described in Ferns and Lang (2003) and Ferns et al (2005). Single dates were used to ensure that the same birds were not counted twice.…”

“…Moreover, birds with the most immaculate chestnut breast bands rear more chicks to a later stage of development (Ferns and Lang, 2003). Similar feeding territories may be defended in freshwater areas, but feeding times are not normally constrained by tidal factors at such sites.…”

‘Elepaio “anting” with a garlic snail and a Schinus fruit

“…Feathers function in thermoregulation (Stettenheim 2000), communication (Andersson 1994, Shuster andWade 2003), and flight (Rayner 1988). Damaged feathers have reduced abilities to perform these functions (Booth et al 1993, Swaddle and Witter 1997, Ferns and Lang 2003, Williams and Swaddle 2003, so there are likely fitness consequences for individuals possessing damaged feathers. A subset of plumage bacteria that can degrade feathers has garnered interest, because it may impose significant evolutionary selection pressures on birds, as arthropod ectoparasites do.…”