Alula size signals male condition and predicts reproductive performance in an Arctic‐breeding passerine

Abstract

While studies of achromatic plumage signaling are scarce relative to chromatic ornaments, achromatic ornaments have the potential to act as an efficient form of visual communication due to the highly conspicuous contrast between black and white body regions. Recently, achromatic plumage reflectance has been shown to indicate condition, yet the condition‐dependence of achromatic patch size remains unstudied. Here we show the first evidence that alula size, an achromatic plumage patch, has the potential to signal a male’s condition and predict reproductive performance. In Arctic‐breeding snow buntings Plectrophenax nivalis, the size of the alula simultaneously predicted pre‐breeding physiological health and the number of offspring produced, through an intermediate variable (lay date). Snow buntings appear to pair assortatively; males and females arriving earlier pair together, and changes in body condition over the breeding season are positively related within pairs. We suggest that simple achromatic plumage patches, like alula size, have the potential to act as condition‐dependent signals. Consequently, females may benefit from assessing these signals to reliably evaluate a male’s condition and reproductive potential as a means of maximizing their reproductive success.

The Oxidative Cost of Acoustic Signals: Examining Steroid Versus Aerobic Activity Hypotheses in a Wild Bird

“…, ), supporting the idea that the earliest arriving females have the broadest choice of breeding partners (Guindre‐Parker et al. ,b). We located all nests, recorded the laying date of the first egg and then subsequent clutch size.…”

“…() reported a negative relationship between song rate and laying date, and Guindre‐Parker et al. () reported that higher quality male plumage signals predicted earlier laying dates. Likewise, Guindre‐Parker et al.…”

“…For example, snow bunting plumage signals may be important in selecting a social mate (see Guindre‐Parker et al. ), while song quality may play an important role in extra‐pair copulation decisions (as in Chiver et al. ).…”

Revisiting the condition‐dependence of melanin‐based plumage

“…As such, previous studies on species possessing both carotenoid‐ and melanin‐based signals may have negatively biased support for the condition‐dependence of melanin‐ relative to carotenoid‐based plumage (although see Parker et al 2003). Recent findings in species that lack any carotenoid plumage ornaments suggest that black plumage may indeed be condition‐dependent (Gladbach et al 2011, Guindre‐Parker et al 2013a). We hypothesized that melanin‐based ornaments are more likely to serve as reliable indicators of condition in species that are achromatic compared to ones that also have a carotenoid‐based trait.…”

The oxidative costs of territory quality and offspring provisioning

“…At 8 days of age – the day before fledging –we counted the number of nestlings present in the nest as our estimate of the number of fledglings. We trust that this is an accurate estimate of fledging success as there is no nest predation at our island study site and nestling deaths occur due to starvation (discussed in Guindre‐Parker et al ., ). Although these deaths may be related to genetic or health problems, we feel that it is more likely that they represent brood reduction from starvation, as suggested previously for snow buntings (Hussell, ).…”