Rate of moult affects feather quality: a mechanism linking current reproductive effort to future survival

Abstract

Life-history theory proposes that costs must be associated with reproduction. Many direct costs are incurred during breeding. There is also evidence for indirect costs, incurred after breeding, which decrease survival and future reproductive success. One possible indirect cost identi¢ed in birds is that breeding activity in some way compromises plumage quality in the subsequent moult. Here we propose a mechanism by which this could occur. Breeding activity delays the start of moult. Birds that start to moult later also moult more rapidlyöan e¡ect of decreasing daylength. Could this result in poorer quality plumage? We kept two groups of male European starlings, Sturnus vulgaris, one on constant long days and the other on decreasing daylengths from the start of moult. Decreasing daylengths reduced the duration of moult from 103 § 4 days to 73 § 3 days (p 5 0.0001). Newly grown primary feathers of birds that moulted fast were slightly shorter, weighed less (p 5 0.05) and were more asymmetrical. They had a thinner rachis (p 5 0.005), were less hard (p 5 0.01) and less rigid (p 5 0.05). They were also less resistant to wear so that di¡erences in mass and asymmetry increased with time. There was no di¡erence in Young's modulus. Poorer quality plumage will lead to decreased survival due to decreased £ight performance and increased thermoregulatory costs. Thus, reproduction incurs costs through a mechanism that operates after the end of breeding.

Pattern of Wing Moult and Its Relationship to Breeding in the Eurasian Stone-CurlewBurhinus oedicnemus

“…Primary moult is also quite slow (>5 months) compared to other wader species, which usually complete their moult cycle in less than 4 months; longer moult cycles are usually associated with moult suspension. It could be hypothesized that this slow and constant rate facilitates the overlap between breeding and moult by spreading the costs of moult homogeneously over the whole period and by avoiding the detrimental effects on feather quality of rapid moult cycles (Dawson et al 2000, Serra 2001. It is interesting to note that, while usually avoided in most temperate species, an extensive moult-breeding overlap is relatively common among tropical birds (Foster 1974, Moreno 2004, where it is associated with small clutches and long breeding seasons (Foster 1974).…”

Optimal annual routines: behaviour in the context of physiology and ecology

“…Nilsson & Svensson suggest that these longterm effects of the experimental manipulation may be the result of the late breeding following the clutch removal interfering with the moult that occurs after breeding. Since the rate of moult in starlings (Sturnus vulgaris) influences the quality of the new feathers (Dawson et al 2000), the manipulation may have resulted in the new feathers being of poorer quality than usual, with thermoregulatory costs in winter being raised because the new feathers provided less insulation.…”

Nanostructural self-assembly of iridescent feather barbules through depletion attraction of melanosomes during keratinization

“…The rate of feather keratinization is strongly influenced by the initial amount and concentration of keratin monomers [67], which in turn is mostly limited by keratin gene transcription and mRNA abundance [68]. Given that keratin gene expression is regulated by various transcription factors that are highly responsive to extracellular condition and hormones [69], and keratinization itself is sensitive to the pH of the cellular environment [67], this crucial step in nanostructural organization is likely to be sensitive to, and therefore indicative of, developmental stressors and individual condition [70][71][72]. In summary, based on the timing and steps of the organization of colour-producing nanostructures, our evidence strongly opposes the suggestion that nanostructural organization results from active cellular processes, instead pointing to the role of energy-minimizing entropic interactions for achieving such patterns.…”