Interspecific variation in deterioration and degradability of avian feathers: the evolutionary role of microorganisms

Abstract

Feathers are essential for avian life, and factors affecting their integrity are important to understand their evolution. These factors should depend on, among other traits, species‐specific bacterial environments and life‐history characteristics. However, interspecific variation in feather deterioration, feather susceptibility to degradation by keratinolytic bacteria (degradability), and bacterial environment, have rarely been quantified. Here, we did so by measuring deterioration and degradability of wing feathers of fledglings in 16 bird species, and characterizing the bacterial environment where they developed. We found statistically significant interspecific variation for all considered variables. On average, non‐melanised were more deteriorated than melanised feathers, but differences depended on the species. Moreover, nest bacterial loads were related to feather wear, but the sign of the association depended on the bacterial group considered and on feather pigmentation. We also found a positive association of feather degradability with wear of non‐melanised feathers, and with bacterial loads. These results suggest that bacterial environments determine the integrity of fledgling feathers as well as their resistance to bacterial degradation, which implies a preponderant role of bacteria in driving the evolution of avian feathers.

Partial or complete? The evolution of post‐juvenile moult strategies in passerine birds

“…Plumage degradation is continuous and starts already in the nest, in part through the action of feather‐degrading bacteria (Azcárate‐García et al., 2020), which are more active and prevalent in warm and humid environments (Burtt & Ichida, 2004). Accordingly, we found that both temperature and, to a lesser extent, precipitation correlated positively with the likelihood of complete post‐juvenile moult (Figure 2).…”

Extra-pair paternity and antiparasitic defence

“…The size of the uropygial gland has been shown to correlate positively with secondary sexual traits (Moreno-Rueda 2010), plumage brightness (Møller and Mateos-González 2019) and colour intensity (Amat et al 2011). Moreover, ornamental feathers are more easily degraded by bacteria (Ruiz-Rodríguez et al 2015;Azcárate-García et al 2020), and individuals with larger uropygial glands were those better protecting their ornamental feathers from degradation, which could result in more attractive plumage (Ruiz-Rodríguez et al 2015). Hence, secretions from the uropygial gland can be an important factor promoting the acquisition of gain extrapair copulations since several of these are likely to be condition-dependent (Andersson 1994).…”

Sexual selection, feather wear, and time constraints on the pre‐basic molt explain the acquisition of the pre‐alternate molt in European passerines

“…Feathers are nonliving integumentary structures that cover most of a bird's body and fulfill important functions, such as thermoregulation (Wolf & Walsberg, 2000), flight (Hedenström, 2002), and social signaling (Chaine et al, 2013). Due to degradation by mechanical abrasion and microorganisms (Azcárate‐García et al, 2020), or the need to adjust plumage to seasonal changes (Beltran et al, 2018), feathers need to be replaced regularly through molting to maintain their functionality. Molt is costly because it requires energy and other resources to grow feathers (Lindström, Visser, et al, 1993; Moreno‐Rueda, 2010; Murphy & King, 1992; Sanz et al, 2004) and because plumage function (e.g., flight ability) may be impaired during the molting process (Swaddle & Witter, 1997).…”