Effect of feather abrasion on structural coloration in male eastern bluebirds Sialia sialis

Abstract

We used observations of male eastern bluebirds captured twice within a breeding season to test whether changes in structural coloration are related to feather abrasion. Between first and second broods, the UV chroma and brightness of feathers decreased, while hue shifted towards longer wavelengths. Observed changes were greatest for feathers on the head, least for feathers on the rump, and intermediate for feathers on the back. For head feathers, we found a significant correlation between reduction in barb length and UV chroma. Plumage coloration at first capture was correlated with change in UV chroma such that the most ornamented males tended to lose more coloration. Moreover, the magnitude of UV color change was positively related to the number of days between color measurements.To test whether these changes were caused by abrasive properties of the nesting sites, we randomly increased or decreased the abrasiveness of nesting‐box entrances by attaching sand paper or smooth plastic tape. The type of box entrance had no signicant effect on either coloration or barb length change. Our results suggest that feather abrasion is a factor in the seasonal color changes of bluebirds.

Supplemental food increases ornamentation of male nestling Eastern Bluebirds

“…), and feather wear over time has been shown to decrease brightness (Surmacki et al. ). Clearly, we need a better understanding of how non‐iridescent plumage coloration is developed and maintained.…”

“…For example, external feather features may influence feather brightness. Birds with thinner keratin cortexes tend to be brighter ), and feather wear over time has been shown to decrease brightness (Surmacki et al 2011). Clearly, we need a better understanding of how non-iridescent plumage coloration is developed and maintained.…”

Evolutionary drivers of seasonal plumage colours: colour change by moult correlates with sexual selection, predation risk and seasonality across passerines

“…Example: The blue plumage of the mountain bluebird (Sialia currucoides) fades noticeably over time (Surmacki et al 2011a). Application of cosmetics: Some birds enhance their plumage colours through the application of coloured substances, or 'cosmetics,' such as preen wax or oils secreted by the skin, powders produced by specialised feathers, and soils that are rich in ironoxide (reviewed in Delhey et al 2007).…”

Climate, crypsis and Gloger’s rule in a large family of tropical passerine birds (Furnariidae)

“…Based on ours and previous results, we suggest that the pattern encapsulated by Gloger’s rule is produced by a combination of the partially correlated effects of habitat type, precipitation, and vegetation density. The effect of habitat type is driven by natural selection for enhanced crypsis in darker light environments (Zink and Remsen 1986, Endler 1993, McNaught and Owens 2002, Gomez and Thery 2004, Dunn et al 2015, Maia et al 2016, Shultz and Burns 2017, Marcondes and Brumfield 2019), whereas the effect of precipitation may be due to featherdegrading bacteria (Burtt and Ichida 1999, 2004, Goldstein et al 2004, Gunderson et al 2008, Kent and Burtt 2016), and the effect of vegetation density may be related to feather abrasion (Kale 1966, Burtt 1986, Surmacki et al 2011, Kroodsma and Verner 2013), though the latter two effects still demand further empirical work to be conclusively demonstrated. It is also still unclear how the effects of temperature fit into this scenario.…”

“…Nevertheless, vegetation density by itself might also favor increased pigmentation, because greater melanin content makes feathers harder and more resistant to abrasion (Barrowclough and Sibley 1980, Burtt 1986, Bonser 1995). This is often considered in the context of abrasion from airborne particles, but it is conceivable that abrasion from vegetation might also be an important selective factor favoring heavier plumage pigmentation (Kale 1966, Burtt 1986, Surmacki et al 2011, Kroodsma and Verner 2013), although this demands further empirical study.…”