The effect of rearing environment on blue structural coloration of eastern bluebirds (Sialia sialis)

Abstract

We used a brood-size manipulation to test the effect of rearing environment on structural coloration of feathers grown by eastern bluebird (Sialia sialis) nestlings. Ultraviolet (UV)-blue structural coloration has been shown to be sexually selected in this species. Our experimental design took advantage of the growth of UV-blue wing feathers in nestlings that are retained as part of the first nuptial plumage. We cross-fostered nestlings to create enlarged and reduced broods with the purpose of manipulating parental feeding rates and measured the effect on nestling growth and plumage coloration. Brood size influenced feeding rates to offspring, but the effect varied with season. In general, male nestlings reared in reduced broods were fed more often, weighed more, and displayed brighter structural plumage compared to nestlings reared in enlarged broods. Female nestlings appeared to experience less adverse affects of brood enlargement, and we did not detect an effect of brood-size manipulation on the plumage coloration of female nestlings. Measures of plumage coloration in both males and females, however, were correlated to hatching date and nestling mass during feather development. These data provide empirical evidence that environmental quality can influence the development of the blue structural coloration of feathers and that males may be more sensitive to environmental fluctuations than females.

Juvenile coloration of Florida Scrub-Jays (Aphelocoma coerulescens) is sexually dichromatic and correlated with condition

“…Further, Blue Tit and Eastern Bluebird nestlings reared in enlarged broods grew tails with less elaborate plumage than those reared in reduced brood sizes (Jacot andKempenaers 2007, Siefferman andHill 2007). Finally, variation in structural coloration associated with hatch date has been demonstrated in juvenile Eastern Bluebirds (Siefferman and Hill 2007). Our data thus add to a growing body of literature suggesting that non-iridescent structural coloration is often condition dependent and may thus function as a signal.…”

“…Measures of structural coloration correlate with feather growth rates of both male and female nestling Blue Tits (Johnsen et al 2003) and with blood protein levels of male nestling Blue Tits (Peters et al 2007). Further, Blue Tit and Eastern Bluebird nestlings reared in enlarged broods grew tails with less elaborate plumage than those reared in reduced brood sizes (Jacot andKempenaers 2007, Siefferman andHill 2007). Finally, variation in structural coloration associated with hatch date has been demonstrated in juvenile Eastern Bluebirds (Siefferman and Hill 2007).…”

Influence of Hatch Order on Begging and Plumage Coloration of Nestling Eastern Bluebirds

“…The color of remiges can be quantified by 14 days after hatching (Siefferman and Hill 2007). Young bluebirds retain these juvenile wing and tail feathers as part of their first nuptial plumage (Gowaty and Plissner 1998).…”

“…Nestling condition also can be honestly signaled by plumage coloration , Tschirren et al 2003, Jacot and Kempenaers 2007, Siefferman and Hill 2007. Juvenal plumage coloration might function in parent-offspring communication and mediate parental favoritism either at the nest (Tschirren et al 2003, Galvan et al 2008, Griggio et al 2009 or later during the post-fledgling dependence period (Tanner andRichner 2008, Ligon andHill 2010).…”

“…Young bluebirds retain these juvenile wing and tail feathers as part of their first nuptial plumage (Gowaty and Plissner 1998). Experimental manipulations of food availability to nestlings demonstrate that male nestling bluebirds reared in poor natal conditions grow more slowly and display duller wing color compared to those reared in better natal environments (Siefferman and Hill 2007). Parents exhibit preferences for the more-colorful fledglings (Ligon and Hill 2010).…”