Egg Colour Covaries with Female Expression of a Male Ornament in the Spotless Starling (Sturnus unicolor)

Abstract

The sexually selected egg colour hypothesis (SSECH) proposes that egg colouration is as a post‐mating sexually selected signal of female phenotypic quality, maintained by a higher allocation of paternal care. Similarly, some female traits can reflect genetic quality or condition and males could use this information in mate choice or in modulating parental investment. In our study, we examined the correlation of individual variation in egg colouration with female expression of a male ornament and how male feeding covaried with these two female traits in the spotless starling, in which egg colour varies widely between clutches and where both sexes possess showy throat feathers that are age dependent and that may signal individual quality. According to the SSECH, high‐quality females (females with longer throat feathers) are expected to lay more colourful eggs than low‐quality females and males should modify their feeding behaviour accordingly. By means of a principal component analysis, we found that most of the variation in egg colouration was due to brightness differences, and in a lower proportion to chromatic variation. Chromatic variation reflected a ultraviolet (UV) vs. greenness trade‐off and was positively associated with throat feather length: females with larger throat feathers laid eggs with higher UV and lower green reflectance. However, egg brightness was not related to female feather length, as the SSECH would predict. Male feedings were positively related to female throat feather length and negatively related to chromatic variation, meaning that males contributed more to nests of females with long throat feathers who laid eggs with higher UV and lower green reflectance. In conclusion, our data provide mixed support for the SSECH: although egg chromatic variation was related to female expression of a male ornament and male parental care, we found no evidence that egg brightness was involved in these processes.

Ultraviolet visual sensitivity in three avian lineages: paleognaths, parrots, and passerines

“…For example, males may attend to UV-reflectance of eggs as a predictor of female quality, as has been suggested in spotless starlings and garnering moderate, if correlative, empirical support (López-Rull et al 2007). Eggshells of extinct moa species are often found in caves, suggesting that UV egg reflectance may have facilitated egg location and recognition in these species.…”

“…Eggshells of extinct moa species are often found in caves, suggesting that UV egg reflectance may have facilitated egg location and recognition in these species. Ostrich, emu, and extinct stout-legged moa eggshells are known to reflect UV light (Igic et al 2010a) which may play a functional role in signaling quality of both mother and chicks in other species (Moreno et al 2005;López-Rull et al 2007. Fadzly et al (2009) has examined the spectral reflectance curves of lancewood tree (Pseudopanax crassifolius) leaves once exploited by moa species as a food source.…”

Are brighter eggs better? Egg color and parental investment by House Wrens

“…Similarly, Moreno et al (2008) found that nestling Pied Flycatchers from nests that received a single experimentally darker blue egg weighed more and were in better condition than those in control nests, suggesting that they received better parental care. In contrast, Krist and Grim (2007) found no relationship between blue egg color and parental investment by male Collared Flycatchers, and Lopez‐Rull et al (2007) found no relationship between egg brightness and the provisioning rates of male Spotless Starlings.…”

Effects of temperature and nest heat exposure on nestling growth, dehydration and survival in a Mediterranean hole‐nesting passerine

“…) and to reproductive success in females (López‐Rull et al . ). In total, we were able to catch 197 adults (2005, 62 females and 49 males; 2006, 45 females and 41 males).…”