Egg-sequence rather than mating preference influences female egg investment in the red-legged partridge

In precocial bird species, the eggs represent a strong maternal allocation of resources and constitute most of the maternal investment since parents do not feed the young after they hatch. Females can differentially allocate resources in their eggs as a response to the environment experienced during the laying period, including the quality of their mate. To assess the importance of female selection on egg composition in the red-legged partridge, we tested breeding females in a choice trial in which they were allowed to choose between males. After the choice trials, the females were mated with their preferred male (P group), with a non-preferred one (NP group) or with a randomly selected male (RND group). Eggs laid by females of the three groups did not differ significantly in mass, shape, yolk, albumen or shell weight. Moreover, there was no significant difference in egg lysozyme concentration (an important albumen antimicrobial component). There was a significant difference in egg characteristics in relation to position in the laying order, with last-laid eggs being heavier and more spherical. Last-laid eggs contained more albumen but their shell was lighter and the albumen contained less lysozyme. This study shows that partner attractiveness may not influence the characteristics of egg quality, and that in this partridge species the females are able to invest in large clutches without a decrease of egg size but with a progressive decrease of egg quality.