The timing of the pre-nuptial moult in RBWs varies extensively between individuals and populations over a period of approximately 6 months. The lengthy timing of the pre-nuptial moult in RBWs is indicative of phenotypic plasticity—the ability to change phenotype in response to environmental triggers (Price et al. 2003, Coquillard et al. 2012)—that allows organisms to match their phenotype to temporally and spatially heterogeneous environments. Importantly, the pre-nuptial moult date, thought to represent endurance because of the duration of the year that males display nuptial plumage, is the main predictor of fitness for congeners M. cyaneus and M. splendens (Mulder and Magrath 1994, Dunn and Cockburn 1999, Brouwer et al. 2011). But, how do the social and ecological environment affect when individuals complete the pre-nuptial moult?
Social network theory has recently emerged as a valuable tool to understand interactions and associations between individuals (Wey et al. 2008; Sih et al. 2009; Croft et al. 2011), and may be utilized to better understand both qualitative and quantitative interactions between individuals. The application of social network theory to social flocks and changing social organization offers a valuable tool to understanding the effects of social organization on potential fitness.
I used observations and capture records of RBWs on our site to create social networks using Gephi software (Bastian et al. 2009) for two periods: 10 July -8 August 2012 (considered the non-breeding season) and from 1 December-13 January (the pre-breeding season). Individuals are represented by nodes, and interactions are represented by undirected ties (meaning that interactions did not have an initiator or recipient). The degree is defined as the number of ties that an individual has, representing the number of other individuals he interacts with. Node color represents sex and phenotype of the birds.
The non-breeding season was characterized by high connectivity (see Social Network figure below). Average degree was 4.4±2.9 individuals, which did not differ based on sex. However, bright males had a significantly higher degree than dull males in the non-breeding season. During the pre-breeding season, most of the birds were in social pairs. This is reflected in a significantly lower degree (1.6±0.8) than during the non-breeding season. Degree did not differ based on sex or on plumage.
During our work this summer, we will continue to investigate social organization, in addition to collecting data on how the ecological environment may affect social structure. Last year we found a difference in social position between bright and dull males; it will be interesting to see if we can use social organization to predict which males will moult earlier, or if phenotype itself predicts social position. In other species of birds, early social interactions were used to predict fitness later in life, and we hope to determine if there are similar patterns in fairy-wrens.