Seasonally breeding animals often exhibit different social structures during non-breeding and breeding periods that coincide with seasonal environmental variation. Therefore, ongoing climate change may play an important role in determining the future structure of animal societies, especially if climate determines when seasonal shifts in social structure occur. However, we know little about the environmental cues that determine the timing of seasonal shifts in social structure, a lack of knowledge that contrasts with our well-defined knowledge of the environmental cues that trigger a shift to breeding physiology in seasonally breeding species. Here we tested whether the environmental cues that drive seasonal shifts in social structure are similar to those that determine timing of breeding in the red-backed fairywren (Malurus melanocephalus), an Australian songbird. Social network analyses revealed that social groups, which are highly territorial during the breeding season, interact in social “communities” on larger ranges during the non-breeding season. Interactions among non-breeding groups were related to rainfall, with more rainfall leading to reductions in home range size and fewer interactions among non-breeding social groups. Similarly, onset of breeding was also determined by rainfall during the non-breeding season, with greater rainfall leading to earlier breeding. These findings reveal that for some species, the cues that determine the timing of shifts in social structure across seasonal boundaries can be similar to those that determine timing of breeding. This study increases our understanding of how social structure and the selection pressures that result from different social structures might respond to changing climates.

See README file for descriptions of each dataset and summaries of each R script. See annotated R code for instructions on how to run the analyses. All analyses were conducted in R version 3.5.2 unless otherwise specified.