Social network connections are positively related to temperature in winter flocks of black-capped chickadees

Social species often share with conspecifics the responsibilities of finding food, defending against predators or caring for young. Within a social group, individuals' roles can be influenced by age, sex and personality. Black-capped chickadees, Poecile atricapillus, are nonmigratory passerine birds that spend their winters living in social flocks. Due to the intense metabolic stress placed on chickadees by low winter temperatures, the role of flocking in resource localization and allocation among flockmates is an important aspect of individual fitness, especially during winter. Understanding changes in flock structure in response to the environment may provide insight into the consequences of social behaviour variability on overwinter survival. Here, we used social network analysis to quantify the effects of ambient temperature on social foraging behaviour in winter flocks of black-capped chickadees over two winters in Massachusetts, U.S.A. Contrary to our expectations, we found that two measures of social connection were higher on warm days than on cold days. We found no evidence that sex or dominance rank influenced birds' behavioural responses to temperature. Furthermore, contrary to previous research, we found male-biased sex ratios in most of our flocks. Our findings that birds had more and stronger social connections on warm days and that an individual's response to temperature was not related to their status in a flock beg further investigation as to the specific costs and benefits of flocking in chickadees and other birds.