Associations on land and at sea? A pilot study on the utility of proximity loggers to assess inter-individual relationships in colonial seabirds

Accurate and extensive data collection is essential for understanding animal sociality, but observing associations between individuals remains challenging. Animals often associate and interact outside of the range of an observer, especially in environments such as underwater or underground. However, proximity loggers using Bluetooth and radio frequency to detect associations allow scientists to access behavioural information that would otherwise be impossible to collect. Here we examined the use of a logger with a proximity feature to capture associations between Atlantic puffin individuals and assessed how it could complement observations in social network studies. To understand the capabilities of the logger, we tested the effect of distance on signal strength and proportion of associations detected, as well as the proportion of contacts recorded by each logger in a dyad, in lab-based and field environments. Thereafter, we tested the loggers on live Atlantic puffins and compared their performance against visual observations. As expected, signal strength decreased with distance, and lab-based values were more consistent than in the field. The proportion of contacts successfully processed decreased with distance, but our experiment in the field was more reliable, probably because we used a lower logger density, limiting opportunities for interference among units. More importantly, the loggers identified more putative associations than detected by observations, including many when and where individuals were not under observation. We further demonstrate that Atlantic puffins that associate frequently on land also associate frequently at sea. Our results bring new insight into the understanding of Atlantic puffin social behaviours, particularly at times and in locations challenging to monitor.