Supplementary material from "Navigating the unknown: How exploratory traits shape juvenile post-fledging behaviour and survival in gulls"

The post-fledging period is a critical phase for inexperienced birds, who must navigate and explore unfamiliar environments to locate essential resources for survival. Successful foraging during this stage relies on acquiring spatial knowledge through exploration, which may develop early in life. In this study, we examined whether the early-life exploratory phenotype, assessed through an Open Field Test during the nestling phase, predicts post-fledging behaviour and survival. GPS tracking data from 34 juvenile Lesser Black-backed Gulls (Larus fuscus) over a 20-day period were used to quantify habitat preferences, spatial use (mean squared displacement and revisitation patterns), and time spent flying, foraging, and resting. Survival was monitored over six months following fledging, encompassing migration. Early-life exploratory phenotype predicted habitat use: individuals with a more exploratory phenotype frequented urban habitats more often, whereas those with a less exploratory phenotype relied more on agricultural areas. However, exploratory phenotypes did not predict spatial use or survival. These findings indicate that behavioural variation established early in life can have lasting ecological consequences. The absence of a link between exploratory phenotype and survival may reflect phenotype-habitat matching, stochastic environmental factors, or that the Open Field Test does not capture the behavioural components most relevant to survival.