Competitive exclusion, experience-based learning, and human fishing, influence activity patterns in Juvenile and Adult Brown Pelicans ( Pelecanus occidentalis )

The activity patterns of young and adult individuals offer insights into exclusion and adaptation dynamics in seabirds. Juveniles often show differences in their daily behaviors compared to adults, especially in activities like feeding. We focus in two contrasting hypotheses to explain the age-related differences in activity patterns of Brown Pelicans ( Pelecanus occidentalis ): the “competitive exclusion” hypothesis and the “experience-based adaptation” hypothesis. The competitive exclusion hypothesis posits that adult pelicans, with superior foraging skills, actively exclude juveniles from prime feeding areas, leading to temporal segregation. In contrast, the experience-based adaptation hypothesis suggests that juveniles exhibit different activity patterns as they undergo a learning process, gradually improving their foraging efficiency through trial and error. Using continuous focal sampling, we analyzed the activity peaks of both juveniles and adults, revealing significant temporal segregation between age groups. Additionally, the impact of human fishing activity on pelican behavior was assessed, showing alterations in natural foraging patterns. These findings contribute to the understanding of resource use and competition dynamics in seabirds and highlight the importance of considering both biological and anthropogenic factors when analyzing seabird behavior.