Assessing meal size in seabirds through head movement dynamics

Abstract

Parental food provisioning is crucial in avian breeding ecology, with significant implications for parental cooperation, sibling competition, and chick survival. Traditional methods for assessing food provisioning in marine birds involve direct observation, video recording, or more invasive techniques like chick weighing and regurgitation induction, which can be stressful for the birds and time-consuming. This study evaluates accelerometers as a less invasive alternative to quantify food provisioning behaviour in Imperial shags (Leucocarbo atriceps). Fieldwork was conducted at Punta León colony (43°04’S,64°29’W), Chubut, Argentina, between mid-November and mid-December of 2019, 2021, and 2022. Adult female shags were equipped with head-mounted accelerometers to monitor the intensity and duration of head movements during food delivery to their chicks. Data from 34 nests were collected, focusing on the relationship between chick age and food provisioning intensity within the first feeding session, which began when the female arrived at the nest with food and started feeding a chick, and ended when no chicks had been fed for 15 min. Our results suggest that head movement intensity (VeDBAsm) significantly influences meal size. Older chicks receive more food when adults exhibit more vigorous movements, while younger chicks do not receive additional food as movement intensity increases. This study demonstrates that accelerometry is a reliable and less invasive method for estimating the quantity of food transferred from parents to chicks older than 7 days. This approach enhances our ability to study Phalacrocoracidae provisioning behaviour while reducing disturbance, offering a valuable tool for future ecological and behavioural research in marine birds.