Estimating the size of the Larus michahellis colony on Bergeggi Island (Liguria, NW Italy) during the nesting season using the Double-Observer Method

Abstract

This work aims to apply the double-observer method to estimate the number of nesting Larus michahellis in the Marine Protected Area of Bergeggi Island in the province of Savona (Liguria, NW Italy). The study was carried out in 2024, during the nesting period of the seagulls on the island. The double-dependent observer method was applied, carrying out two samplings per month from March to June, for a total of eight replicates. The monitoring consisted of dividing the island in three sectors, positioning a boat from a fixed point in front of the island and counting the seagulls that were perched. The data obtained were analysed using DOBSERV and processed through RStudio. The estimated average number of seagulls present on the island during the nesting period was 196.5 ± 53.6. High detection probability and the particular conformation of the study area led to a positive outcome for the application of the method to count the number of seagulls present during the nesting period.