Changes in the Population Size of Yellow-legged Gull Larus michahellis at Essaouira and Mogador Island, West-central Morocco

This study concerns changes in the size and population structure of a Yellow-legged Gull Larus michahellis colony, last assessed in 1985 in the city of Essaouira and on Mogador Island, Morocco. Using point-transect sampling, the average density measured in 2019 was 53.5 ± 2.8 birds/ha (5350 ± 280 birds/km2), which translates to a population size of almost 30 000 birds. The highest density occurred on Mogador Island, with 217.2 ± 28.3 birds/ha, a much higher density than previously recorded. The Yellow-legged Gull breeding population in the Essaouira–Mogador Island area has grown 3.58% per year since 1985, with an annual average reproductive rate of 1.04 chicks/pair. An increased availability of food via open landfill sites seems to be the major cause for this population boom. More detailed studies, however, are needed to better understand the effect of food abundance on population growth for this colony.