[en] In recent decades, there has been a high increase in the numbers of the yellow-legged gull (Larus michahellis) across Europe, which has been linked to an increase in predictable resources of anthropogenic origin (PAFS). In this final degree project, I studied whether mussels (Mytilus edulis) from the mussel purification plant located in the port of Lorbé (A Coruña, NW Spain), which functions as a PAF for the yellowlegged gull, could be an important resource for this species outside the breeding season. To do this, the unique behavior developed by seagulls for breaking the mussels from the air was first studied. In addition, experimental launches were carried out from the same height. Observations and experiments agreed on the number of throws required to break a mussel: 1 for large mussels, 2 for medium mussels, and 3 for small mussels. Likewise, a comparison was made between the sizes of the mussels consumed and those available, concluding that there was no selection by size: the birds consumed the most abundant mussel size at the exit of the plant pipeline. In addition, the age structure of the gull populations of Lorbé and Miño (a close control population that does not foraje on mussels) was compared, finding that in Lorbé the percentage of juveniles was much higher than in Miño (64% vs. 14% ). It was shown, not only that juveniles were the most abundant age class in Lorbé (64% of the birds surveyed) but that they made the most of the launches (52%), being therefore the main consumers of this resource. In addition, the energy profitability of the resource was studied, concluding that a diet based solely on mussels would not be viable for the species, due to the high number of prey that they would need to eat (234-632 mussels) to satisfy their daily energy requirements. Therefore, I conclude that mussels were a secondary resource, used by juvenile and inexperienced birds temporarily (only at low tide), perhaps as a strategy to avoid competition with adults (more aggressive and experienced) for other sources of higher quality.

[gl] Nas últimas décadas produciuse un incremento elevado das poboacións de gaivota patiamarela (Larus michahellis) en toda Europa que se relacionou cun aumento dos recursos predicibles de orixe antropogénico (PAFS). Neste traballo de fin de grao estudouse se o mexillón (Mytilus edulis) procedente do viveiro mexilloeiro do porto de Lorbé (A Coruña, NO España), que funciona como un PAF para a gaivota patiamarela, podería ser un recurso importante para esta especie fóra da tempada de cría. Para iso, estudouse primeiro o singular comportamento desenvolvido polas gaivotas para a rotura do mexillón desde o aire. Ademais levaronse a cabo lanzamentos experimentais desde igual altura. Observacións e experimentos coincidiron no número de lanzamentos necesario para romper un mexillón: 1 lanzamento para mexillóns grandes, 2 para medianos e 3 para pequenos. Así mesmo realizouse unha comparativa entre os tamaños dos mexillóns consumidos e os dispoñibles concluíndo que non houbo selección por tamaño: as aves consumiron a talla de mexillón máis abundante na saída do viveiro. Ademais, comparouse a estrutura de idade das poboacións de gaivotas de Lorbé e Miño (poboación próxima control que non se alimenta de mexillóns) comprobando que en Lorbé a porcentaxe de xuvenís foi moito maior que en Miño (64% fronte a un 14%). Demostrouse, non só que os xuvenís foron a clase de idade máis abundante en Lorbé (64% das aves censadas) senón que estes realizaron a maioría dos lanzamentos (52%), sendo por tanto os principais consumidores deste recurso. Ademais estudouse a rendibilidade enerxética do recurso, concluíndo que non sería viable para a especie unha alimentación baseada unicamente en mexillón, debido á alta cantidade de presas que necesitarían inxerir (234-632 mexillóns) para satisfacer os seus requirimentos enerxéticos diarios. Por tanto concluímos que o mexillón foi un recurso secundario, empregado por aves xuvenís e inexpertas de maneira temporal (só en marea baixa), quizais como estratexia para evitar a competición cos adultos (máis agresivos e experimentados) por outras fontes de alimento de maior calidade.