The status of the European Shag Phalacrocorax aristotelis population on the Atlantic coast of the Iberian peninsula

Velando, A., Docampo, F. & Alvarez, D. The status of the European Shag Phalacrocorax aristotelis population on the Atlantic coast of the Iberian peninsula. Atlantic Seabirds (1999).


A regional analysis of the status of the European Shag Phalacrocorax aristotelis population on the Atlantic coasts of the Iberian Peninsula is presented. This is the first census to be made of this population. The total population was estimated to be approximately 2239 pairs in 1990-94. The first counts from Euskadi and Cantabria are presented, indicating a population of 57-67 pairs in Euskadi in 1994 and 36-41 pairs in Cantabria in 1992. The first census in Asturias dates from 1986 with 98-124 pairs, and the population has increased at an annual rate of 6%, reaching 199-250 pairs in 1997. There are records of partial counts made in Galicia since 1976. The population appears to have stabilised on the Cíes and Ons Islands (Rías Baixas, Pontevedra), where it was increasing at 8-9% annually. The total count of 1462 breeding pairs on Cíes and Ons accounts for 66% of the Atlantic Iberian population. As far as is known, the population in Portugal has stabilised, but there has been no census of the southern colonies since 1983. On the island of Berlenga there were 60 pairs in 1990-94, the number of pairs having changed very little since the first count in 1939.

Henslow’s swimming crab (Polybius henslowii) as an important food for yellow-legged gulls (Larus cachinnans) in NW Spain

Munilla, I. Henslow’s swimming crab (Polybius henslowii) as an important food for yellow-legged gulls (Larus cachinnans) in NW Spain. ICES Journal of Marine Science: Journal du Conseil 54, 631–634 (1997).


An analysis of the contents of 2562 pellets sampled from 1987 to 1993 at breeding colonies and roosting sites showed that Henslow’s swimming crabs (Polybius henslowii) are by far the most important marine prey for yellow-legged gulls (Larus cachinnans) on the coasts of Galicia (north-western Spain), occurring in 36.4% of pellets. The results also suggest that yellow-legged gulls in Galicia are to a great extent marine foragers. Galicia has one of the largest yellow-legged gull populations in western Europe, largely dominating the seabird community. Polybius henslowii is the most abundant decapod crab over the continental shelf of Galicia. It enters coastal waters in large shoals and frequently stays close to the sea surface. Compared with the diets of other yellow-legged gull populations or any of the other closely related gull species, such as the herring (L. argentatus) and the lesser black-backed gull (L. fuscus), Polybius henslowii appears as a characteristic and even exclusive prey of yellow-legged gull populations in the Iberian Atlantic. There is also some evidence that the regular irruption of large Polybius henslowii shoals is a phenomenon peculiar to Iberian Atlantic waters.

Desplazamientos de la Gaviota Patiamarilla (Larus cachinnans) en poblaciones del norte de la Península Ibérica

Munilla, I. Desplazamientos de la Gaviota Patiamarilla (Larus cachinnans) en poblaciones del norte de la Península Ibérica. Ardeola 44, 19–26 (1997).


Se analizan todas las recuperaciones disponibles de gaviotas patiamarillas anilladas como pollos que conciernen al Atlántico norte español (Galicia, Asturias, Cantabria y País Vasco), y se comparan con las recuperaciones de aves anilladas en la provincia de Gerona. Las gaviotas patiamarillas de las colonias del Atlántico norte español no parecen realizar desplazamientos de carácter migratorio, recuperándose la mayoría de las aves a menos de 100 km de la colonia natal, situación que contrasta con el claro comportamiento migratorio de las patiamarillas del Mediterráneo occidental. En las poblaciones del Atlántico se han encontrado diferencias significativas entre clases de edad en las distancias a la colonia natal, correspondiendo los mayores desplazamientos a las aves inmaduras. Por el contrario, los datos de la provincia de Gerona no parecen indicar la existencia de tales diferencias. En ambos casos se observa un marcado ciclo estacional, si bien las menores distancias a la colonia de anillamiento se producen entre mayo y septiembre en el Atlántico, mientras que en Gerona este periodo tiene lugar entre marzo y junio. Por otra parte, los resultados sugieren que las gaviotas del Atlántico norte español constituyen una población cerrada, sin apenas relaciones con otras poblaciones de Larus cachinnans.

Climate Influences Fledgling Sex Ratio and Sex-Specific Dispersal in a Seabird

Barros, Á., Álvarez, D. & Velando, A. Climate Influences Fledgling Sex Ratio and Sex-Specific Dispersal in a Seabird. PLoS ONE 8, e71358 (2013).8): e71358. doi:10.1371/journal.pone.0071358

Climate influences the dynamics of natural populations by direct effects over habitat quality but also modulating the phenotypic responses of organisms’ life-history traits. These responses may be different in males and females, particularly in dimorphic species, due to sex-specific requirements or constraints. Here, in a coastal seabird, the European shag (Phalacrocorax aristotelis), we studied the influence of climate (North Atlantic Oscillation, NAO; Sea Surface Temperature, SST) on two sex-related population parameters: fledgling sex ratio and sex-specific dispersal. We found that fledgling sex ratio was female skewed in NAO-positive years and male skewed in NAO-negative years. Accordingly, females dispersed a longer distance in NAO-positive years when females were overproduced, and on the contrary, males dispersed more in NAO-negative years. Overall, our findings provide rare evidence on vertebrates with genetic sex determination that climate conditions may govern population dynamics by affecting sex-specific density and dispersal.