PUBLICACIÓN CIENTÍFICA

Short-term indirect effects of the Prestige’ oil spill on European shags: changes in availability of prey

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Velando, A., Munilla, I. & Leyenda, P. M. Short-term indirect effects of the Prestige’ oil spill on European shags: changes in availability of prey. Marine Ecology Progress Series 302, 263–274 (2005).

In 2003, immediately following the ‘Prestige’ oil spill in Galicia, Spain, we studied the reproductive performance of European shags Phalacrocorax aristotelis at Illas Cíes, the main breeding ground for the species in Spain. Over the 10 yr preceding the spill, we monitored the breeding and the dynamics of the Illas Cíes population. We performed 1000 simulations of the population dynamics using the population parameters and their variability for the pre-spill period. The number of breeding
pairs counted in 2003 was lower than any of the values predicted by the simulation models, suggesting that population parameters changed after the ‘Prestige’ wreck. Environmental conditions cannot explain the observed effects because weather conditions were far from severe in 2003. The analysis of shag casualities showed that despite the extensive oiling of Illas Cíes and nearby waters it is unlikely that shags were killed in large numbers. Nevertheless, the shag feeding grounds around Illas Cíes, which are mainly sandy bottoms, were continuously exposed to oil pollution throughout the shag breeding season as revealed by the high levels of pollutants in sediments, plankton, and other organisms. In the pre-spill years, shags showed low seasonal dietary variation, feeding mainly on sandeels. Nevertheless, in 2003, there was a dietary shift with a lower occurrence of sandeel that, together with sandeel fishery data, indicate lower sandeel availability at foraging areas. In addition, reproductive performance in 2003 was significantly lower and chick condition was poorer compared to the pre-spill years. When all this information is taken into account, the picture that emerges strongly suggests that the European Shag population in Illas Cíes is suffering a negative impact of an indirect nature mediated through a reduction on the availability of a highly preferred forage-fish.

Begging response of gull chicks to the red spot on the parental bill

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Velando, A., Kim, S.-Y. & Noguera, J. C. Begging response of gull chicks to the red spot on the parental bill. Animal Behaviour 85, 1359–1366 (2013).

In some animals, offspring begging is elicited by parents through behavioural or morphological signals. The red spot on the lower mandible in adult gulls is one of the best-known examples of a signal triggering chick begging. We examined whether the begging response of chicks (pecking for food and the chatter call for drawing parental attention) was affected by the spot size within the natural range of variation on a dummy head. Using a cross-fostering experiment, we examined whether these responses covary with the size of the genetic or social parent’s spot. We found that the natural variation in size of this parental signal strongly influenced intensity of chick begging. Pecking increased when chicks were stimulated by a larger red spot. Additionally, pecking intensity increased in chicks reared by mothers with a large red spot, suggesting that this begging component is influenced by previous experience. In contrast, chick hatching order affected the number of chatter calls produced in relation to the size of the red spot on the dummy, suggesting the presence of different begging strategies according to brood hierarchy. The differential call response to a small/large red spot on the dummy was positively correlated with the original mothers’ red spot size and negatively with that of the original fathers. These results suggest a genetic correlation between biased chick response for a large spot and parental signal in contrasting patterns for mothers and fathers. Our results suggest that the parental red spot and offspring begging are traits subject to coevolution.

Sex ratio in relation to timing of breeding, and laying sequence in a dimorphic seabird

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Velando, A., Graves, J. & Ortega-Ruano, J. E. Sex ratio in relation to timing of breeding, and laying sequence in a dimorphic seabird. Ibis 144, 9–16 (2002).

When the cost of rearing sons and daughters differs and the subsequent survival and reproductive success of one sex is more dependent than the other, on the amount of parental investment, adult females tend to produce more chicks of the more dependent sex if the females are in good condition themselves. One method of varying the total investment in each sex is through modifying the sex ratio of offspring produced. This study shows that in broods of European Shags Phalacrocorax aristotelis, the sex ratio varied with laying date. Presumably in this species, the lifetime reproductive success of males is more dependent on the level of parental investment. Early breeders are in better condition, the brood sex ratio of early broods was male biased (0.63), while that of late broods was female biased (0.36). The overall difference in sex ratio found between early and late nests could be attributed to manipulation of sex in the first laid egg. In early broods, 77% of the first hatched chicks were male but only 30% of the first hatched chicks in late broods were male. The sex combination of the first two chicks in a brood significantly affected growth as measured by asymptotic mass.

Nest site characteristics, occupation and breeding success in the European Shag

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Velando, A. & Freire, J. Nest site characteristics, occupation and breeding success in the European Shag. Waterbirds 26, 473–483 (2003).

The European Shag (Phalacrocorax aristotelis) breeds in a wide range of nest-sites depending on the locality, such as crevices under fallen rocks, open ground caves and open ledges on craggy cliffs. In this paper the habitat selection of shags breeding in cavities on the coastal slopes of Islas Cíes (Galicia, Northwest Iberian Peninsula) are examined. Shags selected sites with more lateral and overhead cover, with better drainage and with average visibility. In addition, sites where breeding was successful differed from unsuccessful sites. Nest-site characteristics especially affected the hatching success. In this colony, shags showed adaptive responses to site-quality variability. Thus, nest-site quality declined with density and with seasonal occupancy. Shag colonies seem to follow an ideal despotic distribution, where some individuals monopolize high quality sites and prevented other individuals from settling in the good sites. Further studies are required to assess the proximal mechanisms used for nest-site selection in this species.

How general is the central-periphery distribution among seabird colonies? Nest spatial pattern in the European Shag

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Velando, A. & Freire, J. How general is the central-periphery distribution among seabird colonies? Nest spatial pattern in the European Shag. The Condor 103, 544–554 (2001).

La distribución de los nidos en aves coloniales puede ser explicada por dos modelos. El modelo centro-periferia implica que las aves que crían en el centro de una colonia son menos accesibles a los depredadores, poseen una mejor condición y tienen un mayor éxito reproductivo. En cambio, el modelo centro-satélite sugiere que aves de baja calidad construyen sus nidos cerca de parejas de alta calidad para obtener ventajas como un mayor número de cópulas extrapareja por parte de hembras de baja calidad o un mejor sitio de cría o pareja en la siguiente estación de cría. En el presente estudio, nosotros contrastamos estos modelos con la distribución de la calidad de las parejas de Phalacrocorax aristotelis en dos colonias (Portelo y Faro) de las Islas Cíes situadas en Galicia, noroeste de España. Hemos utilizado como indicador de la calidad de la pareja los residuales del éxito reproductor, eliminando el efecto de la calidad del sitio de nido. En la colonia del Portelo se observó una correlación negativa entre la calidad de las parejas a una distancia menor de 4 m; en el Faro, en cambio, no hubo evidencias de una distribución diferente al azar. Además, se encontró una correlación espacial negativa entre los sitios de nido en los que se construyó un nido por primera vez y los sitios que fueron reocupados. En global, estos resultados muestran que la distribución de las colonias del P. aristotelis no corresponde al modelo centro-periferia, sino más bien al modelo centro-satélite o en todo caso, a una distribución al azar.

Intercolony and seasonal differences in the breeding diet of European shags on the Galician coast (NW Spain)

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Velando, A. & Freire, J. Intercolony and seasonal differences in the breeding diet of European shags on the Galician coast (NW Spain). Marine Ecology Progress Series 188, 225–236 (1999).

The seasonal and spatial variations in the dlet of the European shag Phalacrocorax aristotelis were studied during the breeding period, based on the analysis of 202 adults’ pellets (February to June, 1995) and 30 regurgitatons of chicks (April, May and June, 1995 and 1996) taken from 2 colonies located in close proximity to one another ( < l 5 km) on the coast of Galicia (W Spain; Islands of Cies and Ons). The diet of birds from the Cies Islands consisted mainly of sandeels (family Ammodytidae), which make up over 70% of the prey during all months. These fishes went practically unreported in a number of previous studies of fish communities in the region, probably due to the low catchability of trawl nets and the possibility that the habitats of sandeels where shags forage, shallow (<10 to 15 m) sandy bottoms, were not sampled adequately. Seasonal changes were found on the Island of Ons, where in winter (February and March) the diet was based on gobids (family Gobiidae) and sand smelts Atherina presbyter, while In spring the dominant prey were the Ammodytidae (in May and June they made up over 86%). The consumption of sandeels established an increased similarity in diet between the colonies throughout the breeding cycle, and they were the only prey whose abundance was negatively correlated with the diversity of each pellet. This study highlights the high plasticity in prey and feeding habitats (both pelagic and benthic with different types of substrates) used by the European shag. It should be noted, however, that the main prey during chick rearing are sandeels. Differences were found in the mean sizes of the different prey consumed, but the modal size for all of them throughout the season was around 9 to 11 cm in total length. The range of sizes available in the environment is greater than the range chosen by the European shag, which suggests that this bird selects a narrow range of prey sizes.

Coloniabilidad y conservación de aves marinas: el caso del cormorán moñudo

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Velando, A. & Freire, J. Coloniabilidad y conservación de aves marinas: el caso del cormorán moñudo. Etología 7, 55–62 (1999).

En el presente trabajo exponemos cómo los estudios de coloniabilidad pueden ser aplicados a la conservación de aves marinas. Los estudios realizados en las Islas Cíes (NO de España) muestran cómo en las colonias del cormorán moñudo (Phalacrocorax aristotelis) existe una atracción de las parejas de baja calidad y/o jóvenes a criar cerca de las de alta calidad. En la Isla de Ons la dinámica espacial de las colonias señala la importancia de la limitación de los sitios de cría, el contexto social y la emigración dependiente de la distancia en los procesos de reclutamiento. Estos estudios nos permiten diseñar criterios de conservación no exclusivamente numéricos. Así para el cormorán moñudo se recomienda la creación de una serie de enclaves protegidos en cadena. También señalan la importancia de la atracción en la restauración de colonias de aves marinas.

Heterozygosity–fitness correlations in a declining seabird population

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Velando, A., Barros, Á. & Moran, P. Heterozygosity–fitness correlations in a declining seabird population. Molecular ecology 24, 1007–1018 (2015).

Loss of genetic diversity is thought to lead to increased risk of extinction in endangered populations due to decreasing fitness of homozygous individuals. Here, we evaluated the presence of inbreeding depression in a long-lived seabird, the European shag (Phalacrocorax aristotelis), after a severe decline in population size by nearly 70%. During three reproductive seasons, 85 breeders were captured and genotyped at seven microsatellite loci. Nest sites were monitored during the breeding season to estimate reproductive success as the number of chicks surviving to full-size-grown per nest. Captured birds were tagged with a ring with an individual code, and resighting data were collected during 7-year period. We found a strong effect of multilocus heterozygosity on female reproductive performance, and a significant, although weaker, effect on breeder survival. However, our matrix population model suggests that this relatively small effect of genetic diversity on breeder survival may have a profound effect on fitness. This highlights the importance of integrating life history consequences in HFC studies. Importantly, heterozygosity was correlated across loci, suggesting that genomewide effects, rather than single loci, are responsible for the observed HFCs. Overall, the HFCs are a worrying symptom of genetic erosion in this declining population. Many long-lived species are prone to extinction, and future studies should evaluate the magnitude of fitness impact of genetic deterioration on key population parameters, such as survival of breeders.

Population trends and reproductive success of the European shag Phalacrocorax aristotelis on the Iberian Peninsula following the Prestige oil spill.

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Velando, A., Alvarez, D., Mourino, J., Arcos, F. & Barros, A. Population trends and reproductive success of the European shag Phalacrocorax aristotelis on the Iberian Peninsula following the Prestige oil spill. Journal of Ornithology 146, 116–120 (2005).

In 2003, immediately following the Prestige oil spill in Galicia, Spain, we studied the population trends and reproductive performance of European shags (Phalacrocorax aristotelis) at oiled and unoiled colonies. This bird is an important member of the nearshore marine community, breeding in the area affected by the Prestige oil spill. The European shag feeds around the breeding colonies throughout the year, making it a useful indicator of environmental change. Before the oil spill, population trends were similar between oiled and unoiled colonies. Nevertheless, colonies located within the path of the oil suffered greater declines (ca. 10%) compared with pre-spill trends and with population trends at unoiled colonies. In 2003, the breeding success was 50% lower in oiled colonies compared with unoiled colonies. The data available from pre-spill years suggest that the annual reproductive success did not differ among colonies before the impact. European shags breeding at colonies affected by oil showed a negative initial impact from the Prestige oil spill. The reduction in reproductive success at oiled colonies may be due to sublethal effects of oil exposure or low food availability after the oil spill.

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

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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.