Movements of Mediterranean Shags (Phalacrocorax aristotelis desmarestii, Payraudeau 1826) between Croatian breeding colonies and non-breeding areas such as the Gulf of Trieste increased consistently ...from the 1980s to become a migratory movement at the present time. In order to characterise the patterns of this migration and the behaviour of first-year Shags at their first migration, we analysed the recoveries of 812 birds that were colour-ringed at the most important Croatian breeding colonies in the northern Adriatic. Within a period of seven years, 568 ring-readings of 234 individual Shags were processed. Most sightings came from the Gulf of Trieste (43.0%) and the newly-discovered post-breeding area in Venice Lagoon (38.9%). Shags from the most distant colonies exploited mainly the Gulf of Trieste. The 48.3% of Shags sighted several times have been recorded in the same post-breeding area during subsequent years. This percentage increased to 93.4%, if we considered just the birds observed during successive years. Variations in the timing of migration within the post-breeding areas occurred and sustained the importance of the Slovenian coast during the return to breeding colonies. The ratio between first-year Shags and experienced Shags (immature and adults) was higher in Venice Lagoon and in general increased with the “novelty” of the site. A relevant portion of the Croatian breeding population moves to the northern Adriatic Sea after breeding. All the studied colonies concurred with this migration. We highlight a high fidelity to post-breeding sites, which reflects the quite sedentary “nature” of the species, and the role of first-year Shags in the discovery of new sites. We suggest that this migration is probably the later stage in a graded response to deterioration of the Shags’ feeding grounds within the breeding area.
Capsule Shags move between breeding and non-breeding areas and this is associated with a significant change in diet.Aims To determine whether the diet of Shags nesting on islets off the Croatian ...coast is the same as their diet after the post-breeding move to the Gulf of Trieste.Methods Diet was determined by the analysis of 611 regurgitated food pellets.Results A total of 23 988 prey items were identified in the sample of pellets. Post-breeding Shags in the Gulf of Trieste focused on demersal and relatively immobile Gobiidae (81.5% by number, 87.1% by biomass). The most frequent prey species was Gobius niger (70.8% by number). In the breeding season at Oruda island, Croatia, the diet was more varied. Breeding Shags fed on bentho-pelagic, mobile prey such as Atherina boyeri (28.4% in frequency), Serranus hepatus (16.1%) and Crenilabrus tinca (12.0%), while Gobiidae had a dietary frequency of only 18.1%. With respect to biomass the most important prey were Crenilabrus tinca (19.0%) and Serranus hepatus (18.4%).Conclusion We suggest that the movement of Shags within the Adriatic Sea is driven by dietary requirements. Most previous studies of Shag diet have shown that Shags tend to have a more specialized diet during the breeding season, concentrating upon demersal prey species. However, we have found that birds breeding at the Croatian study colony show dietary diversity. We suggest that lack of dietary specialization is a facultative response to local prey abundance, and is probably the result of over-fishing of demersal species in the areas around the breeding locations in which the birds find suitable sites and are little disturbed by human activity. Shags may move immediately after breeding to the Gulf of Trieste because demersal species are likely to be more abundant there. As a consequence, the diet becomes more specialized and is then more similar to the diet of other populations of Shags.
From the 1980s, Mediterranean shags Phalacrocorax aristotelis desmarestii have become regular summer visitors in the Gulf of Trieste (N-E Italy), as post-breeding movements from Croatian breeding ...colonies. To characterize such a recent habit and to explore diving optimality models, we investigate foraging strategies and diving patterns at different depths, during breeding and post-breeding seasons. Behavioural data were cross-checked with the species' diet. Shags foraged on and close to the sea bed, with a prevalent anticipatory breathing strategy. In the Gulf of Trieste, the shallow depths and low mobility of prey allowed shags to use just the oxygen of the respiratory tract, reducing the physiological stress for diving. In Croatia, dive costs increased with depth and prey mobility, resulting in a higher oxygen expenditure that involved also respiratory stores. Such ecological and physiological aspects characterize the Gulf of Trieste as an optimal area for feeding and restoring from the costs of breeding season incurred in Croatia and could be the basis of these post-breeding movements.
Several bird species utilize artificial structures for communal roosting. Between 26 May and 28 Jun 2012, the selection of buoys and times of departure by Mediterranean Shags Phalacrocorax ...aristotelis desmarestii were studied at three communal roosts within shellfish farms in the Bays of Sv. Jernej (Debeli rtic), Strunjan and Piran (Secovlje). A total of 3,110 buoys were counted and categorized into two groups according to their shape (horizontal and vertical) and colours. The black horizontally floating buoys were of two types (barrelshaped and oval). The Shags chose to utilize the horizontally floating buoys only, most often black and white in colour. Owing to their poorer stability and smaller standing surface, the vertically floating buoys are clearly unsuitable for them. The highest share of Shags with regard to the number of buoys of separate types was registered on black barrel-shaped buoys. As the percentage of occupied buoys was similar at all roost sites (36-39%), it was deduced that Shags distribute evenly among roosts, regardless of the number of individuals present in the Slovenian sea. At the larger roost at Debeli rtic, the percentage of adult individuals (73.5%) was greater than at Strunjan (42.5%). This could be due to the competition for better places, given that competitively stronger individuals select safer larger roosts. Between 5.42 and 9.00 hrs, 53.3% and 69.1% of Shags departed from the roost sites at Debeli rtic and Strunjan, respectively, with the majority of departures recorded between 7.50 and 8.30 hrs. They left their roosts mostly individually (48.7%) or in pairs (23.3%), at Debeli rtic predominantly in the SW (58.9%) and W (16.9%) directions, and at Strunjan in the NE (42.3%) and N (38.5%) directions.
We determined mercury levels in internal tissues and feathers from corpses of Audouin’sLarus audouiniiand yellow-legged gullsL. cachinnans michaellis, common ternsSterna hirundoand European ...shagsPhalacrocorax aristotelis desmarestii, as well as from fish representative of trawler discards, collected at the Ebro Delta (NW Mediterranean) between March and July (seabird’s breeding season) in 1997 to 1999. The levels of mercury were significantly lower in epipelagic (Clupeiforms) than in demersal fish. When representation of each species in the discards is taken into account, the mean mercury concentration from this resource is more than double that of epipelagic fish (the main natural prey for most seabirds in the area). The shag was the only species with direct access to benthic fish, as it can dive to the seabed, and shags presented high levels of mercury even though they do not feed on discards. The other seabirds showed mercury levels in accordance with their seasonal use of discards. Audouin’s gull, which exploits discards extensively during the breeding season, had the highest levels in those tissues reflecting mercury intake during the breeding season (liver and 1st primary feathers). In contrast, the common tern makes little use of discards and presented the lowest levels of mercury. For those samples reflecting the intake of mercury during the winter (mantle feathers), when only the yellow-legged gull exploits discards extensively, this species presented the highest values. Audouin’s gull and the common tern showed similarly low concentrations of mercury for this period. We conclude that consumption of discarded demersal fish strongly influenced mercury contamination of surface-feeding seabirds.
BirdLife International has so far developed Action Plans for 37 bird species. The plans, although not legally binding, have been approved by the Ornis Committee (EU DG Environment) and most of them ...have also been endorsed by the Standing Committee of the Bern Convention. Three of the species covered by the SAPs are Mediterranean seabirds: Audouin's gull (Larus audouinii), Balearic shearwater (Puffinus mauretanicus) and Mediterranean shag (Phalacrocorax aristotelis desmarestii). The documents, which have been produced through a participatory process involving tens of experts across the range of the taxa, provide information on the biology, ecology and threats, but the most important feature is the list of specific objectives and actions which are ranked according to their priority and urgency. Alongside actions addressing species-specific conservation needs, such as site protection and management, a number of activities aimed at the conservation of these species are common and refer to wide policies such as land-use planning, fishery, tourist development and pollution control. The documents represent the most up-to-date and scientifically-based source of information for planning and implementing conservation activities across the Mediterranean, to be implemented by both governmental and non governmental organisations.Original Abstract: Planes de accion para la conservacion de aves marinas en el Mediterraneo: gaviota de Audouin, pardela balear y cormoran monudo del Mediterraneo. - BirdLife International ha desarrollado hasta la fecha planes de accion para 37 especies de aves. Los planes, aunque no son vinculantes, han sido aprobados por el comite Ornis de la Union Europea y la mayor parte de ellos ha sido ratificados por el comite permanente de la convencion de Berna. Tres de las especies que cuentan con planes de accion son aves marinas: la gaviota de Audouin (Larus audouinii), la pardela balear (Puffinus mauretanicus) y el cormoran monudo del Mediterraneo (Phalacrocorax aristotelis desmarestii). Los documentos, generados a traves de un proceso participativo en el que han colaborado decenas de expertos, proporcionan informacion sobre la biologia, ecologia y amenazas de las especies aunque el aspecto mas importante es el listado de objetivos especificos y acciones que aparecen ordenadas segun prioridad y urgencia. Los planes sugieren acciones de amplio espectro, comunes a todas las especies, tales como una correcta ordenacion territorial, de la pesca, del desarrollo turistico y el control de la contaminacion, junto con acciones referentes a las necesidades de conservacion de cada especie, tales como proteccion y gestion de los lugares de cria. Estos documentos representan la fuente de informacion mas actualizada y con mas base cientifica de que disponemos para llevar a cabo acciones de conservacion en el Mediterraneo por parte de las organizaciones gubernamentales o no gubernamentales. Palabras clave: gaviota de Audouin, pardela balear, cormoran monudo, planes de accion, conservacion, Mediterraneo.
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