Academic literature on the topic 'Larus audouinii'

Predatory and (or) kleptoparasitic interactions are greatly facilitated in mixed-species gulleries, particularly when one of the species is larger than the others. Larus audouinii, the Audouin's gull, is a threatened species breeding in sympatry with the larger L. cachinnans, the yellow-legged gull, throughout the Mediterranean. The yellow-legged gull has often been cited as the main threat to the Audouin's gull. On the Chafarinas Islands, the second largest breeding place for Audouin's gulls in the world, both gull species depend largely on commercial fisheries for food. We analyze the influence of food availability, assessed through fishery activity, on the frequency and intensity of interaction pressure by yellow-legged gulls upon Audouin's gulls during the breeding season. We studied five different types of interaction: (1) flyovers of yellow-legged gulls; (2) ground intrusions; (3) egg predation; (4) chick predation, and (5) aerial kleptoparasitism. Moreover, intensity of interaction pressure was assessed using logistic regression analysis to build a model of the"relationship between Audouin's gulls' response to yellow-legged gull flyovers as a dependent variable and fishing fleet activity as an independent variable. All interactions except aerial kleptoparasitism were significantly more frequent during days without sardine fishery activity. However, chick predation is significantly higher only during the period when yellow-legged gull has fledglings. Overall, the results of the estimated logistic model indicate a positive association between depleted food and the response by Audouin's gulls to aerial intrusions.

We studied chick adoption in Audouin's gull, Larus audouinii, a ground-nesting seabird, to test several predictions made by the intergenerational-conflict hypothesis (ICH). The effects of food availability on adoptions were considered by comparing two breeding seasons with differing food supply. As predicted, adoptions were significantly more frequent when food was in shorter supply (48% of broods affected) than when it was more available (18.5%). Adoptions occurred during the first week of the chick-rearing stage; after that, aggression by adults towards intruding chicks increased significantly, which suggests that mechanisms of parent-offspring recognition were established. Foster parents incurred certain costs, since their offspring had lower chances of survival than those in control broods. However, contrary to the ICH hypothesis, adoptees did not select foster broods in relation to the age of the resident chicks. Survival of wandering chicks was no higher than that of chicks who stayed in their natal brood. Results suggest that chicks move only as a response to neighboring chicks being fed by an adult, and in Audouin's gulls, adoptions might be considered reproductive errors.

The results presented in this thesis have shown the strong dependence of Audouin’s gull from the Ebro Delta on fisheries. Foraging movements of breeding birds showed a great association with fishing activities (specially trawling), determining the most of its at-sea distribution on work days. An increase in the use of rice field habitats was also detected in absence of fishing activities (during weekends) due to the opportunistic feeding on the American crayfish. However, a key aspect presented in this thesis was the significant sex-differences in their foraging behaviour in relation to fisheries. Female Audouin’s gull tended to perform longer at-sea foraging trips on weekends compared to males, probably due to the need of feeding on high quality resources after laying instead of the easily available but lower quality American crayfish. This great dependence on fishing activities was also reflected in the resource allocation into the clutch. An isotopic δ15N enrichment in the albumen of eggs synthesized during the weekends was observed, which is attributed to an increase in the consumption of rice field resources as well as to the mobilization of female reserves. However, rice field diets were associated to lower antioxidant capacity in the eggs. Also, rice field diets were related to smaller egg size. Finally, the limiting nature of calcium (in constraining egg synthesis) and antioxidant molecules (decreasing their concentration especially in the latter eggs of the clutch) were also revealed for females.
Los resultados presentados en esta tesis han mostrado la gran dependencia de las gaviotas de Audouin del Delta del Ebro sobre las pesquerías. Los movimientos de búsqueda de alimento de las aves durante la reproducción mostraron una gran asociación con las actividades pesqueras (especialmente el arrastre durante el día, aunque también es notable la influencia de la pesca de cerco durante noche), determinando la mayor parte de su distribución en el mar los días laborables. Un incremento en el uso de arrozales fue detectado en ausencia de actividades pesqueras (durante los fines de semana). Sin embargo, un aspecto clave presentado en esta tesis fue las diferencias significativas entre sexos para el comportamiento de alimentación en relación a las actividades pesqueras. Las hembras de gaviota de Audouin tendieron a realizar viajes de alimentación más largos que los machos durante los fines de semana. Esta gran dependencia sobre las actividades pesqueras fue también reflejada en la asignación de recursos sobre la puesta. Un enriquecimiento del δ15N fue detectado en el albumen de los huevos sintetizados durante los fines de semana, lo cual puede ser atribuido a un incremento en el uso de recursos de arrozal así como a la movilización de reservas de la hembra. Sin embargo, un mayor uso de dietas de arrozal se asoció con una menor capacidad antioxidante de los huevos. También, dietas de arrozal estaban relacionadas con tamaños del huevo más pequeños. Finalmente, se puso de manifiesto la naturaleza limitante del calcio (restringiendo la síntesis del huevo) y de las moléculas antioxidantes del huevo (decreciendo su concentración especialmente en los últimos huevos de la puesta).

A gaivota-­‐de-­‐audouin (Larus audouinii), colonizador recente em Portugal, nidifica no Algarve, Ilha da Barreta, em simpatria com a gaivota-­‐de-­‐patas-­‐amarelas (Larus michahellis), não tendo sido avaliada, até à data, a potencial competição entre ambas as espécies. Durante o período de reprodução de 2014, através de egagrópilas e amostras de sangue, recolhidas na ilha da Barreta, estudou-­‐se a ecologia alimentar de ambas as espécies e avaliou-­‐se a potencial competição pelos recursos alimentares. Na dieta de L. audouinii o peixe foi a categoria alimentar que apresentou valores mais significativos, destacando-‐se Scomberesox saurus. A L. michahellis apresentou uma dieta mais generalista, embora também com uma predominância de peixe, em especial de Sardina pilchardus e Micromesistius poutassou. Verificou-­‐se uma correlação positiva na variação temporal da abundância de presas presentes na dieta das duas espécies. Apesar de existir um elevado número de presas comuns para ambas as espécies, não se verificou sobreposição nas dietas; ABSTRACT: Audouin’s Gull (Larus audouinii) is a recent colonizer in Portugal that breeds in Algarve, Barreta Island, in sympatry with Yellow-­‐legged Gull (Larus michahellis). To date it has never been evaluated the potential competition between both species. During the breeding season of 2014, the feeding ecology of both species was studied through the analyses of pellets and blood samples collected at Barreta Island and it was evaluated the potential competition for food resources. In Audoin’s Gull diet, fish was the prey item that presented higher values, especially the species Scomberesox saurus. Yellow-legged Gull presented a more generalist diet although it also presented predominance for fish, especially Sardina pilchardus and Micromesistius poutassou. A positive correlation was found in the temporal variation in abundance of prey in the diet of both species. Although there are a great number of preys common to both species, there was no overlap in their diets.

Dissertação de Mestrado em Ecologia apresentada à Faculdade de Ciências e Tecnologia
As pescas sempre foram conhecidas pelo seu grande impacto ambiental, raramente conseguindo alcançar um rendimento sustentável. Assim sendo, um dos maiores impactos ecológicos causados por estas pescas é a chamada “captura acidental”, a captura não intencionada de organismos marinhos sem qualquer utilização para o Homem, sendo estes descartados. Este facto, apesar de ser de grande preocupação ecológica, tem o seu lado positivo, uma vez que há um grande número de aves marinhas que utilizam a disponibilidade de peixes demersais e de fundo providenciado pela pesca, como principal fonte de alimento. O objetivo principal deste estudo foi tentar obter mais informações sobre a interação entre duas espécies de gaivotas, gaivota-de-patas-amarelas (Larus michahellis, LM) e gaivota-de-audouinii (Larus audouinii, LA) presentes na costa algarvia portuguesa, onde estas espécies se reproduzem em simpatria.A presença e o sucesso alimentar de ambas as espécies de gaivotas, incluindo indivíduos imaturos, na pesca de cerco e de arrasto, foram avaliados com observações a bordo. No cerco, esta avaliação foi dividida entre as diferentes fases deste método de pesca: (1) redes montadas e estabilizadas em água, (2) retração das redes cheias de peixes, e (3) descarte de espécies não-alvo. A presença e o sucesso de alimentação foram registrados por períodos de dez minutos, com o posterior cálculo da quantidade de peixes ingeridos por indivíduo de cada espécie e estadio de desenvolvimento. A quantidade de peixes roubados também foi registrada e entre que indivíduos este acto de cleptoparasitismo foi realizado. Obtendo assim uma medida da pressão competitiva entre estas espécies enquanto na presença de actividade piscatória. Os mesmos métodos foram repetidos ao realizar observações em portos de pesca.As LM apresentaram-se igualmente distribuídas entre os dois métodos de pesca, com maior sucesso alimentar durante as rejeições de peixe das mesmas, com uma ligeira tendência a obter mais peixe quando na presença de arrastos. Verificaram-se números mais elevados de LA e um sucesso de alimentação mais alto quando na presença de embarcações de cerco. Indivíduos imaturos estiveram presentes em números mais elevados e sucesso alimentar mais alto quando junto a arrastos. Quando foi efetuada a divisão das artes nas várias fases, foi revelado duas informações importantes: (1) aumento no sucesso de alimentação de LA durante o fecho da rede de cerco, evitando completamente o cleptoparasitismo pelas LM e (2) as LM tendo mais como alvo as presas provenientes das rejeições. As LA estiveram ausentes dos portos de pesca monitorizados. No porto de Olhão, as LM estiveram presentes em números mais elevados e com maior sucesso de alimentação quando comparadas com os imaturos, enquanto no porto da Culatra o oposto foi registado No geral, este estudo apresenta informações válidas de interações das aves estudadas com as pescas no Algarve, com a disponibilidade de rejeições super-abundantes a ser a provável responsável para o actual aumento populacional de ambas as espécies a reproduzir na ilha Deserta. Prevê-se que, após a plena implementação da proibição de descarte ambas as espécies apresentem uma imediata diminuição no sucesso da reprodução e no crescimento populacional.
Fisheries have always been known for their great environmental impact, rarely managing to achieve a sustainable yield. One of the main ecological impacts caused by fishery is the so called “bycatch”, the non-targeted capture of marine organisms without use for the Man, these being discarded. This fact, despite being of great ecological concern, has its positive sides, as there is a large number of seabirds that use the availability of demersal and benthic fish provided by fisheries, as main source of food. The main objective of this study was to try to obtain more information about the interaction between two species of seagulls, yellow-legged gulls (Larus michahellis, LM) and Audouin's Gulls (Larus audouinii, LA) present on the Portuguese Algarve coast where these species breed in sympatry.The presence and feeding success of both species of seagulls, including immature individuals, in purse seine and trawling fisheries, were evaluated with on board observations. In purse-seiners, this evaluation was divided among the different stages of this fishing method: (1) nets assembled and stabilized in water, (2) retraction of the nets filled with fish, and (3) discard of non-targeted species. The presence and feeding success was recorded for periods of ten minutes, with the posterior computation of the amount of fish ingested per individual of each species and stage of development. The amount of fish stolen was also recorded and among which individuals this act of kleptoparasitism was carried out. Thus, obtaining a measure of the competitive pressure among these species while in the presence of fishery activity. The same methods were repeated when performing observations at fishing ports.The LM were equally distributed between the two fishery methods, with higher feeding success during the fish rejections of both fisheries, with a slight tendency to obtain more fish when attending trawls. There were higher numbers of LA and with higher feeding success when attending purse-seiners. Immature individuals were present in higher numbers and with higher feeding success close to trawlers. When the division of the fisheries in the various periods was carried out, two instances of important information was revealed: (1) a marked increase on the feeding success of LA during the enclosure of the purse-seine net, completely avoiding kleptoparasitism by LM and (2) LM targeting much more prey coming from fishery discards. LA were absent from the monitored fishing ports. In the port of Olhão, LM were present in higher numbers and with higher fishing success when compared to immatures, while in the port of Culatra the opposite was noticed.In general, this study presents valid information on the interactions of the studied gulls with the fisheries in Algarve, with the availability of superabundant discards likely being responsible for the current population increase of both species breeding at Deserta Island. It is anticipated that upon the fully implementation of the discard ban both species will exhibit immediate decrease in both breeding success and population growth.