Aggression by adult South American Terns toward conspecific chicks

Infanticide and nonfatal aggression by adults toward unfamiliar chicks have been widely reported in colonial birds, and can be an important cause of chick mortality. We studied intraspecific aggression by adults toward chicks at a South American Tern (Sterna hirundinacea) colony in Patagonia, Argentina, during 2005 to characterize this behavior, evaluate its relationship with nesting density, chick age and microhabitat characteristics, and assess its effect on breeding success. Of 111 chicks in the study area, 45% were attacked at least once. Chicks older than 9 d posthatching were more likely to be attacked than younger chicks, and unattended chicks were more likely to be attacked than guarded chicks (88 vs. 12%). Chicks were also attacked more often when in theirown territories (76% of cases), but were less likely to be attacked in territories with more vegetation cover and high-quality shelters (i.e., vegetation with characteristics that prevented adults from reaching chicks). The number of aggression events was not related to nest density. At least 8% of the chicks in our study area died as a result of adult intraspecific aggression. Our results indicate that intraspecific aggression by adult South American Terns toward chicks is relatively common in the Punta Loma colony and should not be underestimated as a factor affecting their breeding success.Fil: Villanueva Gomila, Gabriela Lujan. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Gatto, Alejandro Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Cabral, Karina. Universidad Nacional de la Patagonia "San Juan Bosco"; ArgentinaFil: Yorio, Pablo Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina. Wildlife Conservation Society Argentina; Argentin

Land birds: species checklist and ecological aspects

Muestreamos la avifauna terrestre de la Reserva de Vida Silvestre San Pablo de Valdés mediante “conteos de puntos” periódicos, entre 2009 y 2014, para detectar tendencias en los ensambles asociadas a la exclusión del ganado. Registramos 48 especies, de las cuales 22 son residentes. Observamos 18 migrantes australes del Neotrópico (15 de la estación cálida y tres de la fría). La lista de especies comprende el 30% de las citadas para la Península Valdés. El Canastero Patagónico y el Cacholote Pardo, endemismos del país, se reproducen en el lugar. El Choique (categoría “Amenazado”) y otras cuatro especies que registramos frecuentemente se consideran aves con problemas de conservación en la Argentina. La primavera es la estación con mayor riqueza y diversidad. La densidad de Passeriformes en la primavera fluctuó entre 50 y 100 indiv/km2. La abundancia y la riqueza fueron máximas en la estepa arbustiva-herbácea y mínimas en la estepa herbácea. Observamos primero un aumento y luego una disminución de la abundancia general y la riqueza a lo largo de los años. Sugerimos que esta variación está asociada con cambios en los hábitats provocados primero por la exclusión del ganado y luego por el aumento de la densidad de herbívoros silvestres.We sampled the terrestrial avifauna of Reserva de Vida Silvestre San Pablo de Valdés by means of periodical point-counts, between 2009 and 2014, to detect trends in the assemblages associated with the exclusion of livestock. We recorded 48 species, 22 of which are residents. We observed 18 Neotropical austral migrants (15 corresponding to the warm season and three to the cold season). The list of species includes 30% of those recorded in the Peninsula Valdes. Breeding endemics, Patagonian Canastero and White-throated Cacholote, were found breeding in the area. The Lesser Rhea (nationally “Threatened”) and four other species are considered birds with conservation concerns in Argentina. Spring is the season with the highest species richness and diversity. The density of passerines in spring fluctuated between 50 and 100 indiv/km2. The abundance and richness were highest in the shrub-grass steppe and minimum in the grass steppe. We observed first an increase and then a decline in overall abundance and richness over the years. We suggest that this variation is associated with habitat changes caused first by the exclusion of sheep and then by the increase in density of wild herbivores.Fil: Krapovickas, Santiago. Aves Argentinas; ArgentinaFil: Gatto, Alejandro Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Lorenzo, Rafael S.. Fundación Vida Silvestre; ArgentinaFil: Fernández, Cynthia. Universidad de Vigo; Españ

The introduced green crab (Carcinus maenas) as a novel food resource for the opportunistic kelp gull (larus dominicanus) in argentine patagonia

Introduced species are one of the main threats to biological diversity, but they can also facilitate native species through mechanisms such as trophic subsidy. We quantified the diet of breeding kelp gulls (Larus dominicanus) and their consumption of the introduced green crab (Carcinus maenas) at five colonies located along over 600 km of coastline in Patagonia, Argentina, and analyzed differences in consumption rates among breeding locations. Results based on pellet analysis (n = 961 pellets) showed that kelp gulls consumed green crabs during most or part of the breeding cycle at all study locations (0–73.9%, depending on location, year and breeding stage). Green crab consumption differed among breeding locations, with lower consumption further from the reported location of first Argentinean introduction (Golfo San Jorge, Chubut, Patagonia) in 1999–2000. Despite kelp gulls regularly consumed green crabs at most breeding locations, this invasive species was not an important component in their diet. Both stomach content and stable isotope analyses from breeding kelp gulls indicated that the main prey were fish such as Argentine anchovy and Argentine hake (Engraulis anchoita and Merluccius hubbsi, respectively) and squat lobster (Munida gregaria). At Isla Vernaci Este and Punta Tombo, green crabs were found in only one stomach of all kelp gull age classes sampled (incubating adults (n = 42), young chicks (n = 75), and old chicks (n = 105)). Based on carbon and nitrogen isotopic values from blood samples from incubating adults (n = 54), Bayesian mixing model outputs showed that green crabs contributed 7.3–23.9% to the overall diet. The study showed that the relatively recent introduction of green crabs supplements the available prey base of a widely distributed and abundant predator, the kelp gull, at least during its breeding season in a large coastal sector of central Patagonia. The extent to which the kelp gull in coastal Patagonia may be shaping the establishment, abundance, and population dynamics of the introduced green crab is still unknown and will require further research.Fil: Yorio, Pablo Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentina. Wildlife Conservation Society; Estados UnidosFil: Suarez, Nicolas Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Kasinsky Aguilera, Lorna Tatiana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Pollicelli, Miriam. Universidad Nacional de la Patagonia "San Juan Bosco"; ArgentinaFil: Ibarra, Cynthia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Gatto, Alejandro Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentin

Changes in the predator-prey interaction between the Kelp Gull (Larus dominicanus) and Royal (Thalasseus maximus) and Cayenne terns (Thalasseus sandvicensis euygnathus) in Punta León, Argentina

Se estudió la depredación por parte de la Gaviota Cocinera (Larus dominicanus) sobre los gaviotines Real y Pico Amarillo (Thalasseus maximus y Thalasseus sandvicensis euygnathus, respecti- vamente) en el Área Natural Protegida Punta León, Argentina, durante el 2005 y 2006 para evaluar los cambios potenciales en dicha interacción en relación con lo registrado en la misma localidad a comien- zos de la década de 1990. Al igual que en las evaluaciones previas, la Gaviota Cocinera fue responsable del total de los eventos de depredación sobre ambas especies. Durante el 2006, la tasa de depredación de huevos fue de 0,01 ± 0,003 huevos/hora/nido, igual a la de 1991 y 1992 y levemente menor que la registrada en 1990. Todos las depredaciones de huevos (n = 71) ocurrieron sobre nidos periféricos. A diferencia de estudios previos, se registró la depredación de pichones de ambas especies de gaviotín. Durante el 2005 y 2006 se registraron 43 y 41 intentos de depredación sobre pichones, respectiva- mente, totalizando 18 y 9 eventos exitosos, respectivamente. En el 2005, el 88% de los intentos se rea- lizó sobre pichones en la periferia de los grupos de nidos, mientras que en el 2006 el 63,5% fue sobre pichones en dicha ubicación y el 36,5% restante sobre aquellos en la periferia de las guarderías. Nin- guno de los intentos de depredación de pichones en las guarderías fue exitoso. La relación entre los eventos de depredación y la ubicación de las presas en la colonia muestran la importancia de la estruc- tura espacial en la determinación de las interacciones de depredación en colonias de aves marinas. Los resultados de este estudio muestran que la Gaviota Cocinera sigue siendo el principal depredador de huevos de los gaviotines Real y Pico Amarillo en la colonia de Punta León, observándose tasas de depredación de huevos similares a aquellas registradas en estudios previos. Sin embargo, el impacto de depredación por la Gaviota Cocinera se extendió en años recientes hacia la etapa de pichones de ambas especies de gaviotín.We studied the predation by Kelp Gull (Larus dominicanus) upon Royal and Cayenne terns (Thalasseus maximus and T. sandvicensis euygnathus, respectively) at the Punta León Protected Area, Argentina, during the 2005 and 2006 breeding seasons to assess changes in the predator-prey interaction with respect to that observed at the same location in the early 1990’s. Similar to previous evaluations, the Kelp Gull was responsible of all predation events on both tern species. During 2006, the predation rate on eggs was 0.01 ± 0.003 eggs/hour/nest, similar to that recorded in 1991 and 1992 and slightly lower that that recorded in 1990. All cases (n = 71) occurred on peripheral nests. In contrast to previous studies, we also recorded predation on chicks of both tern species. During 2005 and 2006 we recorded 43 and 41 predation attempts on chicks, respectively, totaling 18 and 9 successful events, respectively. In 2005, 88% of attempts were on chicks located at the periphery of nest groups, while in 2006 63.5% were on chicks at these locations and the remaining 36.5% on those at the periphery of “crèches”. None of the predation attempts on chicks in “crèches” was successful. The relationship between predation events and the location of prey within the mixed-species colony shows the importance of the spatial structure in the determination of predator-prey interactions in seabird colonies. Our results show that the Kelp Gull is the main predator of Royal and Cayenne terns’ eggs at the Punta León colony, with predation rates similar to those recorded in previous studies. However, the predation impact of Kelp Gulls has extended in recent years to the chick stage of both tern species.Fil: Silva, Laura Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; ArgentinaFil: Gatto, Alejandro Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: García, Germán Oscar. Universidad Nacional de Mar del Plata. Facultad de Cs.exactas y Naturales. Departamento de Biología. Laboratorio de Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; ArgentinaFil: Yorio, Pablo Martin. Wildlife Conservation Society; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Apparent selective advantage of leucism in a coastal population of Southern caracaras (Falconidae)

ABSTRACT Background: Southern caracaras are medium-sized raptors with a large range stretching to the southern tip of South America. An aberrant, leucistic plumage is found commonly along the coast of Chubut Province (Patagonia, Argentina). Leucistic birds do not produce dark melanin in their feathers. However, they are not albinos because their eyes are not red. No genetic studies of caracara plumages are known. Hypothesis: The high frequency of leucistic birds in Chubut Province arises because of natural selection. Methods: Map the distribution of leucistic individuals relative to normal individuals. Combine a variety of anecdotal natural history observations, collected over 20 years, into a logical inference. Observations: Leucistic caracaras were found only along a 250-km stretch of rocky oceanic islands and continental outcrops with large seabird colonies in Chubut Province. In the rest of their range, Southern caracaras have dark plumage. Where they do occur, leucistic birds are frequent and co-occur with dark-plumaged birds. Intermediate individuals, presumabl

Patrones de abastecimiento de presas en relación con la edad de pollos en el Gaviotín Sudamericano (Sterna hirundinacea)

The study of temporal patterns in diet composition is crucial to interpret adequately severalaspects of seabird ecology and life history. The variation in prey composition and prey size in relation tochick age were evaluated in a South American Tern (Sterna hirundinacea) colony at Punta Loma, Argentina, during the 2006 breeding season. The diet of South American Tern chicks consisted of at least 12 prey items. Fish, mostly Argentine anchovy (Engraulis anchoita) and silverside (Odontesthes argentinensis) were the main prey delivered (91%) to the chicks. The relative proportion of prey types varied amongchick age-classes and the proportion of Argentine anchovy in the diet increased with chick age, reaching 58% in older chicks. Larger prey items were delivered to older chicks. Prey stolen by other adult ternswas significantly larger than the prey actually consumed by the chicks. South American terns at thePunta Loma colony appear to confront the increasing demand of growing chicks by increasing the qualityof prey in each feeding trip, reflected in larger and more energetic prey.El estudio de los patrones temporales en la composiciónde la dieta es clave para interpretar ciertos aspectos de la ecología e historia de vida de las aves marinas. La variación en la composición y tamaño de presas en relación con la edad de los pollos fue evaluado en una colonia de Gaviotín Sudamericano (Sterna hirundinacea) en Punta Loma, Argentina, durantela temporada reproductiva del 2006. La dieta de los pollos de Gaviotín Sudamericano incluyó al menos12 especies de presa. El pescado, mayormente anchoíta (Engraulis anchoita) y pejerrey (Odontesthesargentinensis) fue la principal presa entregada (91%) a los pollos. La proporción relativa de tipos depresa varió entre las clases de edad de los pollos, y la proporción de Anchoíta en la dieta se incrementócon la edad de los mismos, alcanzando el 58% en las crías mayores. El tamaño de las presas aumentócon la edad de los pollos. Las presas robadas por otros gaviotines adultos fueron significativamente másgrandes que aquellas consumidas por los pollos. Los Gaviotines Sudamericanos en la colonia de Punta Loma parecen enfrentar la demanda creciente de los pollos en crecimiento aumentando la calidad de lapresa en cada viaje de alimentación, reflejada tanto en presas más grandes como de mayor contenido energético.Fil: Fernández Ajó, Alejandro A.. Universidad Nacional de la Patagonia “San Juan Bosco”; ArgentinaFil: Gatto, Alejandro Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; ArgentinaFil: Yorio, Pablo Martin. Wildlife Conservation Society; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentin

Assessing the trophic niche of South American Terns integrating conventional and isotopic methods

Conventional dietary studies combined with stable isotope analysis allowed the characterisation of the trophic niche of South American Terns (Sterna hirundinacea) breeding in Argentina. Direct observation of prey deliveries during mate- and chick-provisioning showed that the diet of South American Terns comprised at least 18 prey items, mainly pelagic schooling fish with smaller proportions of marine invertebrates. Argentine Anchovy (Engraulis anchoita) was the main fish prey. Adults delivered a higher proportion of fish and smaller prey to their chicks than to their mates. Analysis of stable isotope ratios in blood samples, using Bayesian stable isotope mixing models, indicated that adult Terns used a higher proportion of marine invertebrates for self-feeding than for mate- or chick-provisioning. Analyses of stable isotopes ratios in blood samples from chicks were consistent with the determination of diet from direct observation, and indicated differences from adults in both the proportion of different prey in the diet and trophic niche. In addition, isotopic niche analysis showed that chicks had a significantly higher trophic position compared with self-feeding adults during both mate-provisioning and chick stages. The results highlight the importance of combining stable isotope and conventional methods to adequately assess the food requirements of a population during the breeding season.Fil: Gatto, Alejandro Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Yorio, Pablo Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina. Wildlife Conservation Society; Estados Unido

Evaluating the coexistence of Imperial Cormorant and Rock Shag through isotopic niches at different colonies in central Patagonia, Argentina

Following the competitive exclusion principle, two closely-related species living in sympatry can only coexist if ecological niche partitioning occurs. Throughout their distribution range, Imperial Cormorant (Leucocarbo atriceps) and Rock Shag (L. magellanicus) often breed in mixed-species colonies in Patagonia, Argentina. Isotopic niche assessment of both species was performed during two breeding seasons (2010/11 and 2011/12) in three different colonies were they breed syntopically. The three colonies, Isla Gran Robredo (45°07'54''S, 66°03'40''W), Isla Leones (45°03'28''S, 65°35'08''W), and Isla Viana (45°11'27''S, 63°23'50''W), are located within the 'Patagonia Austral Marine Park'. Whole blood samples were obtained simultaneously from breeding adults of both species during the early chick stage and used for stable isotope analysis. Isotopic niche was described by means of centroid analysis and Bayesian ellipse-based metrics. The isotopic niche overlap between species was in general small or insignificant, suggesting niche partitioning, and the isotopic niche width in the different colonies and seasons was significantly smaller in the Imperial Cormorant than in the Rock Shag. However, the isotopic niche of the Imperial Cormorant in Isla Viana during the second study season was totally included in the isotopic niche of the Rock Shag, suggesting an important niche overlap. Results showed evidence that niche partitioning processes in these cormorants is context dependent. However, further studies are needed including independent measures of prey availability and niche evaluation at additional colonies where these species breed alone and with other cormorant species, considering that the metacommunity framework predicts that the combination of species in metapopulation contexts could be sometimes achieved through pairs of species with similar resource utilization.Fil: Gatto, Alejandro Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Yorio, Pablo Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentina3rd World Seabird ConferenceVictoriaCanadáWorld Seabird Unio

Trophic niche variation throughout the year in the opportunistic Kelp Gull at different trophic scenarios in Patagonia, Argentina

Changes in foraging strategies throughout the year are key determinants of seabird population dynamics. However, due to seabird post-breeding dispersal, year-round trophic ecology studies rarely focus on individuals from known colonies. Using stable isotope analysis (δ15N, δ13C) of blood and primary feathers, we tested during 2012 the trophic niche variation throughout the year in Kelp Gulls Larus dominicanus from three colonies in Patagonia, Argentina, located in areas with different availability of anthropogenic food subsidies. Isotopic niche width, measured using multivariate ellipse-based metrics, was wider at all colonies during the non-breeding season, suggesting that during this period gulls forage on a greater variety of food sources possibly related to post-breeding dispersal, seasonal changes in food resources, and/or the relaxation of central place foraging. Individuals from the colony with yearround availability of fisheries discards (Isla Vernaci) presented the lower isotopic niche width year-round compared to those from the other two colonies, one with discards only available during the breeding season (Punta Tombo) and the other with only open-air refuse dumps available all year-round (Punta León). At Isla Vernaci, an abrupt expansion in niche width occurred later in the non-breeding season, after the start of a fisheries moratorium, suggesting that Kelp Gulls remained in nearby areas and partly associated to trawl fisheries between breeding events. Preliminary diet results indicate that most studied individuals from Isla Vernaci were feeding on demersal prey, only available from fisheries discards as Kelp Gulls are surface feeders. These results suggest that the availability of discards can greatly influence Kelp Gull foraging strategies and non-breeding movements, and that changes in niche metrics can be context dependent. Future studies should complement the assessment of niche variability with studies of diet composition throughout the year.Fil: Lisnizer, Nora. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Gatto, Alejandro Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Yorio, Pablo Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentina3rd World Seabird ConferenceVictoriaCanadáWorld Seabird Unio

Forage fish to growing chicks: shared food resources between two closely related tern species

The assessment of the relevance of forage fsh in seabird diet and how diferent species partition food resources is fundamental to understand predator–prey relationships. We assessed the importance of forage fsh in the diet of Royal (Thalasseus maximus maximus) and Cayenne (T. sandvicensis eurygnathus) terns and their partitioning of food resources during the early and late chick stages of 2013 and 2014 at a colony in Argentina. Direct observation of prey deliveries during chick provisioning showed that diet composition of Royal and Cayenne terns comprised at least 16 and 9 prey species, respectively. In both tern species, Argentine Anchovy (Engraulis anchoita) and fve species of silversides (Odontesthes spp.) were the main prey fed to chicks (over 90% contribution, anchovy and silversides pooled). Both tern species fed their chicks with similar prey species, but Royal terns delivered, in general, larger prey than Cayenne terns. Based on carbon and nitrogen isotopic values from chick whole blood samples, Bayesian mixing models showed that anchovies and silversides contributed similarly to the diet of both tern species’ chicks. Both conventional and stable isotope methods showed a high overlap in their trophic niches. Prey sizes delivered to chicks were larger in the late chick stage and the second study season. Wind speed did not have a signifcant efect on the frequency of the diferent prey species and sizes delivered to chicks by both tern species. As anchovies and silversides are fshery targets, tern trophic requirements should be considered when planning future fsheries development and management.Fil: Marinao, Cristian Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Suárez, Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Gatto, Alejandro Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Yorio, Pablo Martin. Wildlife Conservation Society; Estados Unido