The relationship between structure and location in the nest of the Yellow-winged Blackbird ( Agelasticus thilius)

La estructura y la ubicación del nido deben maximizar el beneficio que proporciona a la nidada, tanto en el aislamiento del ambiente como en la protección contra predadores. El Varillero Ala Amarilla (Agelasticus thilius) construye nidos abiertos entrelazados a la vegetación palustre en zonas de bañado. Se estudió la altura a la que estas aves construyen su nido y el espesor de sus paredes laterales y de la base, buscando un patrón que correlacione estas características. Los nidos fueron construidos en la mitad inferior de las varas de totora y se encontró una correlación positiva entre la altura de la totora y la distancia del nido a la punta de la vara. Tanto el espesor de la pared como el de la base aumentaron con la distancia entre el nido y la punta de las varas a las que estaban entrelazados, lo cual podría reforzar su estructura permitiéndole soportar los efectos del viento sin romperse. El espesor de la pared fue mayor en los nidos construidos a menor altura pero no se encontró el mismo patrón en el espesor de la base. Los factores ambientales que ponen a prueba la fortaleza de la estructura del nido podrían tener importancia en la determinación de la estructura y la posición de los nidos, mientras que la influencia del riesgo de predación podría ser menor.Nest structure and location must maximize the benefit provided to chicks through isolation from the environment as well as protection against predators. The Yellow-winged Blackbird (Agelasticus thilius) builds open nests intertwined to trowel vegetation in marshlands. The height to which these birds build the nest and the thickness of their lateral walls and base were studied to look for a pattern that relates these characteristics. Nests were built in the lower half of bulrush canes and a positive correlation between height of canes and the distance between the nest and the cane tip was found. The thickness of both nest wall and base increased with the distance between the nest and the cane tip. This could reinforce nest structure improving its resistance to the effect of the wind without damage. Wall thickness was higher in nests built at a lower height, but base thickness was not correlated with this distance. Environmental factors that test the strength of the nest structure may be important in determining nest structure and location, while the influence of predation risk would be lower.Fil: Montalti, Diego. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Zoología de Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Graña Grilli, Maricel. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Zoología de Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Variation in diet composition during the breeding cycle of an Antarctic seabird in relation to its breeding chronology and that of its main food resource

This work had two aims related to the diet of brown skuas (Stercorarius antarcticus lonnbergi) breeding at Laurie Island (South Orkney Islands, Antarctic). The first aim was to explore whether there are changes throughout the breeding season. The second aim was to determine whether those changes relate to differences in food resource availability of their main prey, penguins, at different time periods of the penguins’ breeding cycles, or to different moments of the skuas breeding cycle, which may variably restrict the foraging activities of parents. Diet was analyzed from pellet samples grouped in two different ways. They were grouped in three periods defined for the skuas breeding cycle (laying and incubation; early parental care; later parental care), or the pellets were assigned to five periods based on the type of food resources available at the penguin colonies (eggs; eggs and small chicks; small and large chicks; large and fledged chicks; fledged chicks). A temporal variation in diet composition was evident from the analysis of contingency tables for both sample grouping methods. The more represented item in every period for both analyses was adult penguins, which may be related to the proposed cleaning function of the gut of penguin feathers. Both ways of grouping the samples suggest a relationship between the kind of resources available at the penguin colonies and the easiness of delivering them to the skuas chicks, reflected in a successive predominance of use of penguin eggs first and of penguin chicks and other birds later.Fil: Graña Grilli, Maricel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. Departamento Científico Zoología Vertebrados; ArgentinaFil: Montalti, Diego. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. Departamento Científico Zoología Vertebrados; Argentin

Uso del espacio, dieta y estado corporal del skua pardo (Stercorarius antarcticus lonnbergi) durante su período reproductivo en Antártida

Tesis presentada para optar al Grado de Doctor en Ciencias NaturalesFil: Graña Grilli, Maricel. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; Argentin

The relationship between structure and location in the nest of the Yellow-winged Blackbird (<i>Agelasticus thilius</i>)

La estructura y la ubicación del nido deben maximizar el beneficio que proporciona a la nidada, tanto en el aislamiento del ambiente como en la protección contra predadores. El Varillero Ala Amarilla (Agelasticus thilius) construye nidos abiertos entrelazados a la vegetación palustre en zonas de bañado. Se estudió la altura a la que estas aves construyen su nido y el espesor de sus paredes laterales y de la base, buscando un patrón que correlacione estas características. Los nidos fueron construidos en la mitad inferior de las varas de totora y se encontró una correlación positiva entre la altura de la totora y la distancia del nido a la punta de la vara. Tanto el espesor de la pared como el de la base aumentaron con la distancia entre el nido y la punta de las varas a las que estaban entrelazados, lo cual podría reforzar su estructura permitiéndole soportar los efectos del viento sin romperse. El espesor de la pared fue mayor en los nidos construidos a menor altura pero no se encontró el mismo patrón en el espesor de la base. Los factores ambientales que ponen a prueba la fortaleza de la estructura del nido podrían tener importancia en la determinación de la estructura y la posición de los nidos, mientras que la influencia del riesgo de predación podría ser menor.Nest structure and location must maximize the benefit provided to chicks through isolation from the environment as well as protection against predators. The Yellow-winged Blackbird (Agelasticus thilius) builds open nests intertwined to trowel vegetation in marshlands. The height to which these birds build the nest and the thickness of their lateral walls and base were studied to look for a pattern that relates these characteristics. Nests were built in the lower half of bulrush canes and a positive correlation between height of canes and the distance between the nest and the cane tip was found. The thickness of both nest wall and base increased with the distance between the nest and the cane tip. This could reinforce nest structure improving its resistance to the effect of the wind without damage. Wall thickness was higher in nests built at a lower height, but base thickness was not correlated with this distance. Environmental factors that test the strength of the nest structure may be important in determining nest structure and location, while the influence of predation risk would be lower.Facultad de Ciencias Naturales y Muse

The relationship between structure and location in the nest of the Yellow-winged Blackbird (<i>Agelasticus thilius</i>)

La estructura y la ubicación del nido deben maximizar el beneficio que proporciona a la nidada, tanto en el aislamiento del ambiente como en la protección contra predadores. El Varillero Ala Amarilla (Agelasticus thilius) construye nidos abiertos entrelazados a la vegetación palustre en zonas de bañado. Se estudió la altura a la que estas aves construyen su nido y el espesor de sus paredes laterales y de la base, buscando un patrón que correlacione estas características. Los nidos fueron construidos en la mitad inferior de las varas de totora y se encontró una correlación positiva entre la altura de la totora y la distancia del nido a la punta de la vara. Tanto el espesor de la pared como el de la base aumentaron con la distancia entre el nido y la punta de las varas a las que estaban entrelazados, lo cual podría reforzar su estructura permitiéndole soportar los efectos del viento sin romperse. El espesor de la pared fue mayor en los nidos construidos a menor altura pero no se encontró el mismo patrón en el espesor de la base. Los factores ambientales que ponen a prueba la fortaleza de la estructura del nido podrían tener importancia en la determinación de la estructura y la posición de los nidos, mientras que la influencia del riesgo de predación podría ser menor.Nest structure and location must maximize the benefit provided to chicks through isolation from the environment as well as protection against predators. The Yellow-winged Blackbird (Agelasticus thilius) builds open nests intertwined to trowel vegetation in marshlands. The height to which these birds build the nest and the thickness of their lateral walls and base were studied to look for a pattern that relates these characteristics. Nests were built in the lower half of bulrush canes and a positive correlation between height of canes and the distance between the nest and the cane tip was found. The thickness of both nest wall and base increased with the distance between the nest and the cane tip. This could reinforce nest structure improving its resistance to the effect of the wind without damage. Wall thickness was higher in nests built at a lower height, but base thickness was not correlated with this distance. Environmental factors that test the strength of the nest structure may be important in determining nest structure and location, while the influence of predation risk would be lower.Facultad de Ciencias Naturales y Muse

Uniformity of diet composition of Brown Skua chicks at different ages and between siblings

The diet of chicks may change according to their growth and also vary between siblings due to their competitive relationship. Diet composition of 81 Brown Skua (Stercorarius antarcticus lonnbergi) chicks was analysed from regurgitated stomach contents in order to determine changes in diet composition related to chick age and differences between siblings. Fifty-nine of the samples belonged to chicks whose age was estimated by applying culmen measurement to a regression function. The remaining 22 samples belonged to 11 sibling pairs whose stomach contents were simultaneously sampled. The diet was constituted mostly by soft tissues of penguins. Marine resources were a minor part of the diet of chicks, appearing in the third week of their life. The qualitative composition of the stomach content of siblings was similar in most cases, but mass of regurgitates differed between siblings (1.3– 90.0% = 0.5–9 g), which suggests the potential existence of aggressive food monopolization by one sibling, an issue to be elucidated with further research.Facultad de Ciencias Naturales y MuseoConsejo Nacional de Investigaciones Científicas y Técnica

Uniformity of diet composition of Brown Skua chicks at different ages and between siblings

The diet of chicks may change according to their growth and also vary between siblings due to their competitive relationship. Diet composition of 81 Brown Skua (Stercorarius antarcticus lonnbergi) chicks was analysed from regurgitated stomach contents in order to determine changes in diet composition related to chick age and differences between siblings. Fifty-nine of the samples belonged to chicks whose age was estimated by applying culmen measurement to a regression function. The remaining 22 samples belonged to 11 sibling pairs whose stomach contents were simultaneously sampled. The diet was constituted mostly by soft tissues of penguins. Marine resources were a minor part of the diet of chicks, appearing in the third week of their life. The qualitative composition of the stomach content of siblings was similar in most cases, but mass of regurgitates differed between siblings (1.3– 90.0% = 0.5–9 g), which suggests the potential existence of aggressive food monopolization by one sibling, an issue to be elucidated with further research.Facultad de Ciencias Naturales y MuseoConsejo Nacional de Investigaciones Científicas y Técnica

Trophic interactions between brown and south polar skuas at Deception Island, Antarctica

It is broadly accepted that the brown skua (Stercorarius antarcticus lonnbergi) competitively excludes the south polar skua (S. maccormicki) from penguin colonies when breeding sympatrically, forcing the latter to feed on marine resources. The purpose of this work was to examine the diets and trophic niche breadths of each species where they co-occur and to determine the degree of overlap. To this end, we analyzed 169 pellets of brown skuas, collected in two different areas (20 individuals), and 152 of south polar skuas, collected in three different areas (18 individuals), on Deception Island, South Shetland Islands, Antarctica, during the austral summer 2000. Pellet analysis often underestimates the amount of easily digestible prey, but allows for comparisons of the relative contributions of different items in the diet. South polar skuas at our study locations consumed seven different food items and had a trophic niche breadth of 0.133 compared to brown skuas that fed on 10 different items and had a trophic niche breadth of 0.078. The niche overlap between the species was 82.1%. Penguins were the principal food source of both species, however, brown skuas fed mostly on chicks, while south polar skuas fed on adults (carcasses). The use of different age classes of penguins as a food source offers an alternative to competitive exclusion, allowing the coexistence of these species on Deception Island.Facultad de Ciencias Naturales y Muse

A long and troublesome journey: People's perceptions and attitudes along the migratory path of a scavenger bird

In recent decades, there has been a growing interest in integrating the social sciences and conservation studies to inform a more realistic management approach. Indeed, an understanding of people's perception of fauna helps in the evaluation of possible conflicts with humans, and provides tools to solve these conflicts. However, perceptions may change along a species geographical distribution. Scavenger birds are not exempt from these conflicts as many farmers blame them for attacking and killing livestock. We evaluated the knowledge, perceptions and attitude of people regarding New World vultures along a migratory path in South America. We conducted 114 interviews with farmers in six different localities between Argentine Patagonia and central Bolivia. About half (48.2%) of the interviewees considered vultures harmful to livestock and a substantial number (24.5%) considered killing these birds as a solution for the conflict. The perception of the damage caused by these birds was worse in vultures wintering and breeding areas, than along the migration route. People with a higher level of education and greater numbers of livestock exhibited more negative perceptions. However, many people (53%) still believed that scavenger birds are important for the environment. Our results suggest that acknowledgment of services provided by scavengers makes killing of scavengers less likely. Educational strategies are needed to increase levels of appreciation toward the ecosystem services provided by vultures, over those of perceived damages.Fil: Ballejo, Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina. Universidad Nacional del Comahue. Centro Regional Universitario Bariloche. Laboratorio de Ecotono; ArgentinaFil: Graña Grilli, Maricel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina. Universidad Nacional del Comahue. Centro Regional Universitario Bariloche. Laboratorio de Ecotono; ArgentinaFil: Lambertucci, Sergio Agustin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina. Universidad Nacional del Comahue. Centro Regional Universitario Bariloche. Laboratorio de Ecotono; Argentin

The reliability of morphometric discriminant functions in determining the sex of Chilean flamingos Phoenicopterus chilensis

Monomorphic birds cannot be sexed visually and discriminant functions on the basis of external morphological variations are frequently used. Our objective was to evaluate the reliability of sex classification functions created from structural measurements of Chilean flamingos Phoenicopterus chilensis museum skins for the gender assignment of live birds. Five meas-urements were used to develop four discriminant functions: culmen, bill height and width, tarsus length and middle toe claw. The functions were tested on a sample of live flamingos from a zoo. The best classification for museum flamingos was given by a function using tarsus length, bill width and middle toe claw (97%). However, this function did not give the best classification for the zoo-based flamingos (81%) which had the best sex assignment by a function including measurements of tarsus, culmen and bill height and width (85%). This shows that a function giving good results in the sample from which it originated may not be as good when applied to another group of animals. Our study emphasizes the need for assessing the accuracy of a function by testing it with other methods to ensure its suitability when being applied.Facultad de Ciencias Naturales y Muse