Stable isotope analysis has been extensively used to establish trophic relationships within avian communities of marine ecosystems. The Neotropic Cormorant (Phalacrocorax brasilianus) is a good representative of marine bird communities along the northern coasts of South America. The diet and trophic position of the Neotropic Cormorant during the non-breeding season in a tropical lagoon, Bocaripo-Chacopata, in northeastern Venezuela, was determined by using gut content analyses and stable isotope ratios of carbon (d 13 C) and nitrogen (d 15 N), from birds, fish and invertebrates muscle tissue. Gut content and stable isotopes both indicated that cormorants are strict piscivores, whose diet is mainly based on benthonic fish, and thus occupy a high trophic level, above that of the piscivorous fish in the same habitat. Crustaceans and mollusks were circumstantial components of cormorant diet, found in the gut of some cormorant fish prey, as shown from their d 15 N isotope values. A mixing model, MixSIR, estimated that two fish species, Cetengraulis edentulous and Arius sp., were the main components of the diet. However, consumer stable isotope values fell outside the mixing polygon, suggesting that either another food source with a larger 15 N value was present in the diet of the cormorant but we failed to detect it, or, that we used inaccurate discrimination factors in the model. This cormorant species is a trophic specialist. It appears that, at least during the studied period, this population fed only on fish from the lagoon or from the nearby sea. ZusammenfassungDie trophische Stellung der Olivenscharbe (Phalacrocorax brasilianus): Eine Integration von Nahrungs-und Isotopenanalysen Die analyse stabiler isotope wird häufig angewendet, um trophische Zusammenhänge in Vogelgemeinschaften mariner Ö kosysteme zu untersuchen. Die Olivenscharbe (Phalacrocorax brasilianus) ist ein geeigneter Vertreter der marinen Vogelgemeinschaft der nördlichen Küsten Süda-merikas. Die Nahrung und die trophische Stellung dieses neotropischen Kormorans wurden außerhalb der Brutsaison in der tropischen Lagune Bocaripo-Chacopata im Nordosten Venezuelas durch Darmanalysen und Isotopenverhält-nissen von Kohlenstoff (d 13 C) und Stickstoff (d 15 N) in Vogel-, Fisch-, und Invertebratenmuskelgeweben untersucht. Darminhalte und stabile Isotope weisen diesen Kormoran als strikten Fischfresser aus, dessen Nahrung Communicated by P. H. Becker.
Las plantas cactáceas están naturalmente circunscritas al continente americano, y el consumo de sus frutos por las aves ha sido puntualmente estudiado en algunas áreas semiáridas caribeñas.Este estudio cuantifica aspectos ecológicos de la ornitofrugivoría en dos cactáceas columnares: Stenocereus griseus (Sg) y Cereus repandus (Cr), en el nororiente de Venezuela. Se recolectaron frutos maduros para la medición de contenido de semillas y algunos parámetros morfométricos. Durante la maduración de los frutos se practicaron cuatro sesiones de observación, en junio (n=3) y septiembre (n=1), para Sg, y en julio (n=4), para Cr, divididas en cuatro lapsos: 07.00-09.00 am, 09.00-11.00 am, 11.00 am-01.00 pm y 1.00 -03.00 pm, promediándose la temperatura ambiental para cada lapso. Se determinaron número de individuos y especies de aves consumidoras por lapso, frecuencia y duración de las visitas y pugnacidad intra e interespecífica. En promedio, los frutos de Sg fueron ligeramente más grandes que los de Cr, pero con una cantidad similar de semillas, aunque Cr casi duplicó a Sg en el número de semillas estériles. Trece especies consumieron frutos de las dos especies de cactáceas, pero Leucippus fallax sólo consumió frutos de Sg, mientras Saltator coerulescens, Mimus gilvus y Campylorhrynchus griseus sólo de Cr. Coereba flaveola acaparó el mayor porcentaje de visitas en ambas cactáceas. En Sg, la frecuencia de las visitas fue significativamente mayor durante el primer lapso matutino (7-9 am) que en el resto; sin embargo, ésta fue similar para todos los lapsos en Cr. Competitivamente, Melanerpes rubricapillus fue la especie más dominante, mientras C. flaveola tuvo la mayor pugnacidad, intra e interespecífica.
Seasonal flooding of Orinoco river produces spatial and temporal variations in several plant communities with different successional phases, creating transitional habitats and foraging resources for birds. Our primary objective was to enumerate bird species diversity, habitat use and vulnerability, of Mamo island in lower Orinoco river and describe the ephemeral habitat use, viz. Sandbars (SAB), Thickets (THI), Canopy Forests (CAF), Guadua Bamboos (GBA), Bushes (BUS) and aquatic macrophytes (HMF), in relation to flooding pulses, viz.: Low Waters (LW), Waters Rising (WR), High Waters (HW), Descent of Waters (DW). Overall, 141 bird species, belonging to 43 families, were recorded. CAF habitat showed the highest species richness, following this pattern: CAF BUS THI SAB HMF GBA. Species richness by period followed the pattern: LW WR HW DW. TH, CAF and SAB habitats showed the highest vulnerability index. BUS x THI similarity (diversity) showed the higher index (34.28%) however in the other combinations this was less than 9%. Conservation plans for the Orinoco basin should take into account the high dependency of bird species on riverine islands. Mechanical and physical-chemical alterations in normal river flow patterns would generate avian species extirpation in this important ecosystem.
This study was to determine the contents of heavy metals (HM): chromium (Cr), copper (Cu), zinc (Zn), lead (Pb), and cadmium (Cd) on blood and feathers of Japanese Quail (Coturnix coturnix japonica Temminck & Schlegel 1849) in relation to weight and sex. Fifteen individuals (4 males and 11 females) were weighed; a blood sample of approximately 5 mL was drawn and immediately coagulated. Wing and tail feathers were removed. Samples were analysed by using an Atomic Absorption Spectrophotometer matched to an acetylene-flow and deuterium background correction. In blood and feathers tissue samples, Pb and Cd were not detected. Cr, Cu, Zn levels showed statistical differences between tissues and HM. The feathers showed higher concentrations than blood, because they can bioaccumulate HM during their growth, although eliminating metals, partially, during the feather moult, and, internally, during transport of metals in the bloodstream and their fixation to keratin. Zn levels were highest in both tissues. Zn is an essential element and abundant in the organisms and domestic avian diet. Weight versus HM levels showed a negative relation in quails because HM are diluted in larger individuals. Males generally showed higher HM levels than females which may reflect differences in methallotionein synthesis and excretion pathways between sexes. In general, HM concentrations measured in the quails are not alarming.
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