SEASONAL CHANGES IN BIRD ASSEMBLAGES OF A FOREST-STEPPE ECOTONE IN NORTH PATAGONIA

Abstract ∙ We studied seasonal variation in a community of birds inhabiting a forest–steppe ecotone of north Patagonia. We analyzed changes in species richness, species composition and total abundance, and, at the species level, we evaluated differences in breeding and molting seasonality. The bird assemblage showed a low seasonal variation in richness and total abundance, but a great change in species composition between spring–summer and fall–winter. The change in species composition did not lead to changes in richness and total abundance, due to the presence of abundant species that visit the area in different seasons. At the species level, resident birds and short distance migrants tended to begin breeding earlier than long distance migrants, and those bird species began to molt body and flight feathers after breeding. Therefore, we found a low overlap between these two energetically demanding activities. Elaenia albiceps, the only long-distance migrant species, did not molt body and flight feathers in our study area. Our results highlight the importance of bird movements in response to seasonal variations in the availability of resources, which promote migration or local displacements of birds. Resumen ∙ Cambios estacionales en los ensambles de aves en un ecotono bosque–estepa del norte de Patagonia Estudiamos las variaciones estacionales en una comunidad de aves que habitan el ecotono bosque-estepa del norte de Patagonia. Analizamos los cambios en la riqueza de especies, la composición de especies y la abundancia total, y a nivel de las especies, evaluamos las diferencias en la estacionalidad reproductiva y de muda. El ensamble de aves mostró pocas variaciones estacionales en la riqueza y abundancia total, pero un notable cambio en la composición de especies entre la primavera–verano y el otoño–invierno. El cambio en la composición de especies no promovió variaciones estacionales en la riqueza y la abundancia total, debido a la presencia de especies abundantes que visitan el área en las diferentes estaciones. A nivel de las especies, las aves residentes y migrantes de corta distancia tendieron a comenzar la reproducción antes que las migrantes de larga distancia, y aquellas especies de aves comenzaron la muda de plumas del cuerpo y del ala al finalizar la reproducción. Por lo cual encontramos una baja superposición de estas dos demandantes actividades. Elaenia albiceps, la única especie migradora de larga distancia, no presentó muda corporal o del plumaje de vuelo en nuestra área de estudio. Nuestros resultados remarcan la importancia del movimiento de las aves en respuesta a las variaciones en la disponibilidad de recursos, que promueven la migración o el desplazamiento local de las aves

Relationship between bird assemblages and vegetation structure. An analysis at three spatial scales

El objetivo de esta tesis doctoral es evaluar el papel de la estructura de la vegetación como factor próximo que guía a las aves en la selección del hábitat a tres escalas espaciales y como factor último por su asociación con la obtención de alimento por las aves. El análisis regional sugiere que la riqueza de especies de aves passeriformes responde a la disponibilidad de estratos de vegetación, es decir que la estructura de la vegetación es más importante que el clima en la determinación de los patrones de distribución geográfica de las aves. A escala local, tanto la estructura de la vegetación como la composición florística del "stand" influyen en el uso del hábitat. Los gremios de insectívoros y frugívoro-insectívoros son ejemplos de la importancia de estas dos características de la vegetación. Las aves insectívoras responden a las diferencias en estructura de la vegetación, siendo menos abundantes en los bosques con una menor disponibilidad de follaje en altura, mientras que las frugívoro-insectívoras responden a la composición florística del bosque, siendo menos abundantes en los sitios que presentan una menor abundancia y riqueza de especies arbóreas productoras de frutos. Cuando se analiza el uso de microhábitat de alimentación, los patrones de selección antes mencionados pueden ser mejor comprendidos. De las tres aves insectívoras estudiadas, dos son recolectoras de presas en el follaje (Parula pitiayumi y Polioptila dumicola), mientras que la otra se alimenta mediante el revoloteo (Serpophaga subcristata). Las dos primeras usan preferentemente el estrato superior del bosque para forrajear y en consecuencia una disminución en la altura del bosque resulta en una menor densidad de estas aves. Por otro lado, S. subcristata captura sus presas en todos los estratos del bosque y las modificaciones de la estructura de la vegetación no afectan su abundancia en los talares. Finalmente, Elaenia parvirostris (una especie frugívoro-insectívora) se alimenta principalmente mediante la caza por revoloteo, tanto de insectos como de frutos. Esta especie forrajea en todos los estratos, pero a diferencia de S. subcristata, está afectada por la degradación del bosque. Esto se debe a la notable reducción en la abundancia y riqueza de especies arbóreas productoras de frutos en dicho bosque. El análisis detallado del uso de microhábitat de forrajeo por las cuatro especies estudiadas, indicaría que la estructura y composición de la vegetación están asociadas a los factores últimos del hábitat, por su relación con la adquisición de los recursos alimenticios para las aves, y que junto con los condicionamientos comportamentales y/o morfológicos de las aves producen los patrones observados a escala local. A esta escala, la estructura de la vegetación y la composición florística surgen como los dos factores próximos que guían la selección del hábitat por las aves, así como ocurre a escala regional con la disponibilidad de estratos de vegetación y la riqueza de aves passeriformes. De esta manera, se puede concluir que en las tres escalas los factores que actúan en la selección del hábitat por las aves son similares. Esto se debería a que la estructura y composición de la vegetación imponen restricciones a los comportamientos de forrajeo de las aves y tales restricciones permanecen validas a las escalas de microhábitat, local y regional.This doctoral thesis is aimed to evaluate the role of the vegetation structure as a proximate factor guiding to the birds in the habitat selection at three spatial scales, and as an ultimate factor for its association with the attainment of basic food resources by the birds. The regional analysis suggests that species richness of passerine birds responded to the availability of plant strata. At this scale vegetation structure is most important than climate in determining bird habitat occupation. At local scale, vegetation structure and floristic composition of the stand influence bird habitat selection. Both insectivorous and frugivorous -insectivorous guilds rendered clear examples of the importance of these two plant variables. Insectivores responded to variations in vegetation structure, reaching less abundance in forests with smaller foliage availability at great heights; whereas frugivorous-insectivorous birds responded to the floristic composition of the forest, being less abundant in those sites with low abundance and richness of fruit-producing trees. When the use of foraging microhabitat by birds is analyzed, the previous selection pattern may be better understood. Among the insectivorous studied, two species obtain their prey by gleaning on the foliage (Parula pitiayumi and Polioptila dumicola), while the other insectivore (Serpophaga subcristata) take his preys by hovering. The gleaner species use preferably the upper stratum of the forest to forage, and consequently their densities fell in sites where the forest height was lower. On another hand, S. subcristata obtain his preys on all forest strata and the modifications of vegetation structure did not affect his abundance in the forests. Finally, Elaenia parvirostris, a frugivore-insectivore species, take his preys by hovering. This species forage on all strata, but as opposed to S. subcristata, was affected by forest degradation. This was due to the notable reduction in the abundance and richness of fruit-producing trees, caused by forest logging. The detailed assessment of the use of foraging microhabitat by the four species studied seems to indicate that vegetation structure and floristic composition were associated with the ultimate habitat factors, because of their relation with the attainment of the basic food resources for the birds. Those plant characteristics together with the behavioral and morphological restrictions of the birds, produced the observed pattern at local scale. At this scale, vegetation structure and floristic composition arose as the two proximate factors guiding bird habitat selection, such as it happens at regional scale with the availability of plant strata and passerine species richness. In this way, it may be concluded that factors acting in bird habitat selection at the three scales considered were very similar. This was probably due to the fact that the structure and composition of vegetation impose restrictions to the foraging behaviors of bird species and such restrictions remain valid at microhabitat, local and regional scales.Fil:Cueto, Victor Rodolfo. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Wintering areas of White-crested Elaenia (<i>Elaenia albiceps chilensis</i>).

<p>Map of biomes relevant to the elaenia’s annual cycle. Breeding site (red circle), winter and fall areas used by each bird (black circles) are locations with the highest frequency of records by each geolocator, sometimes more than 1 per individual (more details in methods). White circles represent hotspots of areas used by some individuals during more than a week in fall and spring migration.</p

Spring migration route of White-crested Elaenia (<i>Elaenia albiceps chilensis</i>).

<p>Locations recorded by geolocators during spring migration. We only show partial data for some birds because migration occurred partially during the equinox period. Locations of H777 and H775 are not visible because of the the high density of points. Geolocators P872, P859 and P868 stopped recording before spring migration.</p

Longitudinal changes during fall migration.

<p>We detect three patterns of longitudinal changes during migration. (A) longitude constant during 6–8 days, between 62°W—65°W. (B) changes throughout the entire migration. (C) longitude constant during 6–10 days, between 55°W—60°W.</p

Migratory timing, rate, routes and wintering areas of White-crested Elaenia (Elaenia albiceps chilensis), a key seed disperser for Patagonian forest regeneration.

Migratory animals often play key ecological roles within the communities they visit throughout their annual journeys. As a consequence of the links between biomes mediated by migrants, changes in one biome could affect remote areas in unpredictable ways. Migratory routes and timing of most Neotropical austral migrants, which breed at south temperate latitudes of South America and overwinter closer to or within tropical latitudes of South America, have yet to be described in detail. As a result, our understanding about how these birds provide links between South American biomes is almost non-existent. White-crested Elaenia (Elaenia albiceps chilensis) is a long-distance austral migrant that breeds in the Patagonian Forest biome and overwinters in tropical South America. Because this small flycatcher plays a key role in the regeneration of this ecosystem, our objective was to describe the annual cycle of White-crested elaenias to evaluate the degree of migratory connectivity between breeding and wintering areas and therefore to determine if there are specific biomes of northern South America linked by elaenias to Patagonian forests. Fifteen individuals were successfully tracked throughout a complete migration cycle using miniature light-level geolocators. All individuals resided and moved through the same general regions. During fall (March-April-May), elaenias were located in the Caatinga and the Atlantic Forest biomes, from Rio de Janeiro to the region near Salvador da Bahia, Brazil. During winter (June-July-Aug.), birds were located further inland, within the Cerrado biome. Birds used three different routes during fall migration. Our results indicate that some individuals use a direct route, flying between 500-600 km/day, crossing desert and grasslands, while others took a detour, flying 100-200 km/day through forested areas with refueling opportunities. All birds used the Yunga forest during spring migration, with ten out of 15 individuals showing a clear counterclockwise loop trajectories throughout their annual cycle. None of the elaenias passed through Amazonia, traveled to western South America or crossed the Equator. Eleanias exhibited a high migratory connectivity between breeding area in Patagonian Forests and winter areas, Atlantic Forest and Cerrado. Our results suggest that Patagonian Forests could be strongly impacted by changes in those biomes or in the Yungas

Genetic Association Study Of Exfoliation Syndrome Identifies A Protective Rare Variant At Loxl1 And Five New Susceptibility Loci

Exfoliation syndrome (XFS) is the most common known risk factor for secondary glaucoma and a major cause of blindness worldwide. Variants in two genes, LOXL1 and CACNA1A, have previously been associated with XFS. To further elucidate the genetic basis of XFS, we collected a global sample of XFS cases to refine the association at LOXL1, which previously showed inconsistent results across populations, and to identify new variants associated with XFS. We identified a rare protective allele at LOXL1 (p.Phe407, odds ratio (OR) = 25, P = 2.9 x 10(-14)) through deep resequencing of XFS cases and controls from nine countries. A genome-wide association study (GWAS) of XFS cases and controls from 24 countries followed by replication in 18 countries identified seven genome-wide significant loci (P < 5 x 10(-8)). We identified association signals at 13q12 (POMP), 11q23.3 (TMEM136), 6p21 (AGPAT1), 3p24 (RBMS3) and 5q23 (near SEMA6A). These findings provide biological insights into the pathology of XFS and highlight a potential role for naturally occurring rare LOXL1 variants in disease biology.Wo