Cueto, V. R. | Search bioRxiv

bioRxiv2018

SEASONAL CHANGES IN BIRD ASSEMBLAGES OF A MAITENAL FOREST IN NORTH PATAGONIA

We evaluate seasonal variations at the community level, analyzing changes in species richness, species composition and total abundance, and at the species level, evaluating differences in breeding and molting seasonality among bird species in a forest-steppe ecotone of north Patagonia. 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 promoted few seasonal variations in richness and total abundance, because they were compensated by 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 birds began to molt body and flight feathers after breeding. Therefore, we found a low overlap of these two demanding activities. 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.\n\nResumen. Cambios estacionales en los ensambles de aves en un ecotono bosque-estepa del norte de PatagoniaEvaluamos las variaciones estacionales a nivel comunitario, analizando la riqueza de especies, la composicion de especies y la abundancia total, y a nivel de las especies, evaluando las diferencias en la estacionalidad reproductiva y de muda entre las especies de aves en un ecotono bosque-estepa del norte de Patagonia. El ensamble de aves mostro pocas variaciones estacionales en la riqueza y abundancia total, pero un notable cambio en la composicion de especies entre la primavera-verano y el otono-invierno. El cambio en la composicion de especies promovio pocas variaciones estaciones en la riqueza y la abundancia total, porque fueron compensadas por la abundancia de las especies que visitan el area en las diferentes estaciones. A nivel de las especies, las aves residentes y migrantes de corta distancia tendieron a comenzar la reproduccion antes que las migrantes de larga distancia, y las aves comenzaron la muda de plumas del cuerpo y del ala al finalizar la reproduccion. Por lo cual encontramos una baja superposicion de estas dos demandantes actividades. Nuestros resultados remarcan la importancia del movimiento de las aves en respuesta a las variaciones en la disponibilidad de recursos, que promueven la migracion o el desplazamiento local de las aves.

ecology↗

bioRxiv2018

Which food patches are worth exploring? Foraging desert birds do not follow environmental indicators of seed abundance at small scales: a field experiment

Consumers should show strong spatial preferences when foraging in environments where food availability is highly heterogeneous and predictable from its correlation with informative environmental features. This is the case for postdispersal granivores in most arid areas, where soil seed bank abundance and composition associates persistently with vegetation structure at small scales (e.g., decimeters to meters). We analysed seasonal single-seed removal by granivorous birds from 300 experimental devices in the algarrobal of the central Monte desert. Spatial selectivity was analysed by comparing the structural characteristics of used vs. available microhabitats and evaluated against bottom-up and top-down hypotheses based on our previous knowledge on local seed bank abundance, composition and dynamics. Seed removal, which showed its expected seasonal variability, was also explored for spatial autocorrelation and environmental dependencies at bigger scales. Postdispersal granivorous birds were less selective in their use of foraging space than expected if patch appearance were providing them useful information to guide their search for profitable foraging patches. No kind of microhabitat, as defined by their vegetation and soil structure, was safe from bird exploration. The only consistent selective pattern at this scale was closer to a top-down spatial effect by birds, i.e., a cause (and not a consequence) of the seed bank dynamics. Bigger spatial scales proved more relevant to describe heterogeneity in the use of foraging patches in this habitat. Closeness to tall trees, probably related to bird territoriality and reproduction or to their perception of predation risk, seems to determine a first level of selection that defines explorable space, and then microhabitat openness exerts an influence on which patches are effectively exploited (or more frequently explored) among those accessible.

ecology↗