RESUMO
We collected and analyzed 286 Barn owl, Tyto alba (Scopoli, 1769), pellets from two nests in different environments along the mid-Araguaia River in central Brazil. Our analyses revealed that these owls feed mainly on small mammals, especially rodents. Owls from the riverbanks at Fazenda Santa Fé had a more diverse diet, preying mainly on rodents that typically inhabit riparian grasslands - Holochilus sciureus Wagner, 1842 - and forests - Hylaeamys megacephalus (Fischer, 1814) and Oecomys spp., which probably also occur in forest borders or clearings. On the other hand, owls from an agroecosystem at Fazenda Lago Verde preyed mostly on rodent species common in these agrarian fields, Calomys tocantinsi Bonvicino, Lima & Almeida, 2003. Additionally, we compared small mammal richness estimates based on the analysis of owl pellets with estimates from live-trapping in the same areas. Owl pellets revealed two rodent species undetected by live traps - Euryoryzomys sp. and Rattus rattus (Linnaeus, 1758) - and four rodent species were trapped, but not found in owl pellets - Oecomys roberti Thomas, 1904, Pseudoryzomys simplex (Winge, 1887), Rhipidomys ipukensis Rocha, B.M.A. Costa & L.P. Costa, 2011, and Makalata didelphoides (Desmarest, 1817). Traps yielded higher species richness, but these two methods complement each other for surveying small rodents.
RESUMO
We collected and analyzed 286 Barn owl, Tyto alba (Scopoli, 1769), pellets from two nests in different environments along the mid-Araguaia River in central Brazil. Our analyses revealed that these owls feed mainly on small mammals, especially rodents. Owls from the riverbanks at Fazenda Santa Fé had a more diverse diet, preying mainly on rodents that typically inhabit riparian grasslands - Holochilus sciureus Wagner, 1842 - and forests - Hylaeamys megacephalus (Fischer, 1814) and Oecomys spp., which probably also occur in forest borders or clearings. On the other hand, owls from an agroecosystem at Fazenda Lago Verde preyed mostly on rodent species common in these agrarian fields, Calomys tocantinsi Bonvicino, Lima & Almeida, 2003. Additionally, we compared small mammal richness estimates based on the analysis of owl pellets with estimates from live-trapping in the same areas. Owl pellets revealed two rodent species undetected by live traps - Euryoryzomys sp. and Rattus rattus (Linnaeus, 1758) - and four rodent species were trapped, but not found in owl pellets - Oecomys roberti Thomas, 1904, Pseudoryzomys simplex (Winge, 1887), Rhipidomys ipukensis Rocha, B.M.A. Costa & L.P. Costa, 2011, and Makalata didelphoides (Desmarest, 1817). Traps yielded higher species richness, but these two methods complement each other for surveying small rodents.
RESUMO
We collected and analyzed 286 Barn owl, Tyto alba (Scopoli, 1769), pellets from two nests in different environments along the mid-Araguaia River in central Brazil. Our analyses revealed that these owls feed mainly on small mammals, especially rodents. Owls from the riverbanks at Fazenda Santa Fé had a more diverse diet, preying mainly on rodents that typically inhabit riparian grasslands - Holochilus sciureus Wagner, 1842 - and forests - Hylaeamys megacephalus (Fischer, 1814) and Oecomys spp., which probably also occur in forest borders or clearings. On the other hand, owls from an agroecosystem at Fazenda Lago Verde preyed mostly on rodent species common in these agrarian fields, Calomys tocantinsi Bonvicino, Lima & Almeida, 2003. Additionally, we compared small mammal richness estimates based on the analysis of owl pellets with estimates from live-trapping in the same areas. Owl pellets revealed two rodent species undetected by live traps - Euryoryzomys sp. and Rattus rattus (Linnaeus, 1758) - and four rodent species were trapped, but not found in owl pellets - Oecomys roberti Thomas, 1904, Pseudoryzomys simplex (Winge, 1887), Rhipidomys ipukensis Rocha, B.M.A. Costa & L.P. Costa, 2011, and Makalata didelphoides (Desmarest, 1817). Traps yielded higher species richness, but these two methods complement each other for surveying small rodents.
RESUMO
Influence of three types of riparian vegetation on fluvial erosion control in Pantanos de Centla, Mexico. Wetlands constitute very important ecological areas. The aim of this study was to quantify the soil losses due to fluvial erosion from 2006 to 2008 in two riverbanks under three types of vegetal coverage dominated by Haematoxylum campechianum, Dalbergia brownei and Brachiaria mutica, in the Pantanos de Centla Biosphere Reserve, SE Mexico. The relationship between the texture, organic matter and pH of soils and soil losses was evaluated. We used erosion sticks to estimate soil losses in 18 plots (three plots per type, three vegetation types, two riverbanks). Soil loss decreased in this order: H. campechianum>B. mutica>D. brownie indicating that D. brownei scrubland has the most potential to retain soil. The higher erosive impact within H. campechianum sites can be related with the low density of these trees in the study areas, as we ll as the lack of association with other types of vegetation that could reinforce the rooting of the soil profile. Furthermore, soil losses in H. campechianum sites were dependent on soil texture. The soils under this type of vegetal coverage were mainly sandy, which are more vulnerable to the erosive action in comparison with fine textured soils or soils with higher clay content, like the ones found in D. brownei and B. mutica sites. Soil losses of 100 % in the second year ( B. mutica plots) can be attributed to the distribution of roots in the upper soil layer and also to livestock management along riverbanks. This study recognizes the importance of D. brownei scrublands in riverbank soil retention. Nevertheless it is necessary to consider the role of an entire vegetal community in future research. Rev. Biol. Trop. 57 (4): 1153-1163. Epub 2009 December 01.
En el presente trabajo se cuantificaron las pérdidas de suelo por erosión fluvial (2006-2008) en dos cauces ribereños con cobertura de Haematoxylum campechianum, Dalbergia brownei y Brachiaria mutica en la Reserva de la Biosfera Pantanos de Centla, SE de México. Se evaluó la relación entre la textura, materia orgánica y pH de los suelos con la pérdida de los mismos. Las pérdidas de suelo se estimaron en 18 parcelas con varillas de erosión. La principal tendencia de las pérdidas de suelo por tipo de cobertura vegetal se dio en el orden H. campechianum>B. mutica>D. brownei. El mayor impacto erosivo en sitios con H. campechianum se relacionó con la textura arenosa de los suelos y el grado de perturbación de los sitios (baja densidad de árboles, alta dispersión y falta de asociación con otros tipos de vegetación). Las pérdidas totales de suelo en parcelas con B. mutica al segundo año de estudio pueden relacionarse con la distribución superficial de las raíces de este pasto y con la actividad ganadera. Con este estudio se reconoce la importancia de los matorrales de D. brownei en la retención de suelos ribereños, sin embargo hay que considerar que la sola influencia de un tipo de cobertura vegetal puede no ser tan significativa como el papel de una comunidad vegetal, en la que su composición y densidad, así como su diversificación en morfología tenga un papel importante en la conservación de los suelos.