863 resultados para farmland birds
Resumo:
Birds of prey forage over large areas and so might be expected to accumulate contaminants which are elevated but heterogeneously distributed in the general environment. The aim of this study was to test the hypothesis that arsenic levels in raptors from a region with elevated environmental arsenic concentrations were higher than those in birds from an uncontaminated part of Britain. Arsenic concentrations in the liver, kidney and muscle of kestrels, Falco tinnunculus, sparrowhawks, Accipiter nisus, and barn owls, Tyto alba, from south-west (SW) England, an area with naturally and anthropogenically (through mining) elevated environmental arsenic concentrations, were compared with those in birds from SW Scotland, where no such geochemical anomaly exists. Arsenic residues in kestrels from SW England were approximately three times greater than those in birds from SW Scotland for the three tissue types analysed. This was not the case for the other species in which arsenic residues were similar in birds from both regions. It is suggested that differences between species in both diet and arsenic metabolism could explain why kestrels have elevated arsenic tissue burdens in response to general environmental contamination but sparrowhawks and barn owls do not.
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The bones (humerus and/or femur) of 229 birds of prey from 11 species were analyzed for Pb and As to evaluate their exposure to Pb shot. The species with the highest mean Pb levels were red kite (Milvus milvus) and Eurasian griffon (Gyps fulvus), and the species with the lowest levels were Eurasian buzzard (Buteo buteo) and booted eagle (Hieraaetus pennatus). Red kite also had the highest mean As level, an element present in small amounts in Pb shot. Elevated bone Pb concentrations (>10 microg/g dry weight) were found in 10 birds from six species. Clinical signs compatible with lethal Pb poisoning and/or excessive bone Pb concentrations (>20 microg/g) were observed in one Eurasian eagle-owl (Bubo bubo), one red kite, and one Eurasian griffon. Pb poisoning has been diagnosed in eight upland raptor species in Spain to date.
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The greatest common threat to birds in Madagascar has historically been from anthropogenic deforestation. During recent decades, global climate change is now also regarded as a significant threat to biodiversity. This study uses Maximum Entropy species distribution modeling to explore how potential climate change could affect the distribution of 17 threatened forest endemic bird species, using a range of climate variables from the Hadley Center's HadCM3 climate change model, for IPCC scenario B2a, for 2050. We explore the importance of forest cover as a modeling variable and we test the use of pseudo-presences drawn from extent of occurrence distributions. Inclusion of the forest cover variable improves the models and models derived from real-presence data with forest layer are better predictors than those from pseudo-presence data. Using real-presence data, we analyzed the impacts of climate change on the distribution of nine species. We could not predict the impact of climate change on eight species because of low numbers of occurrences. All nine species were predicted to experience reductions in their total range areas, and their maximum modeled probabilities of occurrence. In general, species range and altitudinal contractions follow the reductive trend of the Maximum presence probability. Only two species (Tyto soumagnei and Newtonia fanovanae) are expected to expand their altitude range. These results indicate that future availability of suitable habitat at different elevations is likely to be critical for species persistence through climate change. Five species (Eutriorchis astur, Neodrepanis hypoxantha, Mesitornis unicolor, Euryceros prevostii, and Oriola bernieri) are probably the most vulnerable to climate change. Four of them (E. astur, M. unicolor, E. prevostii, and O. bernieri) were found vulnerable to the forest fragmentation during previous research. Combination of these two threats in the future could negatively affect these species in a drastic way. Climate change is expected to act differently on each species and it is important to incorporate complex ecological variables into species distribution models.
Resumo:
For many years, orientation in migratory birds has primarily been studied in the laboratory. Although a laboratory-based setting enables greater control over environmental cues, the laboratory-based findings must be confirmed in the wild in free-flying birds to be able to fully understand how birds orient during migration. Despite the difficulties associated with following free-flying birds over long distances, a number of possibilities currently exist for tracking the long distance, sometimes even globe-spanning, journeys undertaken by migrating birds. Birds fitted with radio transmitters can either be located from the ground or from aircraft (conventional tracking), or from space. Alternatively, positional information obtained by onboard equipment (e.g., GPS units) can be transmitted to receivers in space. Use of these tracking methods has provided a wealth of information on migratory behaviors that are otherwise very difficult to study. Here, we focus on the progress in understanding certain components of the migration-orientation system. Comparably exciting results can be expected in the future from tracking free-flying migrants in the wild. Use of orientation cues has been studied in migrating raptors (satellite telemetry) and thrushes (conventional telemetry), highlighting that findings in the natural setting may not always be as expected on the basis of cage-experiments. Furthermore, field tracking methods combined with experimental approaches have finally allowed for an extension of the paradigmatic displacement experiments performed by Perdeck in 1958 on the short-distance, social migrant, the starling, to long-distance migrating storks and long-distance, non-socially migrating passerines. Results from these studies provide fundamental insights into the nature of the migratory orientation system that enables experienced birds to navigate and guide inexperienced, young birds to their species-specific winter grounds.
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The recent growth in bioenergy crop cultivation, stimulated by the need to implement measures to reduce net CO emissions, is driving major land-use changes with consequences for biodiversity and ecosystem service provision. Although the type of bioenergy crop and its associated management is likely to affect biodiversity at the local (field) scale, landscape context and its interaction with crop type may also influence biodiversity on farms. In this study, we assessed the impact of replacing conventional agricultural crops with two model bioenergy crops (either oilseed rape Brassica napus or Miscanthus × giganteus) on vascular plant, bumblebee, solitary bee, hoverfly and carabid beetle richness, diversity and abundance in 50 sites in Ireland. We assessed whether within-field biodiversity was also related to surrounding landscape structure. We found that local- and landscape-scale variables correlated with biodiversity in these agricultural landscapes. Overall, the differences between the bioenergy crops and the conventional crops on farmland biodiversity were mostly positive (e.g. higher vascular plant richness in Miscanthus planted on former conventional tillage, higher solitary bee abundance and richness in Miscanthus and oilseed rape compared with conventional crops) or neutral (e.g. no differences between crop types for hoverflies and bumblebees). We showed that these crop type effects were independent of (i.e. no interactions with) the surrounding landscape composition and configuration. However, surrounding landscape context did relate to biodiversity in these farms, negatively for carabid beetles and positively for hoverflies. Although we conclude that the bioenergy crops compared favourably with conventional crops in terms of biodiversity of the taxa studied at the field scale, the effects of large-scale planting in these landscapes could result in very different impacts. Maintaining ecosystem functioning and the delivery of ecosystem services will require a greater understanding of impacts at the landscape scale to ensure the sustainable development of climate change mitigation measures.
Resumo:
In eight European study sites (in Spain, Ireland, Netherlands, Germany, Poland, Estonia and Sweden), abundance of breeding farmland bird territories was obtained from 500 × 500 m survey plots (30 per area, N = 240) using the mapping method. Two analyses were performed: (I) a Canonical Correspondence Analysis of species abundance in relation to geographical location and variables measuring agricultural intensification at field and farm level to identify significant intensification variables and to estimate the fractions of total variance in bird abundance explained by geography and agricultural intensification; (II) several taxonomic and functional community indices were built and analysed using GLM in relation to the intensification variables found significant in the CCA. The geographical location of study sites alone explains nearly one fifth (19. 5%) of total variation in species abundance. The fraction of variance explained by agricultural intensification alone is much smaller (4. 3%), although significant. The intersection explains nearly two fifths (37. 8%) of variance in species abundance. Community indices are negatively affected by correlates of intensification like farm size and yield, whereas correlates of habitat availability and quality have positive effects on taxonomic and functional diversity of assemblages. Most of the purely geographical variation in farmland bird assemblage composition is associated to Mediterranean steppe species, reflecting the bio-geographical singularity of that assemblage and reinforcing the need to preserve this community. Taxonomic and functional diversity of farmland bird communities are negatively affected by agricultural intensification and positively affected by increasing farmland habitat availability and quality. © 2011 Springer Science+Business Media B.V.
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Birds are capable of true navigation, the ability to return to a known goal from a place they have never visited before. This is demonstrated most spectacularly during the vast migratory journeys made by these animals year after year, often between continents and occasionally global in nature. However, it remains one of the great unanswered questions in science, despite more than 50 years of research in this field. Nevertheless, the study of true navigation in birds has made significant advances in the previous 20 years, in part thanks to the integration of many disciplines outside its root in behavioural biology, to address questions of neurobiology, molecular aspects, and the physics of sensory systems and environmental cues involved in bird navigation, often involving quantum physics. However, true navigation remains a controversial field, with many conflicting and confusing results making interpretation difficult, particularly for those outside or new to the field. Unlike many general texts on migration, which avoid discussion of these issues, this review will present these conflicting findings and assess the state of the field of true navigation during bird migration.
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On 25 April 1998 part of the tailings pond dike of the Aznalcollar Zn mine north of the Guadalquivir marshes (Donana) in southern Spain collapsed releasing an estimated 5 million m3 of acidic metal-rich waste. This event contaminated farmland and wetland up to >40 km downstream, including the 900-ha 'Entremuros', an important area for birds within the Donana world heritage site. In spite of the contamination, birds continued to feed in this area. Samples of two abundant macrophytes (Typha dominguensis and Scirpus maritimus) were taken from the Entremuros and nearby uncontaminated areas; these plants are important food items for several bird species. Analyses showed that in the Entremuros mean plant tissue concentrations of Cd were 3-40-fold (0.8-7.4 ppm) and Zn 20-100-fold (20-3384 ppm) greater than those from control areas. Comparable dietary concentrations of Zn have been reported to cause severe physiological damage to aquatic birds under experimental conditions. Elevated Cd concentrations are of concern as Cd bioconcentrates and is a cumulative poison. Metals released in this accident are moving into this food-chain and present a considerable risk to species feeding on Typha sp. and Scirpus sp. Many other food-webs exist in this area and require detailed examination to identify the species at risk, and to facilitate the management of these risks to minimise future impacts to the wildlife of Donana. Copyright (C) 1999 Elsevier Science Ltd.
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This document contains notes on eight species of birds observed by Arthur T. Wayne in Charleston, South Carolina including the Horned Grebe, the Yellow-crowned Night Heron, Bachman’s Warbler, the Rocky Mountain Orange-crowned Warbler, the Cape May Warbler, the Black-poll Warbler, the Red-breasted Nuthatch, and the Blue-gray Gnatcatcher.
Resumo:
This document contains notes on seven species of birds observed by Arthur T. Wayne in Charleston, South Carolina including the Yellow-bellied Flycatcher, the Purple Martin, the Black-throated Blue Warbler, Cairn’s Warbler, Grinnell’s Water-Thrush, the Kentucky Warbler, and the Mockingbird.