In Nahuel Huapi National Park in southwestern Argentina, livestock and exotic deer pose important management problems. Due to the economic and social benefits of sport hunting and production of livestock, it is politically impractical to completely eradicate these animals from the park. Instead, park managers attempt to minimize the effects of these introduced animals by preventing their spread into more pristine parts of the park and by trying to diminish their population densities. Managers are also promoting the relocation of livestock production to appropriate sites in the National Reserve part of the park where livestock raising is permitted. Detailed information on the ecological impacts of introduced herbivores is needed both to guide management of the different vegetation types of the park and to support the park managers' public relations campaign justifying exotic animal control. We examined the ecological effects of introduced animals along the vegetation gradient from Andean rain forests through xeric woodlands to the Patagonian steppe. We sampled 30 stands for floristic composition and structure, assessed browse intensity, and compared stands of similar abiotic habitat but of different browsing regimes. Deer and livestock have significantly altered floristic composition and stand structure along this gradient. They impair tree regeneration and pose a long‐term threat to the continued existence of a forest cover.

The traffic load near large cities may show dramatic cyclical changes induced by weekend tourism, and this could induce cyclical changes in the activity patterns of wildlife. We studied a 19-km-long section of a road that crossed a high-use raptor area near a large city in Spain. We observed 18 raptor species along this segment of the road, including some threatened species, such as the Spanish Imperial Eagle (Aquila adalberti). The number of cars increased dramatically on Saturdays and Sundays, so we assessed the effect of varying traffic loads on raptor behavior by recording all birds of prey as close or distant to the road during working days and weekend days. On weekends, the occurrence of Spanish Imperial Eagles and vultures decreased near the road. The occurrence of other species did not change between working days and weekend days. The activity decrease on weekends by Imperial Eagles and other large raptors suggests that there are weekly cycles in raptor activity. Weekly cycles in wildlife caused by human activity are a source of concern in conservation biology. Efecto del Tráfico de Fin de Semana sobre el Uso de Espacio por Rapaces Resumen: El tráfico en carreteras cercanas a las grandes urbes muestra incrementos cíclicos debidos al turismo de fin de semana, lo que podría inducir ciclos semanales en los patrones de actividad de las aves de presa. Cerca de una gran ciudad estudiamos una sección de 19 Km en una carretera que cruza una de las mejoresáreas para las rapaces de toda España. Observamos 18 especies de rapaces en elárea de estudio, incluyendo varias en peligro de extinción, como eláguila imperial ibérica (Aquila adalberti), una de las rapaces en mayor peligro de extinción del mundo. Registramos los movimientos de todas las rapaces observadas en una malla de cuadrículas UTM clasificadas como cercanas o lejanas a la carretera para estudiar si las observaciones de rapaces eran diferentes en días de semana y en fines de semana, dado que hubo un incremento muy marcado en la intensidad de tráfico los fines de semana. Comprobamos que eláguila imperial y los buitres utilizaban con menor frecuencia las inmediaciones de la carretera durante los fines de semana, restringiendo su actividad a lasáreas remotas y poco transitadas. Los cambios cíclicos en actividad humana durante los fines de semana podrían por tanto inducir también cambios cíclicos en los patrones de actividad † †Current address: Instituto de Agrobiotecnología y Recursos Naturales, Consejo Superior de Investigaciones Cientificas, Carretera Disturbance of Raptors by Road Traffic 727de especies amenazadas como eláguila imperial. Los ciclos semanales de actividad en la fauna tienen mucho interés para la biología de la conservación, ya que son consecuencia de la actividad humana.

Summary 1.Great bustards Otis tarda are globally endangered and 50% of the world population now occurs in agro-steppe habitats in Spain. An understanding of the relationship between land use and the species' habitat requirements is necessary to predict the consequences of land-use change on this declining species. 2. A 2-year study of great bustard substrate preferences was conducted in a large region in central Spain where most cereals are still cultivated in a traditional 2-year rotation. 3. Great bustards showed year-round selection of stubble fields, but avoided ploughed and uncultivated areas. Other substrate types were variously selected, avoided or used in proportion to availability depending on season. Patterns were consistent over 2 years. 4. Human artefacts such as roads, tracks and powerlines were avoided. 5. Variables correlating with flock locations could not discriminate between occupied and unoccupied but apparently suitable areas of traditionally managed cereal steppe. This suggests that great bustard distribution in central Spain is not limited by inappropriate land use in steppe areas. 6. The evidence suggests that great bustards show fidelity to sites regardless of the availability of suitable habitat elsewhere. Settlement patterns are probably determined by the presence of conspecifics rather than habitat cues. This result demonstrates the value of integrating observations of habitat use with knowledge of species' behaviour in order to understand distribution more fully. 7. We propose that conservation efforts should be directed towards securing traditional lek sites and we make three recommendations: first all great bustard lek sites should be identified; secondly, existing European Union legislation should be used to protect these and to ensure that compatible land management practices are applied or maintained; and finally, research programmes should be conducted that aim to enhance the conservation value of stubble fields rather than simply demonstrate their selection.

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