Assessing strategies to reconcile agriculture and bird conservation in the temperate grasslands of South America.

Globally, agriculture is the greatest source of threat to biodiversity, through both ongoing conversion of natural habitat and intensification of existing farmland. Land sparing and land sharing have been suggested as alternative approaches to reconcile this threat with the need for land to produce food. To examine which approach holds most promise for grassland species, we examined how bird population densities changed with farm yield (production per unit area) in the Campos of Brazil and Uruguay. We obtained information on biodiversity and crop yields from 24 sites that differed in agricultural yield. Density-yield functions were fitted for 121 bird species to describe the response of population densities to increasing farm yield, measured in terms of both food energy and profit. We categorized individual species according to how their population changed across the yield gradient as being positively or negatively affected by farming and according to whether the species' total population size was greater under land-sparing, land-sharing, or an intermediate strategy. Irrespective of the yield, most species were negatively affected by farming. Increasing yields reduced densities of approximately 80% of bird species. We estimated land sparing would result in larger populations than other sorts of strategies for 67% to 70% of negatively affected species, given current production levels, including three threatened species. This suggests that increasing yields in some areas while reducing grazing to low levels elsewhere may be the best option for bird conservation in these grasslands. Implementing such an approach would require conservation and production policies to be explicitly linked to support yield increases in farmed areas and concurrently guarantee that larger areas of lightly grazed natural grasslands are set aside for conservation.

Distribución y densidad de la avifauna de la Península de Osa, Costa Rica (1990-1991) / Distribution and density of the avifauna of the Osa Peninsula, Costa Rica (1990-1991)

Distribution and density of avifauna in Península de Osa, Costa Rica (1990-1991). We recorded 205 bird species at the Península de Osa. The geographical distribution of most forest bird species within the peninsula is discontinuous (e.g., Corapipo altera and Tangara guttata), even within large forest tracts, indicating the adaptation of species to particular habitats, microhabitats, strata and/or diet within the forest. Birds use the forest strata in different proportion resulting in three different patterns: understory birds (e.g., Arremon aurantiirostris and Habia atrimaxillaris), supdosel birds (e.g., Cacicus uropygialis and Euphonia imitans), and birds that use several strata in similar proportion (e.g., Dendrocincla anabatina). Most of these forest birds feed upon insects and fruits. The density and relative abundance is very low for most species, with more than 90% of the species having less than an individual per hectare or kilometer of transect. These characteristics make this avifauna highly susceptible to deforestation and forest fragmentation. Rev. Biol. Trop. 57 (Suppl. 1): 323-332. Epub 2009 November 30.

Observamos 205 especies de aves en la Península de Osa. La distribución geográfica de la mayoría de las especies de bosque en la península es discontinua (e.g., Corapipo altera y Tangara guttata), aún dentro de grandes áreas de bosque continuo, lo cual indica la posible adaptación de las especies a habitats, microhabitats, estratos y dietas particulares dentro del bosque. Las aves utilizan los estratos del bosque en diferente proporción lo que resulta en tres diferentes patrones: aves de sotobosque (e.g., Arremon aurantiirostris y Habia atrimaxillaris), aves de subdosel (e.g., Cacicus uropygialis y Euphonia imitans) y aves que utilizan diferentes estratos en similar proporción (e.g., Dendrocincla anabatina). La mayoría de estas especies de bosque se alimentan de insectos y frutos. La densidad y la abundancia relativa son muy bajas para la mayoría de las especies, con más de 90% de las especies con menos de un individuo por hectárea o kilómetro de transecto recorrido. Este conjunto de características hacen que esta avifauna sea muy sensible a la destrucción y fragmentación del bosque.

Effect of bird density on the decision to join a group in the Sicalis flaveola pelzeni (Passeriformes, Emberizidae)

A change in bird density within a captive flock of Sicalis flaveola pelzeni (Sclater, 1872) affected the decision to join a group. Ruling out inter-individual differences and maintaining constant the size of a food patch, birds were found to fly more often to the food source and spend a longer time in its environs when kept in greater groups.

Effect of bird density on the decision to join a group in the Sicalis flaveola pelzeni (Passeriformes, Emberizidae)

A change in bird density within a captive flock of Sicalis flaveola pelzeni (Sclater, 1872) affected the decision to join a group. Ruling out inter-individual differences and maintaining constant the size of a food patch, birds were found to fly more often to the food source and spend a longer time in its environs when kept in greater groups.

Desempenho de frangos de corte criados em diferentes densidades populacionais, no inverno, no Sul do Brasil

The objective of this research was to determine the influence of the bird density: 10, 12, 14 and 16 birds/square meters on broilers performance, during winter time. After 21 days, the feed consumption was affected by different densities. The highest feed consumption was found on the lowest bird density (10 birds/square meters). The body weight was influenced by the density after 35 days. The lowest body weight was obtained on the highest density (16 birds/square meters). However, the carcass yield was not affected by density. The feed conversion was not affected significantil, When the body weight was reduced, the food intake was decreased too. The viability was not influencied by the densities. The economic analysis concluded that a linear benefit was found in increasing the bird density by 10 to 16 birds/square meters.

O trabalho teve por objetivo determinar a influência da densidade de 10, 12, 14 e 16 aves/m² no desempenho de frangos de corte, durante a época de inverno. Aos 21 dias, já ocorreram diferenças de consumo, sendo o maior para as aves criadas na menor densidade (10 aves/m²). O peso corporal foi influenciado pela densidade a partir dos 35 dias; o menor peso foi das aves com maior densidade, mas, não foi verificada influência sobre as características de carcaça avaliadas. A conversão alimentar não sofreu grandes variações, pois sempre que houve redução no peso corporal observou-se redução no consumo alimentar. A viabilidade criatória não foi influenciada pelas densidades avaliadas. Através de análise econômica, concluiu-se que houve benefício econômico linear com o aumento da densidade de 10 para 16 aves/m².

Desempenho de frangos de corte criados em diferentes densidades populacionais, no inverno, no Sul do Brasil

The objective of this research was to determine the influence of the bird density: 10, 12, 14 and 16 birds/square meters on broilers performance, during winter time. After 21 days, the feed consumption was affected by different densities. The highest feed consumption was found on the lowest bird density (10 birds/square meters). The body weight was influenced by the density after 35 days. The lowest body weight was obtained on the highest density (16 birds/square meters). However, the carcass yield was not affected by density. The feed conversion was not affected significantil, When the body weight was reduced, the food intake was decreased too. The viability was not influencied by the densities. The economic analysis concluded that a linear benefit was found in increasing the bird density by 10 to 16 birds/square meters.

O trabalho teve por objetivo determinar a influência da densidade de 10, 12, 14 e 16 aves/m² no desempenho de frangos de corte, durante a época de inverno. Aos 21 dias, já ocorreram diferenças de consumo, sendo o maior para as aves criadas na menor densidade (10 aves/m²). O peso corporal foi influenciado pela densidade a partir dos 35 dias; o menor peso foi das aves com maior densidade, mas, não foi verificada influência sobre as características de carcaça avaliadas. A conversão alimentar não sofreu grandes variações, pois sempre que houve redução no peso corporal observou-se redução no consumo alimentar. A viabilidade criatória não foi influenciada pelas densidades avaliadas. Através de análise econômica, concluiu-se que houve benefício econômico linear com o aumento da densidade de 10 para 16 aves/m².