Recommendations for monitoring avian populations with point counts: a case study in southeastern Brazil (original) (raw)
Related papers
Diurnal and seasonal variability in bird counts in a forest fragment in southeastern Brazil
Revista Brasileira de Zoologia, 2008
Diurnal variation in detection can influence bird census results. I measured variation in daily and seasonal detections of birds in a forest fragment at Barreiro Rico ranch, Anhembi, state of São Paulo. Birds were recorded on transects of unlimited distance, sampled one day per month, dawn to dusk, between December 2000 and March 2001 (rainy season) and between May and August 2001 (dry season). Significant daily variation in detection occurred during the rainy season, with most detections between dawn and 9 h. In the dry season detections declined for total numbers of individuals and species and most detections occurred during late morning and mid afternoon. Detection patterns might reflect seasonal variation in bird behavior rather than seasonal variation in species composition.
2012
Due to rapid and continuous deforestation, recent bird surveys in the Atlantic Forest are following rapid assessment programs to accumulate significant amounts of data during short periods of time. During this study, two surveying methods were used to evaluate which technique rapidly accumulated most species (> 90% of the estimated empirical value) at lowland Atlantic Forests in the state of São Paulo, southeastern Brazil. Birds were counted during the 2008-2010 breeding seasons using 10-minute point counts and 10-species lists. Overall, point counting detected as many species as lists (79 vs. 83, respectively), and 88 points (14.7 h) detected 90% of the estimated species richness. Forty-one lists were insufficient to detect 90% of all species. However, lists accumulated species faster in a shorter time period, probably due to the nature of the point count method in which species detected while moving between points are not considered. Rapid assessment programs in these forests will rapidly detect more species using 10-species lists. Both methods shared 63% of all forest species, but this may be due to spatial and temporal mismatch between samplings of each method.
The use of the point count method for bird survey in the Atlantic forest
Zoologia, 2009
The point count method has been widely used in tropical forest for sampling bird communities. In the present study, we investigated if data on richness and abundance acquired using the point count method are different comparing spring/summer (breeding season) and fall/winter (non-breeding season) in three types of the Brazilian Atlantic forest. Twelve sites were sampled seasonally during one year. In general we recorded more species and individuals during the breeding seasons. However, bird communities vary seasonally among the forest types and functional groups. We demonstrate that the use of point counts in tropical forest should be adjusted considering the differences in forest types and feeding guilds.
2008
Resumen. -Influencia del horario, tiempo de duración y número de puntos de conteo de aves en el Bosque Atlántico del Paraguay. -Puntos de conteo de 10 o 20 min de duración se han utilizado para prospectar comunidades de aves del Bosque Atlántico Neotropical. Sin embargo, los factores que afectan la eficiencia del método aún no han sido evaluados para un diseño de muestreo efectivo. En este trabajo, se evalúa la influencia de varios factores que intervienen con puntos de conteo de distancia ilimitada, en una comunidad de aves en época reproductora en el Parque Nacional de San Rafael, Paraguay. Los conteos de 20 min se dividen en cuatro intervalos de 5 min, desarrollados desde 30 min antes del amanecer hasta 3 h después, siendo cada punto censado varias veces durante la estación. El número total de individuos y especies detectadas por conteo varía significativamente, siendo máximo en la primera hora después del amanecer. Sin embargo, algunas especies difieren del patrón de detección. Un 87% y 93% de las especies son detectadas en los primeros 5 y 10 min de conteo, respectivamente, pero el número de especies detectadas por primera vez es tres veces mayor durante los primeros 5 min, que en intervalos posteriores. Se observa una disminución significativa de detecciones en los dos últimos intervalos de conteo. El número de especies se incrementa con cada conteo adicional en determinado punto, pero este rango disminuye después de la cuarta visita. Sugerimos que conteos de 10 min de duración son suficientes para muestrear esta comunidad de aves, y que cuatro visitas a un punto de conteo son necesarias, pero deben realizarse a diferentes horas de la mañana para cubrir la variabilidad de actividad de las distintas especies.
Diversity
The effects of forest degradation, fragmentation, and climate change occur over long time periods, yet relatively few data are available to evaluate the long-term effects of these disturbances on tropical species occurrence. Here, we quantified changes in occupancy of 50 bird species over 17 years on Barro Colorado Island (BCI), Panama, a model system for the long-term effects of habitat fragmentation. The historical data set (2002–2005) was based on point counts, whereas the contemporary data set (2018) was based on acoustic monitoring. For most species, there was no significant change in occupancy; however, the occupancy of four species (Tinamus major, Polioptila plumbea, Myiarchus tuberculifer, and Ceratopipra mentalis) increased significantly, and the occupancy of three species (Saltator grossus, Melanerpes pucherani, and Cyanoloxia cyanoides) decreased significantly. Forest age explained the majority of occupancy variation and affected the occupancy of more bird species than su...
New approaches to the analysis of population trends in land birds
1996
Although there is strong evidence that a few Neotropical migrant land birds have severely declining populations, we know of no evidence of general overall declines. One widely cited analysis of data from the Breeding Bird Survey (BBS), the only continental-scale monitoring program for land birds in the breeding season, indicates declining populations in eastern forests in the 1980s, but other analyses conclude that most species have had stable or increasing populations in the last 25 yr. These conflicting results call for a new perspective. Here, we propose two approaches to the analysis of BBS data that emphasize the detection of temporal and geographic variation in population trends. The first approach uses nonlinear regression to detect temporal changes in population trends, and permits the construction of graphs that compare nonlinear trends among regions. The second approach provides statistical tests of multispecies patterns of geographic variation in population trends. We report analyses of BBS data for 1966 to 1992 for the 26 species of wood warblers (Parulinae) for which the most data are available and the chance of obtaining reliable estimates is best. Using pooled data for all 26 species for eastern and central North America, nonlinear regression indicated declining populations in the Appalachian Mountains and the Eastern Foothills in the 1970s, and stability elsewhere. As examples of the use of this first approach in single-species analyses, we give maps, graphs, and statistical tests to illustrate variation in population trends by physiographic strata in the Blue-winged Warbler (Vermivora pinus) and the Ovenbird (Seiurus aurocapillus). As an example of the second approach, we applied a probit-normal model to a matrix of increases and decreases in the 26 species in 37 geographic strata. The analysis identified specific highland areas as having unusually high proportions of declining populations. These results suggest that correlates of elevation should be considered as factors possibly regulating populations of warblers and other land birds. Our perspective is that focus on studies of temporal and geographic variation in population trends of all birds, including Neotropical migrants, could help conservation biologists identify where species and groups of species are in the most trouble.
Zenodo (CERN European Organization for Nuclear Research), 2020
Population size is a key predictor of extinction risk and is critical to listing species in IUCN threat categories. Assessing population size can be particularly difficult for gregarious species, such as parrots-one of the most threatened bird families-whose ecology and behavior generate multiple sources of uncertainty that need to be addressed in monitoring efforts. To improve estimates of abundance for the endangered Vinaceous-breasted Parrot (Amazona vinacea), we combined extensive roost counts over the global range of the species (Argentina, Paraguay, Brazil) with an intensive regional survey designed to address five sources of uncertainty about parrot abundance in western Santa Catarina state (WSC), Brazil, in 2016 and 2017. We estimated abundance at both regional and whole-range scales using N-mixture models of replicated count data, which account for imperfect detection. The regional-scale estimate was 1,889 ± 110 and 1,872 ± 37 individuals for 2016 and 2017, respectively; global abundance was estimated at 7,795 ± 260 and 8,492 ± 276 individuals for the same two years. We found no statistical evidence of population change at either scale of the analysis. Although our assessments of abundance and geographic range are larger than those currently reported by the IUCN, we suggest the Vinaceous-breasted Parrot should remain in the 'Endangered' IUCN threat category pending further investigation of population trends. We recommend that roost-monitoring programs for parrots consider and address sources of uncertainty through adequate field protocols and statistical analyses, to better inform assessments of population size, trends, and threat status.
Biota Neotropica
Determining the relative risks of extinction of declining taxa is important to delineate conservation priorities and to guide the investments in conservation. Brazil concentrates the greatest number of endangered avian taxa on Earth, yet demographic information is lacking for most of them. Here we present distance-sampling population density estimates for three endangered bird taxa endemic to the Pernambuco Endemism Center (PEC), the most critically disturbed Atlantic Forest region. The analyzed taxa were the White-shouldered Antshrike Thamnophilus aetiops distans (Endangered), the Brown-winged Mourner Schiffornis turdina intermedia (Vulnerable), and the White-bellied Tody-tyrant Hemitriccus griseipectus naumburgae (Vulnerable). The estimated numbers of individuals/ha in an approximately 1,000 ha forest fragment were 0.21, 0.14, and 0.73, respectively. Our findings corroborated the premise that even taxa classified in similar threat categories based on habitat characteristics alone ...