Raptor assemblages in grasslands of Southern Brazil: species richness and abundance and the influence of the survey method

Abstract

Background: Raptor distributions and abundances are poorly known in southern Brazil. Given that raptors have low population densities, methods typically applied to census birds are usually inappropriate for surveying raptors. Roadside surveys allow large areas to be searched at a relatively low cost and are often applied to count raptors. We conducted eight paired roadside surveys (roadside point transects and roadside strip transects of 54.5~58.6 km long) to assess the species richness and abundance of raptors in two grassland landscapes of southern Brazil and to compare results of the two methods. −1 · h −1 ). No significant differences were found in relation to species richness, although five species were exclusively recorded with point transects versus one with strip transects. Conclusions: Roadside point transects may reduce bias due to differences in species detection caused by habitat features and in abundance estimates resulting from survey habitat being disproportional to their availability. Point counts may enhance the quality of the search for raptors in a surveyed area, increasing the detection probability. The choice of survey method depends on the objectives of the study, but our results favor the use of point transects rather than strip transects to survey raptors in open landscapes.

Comparison of point and roadside transect methods to evaluate the abundance and richness of diurnal raptors in the arid region of Rajasthan

“…This is a common method to study raptors, affording access to most habitats, landscape features, and larger areas at a relatively low cost [ 10 , 12 ]. Roadside strip transects are useful to study the raptor distribution [ 13 ], relative abundance and assemblage [ 14 , 15 ], composition and diversity [ 16 ], and habitat use and preferences at a broad scale [ 10 , 12 , 17 , 18 ]. They have been extensively used, especially in areas where information related to raptor ecology is very scarce.…”

Comparison of Diurnal Birds of Prey Community Between Natural and Anthropized Environments in Highland Grasslands of Rio Grande Do Sul, Brazil

“…In the state of Rio Grande do Sul, 64 species have already been recorded: 35 are represented by eagles or hawks, 11 by falcons, 14 by owls, and four by vultures (Franz et al 2018). Among the diurnal species that inhabits open fields, 23 have already been recorded in the highland grasslands of Rio Grande do Sul (Voss et al 1998, Petersen et al 2011, Zilio et al 2013, Chiarani & Fontana 2019, WikiAves 2019. It is important to say that some of them depend exclusively on these environments, not tolerating drastic changes due to anthropogenic changes (Bencke et al 2003).…”

Population Dynamics and Distribution Patterns of Diurnal Raptors in Northeastern Algeria: Seasonal Variation and Some Nesting Characteristics

“…Apart from the rudimentary censuses performed by Moali and Gaci (1992) and Moali and Isenman (1990), birds of prey, however, have been carried out by a relatively few biologists who only documented the dietary and nesting characteristics of only some single species (as in Souttou et al, 2006Souttou et al, , 2007Telailia et al, 2013). Hence, there have been no attempts to describe spatial ecology and raptor community composition in detail comparable to those of raptor researchers around the world (see Thiollay 1977aThiollay , b, 1989Thiollay , 2007Piana, Marsden, 2012;Zilio et al, 2013).…”