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

Abstract

Diurnal raptors show a wider distribution compared to other groups of birds including passerines, woodpeckers, and seriemas, but occur at lower-than-expected densities. Estimating the precise abundance is essential to achieve conservation goals but the methods used to estimate the populations of birds need to be appropriate to arrive at meaningful conclusions. We compared the two survey methods: roadside point count and strip transects, for estimating species richness and abundance of raptors in the arid landscape of Rajasthan. Roadside point counts and roadside strip transects were done on 50 transects between December 2019- February 2020 (with an average length of 20 km and a total distance of 3000 km) to assess the species richness and abundance of raptors. A total of 2954 observations of raptors belonging to 35 species were recorded using both methods. Mann Whitney U test result showed no significant difference in species richness and abundance estimates between both methods (p = 0.206). The point count method yielded a higher relative abundance of 2.79 individuals [10 km2]-1h-1 than the 1.90 individuals [10 km2]-1h-1 obtained during the strip transect. Also, the number of unidentified species were less for point counts. Extrapolation values indicated that both the methods do not differ much for the detection of unsampled species. The choice of survey method depends on the objectives of the study, but our results favor the use of point counts rather than strip transects to survey raptors in open habitats. The information generated from this study is expected to provide the most efficient method to study the abundance and distribution of raptors in similar landscapes.

Farmers’ perception of the ecosystem services provided by diurnal raptors in arid Rajasthan

“…In the hot arid region of Rajasthan, India, we have studied ( Tiwari et al, 2021 ; Tiwari et al, 2023 ) community of diurnal raptors ( Fig. 1 ).…”

Forest Management Practice Influences Bird Diversity in the Mid-Hills of Nepal

“…We calculated sample size-based rarefaction and extrapolation curves for all bird species from each of the two forest management types using the ‘iNEXT’ package [ 42 , 43 , 44 ]. We calculated bird diversity in each forest with Shannon’s diversity index using the ‘BiodiversityR’ package [ 45 ].…”

Sustaining Increasing Wintering Raptor Populations in Central Israel: A 38 Years Perspective

“…The census of raptor populations, as apex predators, is especially challenging because of their hunting behaviors in open vegetation and their lack of vocalizations on wintering grounds [11][12][13]. Moreover, it also occurs at lower than expected densities in comparison to other avian species [14]. Road transects allow to cover great distances, require minimal manpower, and large sample sizes can be obtained [13].…”

“…In a comparison of point counts versus road transects, researchers found an advantage to point counts in that a greater number of individuals were spotted and a larger number were identified to the species level [12,14,19]. However, they also discovered that there were no significant differences in species richness and abundance estimates.…”

“…It is a well-known bottleneck for migrating raptors and other soaring birds that circumvent the Mediterranean Sea to reach their wintering grounds in Africa in the autumn and return to their breeding grounds across Eurasia in the spring [1,2]. Despite the plethora of studies on migratory raptors worldwide (e.g., Spain [6], Italy [22], Poland [23], and India [14]), and locally in Israel [24][25][26][27], no sustained survey was conducted over the years in Israel. A limited survey of the wintering raptors in Israel was undertaken in the late 1980s [28], and since then, no surveys have been conducted, and none have persisted over a long period.…”