Avian diversity along a precipitation gradient in southern Africa
In April 2013, a transect c. 1100 km long with 100 points arranged in 5 sections was designed in northern Namibia between Ruacana Watefall (W) and Kongola (E) to study avian diversity in relation to gradual changes in precipitation (c.350 mm in W to c.600 mm in E). In total, 81 bird species were recorded in all 100 points, but in particular section, the numbers were low, ranging from 22 to 38 species. In overall, the most frequent and most numerous (dominant) were the following species: Cape Turtle Dove, Blue Waxbill, Grey-headed Sparrow, Laughing Dove and Fork-tailed Drongo. Together they comprised 42.2% of all individuals recorded. All of them, except for the Fork-tailed Drongo, were granivores. Only nine species were recorded in ten or more points. Besides the above-mentioned dominant species, the following other were in this group: Black-chested Prinia, Black-throated Canary, Pied Crow and White-browed Scrub Robin. In particular section the number of dominant species ranged from 5 to 7, without a gradient. Two species, the Cape Turtle Dove and Blue Waxbill, remained dominant in all five sections. The Laughing Dove and Fork-tailed Drongo – in four sections, and the Grey-headed Sparrow – in three sections. Although, no gradient in species diversity, evenness, and dominance structure was recorded, significant differences between two most western and two most eastern sections were apparent. Two species were more frequent and numerous in the eastern than in the western sections: White-browed Scrub Robin and Cape Turtle Dove; while the following species were more frequent and numerous in the western than the eastern sections: African Palm Swift, Black-chested Prinia, Black-throated Canary, Blue Waxbill, Grey-headed Sparrow and Pied Crow.
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