Year-to-year changes in population density and site fidelity of psittaciform, coraciiform and piciform species in an acacia savanna, north-central Namibia
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Abstract
Background: Bird species belonging to the orders of Coraciiformes, Psittaciformes and Piciformes may be regarded as good indicators of environmental quality. Since most species are fairly large and have distinctive plumage colouration, they attract human attention. Most of them are also strongly territorial and vocally conspicuous. However, not much is known about their population densities and virtually nothing about interannual population changes.
Objectives: The aims of this study were to: 1) estimate population densities; 2) assess interannual variations in population densities; 3) study site fidelity; 4) find preferences (or their lack) for natural or man-modified savanna of all coraciiform, piciform and psittaciform species breeding in a mosaic of natural and man-modified savanna; and 5) compare population densities of all these species recorded in the study area with those obtained in other regions of southern Africa.
Methods: Population densities of coraciiform, psittaciform and piciform species were assessed by means of the territory mapping method in an acacia savanna in the Cuvelai Drainage System, north-central Namibia. Studies were carried out in three separate years: 2012, 2017 and 2020.
Results: In total, 15 species representing these orders were recorded as breeding in the study plot (400 ha). In 2020, all three parrot species, namely Meyer’s Parrot (Poicephalus meyeri), Rüppell’s Parrot (P. rueppellii), and Rosy-faced Lovebird (Agapornis roseicollis), nested in a similar density of 0.50–0.75 pairs per 100 ha. The African Hoopoe (Upupa epops) was the most abundant coraciiform species reaching a density of 3.3 pairs per 100 ha in 2017. The second most abundant coraciiform species was the Lilac-breasted Roller (Coracias caudatus), which population increased from 0.5 pairs per 100 ha in 2012 to 1.4 pairs per 100 ha in 2020. Among the other coraciiform species, only the Common Scimitar-bill (Rhinopomastus cyanomelas) reached a density higher than one pair per 100 ha, in 2017. Among piciform species the most abundant was the Acacia Pied Barbet (Tricholaema leucomelas; up to 2.5 pairs per 100 ha).
Conclusion: Contrary to expectation, for most species and species groups studied, their population densities were negatively related to the precipitation. No other species of this order reached a density higher than 1 pair per 100 ha in any year. These population densities are compared with those obtained in 10 sites in Namibia and the South African Highveld. Lilac-breasted Roller, Common Scimitarbill, parrots and hornbills showed high, while barbets showed low site fidelity.
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