Abundance and community structure of birds breeding in Kalahari woodland used as rangeland

Study Extent

The study was conducted in the Sachinga Livestock Development Centre of the Ministry of Agriculture of the Namibian Government. The centre is situated in NE Namibia, in the Zambezi region, about 40 km west of Katima Mulilo (fig. 1), between S17.39.40-S17.40.20 and E 24.23.55-E24.24.02. The Centre is a ranch of 3,243 ha. The aim of the centre is in situ conservation, livestock improvement programmes and provision of breeding animals to the farmers, and farmer education. The centre is surrounded by communal areas with subsistence farming. Most of the Sachinga LDC is covered by teak woodland, with smaller portion of Burkea-Kisat-False Mopane woodland and Omuramba grassland. The natural vegetation is well-preserved and represented by three classes of Kalahari woodland: 1) Colophospermum mopane , with two dominant associations: Nymphaea nouchali–Eragrostis rotifer which contains water species, and Combretum imberbe–Acacia nigrescens in association with sparse woodlands; 2) Baikiaea plurijuga woodland, comprising Guibourtia coleospherma–Burkea africana Association and Combretum collinum–Boscia albitrunca association; and 3) Baikiaea plurijuga – Terminalia sericea class with Pterocarpus angolensis–Diploryhnchus condylocarpon association, Dalbergia martinii–Berchemia discolor association, and Acacia fleckii–Baphia massaiensis association (Lushetile, 2009).

Sampling

The American version of the transect line method (Bibby et al., 2012; Sutherland, 1996) was used to assess the population density and community structure of birds occurring in the ranch. A transect of 10 km in length and 100 m width (50 m on each side) was designed along roads traversing the ranch. The transect was divided into four equal sections (fig. 2). Each section was 2.5 km in length, and was surveyed three times (03/09/2014. 07/03/2015, 29/04/2015), each time in the same direction. Counts were conducted by the same observer, in the mornings, and in calm and cloudless weather conditions. Dominance is expressed as the percentage of the total number of pairs of a given species in relation to the total number of all pairs of all species recorded. A dominant species is defined as that comprising 5% or more of all individuals of all species recorded, and a subdominant species is defined as that comprising 2-4.99%.

Quality Control

All birds showing breeding (e.g. transporting nesting material, constructing nests, feeding chicks etc.) or territorial (e.g. singing males) behaviour were recorded. Special attention was paid to simultaneously singing males, as they were important in determining the number of occupied territories. Special care was taken not to count the same birds twice, as this could overestimate the number of territories. The number of breeding pairs was estimated for each section on each transect. The maximumnumber of breeding pairs at each survey and on each section was assumed as the real number of breeding pairs. The total number of breeding pairs of each species on a particular transect was calculated as the total of maximum numbers recorded on each section within the transect.

Method steps

1. The following indices were used to characterise diversity, evenness and similarity between the communities: 1) Shannon’s diversity index: H’ = -∑ pi ln pi where: pi is the proportion of breeding pairs belonging to the ith species 2) Simpson’s diversity index: D = ((∑n(n-1))/N(N-1) where: n – total number of breeding pairs belonging to a given species, N – total number of breeding pairs of all species 3) Pielou’s evenness index: J’ = (-∑ pi ln pi)/ln S where pi is the proportion of breeding pairs belonging to the ith species; S – total number of species. J’ varies between 0 and 1. The lower the variation between species in a community, the higher the J’. 4) Community dominance index: DI = (n1 + n2)/N where n1, n2 – number of pairs of the two most abundant species, N – total number of pairs of all species. 5) Sörensen’s Coefficient: I = 2C/A+B where A – the number of bird species in one plot, B – the number of bird species in another plot, C – the number of bird species common to both plots. Systematics and nomenclature of bird species follow Hockey et al. (2005). Scientific names of bird species are listed in appendix 1.

1. Alcedinidae
   rank: family
2. Bucerotidae
   rank: family
3. Buphagidae
   rank: family
4. Caprimulgidae
   rank: family
5. Cisticolidae
   rank: family
6. Columbidae
   rank: family
7. Coraciidae
   rank: family
8. Dicruridae
   rank: family
9. Emberizidae
   rank: family
10. Estrildidae
    rank: family
11. Laniidae
    rank: family
12. Leiothrichidae
    rank: family
13. Macrosphenidae
    rank: family
14. Malaconotidae
    rank: family
15. Meropidae
    rank: family
16. Monarchidae
    rank: family
17. Muscicapidae
    rank: family
18. Nectariniidae
    rank: family
19. Numididae
    rank: family
20. Oriolidae
    rank: family
21. Paridae
    rank: family
22. Phasianidae
    rank: family
23. Phoeniculidae
    rank: family
24. Picidae
    rank: family
25. Platysteiridae
    rank: family
26. Pycnonotidae
    rank: family
27. Sturnidae
    rank: family
28. Trogonidae
    rank: family
29. Vangidae
    rank: family
30. Vangidae
    rank: family

The study was conducted in the Sachinga Livestock Development Centre of the Ministry of Agriculture of the Namibian Government. The centre is situated in NE Namibia, in the Zambezi region, about 40 km west of Katima Mulilo, between S17.39.40-S17.40.20 and E 24.23.55-E24.24.02. The Centre is a ranch of 3,243 ha. Most of the Sachinga LDC is covered by teak woodland, with smaller portion of Burkea-Kisat-False Mopane woodland and Omuramba grassland. The natural vegetation is well-preserved and represented by three classes of Kalahari woodland: 1) Colophospermum mopane , with two dominant associations: Nymphaea nouchali–Eragrostis rotifer which contains water species, and Combretum imberbe–Acacia nigrescens in association with sparse woodlands; 2) Baikiaea plurijuga woodland, comprising Guibourtia coleospherma–Burkea africana Association and Combretum collinum–Boscia albitrunca association; and 3) Baikiaea plurijuga – Terminalia sericea class with Pterocarpus angolensis–Diploryhnchus condylocarpon association, Dalbergia martinii–Berchemia discolor association, and Acacia fleckii–Baphia massaiensis association (Lushetile, 2009).