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Weaver Wednesday 3 [238] - Range changes [1]: Red-billed Buffalo-Weaver

2017-01-04 (760)

gravit8 Weaver Wednesday 3: range changes S Africa (species text)

Red-billed Buffalo-Weaver Bubalornis niger

Red-billed Buffalo-Weaver, Range-change map between SABAP1 (1987-1991) and SABAP2 (2007-current).
Red, orange and yellow = cells with very large, large, and small relative decreases
Blue, dark green and light green = cells with very large, large and small relative increases.
Cells = quarter-degree grid cells; Only cells with at least 4 checklists in both SABAP1&2 shown. All cells had this species recorded in SABAP1 or in SABAP2 or in both (more about interpretation at Biodiversity Observations 7.62: 1-13).

Range changes in SA

Red-billed Buffalo-Weaver,
figure from Birdpix

Range change summary
More 4 lists 30 lists
decreases n % n %
Decrease 125 48 47 49
Tiny change 39 15 17 17
Increase 99 37 32 34
Total 263 100 96 100
In South Africa the Red-billed Buffalo-Weaver has more grid cells with decreases in reporting rate than cells showing increases, between SABAP1 (1987-1991) and SABAP2 (2007-). The points below match the points on the map above.

1. Range expansion westwards from Kathu to Askham
The blue grid cells on the western edge represents a large westward range expansion (between SABAP1 and SABAP2) from Kathu and the Botswana border west to Van Zylsrus and as far as Askham, a distance of about 100km. There is also a PHOWN record from Askham based on the 2010 Google Streetview, indicating nest building and possible breeding.

2. Range extinction in the Free State
The two red cells in the Free State represent the isolated population that was present around Bloemhof Dam, Free State. Birds were first seen in 1981 and nests were seen in 1986. The last published report appears to be from May 2000 and the species no longer occurs here (SABAP2).

3. Range stable along the 26S line of latitude
In South Africa it is found mostly north of 26S (although it ranges to 26S in the western and eastern parts of its range). The 26S line divides the grassveld (south) from the savanna (north) in this area. The Red-billed Buffalo-Weaver is clearly absent south of Pretoria, as in the past.

4. Range stable but low density in eastern corridor
The eastern population of the Red-billed Buffalo-Weaver in South Africa extends southwards in the savanna corridor from Mpumulanga, through the lowlands of eastern Swaziland, and into northern KwaZulu-Natal. The southernmost record is from the Zululand Rhino Reserve. The earliest published record from this corridor is of nests seen in July 1951. An earlier record is a specimen collected on 29 May 1937 in north-eastern Swaziland, suggesting that the species has occurred here in historical times, although early authors did not list it from here. The buffalo-weaver occurs at a very low density in this corridor, with the estimated population being 80 birds in Swaziland.

Range changes elsewhere

Botswana: expansion in SW (Tyler 2012a).
Uganda: recent new records (Rossouw 1998a, Demey 2011b).
Zambia: expanding north-eastwards in Kafue (Robertson 1995b).