Working for birds in Africa

Two new resident birds of northern Zambia

p 56-58
Lake Tanganyika Weaver
P.M. Leonard
White-winged Warbler
P.M. Leonard

During three New Year trips in 1996-1998, we undertook fieldwork for the Zambia Bird Atlas Project (3) in several wetlands on the country's northern border. Among our findings were two resident species previously unrecorded in Zambia: Lake Tanganyika Weaver Ploceus reichardi and White-winged Warbler Bradypterus carpalis.

Lake Tanganyika Weaver, Ploceus reichardi

On 8-10 January 1996, we found Lake Tanganyika Weaver to be common along the Saisi River at the point where it enters Tanzania (08°58'S 31°40'E) (4,7). Its occurrence here is unsurprising given that the species was known to be present in nearby Tanzania. The Saisi River and its immediate tributaries constitute the only cross-border river system, draining into the Rukwa basin to which this species appears to be largely restricted. It therefore appears unlikely that the species will be found elsewhere in Zambia

Lake Tanganyika Weaver is the third member of the masked weaver complex to be recorded in Zambia: P. velatus occurs in much of the south and east of the country and P. katangae in the Luapula drainage. The taxonomy of these forms is a matter of some debate; P. reichardi and P. katangae are swamp dwellers whereas P. velatus is not. They are allopatric and, although Dowsett & Forbes-Watson (5) considered P. reichardi as conspecific with P. ruweti under the English name Lake Lufira Weaver, this treatment obscures the situation and Lake Tanganyika Weaver appears a more appropriate name (R. J. Dowsett pers comm). Lake Tanganyika Weaver is considered a restricted-range species by BirdLife International6 and the site has been proposed as an Important Bird Area (IBA) (9). In this area, the species appears unthreatened.

White-winged Warbler, Bradypterus carpalis

On 30 December 1996, during fieldwork in papyrus swamp in the Luapula River near Chabilikila (09°32'S 28°42'E), we heard what appeared to be unusual Little Rush Warbler Bradypterus baboecala songs. However the birds, when seen, proved to be White-winged Warblers (4,8), a species previously known from no nearer than north-west Tanzania.

The vocal similarities between White-winged Warbler and Little Rush Warbler, which was also present, are remarkable. Both songs consist of an accelerating sequence of short ch-rip notes, often completed during an aerial wing-whirring display. In carpalis, the overall phrase lasts little more than 5s, considerably shorter than that of baboecala which lasts 10-15s or longer. The voice of carpalis is more metallic in timbre, with the notes being delivered faster and apparently at a higher pitch. Once, a bird was attracted by playing the song of baboecala speeded up by 20%. The wing-whirring is not consistently performed, and may be present in several short bursts or as a single longer sequence. In baboecala this display tends to be in 1-3 longer bursts. Many carpalis exhibit either an obvious drop in register or a general fall in pitch over the whole phrase whereas the song of baboecala remains at a constant pitch, but this is also an inconsistent feature. In other areas where the two species are sympatric, the voice of baboecala is very high-pitched unlike that of carpalis, which is on a much lower pitch (D. Turner pers. comm.). In Zambia, it is apparently carpalis that has altered its song with baboecala retaining its normal song.

The density of carpalis was estimated to be c2 pairs per ha in suitable habitat and the ratio of carpalis : baboecala was estimated as 3:1. White-winged Warbler has subsequently been found in additional areas south to 10°02'S. Interestingly, the species' global distribution resembles that of Papyrus Yellow Warbler Chloropeta gracilirostris, and in common with that species, the Zambian population of White-winged Warbler may represent a separate subspecies. Papyrus Yellow Warbler is classified as Vulnerable by BirdLife International (2) and consequently the papyrus swamp at the mouth of the Luapula has been proposed as an IBA. At present the only threat to the habitat is fire, but the nature and extent of this problem has yet to be investigated. It is worth noting that the Zambian subspecies of Papyrus Yellow Warbler C. g. bensoni is highly distinctive due to its white iris - a feature omitted from both the text and illustrations in Urban et al (10).

References

  1. Benson, C.W., Brooke, R.K., Dowsett, R.J. and Irwin, M.P.S. 1971. The Birds of Zambia. London, UK: Collins.
  2. Collar, N.J., Crosby, M.J. and Statterfield, A.J. 1994. Birds to watch 2: the world checklist of threatened birds. Cambridge, UK: BirdLife International.
  3. Dowsett, R.J. and Aspinwall, D.R. in prep. Zambia Bird Atlas.
  4. Dowsett, R.J., Aspinwall, D.R. and Leonard, P.M. in press. Further additions to the avifauna of Zambia.
  5. Dowsett, R.J. and Forbes-Watson, A.D. 1993. Checklist of Birds of the Afrotropical and Malagasy Regions. LiËge: Tauraco Press.
  6. Fishpool, L.D.C. 1997. Important Bird Areas in Africa: IBA criteria. Cambridge, UK: BirdLife International.
  7. Leonard, P.M. and Beel, C. 1996. Lake Lufira Weaver (Ploceus reichardi) - new to Zambia. Newsletter Zambian Orn. Soc. 26 (1): 3-5.
  8. Leonard, P.M. and Beel, C. 1996. White-winged Warbler Bradypterus carpalis - new to Zambia. Newsletter Zambian Orn. Soc. 26 (12): 139-140.
  9. Leonard, P.M. in prep. IBAs of Zambia.
  10. Urban, E.K., Fry, C.H. and Keith, S. (eds) 1997. The Birds of Africa. Vol 5. London, UK: Academic Press

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