Green-breasted Bush-shrike and its relationship with Monteiro's Bush-shrike: 2

Discussion
In view of these observations, I believe it is unsafe to distinguish between Green-breasted and Monteiro's Bush-shrikes on the basis of call alone. Furthermore, I believe it is consequently worth considering that they might be colour morphs of the same species, with Monteiro's possibly replacing Green-breasted further south in Angola, where the latter remains unknown. Further evidence to support this possibility is provided by Andrews (1), who observed Monteiro's responding to imitations of Green-breasted and consequently interacting with one by a duet.

Also relevant is the fact that both Monteiro's and Green-breasted appear to be the only two species of larger Malaconotus which are sympatric at the same altitude and in the same habitat. All other large Malaconotus usually appear to be mutually exclusive. For example, on Mt. Kupe (Cameroon), Fiery-breasted Bush-shrike, M. cruentus, occurs in lower altitude farmbush and secondary growth (pers. obs.), Mount Kupe Bush-shrike, M. kupeensis, is in primary forest from 950-1,450 m, with Green-breasted and apparently Monteiro's Bush-shrikes occurring above 1,400 m2. (The 50 m range of apparent overlap is probably due to variability in altitudinal calculations by observers.) While individuals do wander between altitudes, the vast majority of records conform to this rule. However, in the Bakossi mountains M. kupeensis has been recorded twice in the Edib area (by I Faucher; FDL and R J Dowsett) at 1,150 m and 1,150-1,200 m, and thus overlapping with gladiator. Indeed one bird was observed within 500 m of a Green-breasted Bush-shrike, although the two species occupy different niches, with kupeensis favouring the middle strata and gladiator the canopy (FDL pers. comm. to G Kirwan 1998). On mountains where Mount Kupe Bush-shrike is absent, it is noticeable that Green-breasted Bush-shrike occurs regularly at much lower altitudes, down to 950 m on Mt. Cameroon for instance; although, at this locality montane species typically occur at lower altitudes due to the very high rainfall and lower temperatures experienced there (9).

There remains an anomaly regarding the size of Monteiro's Bush-shrike. In the field it is described as appearing larger than Green-breasted and heavier loooking than Grey-headed Bush-shrike. Conversely an examination of skins revealed that Monteiro's appeared smaller than Green-breasted (1). Malaconotus species, however, are known to be variable in size within species (4), although there is room for further study of this issue.

The taxonomic position of Monteiro's Bush-shrike is addressed at length by Hall et al (4). These authors provide a convincing argument for the separation of Monteiro's from Grey-headed which I believe also has a bearing on its relationship with Green-breasted. They maintain that it is highly unlikely that the Monteiro's Bush-shrike collected on Mt. Cameroon in 18947 could be independently derived from Grey-headed Bush-shrike, in forest habitat 300 km from the nearest savanna-dwelling population of the latter, by changes in facial and iris coloration exactly parallelling those in the Angolan population. The recent discovery of the Mt. Kupe population – also isolated from any population of Grey-headed Bush-shrike – reinforces this argument. Green-breasted Bush-shrike appears to have evolved in a similar manner to Monteiro's, in geographically and ecologically isolated areas from those of Grey-headed.

Although Hall et al (4) considered Green-breasted Bush-shrike a monomorphic species they do mention its grey iris, identical in colour to that of Monteiro's, another relevant factor when considering its relationship. Grey-headed Bush-shrike has a yellow iris. Hall et al (4) also considered that Monteiro's could be a colour morph or race of Fiery-breasted Bush-shrike on account of its identical iris colour and similar facial pattern. They do not consider, however, differences in habitat (discussed above) and vocal differences: the most regular calls of Fiery-breasted being a series of 5-6 short barbet-like hoots (pers. obs.), totally unlike the long mournful whistles of Monteiro's and Green-breasted.

The differences between the plumages of Green-breasted and Monteiro's Bush-shrikes are less relevant than they would otherwise seem when we consider the fact that the African bush-shrikes taken as a whole contain some of the most extreme and varied examples of polymorphism known among birds. Intra-genus polymorphism is also discussed in detail by Hall et al (4) and is, in any case, beyond the scope of this article. One example worthy of mention, however, is the occurrence in south-west Cameroon of a yellow-breasted variant of Fiery-breasted Bush-shrike. Individuals have been collected at Kumba (8) and I observed one on Mt. Kupe in June 1997. Given a good view, it can be separated from Monteiro's by the lack of yellow crescent-shaped tips to the wing-coverts and smaller yellow tips to the tertials. The existence of these individuals should be borne in mind by observers presented with a possible Monteiro's, especially one seen only from below (a highly probable scenario), in which case habitat and calls would be the only clues to the birds identity.

To summarise, I believe there is a some evidence to suggest that Green-breasted and Monteiro's Bush-shrikes are conspecific. Further study, including that based upon DNA testing, is clearly required, although this will be no easy task given the rarity of the subjects and their elusive habits. Perhaps the greatest problem facing future researchers is the continuing depletion of montane forest in the region, and that these enigmatic birds will consequently disappear before these issues can be resolved.

Acknowledgements
I would like to thank Richard Ranft, of the National Sound Archive, for producing the sonograms using Avisoft-Sonograph Pro, Guy Kirwan for reading an early draft of this article and providing information used to improve it, and Françoise Dowsett-Lemaire for her extensive comments on the manuscript and allowing me to include her unpublished data. I would also like to thank Mark Andrews for listening to the tape-recordings and providing useful comments.

References

1. Andrews, S.M. 1994. The re-discovery of Monteiro's Bush-shrike Malaconotus monteiri in Cameroon. Bull. ABC 1: 26-27.
2. Bowden, C.G.R. and Andrews, S.M. 1994. Mount Kupe and its birds. Bull. ABC 1: 13-16.
3. Collar, N.J., Crosby, M.J. and Stattersfield, A.J. 1994. Birds to watch 2: the world list of threatened birds. Cambridge, UK: BirdLife International.
4. Hall, B.P., Moreau, R.E. and Galbraith, I.C.J. 1966. Polymorhism and parallelism in the African bush-shrikes of the genus Malaconotus (including Chlorophoneus). Ibis 108: 162-182.
5. Keen, S. Cameroon 16 September-3 December 1992. Unpublished trip report.
6. Mackworth-Praed, C.W. and Grant, C.H.B. 1973. Birds of West Central and Western Africa. London, UK: Longmans, Green & Co.
7. Reichenow, A. 1894. Zur Vogelfauna von Kamerun. Zweiter Nachtrag. J. Orn. 42: 29-43.
8. Serle, W. 1952b. Colour variations in Malaconotus cruentus (Lesson) Bull. Brit. Ornithol. Cl. l 72: 27-28. 9.Stuart, S.N. (ed) 1986. Conservation of Cameroon Montane Forests. Cambridge, UK: International Council for Bird Preservation.
   
   

Last page update 4th August 2010