key: cord-0041688-cr1qaoc8
authors: HALL, B. P.
title: THE FAUNISTIC IMPORTANCE OF THE SCARP OF ANGOLA
date: 2008-06-28
journal: Ibis (Lond 1859)
DOI: 10.1111/j.1474-919x.1960.tb08418.x
sha: b2af25efa59c2bb369db85ad19de1e2ad050ea8c
doc_id: 41688
cord_uid: cr1qaoc8

1.. The geographical features, in particular the western escarpment, and the climate and vegetation of western Angola combine to divide the area into three avifaunal zones. 2.. An unusual relationship exists between some related forms of different zones. This is illustrated by two groups of examples in which the characters of the forms are summarised, their distribution is shown on maps, and an attempt is made to interpret in evolutionary terms the picture presented. 3.. Endemic or near‐endemic forms of the Escarpment Zone are listed with some notes on their affinities with other species. 4.. The botanical history of the area is discussed in relation to the conclusions reached on the evolution of the birds. 5.. The Escarpment Zone of Angola has been of considerable importance in the evolution of species in western Africa, south of the Equator.

When working on the birds collected on the 1957 expedition to Angola I was impressed by the part played by the escarpment of western Angola in the avifaunal distribution. I n writing the report on thcsc birds (Hall, in press) it was suggested that the climatic and vegetational conditions produced by the escarpment had formed a marked avifaunal zone in which speciation was taking place: this was termed the Escarpment Zone. T h i s idea was not developed in that report but I have since been fortunate in interesting Ilr. A. J. Cain of Oxford in the faunistic importance of this zone and it is with his help that the present paper is compiled.

T h i s importance seems to lie firstly in the zone as a centre of speciation: this is illustrated by a number of examples in which birds found in the Escarpment Zone differ in somc striking character from all others of the same spccies throughout Africa, and d o not apparently interbreed with their relatives in other zones. Secondly, the Escarpment Zone is of importance in providing a barrier for some distance between two drier zones, allowing subspecies t o develop in each. 'I'hirdly, the zone is important in containing a number of endemic or near-endemic species.

T h e esamples quoted to illustrate the first two of these groups are all of species which were collected on the 1957 expedition and to which my attention was drawn in the subsequent systematic study of the collection. Thcre are undoubtedly other examples but the lack of data on most specimens from Angola makes it difficult to discuss the relationships and habitats of birds of which one has had no personal field experience: furthermore little systematic work has been done on such collections as have becn made in Angola so that subspecific identification in published works is unreliable. l;or this reason I have referred only t o specimens which have been examined by me personally, or for me by kIr. hl. A. Traylor in Chicago, or by Dr. J. P. Chapin when preparing his work on the birds of the nelgian Congo. I n some of the species discussed the material available in London was supplemented by loans from the American Museum of Fiatural History and the Chicago Natural History Museum. 1 his paper is intended primarily to draw the attention of othcr workers to somc of the interesting evolutionary problems presented by the birds of Angola, and while some attempt has been made in the different sections to interpret the problems it is realised that these interpretations must be very spcculativc in thc formidable limitations of our present knowledge.

It is necessary at the outset to make some reference to apparent inconsistcncics in nomenclature that will appear in this paper. 'The whole conception that speciation is taking place presents the problem that many of thc forms under discussion have a status somewhere between that of a subspecies and that of a species, and there is no method in trinomial nomenclature for indicating this. I have therefore avoided trinomials where possible when the discussion indicates doubt on the status of a particular form. Also, while I helieve many of the forms now considered as subspecies are at least close to achieving specific rank, I am rcluctant to recommend that they should be treated as species, with the consequent nomenclatorial changes, until they have been further studied in the field. In other cases, such as the Boubou Shrike, and the Grey and ,.

Black Tits, which have been the subjects of separate papers, the nomenclature here is consistent with the conclusions reached in those papers. I am most grateful to Dr. A. J. Cain, Mr. R. E. hloreau and Mr. C. 11. N.

White for helpful comment and criticism on this paper : to Dr. Dean Amadon, Dr. C. Vaurie, Dr. A. Rand, M r . M. A. Traylor, and Mr. 11. P. Stuart Irwin, for loans and information on specimens in New York, Chicago, and Bulawayo : to Dr. G .

Rudebeck for allowing me to examine specimens collected on the Visser-l'ransvaal Museum Expedition to Angola in 1956: finally to my colleague Mr. A. W. Exell for his help on the botany of Angola and for his permission to quote from an essay awaiting publication on the botanical history of southern Africa.

The dominati ?g factor in the ecology of western Angola is the rapid change of altitude within a short distance of the coast. South of the Cuanza River the coastal plain is under a hundred rniles broad and the inland plateau is above 3000 ft. at Calulo and Gabela, rising to over 6000 ft. in the Bailundu highlands, with peaks such as Mt. Moco over 8000 ft. In the Cacorida area the plateau lies between 4000 and 5000 ft., rising to 6000 ft. further south at S B da Bandeira. The escarpment which separates the plain from the plateau is precipitous in places, notably in the Sierra de Chela west of SB da Bandeira, where rocky cliffs drop from 6000 ft. to foothills at Capangombe and Cahinde at about 2500 ft. At Gabela it is also steep, but not precipitous, while at other points it rises in a series of steps.

The inland piateau in the centre of the country east of the escarpment is largely covered by savannah woodland of the brachystegia type, interspersed with patches of grassland, which are more extensive in the north. On the highest mountains there are some patches of montane forest. There is high summer rainfall but the winter is dry with low humidity. In the southern part of the plateau it is drier and the brachystegia woodlands give way to thorn and mopane. T h e coastal plain is drier still, the Namib Desert of South West Africa extending in a narrow strip up the coast to north of Moqamedes : this is fringed by semi-desert thornveld extending to Benguela, which gives way northwards to Luanda to dry coastal grasslands with scattered acacia. All along the coast there is high humidity all the year round but little rain, and that in summer.

Off-shore the cold Benguela current meets the warm equatorial waters and produces mists that are precipitated by the escarpment. Hence a narrow belt on and below the escarpment combines the high summer rainfall of the inland districts with the high all-yearround humidity cd the coastal plains (see Figs. 1 and 2): in consequence it supports a richer and more varied vegetation. The southern tip of this belt is found at the base of the escarpment at Capangombe and Vila Arriaga, where there are fertile pockets between the semi-desert thornveld and the escarpment face. There may be other pockets even further south but there is no continuous belt for, at Cahinde, 40 miles south of Capangombe, the thornveld comes right to the foot of the escarpment. Above the escarpment in the south the brachystegia woodlands and the acacia of the plateau merge gradually into the richer vegetation belt at about Quilengues. 1'0 a traveller coming from the monotony of the brachystegia woodlands or the semi-desert the change is indicated by the increase in cultivation, new species of trees and bushes, among which are palms and baobabs, and areas of tangled thickets. Further north at Chingoroi the contrast is even more emphasized by a forest patch bordering the stream.

Further north at Gabela there is more extensive forest along the face of the escarpment-the "Amboim forest " of old authors. Northwards again, as the coastal plain widens north of tlie Cuanza, there is more forest at Dondo, Vila Salazar (Ndala Tando),

Camabatela and Quicolungo. These forests are impoverished outliers of the true lowland forest of the Congo and are not comparable to it either in the size of the trees or in the density and the undergrowth. For this reason I have distinguished them under the term " escarpment forests ": I do not include with them some small patches on the Chela escarpment which have been found to be relict montane forest. I I have no personal knowledge of the country north of the Cuanza, and it is not easy to form a picture of it from maps and literature. It is evident that the escarpment is not such a dominant feature as in the south, there being a rise of only 1000 ft. between Vila Salazar and Malanje, which lies at about 3400 ft. on the central plateau. Apart from the forest patches, the vegetation of the wide coastal plain would seem to be similar to that found along the base of the escarpment further south, though getting progressively richer northwards, and rather richer in the centre of the plain, with more grassland on the coast. Inland it changes in the vicinity of Duque de Braganqa to savannah grassland and brachystegia woodland. In western Angola there is thus a wedge of richer vegetation lying between the drier areas of thornveld or grassland and brachystegia woodland. In the north it is wide with considerable patches of forest; in the south it tapers to a very narrow belt along the escarpment with forest patches rarer and less extensive. This wedge is indicated on the Vegetation Map of Africa south of the Tropic of Cancer (Oxford University Press 1958) by the area described under " Woodlands, savannas " as " undifferentiated:relatively moist types ", in which " Isoberlinia, Brachystegia and Julbernardia are absent or rare ". On the map some, but not all, of the escarpment forest patches are shown.

The small scale of the map does not allow for great detail and it is probably for this reason that the extreme narrow tip of the wedge south from Chingoroi to Capangombe is not shown, neither is any forest marked south of Gabela. I t is this wedge that forms what I have termed the Escarpment Zone and the areas of thornveld and brachystegia woodland form the two drier avifaunal zones, the Acacia and Brachystegia Zones, as comparison between the Vegetation Map of Africa and Map 1 will show. AVIFAUNAL ZONES 1. The Bruchystegiu Z m . The birds found in the brachystegia woodlands of Angola are predominantly of species occurring in the woodlands of Central and East Africa. They show little subspecific variation over large areas. T h e western limit of many species is along a line running slightly west of Malanje, Pungo Andongo, Calulo, Mt. Moco, Caconda to Huila. Both the northwestern and southeastern boundaries of the Zone are uncertain but in the southwest there are interlocking patches of woodland 3Iention should he made here of the relict montane species found in the forest on such peaks as 1Ioco and Soque. Although they lie within the geographical limits of the Brachystegia Zone I d o not include these species in the avifauna of the zone since they belong to the old montane avifauna found isolated on the highest mountains fringing the Congo basin. T h e problems of this old avifauna have been discussed by both Chapin (1932) and lloreau (1952) and they lie rather outside the scope of this paper.

T h i s zone includes the h I o p m c d e s desert, the scmi-desert thornveld, the dry coastal grasslands north to I,uanda, and the sliglitly less arid acacia and mopane country on the plateau in the south. All the birds of tlic Acacia Zone Iwlonq to species found in South LVest Africa except for a few. typical of the Escarpment Zone, which are found in fertile pockets on the edges of rivers north of Renguela, and in marshes and cultivation behind Benguela and Caturnbela.

T h e Escarpment Zone, formed by the wedge of richer vegetation and the included forest patches, is shown by the distrihution of its endemic forms to stretch northwards at least to Landana and the lower reaches of the Congo. Its boundaries d o not apply to the many species which reach the southcrn limit of their range in one or other of the Angola forest patchcs and are common also to the Guinea and Congo forests; with these forest species I am not primarily concerned in this paper.

T h e other species are in some cases endemic or near-endemic, in others arc common to either one or hoth of the neighbouring zones, in many cases being represented in the Escarpment Zone by an esceptionally well-marked form.

T h e boundaries of the Escarpment Zone are not wholly rigid since typical birds may ovrrlap into richer patches of vegetation in neighbouring zones, such as the fertile pockets in the Acacia Zone already discussed or, occasionally. gallery or montane forest in the Brachystegia Zone.

3. 7 %~ .Icncicr %om.

In the introduction it was indicated that the faunistic importance of the Escarpment Zone is shown in three ways. T h e examples that illustrate this are therefore divided into three groups :-G r o u p I . Birds with a representative form in the Escarpment Zone, and in either, or both, of the other zones.

In seven out of the eight examples given it will be seen that the form found in the zone has some character which distinguishes it from all others of the species; and that there is no apparent interbreeding although the different forms live in close proximity, usually along the zonal boundary. I n the eighth example, the Black Tit, the significant variation lies between the forms of the Acacia and Brachystegia Zones and in this respect it is similar to the examples in the next G r o u p ; however, since it has, unlike the next Group, a representative form in the Escarpment Zone, it must be included here.

Group 2. Birds with representative forms in the Brachystegia and Acacia Zones, partly isolated from each other hy the Escarpment Zone.

I he live examples in this group arc of birds with csccptionally well-marked forms in the Acacia and Brachystegia Zones but u hich are absent from the Escarpment Zone. T h e true relationship between members of each pair u i l l not be known until specimens are available from thc southcastern districts of Angola whcre the two zones meet without a harrier, such as is formed by the Escarpment Zone in the west. T h c species which I consider truly endemic to the Escarpment Zone are those whose range lies within the defined limits of the zone in western Angola and which are not found north of Landana or eastward of Leopoldville in the Lower Congo. I include among the near-endemic species some that overlap the zonal boundaries slightly in Angola and one, Chlorocichla falktxsteini, that is found as far north as the Cameroons but appears to be restricted to the western part of the country.

Angola and South West Africa have many other endemic species, but they do not enter the Escarpment Zone. A number of them such as Hartlaub's Francolin Francolinus hartfaubi, the Damara Rock-jumper Achaetops pycnop-vgius, and the Angola Chat .Yenocopsychus a?lsor~e,: are primarily associated with rocks and have their range limited by the extent of suitable mountains; others, such as Gray's Lark Ammomanes gravi, are desert species. The lack of close relatives to many of these make them exceptionally interesting but they cannot be discussed here.

It may be thmght that the 27 examples quoted in the three groups represent an insignificant part of the very rich avifauna of western Angola, but this is to overlook the fact that the riajority of species are found in only one of the three zones. It is indeed rare among the pilsserines to find a species common to all and only five such were collected among 250 passerine species on the 1957 expedition, other than those listed among examples in Group 1. These five were the Pus-back and Helmet Shrikes Dryoscopw cubfa and Prionops pfumata, the Tawny-flanked Prinia Prinia subjava, the African White-eye Zostnops senegalensis, and the Golden Weaver Ploceus .ranthops, all of which are widespread species clearly adaptable to varying conditions. Species less adaptable may well have di-d out in one zone or another in the course of climatic and vegetational change.

In Groups 1 & 2 the characters and ranges of the forms are summarised and the distribution is illustrated by maps, except in the last example. On these maps the boundary of the zone is indicated by a red line: localities in critical areas from which specimens have been collected are marked with dots or crosses, and the approximate distribution outside critical areas is indicated roughly. It has been shown (Hall 1954 ) that the widespread L. aethiopicw is replaced in Gaboon, western and southwestern Angola and Ngamiland by L. bicolor, and that the two species are sympatric on the Chobe River and in northwestern Rhodesia, though ecologically segregated, bicolor in the reed beds and aethiopicus in thickets and bushes of the surrounding country. Recently Dr. W. Serle has found that bicofor occurs in the British Cameroons, where he collected specimens in stunted mangroves at Tiko in the south.

The only difference perceptible in the hand between I,. uethiopicus and L. bicolor is that L. aethiopichs has a pink tinge of varying intensity on the under-parts, which is more pronounced towards the base of the feathers, while L. bicolor below is a pure, silky white particularly pronounced towards the clean base of the feathers. In the field differences in the voices of the two have been noted by Serle, Heinrich and Winterbottom, even when it was not realized that they belonged to different species; there is also difference in the colour of the eye, which is red-brown in aethiopicus and dark brown in bicolor. There are more pronounced differences between the sympatric subspecies, L. b. sticturus, the eastern race of L. bicolor, being larger with more white in the wing than either L. u. major or 1,. a. m,mambicus of the Zambezi and Chobe valleys. L. b. sticturus has been found as far west as the Cunene and intergrades near SB da Bandeira with the smaller L. b. guttatus of western Angola, from which it differs only in size and in the amount of white in the wing. Specimens of L. 6. guttatus have been examined from 20 miles southwest of SB da Bandeira, Capangombe, Chingoroi, the Benguela area, Dondo and the other zones.

Vila Salazar in Angola, and from Boma and Landana in the Belgian and Portuguese Congo. At Landana it intergrades with the race of Gaboon and the Cameroons, L. 6. bicolor, in which the white in the wing is further reduced. L. b.guttatus has been collected in various habitats including reeds, tangled thickets and forest undergrowth.

Specimens of I,. aethiopicus from Angola are close to the widespread L. a. major but rather whiter below, as are those of the southern Belgian Congo. They are similar in size to L. b. guttatus and with about the same amount of white in the wing, so that the two forms are therefore not easy to distinguish in the hand without comparing series and lifting the feathers of the breast. Specimens of L. a. major from western Angola have been examined from Duque de Braganqa, Mt. Moco, and Mt. Soque (all identified as L. fmrugineus guttatus by Heinrich 1958 : 403), Malanje and Pungo Andongo, and from Tumba and Thysville in the Lower Congo. They have been collected in thickets in the grasslands and woodlands, and along the edges of streams.

All the populations of L. bicolor have been isolated at some time from those of L. aethiopicus, but the clinal variation found within I,. bicolor indicates that there has been reasonably continuous distribution within its range. It can be postulated that this isolation occurred at a period of low annual rainfall during which the vegetation became poorer and all natural cover for Roubous disappeared except along the escarpment where there was a moister zone of richer vegetation due to precipitation, and in the reed beds along such permanent rivers as the Okavango, Chobe and Zambezi. With the return of moister conditions Angola and northwestern Rhodesia were re-populated by L. aethiopicus except in those habitats or zones in which 1,. bicolor was established: thus along the Chobe and the Zambezi, where L. bicolor was restricted to reed beds, L. aethiopicus became re-established in the thickets and undergrowth of the woodlands and ecological segregation enabled the two species to live alongside, but along the escarpment, where L. bicolor was established in all suitable habitats, there was no room for re-penetration by L. aethiopicus.

Much remains to be learnt of the relationships of the two species and the extent of their ranges in southeastern Angola but it is to be expected that the range of L. aethiopicus will be found to coincide with that of the brachystegia woodlands and that, if L. bicolor is found within this range, it will be restricted to reed beds.

(b) Grey-backed Camaroptera, Camaroptera brewicaudata races and hurterti, Map 3.

Characters and ranges. Throughout the wide range of the Grey-backed Camaroptera there is a certain amount of geographical variation but mostly intergrading. In the Escarpment Zone there is, however, a very distinct form, hurterti, with a green, not a brown, tail, and very white under-parts; it has little or no seasonal variation in dress. Specimens of hurterti have been examined from Luanda, Vila Salazar and Gabela and its range is apparently restricted to the centre of the Escarpment Zone.

Three other forms are also found in western Angola, all of them brown-tailed: (1) tincta, a dark, grey-chested race which has no seasonal dress; widely distributed through the Congo forest and reaching the northern part of the Escarpment Zone at Canzele, just south of Camabatela (Heinrich 1958 : 349 " C . b. hurterti"). ( 2 ) sharpei, a race with marked differences in breeding and non-breeding dress: in breeding dress greyish, but paler than tincta, in non-breeding dress browner on the back and washed with buff below: widely distributed over southern Africa, but not in the arid thornveld districts of the Kalahari and South West Africa: sharpei reaches the southern part of the Escarpment Zone at Chingoroi, where a specimen in the distinctive non-breeding dress and a young bird were obtained in the forest. (3) an unnamed population (see Hall, in press) intermediate in colour between sharpk in breeding dress and tincta, having apparently little or no seasonal change: found in a belt across central Africa from Malanje to western 'Tangnnyika.

T h e escarpment population of harterti has at one time been isolated for a considerable period from the brown-tailed populations of the north, east and south. This must have occurred at a period when Kalahari-like conditions prevailed above the e:,carpment. T h e area has subsequently been re-invaded from both north and south, as indicated by the presence of tincta at Canzele and sharpei at Chingoroi. That the drycountry form, sharpei, with marked seasonal change, is found in the moist forest a t Chingoroi argues a comparatively recent invasion for, from the climatic and vegetational character of Chingoroi, it would be expected that a form there would develop the characteristic of the tropical forms in which there is little or no seasonal change. That the ranges of the brown-tailed forms adjoin that of harterti without any intergradation and that these forms are found in the same habitat as harterti, indicate that hurterti has achieved specific status. Furthermore, since harterti in the time of isolation must have been the form found at both Canzele and Chingoroi, it is not improbable that it may be found at both places alongside tincta and sharpei.

(c) African Fire-finch, Lagonosticta rubricata races and landanae, Map 4.

Like the Camaroptera, the African Fire-finch has a wide distribution throughout tropical Africa, mostly of a clinal nature, but has a very distinct form in northwestern Angola and the Lower Congo. This form, landanae, differs from all others in having a largely rose-coloured instead of a slate-black bill. In Angola lcdanae is not entirely confined to the Escarpment Zone having been found as far east as Pedreira (12'02' S., 17'13' E.) in Bik province, but in the Lower Congo its range corresponds so well with other escarpment forms that it seems it should be considered amongst them. Here the forms landanae and congica, one of the black-billed forms, are found in close proximity, the former in the coastal districts at Landana, Boma and Matadi, the liitter at Kwamouth. Further south Iandanue is found at Tembo Aluma on the Cuango near the Angola-Congo border, and congica is the form of the Kasai. In northeastern Angola the range of the two forms is unknown but on the southern Angola-Congo border cmgica has been collected near Dilolo. Chapin (1954 : 523) found that landanae in ti?e Lower Congo behaved like other races of L. rubrkata and was a common savannah bird. Little is known of its field characters in Angola other than that it was found in tangled grasses bordering the River Cuvo near Gabela.

Like the escarpment forms discussed previously, landanue would stem to have been isolated at one time from other races of L. rubricata. In this period it: was probably confined to the Escarpment Zone but has since spread eastwards SO that the northern part of the Brachystegia Zone has been partly re-populated by landanae and partly by L. rubricata congica. Only more collecting in the critical areas can establish whether the two forms are now able to live as good species or whether there is intergradation between them.

Characters and ranges.

(d) Grey-headed Bush-shrike, Malaronotus hypoi?yTrhus races and monteiri, Map 5.

Characters and ranges. The Grey-headed Bush-shrike ranges throughout the savannah woodlands of tropical Africa. Populations vary in the prevalence and degree of orange wash on the chest, but the only well-marked form is monteiri of the Escarpment Zone which has the white of the lores extending in a complete circle round the eye. T h e only other known specimen with this character is the type ofperspicilIatus from Cameroon Mountain which is possibly not even subspecifically distinct from montkri. (Serle 1954 : 72) . Specimens of monteiri have been examined in London or Chicago from Rio Dande, near Luanda (the type), Vila Salazar, Dondo and Gabela, and " Bucaso " (not located). Others from western Angola without the eye-ring have been examined from Malanje, Mt. MOCO, Caconda, Huila and Bi6. These have provisionally been referred to the 13. P. IIALL : FAUNISTIC IhlPORTASCE 01; Tl1E SCARP OF ANGOI..\

Katanga race interpositus (Hall, in press) though they are rather clearer yellow below than typical birds.

Sothing is known of the habitats in which the specimens of monteiri were collected but Serlc emphasises that Cameroon l l t . does not provide the habitat usually associated with 111. IiJpopyrhus.

Interpretation. It semis probable that at one timc there was a continuous population of this shrike in coastal districts from Angola to Cameroon RIt. and that this populaticn was isolated during a dry period from other forms of M. hypop-vrrhus, in the same way that Lnniarius bicolor was isolated from I,. ueihiopicus in the same area. 'l'he link between Angola and Cameroon hlt. may have been broken with the return of moister conditions and a westward encroachnient of the forest, or more extensive collecting may show that it still exists. T h e vegetational differences between the Escarpment and Brachystegia Zones and Serlc's remarks on the vegetation of Cameroon Ylt. suggest that nionteiri and i t i t e~p~~i t~~ may have developed preferences for rather different types of habitat and it may be found that the two forms d o not mix or interbreed along their common boundary.

( e ) ;\Ieves' 1,ong-tailcd Glossy Starling, Laniprotornis meresiz and he?JpehSiS, JIap 6.

YIeves' Starling is a bird of the mopane belt ranging from ISyasaland through the Rhodesias, northern Bechuanaland, northern South West Africa and southern Angola to the base of the Chela escarpment. It is not found in the more arid thornveld of the Kalahari and central South West Africa. Xlost of the range is occupied by the form mmesii which has a purple-blue gloss, but mevesii is replaced along the base of the escarpment and north to near Chingoroi by he?f#Udf?JSiS ( -I , . m. purpureus Bocage) which has a distinctive bronze gloss. I!nfortunately few specimens arc available from the critical area around S I da Bandeira but the two forms certainly occur within 50 miles of each other without apparent intergradation. Specimens of mezwii have been All the localities from which beiiguelensis has been taken lie in the richer vegetation of the Escarpment Zone, though Capangombe is at the southern limit and Quilcngucs in an area where the vegetation is changing from the drier thorn and brachystegia on top of the escarpment to the richer type found at Chingoroi. Since ben,oueZensis must have been isolated at one time from mmesii this was probably in a period when it was either too dry o r too cold for m o p a n e o n th: plateau, Iiut it survived in tlic Escarpment Zone.

Since there is no indication that the two forms interbreed now that they are no longer isolated it seems probable that ben~uelensis has achieved specific status.

Interpretation. T h e interest in the Paradise Flycatchers lies in the fact that both T. m. bannermani and T. v. plumbeiceps appear to be products of hybridization between birds of the melampyra and violacea groups. This is most evident in bannermani, which is closest to melampyra in having an orange-rufous mantle and rufous under tail-coverts, but shows the influence of violacea in havinga longer crest and paler head and under-parts ancI a longer tail in the male than melampyra. In plumbeiceps the influence of melampyra is shown only in the large proportion of Angola birds which have some rufous in the the under tail-coverts and have the white of the abdomen very restricted; whereas in the east of the range, and in South West Africa, the under tail-coverts and the abdomen are predominantly white.

At some time there was free interbreeding between the melampyra and violacea groups in northern Angola. At a later date the hybrid population was divided, possibly in a dry period when the country on top of the escarpment was unsuited to Paradise Flycatchers. The part of the hybrid population in the Escarpment Zone was then still linked with melampyra but not with violacea, so that the violacea influence diminished,. developing the form bannermani: meanwhile the other part of the hybrid population had been forced eastwards and was linked with violacea but not melampyra, so that the melampyra influence diminished, developing the form plumbkceps. This would account for many birds of the plumbeiceps type being found as far east as the Katanga and Rhodesia.

(g) Blue Flycatcher, Elminia nlbicauda and E. longicauda, Map 8. Characters and ranges. T h e two species of Blue Flycatcher are readily distinguished even in the field. E. albicauda, the species found south and east of the Congo forest mostly in brachystegia woodlands, is greyish blue above and has a conspicuous amount of white in the tail. E. longicauda is found in forest fringes, but not deep forest, in West Africa and the northern Congo. I t is bright blue with no white in the tail. 'The ranges of the two meet, but do not apparently overlap, in northwestern Angola and in the Lake Edward area. In Angola E. albicauda has been recorded at Pungo Andongo, Malanje, Caconda, and in gallery forest 40 miles S.E. of Calulo, and in both montane forest and brachystegia on Mt. .Moco. E. longicauda has been found only within the Escarpment Zone at Canhoca, Golungo Alto, Vila Salazar, Quicolunga and Gabela, where it was seen in the forest. In the Lake Edward area Chapin (1953 : 692) records E. albicauda from Luofu and Mohanga and E. longicauda from Kabiabo and Karebumba about 60 miles north. In neither area where the two meet is there any sign of intergradation and the Angola race of E. longicauda, E. 1. loandae, is a brighter blue than the Congo race, E. 1. teresita, and therefore even more distinct from E. albicauda. Interpretation. T h e northern and southern populations of the Blue Flycatcher must have been divided from each other at one time for a considerable period to allow for such distinct characters to develop, though the division in the east may not necessarily have been concurrent with, or due to the same cause as, that in the west.

T h e division in the west could have occurred at a dry period when the Brachystegia Zone was unsuitable for Blue Flycatchers, or in a very wet period when the escarpment forests were part of the deep Congo forest: a slight extension of the true forest eastwards would also serve to divide the two populations in the northeast Congo. If the division occurred at a wet period it is reasonable to think that the Escarpment Zone was later re-populated by E. longicaudu from the north rather than E. aZbicauda from the Brachystegia Zone since E. Zongicauda would be more adapted to lower altitudes and moister conditions.

(h) Black Tit, I'urus nigu and P. leucomelus, Map Y. C'lruracters and ranges. It was shown (Hall 1960 ) that there are three recognizable populations in Angola, as follows:-(1) 1'. n&u carpi, ranging from the highlands of South West Africa to the Sa da Bandeira area, Quilengues and the coastal grasslands near Novo Kedondo. It is a small form with a bluish sheen and little or no sexual dimorphism, resembling most closely P. 1. guineensis of West Africa and thc Sudan except that it has a brown, not a yellow, eye. It is very distinct from the duller and larger P . N. nz&r of eastern southern Africa in which the fcmales are pale and grey; but carpi is linked with niger ecologically and through some apparent intergrades from Elephant Vley, just south of the Angola border in South West Africa.

(2) P. leucomelus insignis (typical), ranging from above the escarpment in the brachystegia woodlands eastwards through the southern Congo to Uganda and Kyasaland. It is sympatric with P. n. niger in Northern Rhodesia and Nyasaland but ecologically segregated. P. 1. inslgnis is distinguished from all other forms by a greenish sheen. T h e females are slightly duller than the males. Specimens have been examined from Duque de Braganqa, Malanje, Calulo and Caconda in western Angola.

(3) P. leuconrelas imgnis (atypical). In the Escarpment Zone the Black Tits resemble insignis in all respects except that they are smaller, though not as small as carpiorguineensis.

In other species of western Angola that have been discussed the interest has centred on the population of the Escarpment Zone: in the Black Tit it seems to lie in the relationship of carpi of the Acacia Zone to all other forms. T h e similarity of carpi to guineensis in all but eye-colour seems to indicate a dry coastal link at one time between West Africa and Angola, and through carpi to niger of South Africa; but it is difficult to speculate until more collecting has been done in southern Angola. 1 here must also have been a period in which carpi in the west and niger in the east were isolated from insignis in the centre. Beyond this it is not easy to go, for the evolutionary problems set by the African Black Tits are exceedingly complex and lie rather outside the scope of this paper: furthermore, the evolution and ecology of the Black Tit is closely bound up with that of the forest representative P. funereus and the Grey Tits P. ajer and P. griseiventris.

,.

Most of the birds discussed in this Group indicate that at some dry period in Africa an isolated area was provided in the Escarpment Zone in which species requiring moderately wet conditions could exist, since this Zone was not, like the inland districts, dependent for moisture on the seasonal rain. In this period it can be postulated that there was no brachystegia woodland in the centre of Angola and therefore among woodland birds there was a complete break between those members of a species left isolated in the Escarpment Zone and those members left in woodlands further north or east. T h e examples of Lamprotornis mevesii and Camaroptera breericaudata suggest that during this period conditions above the escarpment at SB da Bandeira and throughout most of the centre of the country approximated to the semi-desert thornveld unsuitable for woodland forms. Support for this hypothesiscan be found today in the presence at Vouga, in an area of high annual rainfall (over 40 inches) in central Angola, of such typical dry-country forms as the Spike-heeled Lark Certhilauda afbofascinin and the Black-breasted Prinia Prinia jhvicans.

When the brachystegia and the woodland birds returned to the centre of Angola the different characters which had developed during the period of isolation reduced the likelihood of interbreeding between the newly returned birds and the resident birds of the Escarpment Zone. Interbreeding may have been further inhibited by different breeding seasons having developed in the two populations; most birds in the Brachystegia Zone seem to breed in the early rains, from August onwards, while a number of species collected at Chingoroi and Gabela gave evidence of breeding from May to July (Hall, in press) .

It is possible that the dry period postulated above was preceded by a wet period in which the escarpment forests formed part of the true Congo forest and during which the northern and southern species of Hminia were separated. These two forms differ more than other pairs discussed and may be presumed to have attained specific rank at an earlier date.

The Boubou Shrike Laniarius bicolor has a more or less continuous coastal distribution north to the Cameroons which suggests a corridor west of the forest. If this corridor h;is at times been more extensive it might also account for the reappearance in the Cameroons of the Bush Shrike Malaconoiur monteiri and for the affinity of the Angola Black'Tit P. n. carpi with the West African P. 1. guineensis.

(a) Grey Tit, Parus afer and P. griseiventris, Map 10. The relationship of the Grey Tits P. afer and P. griseiventris was discussed in previous papers (Hall & Traylor 1959 , Stuart Irwin 1959 in which it was shown that P. griskutntris of the brachystegia woodlands should be treated as a separate species from P. ufer of the acacia country and scrub since two forms behaved as good species in part of Southern Rhodesia, being sympatric but ecologically segregated, and showing no hybridization. P. griseiventris ranges east and south of the Congo forest from Lake Tanganyika to Mt. Moco, Caconda and Huila in western Angola and south to Rusape in Southern Rhodesia. Forms of P. afer range southward and eastward from the semi-desert behind Btmguela through South West Africa and Bechuanaland to the Rusape area. Other isolated forms of P. afer are found in the acacia country of northeastern Kenya, southern Abyssinia and Somaliland. The ranges of P. afer and P. griseiventris overlap only in Southern Rhodesia; in Angola they are separated in the west by the Escarpment Zone and probably in the south by the acacia-mopane belt in which, in northern Bechuanaland and South West Africa, the Grey Tit is replaced by the Black Tit.

(b) Familiar Chat, Cercomela familiaris races and falkensteini, Map 11. The picture presented by the Familiar Chats in the Brachystegia and Acacia Zones is in some ways analogous to that presented by the Blue Flycatchers E. fongicauda and E. albicauda in the Escarpment and Brachystegia Zones. I n each case there are two well-marked groups, one in the north and one in the south, each with a representative in different zones in Angola. In the chats there is a northern group in West, East and Central Africa ranging south to the Zambezi valley on the east and to Mt. Moco and Huila on the west. In this group thc underparts are predominantly washed with grey and there is very little constant geographical variation, though many names have been proposed. Birds from the Zambezi valley can be matched with those of West Africa and Angola and all can be calledfalkensteini, the grcycr ornoensis of Abyssinia being closcly allied. In Angola fulketzsteini has been collected on Mt. hIoco and at Huila (Heinrich 1958 : 357, " C. f. artgolensis "). I n the southern group the undcrparts are washed with butf varying from a very pale wash in angolensis of the Acacia Zone to the rich buff races funriliaris and hellnzuyri of Cape Province, the Transvaal and Southern Rhodesia. T h e palc angolensis has heen collected at Luanda, in the Benguela area, and at Cahindc. It intergrades through the South West African races hoeschi, p l t o n i and richardi with hellnrayri, which in Southern Rhodesia is found in all the country away from the Zarnbezi and its tributaries (Smithers et ul. 1957 : 1OY) . T h e limited material from Angola shows no intergradation between thc grey and buffish groups though their ranges come very close, but Stuart Irwin informs me that thcre is one specimen in the Sational AIuseum of Southern Rhodesia from Gadzema, Hartley district, S. Rhodesia, which is intermediate betweenfalkerrsteini and hellmapi. (This specimen is shown on the map with a combined dot and cross.) 'I'he relationship betwcen the two groups may thereforc be different in the east and in the west. T h i s is also suggested by the fact that in the west the ranges of the two groups coincide with the range of brachystegia and thorn country-although the Familiar Chat is a typical bird of rocky hills rather than of woodland or bush. In the east there seems no such coincidence.

(c) Yellow-bellied Eremomela, E. icteropygiulis and E. salzadorii, >lap 12.

In western Angola the Acacia Zone form of this eremomela, B. i. pziellula, is confined, like Purus afer benguelae, to the semi-dcscrt below the escarpment, and it has been collected in the Benguela area and at Cahinde. I t is small and very pale, with the yellow restricted on the abdomen, and it is closely allied t o E. i. icteropy*i+zlis of South West Africa.

In the Brachystegia Zone thcre arc two forms, one of which, poliosuntha, is linked to piiellulu and icteropygiulis by the intergrading race perimucha of Bechuanaland. However, since puellirla and polio.rantha represent the opposite ends of a cline they differ quite strongly from each other, polioxantha being larger with the yellow of the underparts brighter and extending t o the breast where it merges with grey of the thoat and upper breast. In Angola poliosantha has been collected at Vouga and at a locality 100 miles west of Vila Luso: it ranges eastwards through the Rhodesias t o parts of Portuguese East Africa and Natal. being found in either woodland or acacia country.

T h e other form of the Brachystegia Zone is E. salvadorii, which differs from all forms of I<. ictmopygiulis in having a green not a grey back. I t also has the yellow of the underparts brighter and more sharply divided from t h e grey of the breast than po[io.~aniha. 'The relationship between polir,.wtztha and sulvudwii i s obscure and it has been suggested that they are conspecific and that intermcdiates are found between them; no specimens which I have examined support this, typical green-backed salwadorii having been examined from S o v a Lisboa, Vila I,uso, Vila Flor, and \'ila Artur de Paiva (i'isser-Transvaal 1Iuseum Expedition) in Angola, thus overlapping the range of poliorantha. Outside Angola salvadorii has been collected in the Kasai, Lower Congo and the Balovale district o f Northern Rhodesia, and it appears everywhere to be confined to brachystegia woodland.

(d) Fiscal Shrikc, Lanius collaris, h l a p 13. \'ariation in the Fiscal Shrikes throughout Africa is largcly in three charactcrs, the presence or absence of an cyc-stripe, the amount of white in the tail, and size. In all these characters the two forms of the Brachystegia and Acacia Zones respectively are as strongly differentiated as any other two forms. 'I'he Acacia Zone form, L . c. subcoronatus, has a pronounced eye-stripe, a considerable amount of white in the tail and is large.

It ranges from Benguela through South West Africa and the Kalahari. The Brachysregia Zone form, capelli, has no eye-stripe, very little white in the tail and is small. It rmges from Malanje, Vila Salazar and Huila in western Angola, through the Congo and Northern Rhodesia, and is closely allied to the West African form smithii. The East African forms marwitzi and humeralls (in its broadest usage) ranging from Kenya to the Transvaal are intermediate in one or other character between subcoronatus and capelli, humeralis intergrading with slrbcoronatus in the Transvaal (Clancey 1954 : 79) .

(e) Brubru Shrike, Nilaus afer. (No Map.) The Brubru Shrike of the Brachystegia Zone, Nilaus a. aflinis, differs from all other forms in lacking chestnut on the flanks. It has a narrow white eye-stripe which terminates above the eye, and is similar in this character to the chestnut-flanked nigritemporalis of Northern Rhodesia. The representative in the Acacia Zone is N . a. brubru, which has the eye-stripe broad and protracted beyond the eye. It ranges from South West Africa to Southern Rhodesia and intergrades with nigritemporalis in the southern districts of Northern Rhodesia.

Specimens typical of affinls have been collected from Tembo Aluma near the Congo border in Malanje district, Duque de Braganqa, the central highlands and Caconda.

At Quilengues and at Jau in the Huila district intergrades between aflinis and brubnr have been found (Chapin 1954 : 17 and Heinrich " N . a. affinis " 1958 : 400), while Heinrich also collected a specimen typical of brubru at Jau. An intergrade between stfinis and nigTitempwaZis has been recorded from Mwinilunga by White (1949 : 286).

All the examples quoted point to there having been a barrier at some period that allowed the forms found in the Acacia and Brachystegia Zones of Angola to develop so differently. It is not easy to visualize how this barrier could have been formed unless in a dry period when the brachystegia woodlands disappeared from the plateau above the emrpment the invading acacia and thornveld petered out in the north into grasslands, as it does now on the coast, thus separating forms of the acacia from those in woodlands further north: with the return of the brachystegia the area must then have been re-populated by northern forms. This is suggested strongly by both the Familiar Chat and the Fiscal Shrike, in both of which the form of the Brachystegia Zone is the same as, or close to, the West African form. The green-backed Eremomel0 salvudorii is another form that probably developed in isolation north of Angola, but the grey-backedpolioxaniha may have been primarily an acacia form that has proved adaptable and has not been e.ntirely driven out by the re-invasion.

It has been pointed out that no satisfactory conclusions can be reached on the relationships between the forms of the Brachystegia and Acacia Zones until more collecting is done in the south, but present knowledge indicates that the Grey Tits, P. afer and P. griseiventris, which behave as good species in Rhodesia, are possibly isolated from each other in the west by the acacia-mopane belt and so can reasonably be regarded as species unlikely to interbreed. Eremomela salvadorii also seems to have achieved specific slatus, but it is not yet known whether there is intergradation in southern Angola between the coastal E. i. puellula and the central E. i. polioxantha. Above and below the escarpment near Sii da Bandeira the ranges of the Brachystegia and Acacia Zone forms of the Familiar Chat come very close without apparently interbreeding, although, since it is a bird of the rocks, the escarpment itself should be no barrier. T h e two forms representing the grey and buffish groups may therefore behave here as good species, though it is apparent that there is some interbreeding between the two groups in Southern Rhodesia, though not extensive intergradation. The Familiar Chat may be comparable IBIS 102 to the Fiscal Shrike, which seems to present an example of two extreme forms coming together and behaving as good species in Angola, but being linked elsewhere by intergrading races.

T h e Brubru Shrike does not seem to have achieved specific status, since intergrades are found between N . a. affinis and both N . a. bruhru and N . a. nigritemporalis; on the other hand the marked differences between aj-nis and other forms suggest that there has been a period of isolation and that interhreeding has taken place after the forms have come together again.

T h e Angola Batis ranges the full length of the Escarpment Zone from Capangombe to the Lower Congo and parts of the Rasai. It does not appear to have been recorded outside the Zone, its place heing taken in the Acacia Zone by R. pririt, in the Brachystegia Zone by B. molitor, in northern grasslands by B. minor and in montane forest on Mt. Moco by B. margaritae. At Gabela and Chingoroi R. minulla was collected in high trees on the edge of the forest but it has also been found at such places as Capangombe where there is no forest. It seems most closely allied to B. poensis, a forest species of West Africa.

This cisticola has been found throughout the Escarpment Zone from Quilengues north to Landana, and also in suitable habitat in the Acacia Zone, such as the marismas or " saltings " at Benguela and in rich bush and tangled undergrowth bordering some of the rivers north of Lobito. It is not found in acacia or on the inland plateau (Lynes 1930 : 319) . It is closely allied to C. chinzatta of thorn country throughout Africa and C. lateralis of the woodlands surrounding the Congo forest and which enters Angola in the Brachystegia Zone at lblalanje and Duque de Braganqa.

The Red-rumped Coly has a more limited distribution than the last two species being confined to Angola, from Capangombe north through the Escarpment Zone to Duque de Braganqa. Like the cisticola it is found also in suitable habitat in the Acacia Zone in cultivation behind Benguela and Catumbela, and is common as well in both woodland and forest on Mt. Moco. It does not therefore seem to be restricted by narrow choice of habitat and its limited distribution seems to be due more probably to competition from the widespread C. striatus. C. striatus appears to have invaded the territory usually occupied by Escarpment birds in the north since it has been collected at Landana and Noqui in the Lower Congo and at Camabatela: its range in eastern Angola has not been defined. C. striutus and C. castanotus are rather alike in colouring but the chestnut rump and lower back of C. castanotus distinguish it from C. striaius and all other species of coly.

T h e Angola Morning Warbler ranges from Chingoroi through the Escarpment Zone to the Lower Congo and southern Gaboon, and, like the Coly, is found also in cultivation behind Benguela and probably on ILIt. Moco, where a Morning Warbler was seen in thick undergrowth by a mountain stream. Chapin (1953 : 514) records its association with Borassus and Efaeis palms and baobab trees and it was collected at Chingoroi in small trees and undergrowth near the stream.

T h e only two other species of Morning Warbler, C. guttatn and C. arquata are both East African. C. ruficauda is clearly closely allied to the southern C. arguata, which ranges locally from Kenya westwards into the eastern Belgian Congo and Korthern Rhodesia, but there are sufficient differences in pattern and eye-colour for most workers to consider them distinct species.

(e) Tauraco erythrolophus. T h e Red-crested Turaco is another species apparently confined to Angola and found in the Escarpment Zone from Chingoroi northwards to the south bank of the Congo. I t spreads eastwards to BiC province in the Brachystegia

(a) Batis minulla.

(c) Colius castanotus.

Zone in gallery forest of such rivers as the Cuanza and this seems to be its usual habitat. Its only close relative is T. bannermani of the Bamenda-Banso highlands of the British Cameroons, from which it differs significantly only in the shape and colour of the bill (see Moreau 1958 : 104) .

This wattle-eye is another species about which little is known. Chapin (1953 : 682) gives its range as from the vicinity of Lobito north to Canhoca and Ambriz but has no confirmation that it reaches the Congo. There is a series in the British Museum from Dondo but I can find no definite records of specimens which have been taken from further south, nor any account of its habitat. It appears to be the representative in Angola of P . cyanea of the northern Belgian Congo and East Africa, and is sometimes considered as conspecific. The male differs from that of P. cyanea in the colour of the back and the female in lacking the conspicuous marooncoloured throat.

(g) Chlorocichlafallretls2eini. This greenbul has a rather wider range than other species in this group, being found north to Landana, reappearing in the Cameroons. It has been included since in the southern part of its range it is confined to the Escarpment Zone, and further north is restricted to the extreme western part of the forest. It has been collected in escarpment forest at Gabela and Chingoroi and is said by Chapin (1953 : 138) to be a bird of secondary growth and isolated forest patches, keeping near clearings in real rain forest. With its combination of green head, bright yellow throat and grey underparts it seems to have no close affinities with any other species.

This greenbul has a more limited distribution than the Chlolocichla but has been found further south at Vila Arriaga (= Biballa of Anchieta) and ranges northward through the Escarpment Zone to the Lower Congo at Manyanga and Ngombe Lutete (Chapin 1953 : 161) and Landana. At Chingoroi and Gabela specimens were netted in thick undergrowth of the escarpment forests and Chapin believes it to be a bird of gallery forest rather than main forest. P. fulviventris is very similar in colour and pattern to P. cerviniventris of Nyasaland and eastern Africa (from the Zambezi to Mt. Kenya), but is larger with a disproportionately longer bill.

This helmet-shrike and the following species to be discussed, are known only from a very limited number of specimens and little can be said about them. P. gubela was collected first in secondary forest 12 miles south of Gabela and has since been found in thickets on the plain below the escarpment 40 miles south of Mumbondo (Hall, in press) . In appearance it is closest to the widespread P. retzii, which is found at least as near to Gabela as Mt. Moco, but P . gabela differs from it in size and pattern and shows affinities with other species, such as P. plumatus, in having the frontal feathers growing forward.

The Gabela Flycatcher is known only from the same secondary -forest south of Gabela as the Prionops. Systematically it has been placed between M . aquaticus, which ranges from West Africa north and east of the Congo forest to Lake Bangweolo, and M. olivuscens of the Congo forest (Rand 1957 : 41) .

This Long-billed Warbler is known only from the type which Mr. Rudyerd Boulton tells me was collected in " dry, evergreen forest " at Chin-,yoroi. It is allied to M. concolor of the Congo Forest, but in greater size and longer tail it shows some affinities also with M. Kretschmeri of East Africa (Chapin 1953 : 245).

This waxbill is also known only from the type collected in the Escarpment Zone at " Deep Sloot " (about 13" S., 13"50' E.), Benguela. It is possibly conspecific with, or even identical with E. thornensis (see Chapin 1954 : 527) but this gives no clue as to its relationships as there is considerable doubt as to whether the only known specimen of t h o r n i s actually came from S l o Tome (Bannerman 1949 : IUIS 102 350). fi;. cinderellu appears to be closely allied to I;. caerulescens of West Africa and E. perreini of East and Central Africa but cannot be considered conspecific with E. perreini since R. p. perreini has been collectcd at Chingoroi within 50 miles of the type locality.

Heinrich's Cossypha with its distinctive white head is known only from the type locality 30 kilometres northeast of Duque de nraganqa and therefore cannot, perhaps, be considered as truly endemic to the Escarpment Zone. However its associations seem to lie with this zone rather than the Brachystegia Zone since it was collected in undergrowth and thickets of gallery forest bordering a stream in savannah country (Heinrich 1958 : 356) . It shows no close affinities to other cossyphas though nearest to C. albicapilla of West Africa.

The relationship of the two very distinct forms brauni and aniboimensis to Laniarius luhdcri and to each other is largely a matter of conjecture since so little is known about either. Since they are interesting forms which may have achieved specific status it is not out of place to mention them among the so-called endemic species of the Escarpment Zone. T h e tangerine-breasted brauni has been found at Quicolungo, Quibaxi (50 km. north of Vila Salazar) and Camabatela in gallery forest, and the white-breasted amboiniensis only at Gabela (Amboim). L . 1. lu/idtri, which has a fawn-brown chest and throat, ranges along the northern edge of the Congo forest reaching its southern limits at Stanley Pool in the west and XIt. Kungwe in the east: it is found in thickets and secondary growth om the edge of the forest.

E. cinderella is distinguished by having the whole lower abdomen red. (m) Cossypha heinrichi.

(n) Laniarius (luhdui) brauni and aniboinimsis.

Conclusions from Group 3 It can be argued that an old avifauna is represented by the endemic or ncar-endemic species of the Escarpment Zone, some of which have their closest relatives in widely separated parts of Africa (i.e. Tauraco bannermani in the British Cameroons, Cichladusa a r p a f n and Platysteira cyanea in East Africa, Ratis poensis in West Africa and possibly Phyllastrephus cervinizentris of eastern Africa). They thus seem to be relicts, comparable in some ways to the relict montane species on the mountains fringing the Congo basin, and amongst them are several which seem to be nearing extinction. Many of them do not seem to be primarily associated with the escarpment forests: Colius castanotus, Cisticola bulliens, Ratis minulla and Prionops gabela are none of them exclusively forest species. It is also possible that those, like the greenbuls Clzlorocichla falkensieini and Phyllastrephus fulvzvetztris, that now appear to be forest species, may have only recently adapted themselves to forest conditions since it is otherwise difficult to account for their limited distribution in the Belgian Congo.

T h e extent of the forest in the Escarpment Zone fluctuated with successive dry and wet periods. In a dry period, such as has been presupposed in the discussion on Groups 1 and 2, there can have been little forest anywhere in Angola. On the other hand it seems likely that there have been periods when the forest patches of Angola were continous with the Guinea and Congo forest, since there is often little variation among the typical forest birds that are found throughout.

Thus whilc the forest may be presumed to have advanced and receded, bringing with it its own distinctive avifauna, the endemic species remained in the Escarpment Zone, the forest itself serving to isolate them in the north, and the two dry zones isolating them in the south. In the course of these changes it is evident that only adaptable species would survive and only a small number now remain of what may once have been a rich avifauna.

In the foregoing discussions the climatic and vegetational changes which have been postulated have been deduced solely from the picture of evolution presented by the birds. It is therefore gratifying to find that the conclusions reached are largely consistent with those of Mr. A. W. Exell working on the flora of southern Africa. He has been kind enough to allow me to quote freely from the manuscript, awaiting publication, of an " Essay on the Flora of Southern Tropical Africa ". In this he speaks of the recurrent alternation of pluvial and dry periods in Africa during which the forests have swollen and shrunk in area and reciprocally the savannahs and grasslands have retreated and advanced. In the interpluvial periods the Kalahari desert was prompt to advance and Kalahari sand has occupied a vast wedge of territory extending through eastern and northeastern Angola right up to the Belgian Congo and almost to the Equator. Similarly the deciduous woodlands have advanced and retreated. This is all compatible with the suggestion that at one time the woodlands retreated from the plateau above the escarpment, while the Escarpment Zone provided an island in which birds not tolerant of dry Conditions have survived in isolation from others of their kind, which have retreated e astwards and northeastwards with the woodlands.

Speaking of the history of the vegetation Exell gives the earliest picture of which traces can still be seen as that of a coniferous forest extending over a large area, the remaining traces being found in isolated patches of such trees as Podocarpus, usually in montane evergreen forest. It is these patches, found in Angola on such mountains as Mt. NIoco amd Mt. Soque, and in remnants on the Chela Escarpment, which contain the specialized montane avifauna.

Exell goes on to say that following the coniferous forest in time was a dicotyledenous rain-forest, both lowland and submontane, which mingled with the coniferous forest, a t least at higher altitudes, and in its turn retreated leaving behind it its own relicts rather rnore widely distributed and usually less discontinuous than those of the coniferous forest. It is tempting to try and associate the old avifauna of the Escarpment Zone, which has its nearest relatives widely distributed, with this period of history. If so, with the retreat of the forest the relict species must have become adapted to non-forest conditions.

The present evergreen dicotyledonous rain-forest of Gaboon and the Congo, and the associated escarpment forests of Angola are probably of a later date. T h e majority of the woody plant species associated with these present forests have, like many of the forest birds, a continuous distribution through the forests of Guinea and the Congo. This supports the conception that the forests in Angola, now isolated, have at times been continuous with the Congo forest. There is evidence that they are now diminishing in extent.

The examples given in the three groups show that an unusual and interesting situation prevails in western Angola in the relationship between forms of the three avifaunal zones. Examples in Group 1 suggest that some forms of the Escarpment Zone are in the process of speciation. In Group 2 the examples are of forms developing specific characters in the two zones, on either side of the Escarpment Zone. Group 3 shows that there are an unusual number of endemic species in the Escarpment Zone. All this indicates that western Angola is an area of considerable importance in evolution but any explanation of how this situation has developed must necessarily be very speculative. T h e most tenable one seems to lie in the conception of the Escarpment Zone as an area less affected by climatic changes than surrounding areas, and one in which birds have been able to develop in isolation during successive wet and dry periods. In this zone also some species of an old avifauna have survived which have died out elsewhere under more extreme conditions. 15. P. HALL : FAUNISTIC IMPORTANCE OF THE SCARP OF ANGOLA

T o secure isolation between all forms in the Escarpment Zone and those in the Brachystegia Zone it is necessary to visualize a dry period in which Kalahari-like conditions spread all along the top of the escarpment into central Angola and mopane disappeared from the plateau. T o secure isolation between forms of the Acacia and Brachystegia Zone it must be supposed that at this period the brachystegia woodlands retreated away from all parts of the plateau of western Angola and, in the north, were separated from any that remained in the Congo or Gaboon, possibly by a belt of grassland. With the return of wetter conditions the acacia and the acacia forms retreated south, leaving occasional islands behind as a t Vouga, and the returning woodlands were re-populated largely from the north and northeast. In the period of isolation the forms in different zones developed independently and, on coming together again, in many cases behaved as good species in relation to each other. In other cases speciation was not so advanced and two forms have interbred. I t must be emphasized that much remains to be learnt of the relationships between most of these forms; more extensive collecting is likely to show that some of the conclusions are wrong regarding the individual status of forms, but this does not alter the conclusion that these forms represent stages in the development of species.

It can further be concluded from the distribution of Escarpment Zone forms that the conditions which pertain in that zone are found at least noith to Landana and that there has been a link at some time northward to the Cameroons. SUMMARY 1. Thc geographical features, in particular thc westcm cscarpment, and the climate and vegetation of western Angola combine to divide the area into three avifaunal zones.

2. An unusual relationship exists betwccn some related forms of diffcrent zones. 'I'his is illustrated by two groups of examples in which the characters of the forms are summarised, their distribution is shown on maps, and an attempt is made to interprct in evolutionary terms the picture presented.

3. Endemic or near-endemic forms of the Escarpment Zone are listed with some notcs on their aflinities with other species. 4. T h e botanical history of the area is discussed in relation to the conclusions reached on the evolution of the birds. 

Variation and hybridisation among the Paradise Flycatchcrs of

Miscellaneous taxonomic notes on African birds 4. Durban hlus. Nov

A review of the Houbou Shrike Ianiarius fernrgineus

59. T h e systematics of the African Grey Tits

T h e specific relationship of Parus afer and Parus griseizmfris

Essay on the Flora of Southern Tropical rifrica. (hl S awaiting publication.) Variation in the African Black 'l'its Parus niger and Parus kwcornelns

T h e ecology and taxonomy of sonic Angola birds

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Some aspects of the IMusophagidae

A second contribution to the ornithology of the British Cameroons. T w o new species of birds from Angola

A Check List of the Birds of Southern Rhodesia. Cambridge. Systematic notes on African birds