THE IBIS Vol. 103a, No. 4, 1961

HYBRIDIZATION OF CORVUS ALBUS AND CORVUS EDITHAE IN ETHIOPIA

C. M. G. BLAIR

Received on 2 November 1960

In 1949 I went to live in the highland plateau of eastern Arussi, 100 miles southeast of Addis Ababa in Ethiopia, and I lived and travelled in the area for ten years. A wide and systematic collection of skins was not possible, but I believe the following observa- tions are sufficient to establish the fact of hybridization between Corvus albus and Corvus edithae beyond reasonable doubt, thus confirming what Friedmann (1937) suspected.

The two species. Corvus edithae and the more widely spread north African Corvus rufcollis are some-

times regarded as conspecific with Corvus corax, but Vaurie (1954) made a case for keeping C. ruficollis as a separate species. If this conclusion is accepted then it must follow that C. edithae can no longer be attached to C. corax because it is geographically separated from it by ruficollis. It is possible that edithae and ruficollis may be conspecific but the probability that C. edithae interbreeds with C. albus suggests a close affinity also with that species. Until the matter has been studied more closely, and for the purpose of this note, I will refer to C. edithae as a separate species.

At present C. edithae is known either as the Somali Dwarf Raven or, because of its association with Corvus corax, as the Lesser Brown-necked Raven. Both are cumbersome names and neither is satisfactory, especially the latter. I t seems to me that " crow " is a more appropriate name than " raven " and if edithae is removed from C. corax, as it seems it should be, then there is no reason to retain the name " raven ". I suggest that an adequate and simple name for C. edithae would be " Somali Crow ". The Somali Crow inhabits the Somalilands and southeastern Ethiopia as far west as the Galama (Chilalo) range of mountains in central Arussi. It is not known on the west side of the rift valley and is non-migratory. The Pied Crow Corvus albus which extends over most of the Ethiopian region from Senegal to the Cape, is the common crow of the western Ethiopian highlands. It is occasionally seen in the rift valley itself, and it breeds on the eastern slopes of the rift east of Lake Zwai, in southeast Ethiopia, where it almost reaches the western limit of C. edithae. In the non-breeding season the Pied Crow migrates outside its breeding limits, and parties of three to six birds have been seen flying into eastern Arussi in August.

Phenomenon of " speckled " uows. The Somali Crow is wholly black and the Pied Crow is black with a broad white

collar and a broad band of white on chest and upper belly. Intermediates with varying amounts of black on the white chest and collar have been observed at a number of points along the northwestern limits of the C. edithae area. They were probably first observed by Erlanger, who obtained a male crow with speckled breast and upper mantle at Dangasela in " Arussi-Gallaland " in 1900. Although I have not been able to identify

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Dangasela, the old " Arussi-Gallaland I' represents the modern provinces of Arussi and Bale and would include most of the area in which my own observations were made. Kleinschmidt (1906) referred to this specimen and described and illustrated three such birds from Abyssinia. He regarded them as dark forms of C. albus, and gave them the name C. a. phaeocephalus. Two of them had odd black feathers on the white areas, and the third had light brown ends to the feathers of the same parts.

Since 1949 I have seen several hundred intermediate birds in this area (Fig. 1). In appearance they range from birds which seem to be albus with a few dark spots on the white areas, through heavily speckled birds to others which seem to be edithae except that some of the breast feathers are tipped with white or the whole chest and breast are light brown instead of black. In intermediates the white of the upper mantle tends to disappear before that of the chest, so that some birds observed had a considerable amount of white on the chest but none on the back of the neck.

I DIRE W W A

i J BALE

FIGURE 1. Sketch map of Arussi area in Ethiopia with shaded areas indicating whcre hybrid breeding populations of Corms albus and C. edithue have been noted.

Migration and mixed jocks . The migrations of the Pied Crow in Arussi are erratic and ill-defined. Small parties

(probably families) enter the area about August and mix with the flocks of resident Somali Crows through the dry season. Pied Crows leave the Arussi area between January and March but an occasional straggler will stay right through the breeding season (March to June). It is presumed that the birds of intermediate plumage are the descendants of such stragglers which have successfully bred with the Somali Crow.

I have only seen mixed flocks" near the northern and western limits of the Somali Crow range (Fig. 1). A flock of 30 crows in the SoudC area on 25 August 1955 contained 19 Somali Crows, 10 intermediates and one Pied Crow. One wonders whether the single Pied Crow was a resident breeder, although the date indicates that the migration

* By " mixed flock " is meant one (invariably edithue) or both species, plus intermediates.

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season had begun. Most of the intermediates showed only white or fawn flecks on the breast and only three or four showed enough white to be probable first generation hybrids, On another occasion, in November 1954, a flock of about 100 crows circling over the town of Haramaya, midway between Dire Dawa and Harar, contained 90 Somali Crows, five Pied Crows and five intermediates. These two examples are almost extremes at opposite ends of the scale as far as the proportion of intermediates is concerned, but the proportion of C. albus in any mixed flock is always low. Within the critical area mixed flocks are common, but pure flocks would nevertheless be commoner.

Breeding and hybridization. In the Arussi highlands the Somali Crow breeds in tall trees which are found here

and there on the extensive grass plain, and there may be a mile or two between neighbour- ing breeding pairs, For this reason one normally observes few nests and it is not surprising that I have never seen a breeding pair of apparently pure birds of the two species of crow, which must in any case be rare. The comparatively large number of intermediately marked birds in the critical areas must therefore be accounted for by the fertility of the hybrids.

During the three breeding seasons 1955, 1956 and 1957 a pair of crows bred in a large tree near my house at SoudC. The male of the pair was wholly black and evidently a pure Somali Crow, with a broken toe which hung down in flight making him easily recognizable; and the female was a hybrid with the typical black and white speckling of the breast and neck. In 1955 breeding began in May and three young birds left the nest in June. One of these was shot on the edge of the nest on 11 June (?CH/l). Another (?CH/2) was collected exactly one month later while still consorting with the parent birds. CH/l has very slight white specks on the breast and CH/2 had a light brown breast. The female of the pair (CH/4) was shot in January 1958. The skins of these birds are in the British Museum (Natural History). In each of the three breeding seasons observed all the offspring of this pair of crows (three in 1955, four in 1956, four in 1957) had markedly less white in the plumage than the hybrid parent, and some of the young birds could not be distinguished in the field from pure Somali Crows.

Assuming the speckled parent to be a first-generation hybrid of the two species of crow, it is evident that such hybrids are fertile. The fact that white in the plumage is passed on for at least one further generation is equally evident, obviating the necessity to presume frequent interbreeding between pure birds of the two species to account for the comparatively large number of speckled birds observed.

Observations on plumage. In order to trace affinities within the genus Corvus in northeast Africa skins of the

following species were examined at the British Museum (Natural History); 10 of C. edithae from Somaliland, Ethiopia and north Kenya; 6 of C. ruficollis from the Sudan; and 7 of C. albus from Ethiopia and the Sudan. There is no obvious structural difference between the three kinds of crow examined. C. albus (wing 338-380mm.) is on the average slightly larger than C. edithae (wing 317-362 mm.), and C. ruficollis (wing 366-404 mm.) is on average larger than C. albus. The relative lengths of the primaries is the same in each species. The ratio of length of culmen to length of wing is almost exactly the same in ruficollis (1 : 6.1) and albus (1 : 6.2), and 10% less in edithae (1 : 6.9).

It is of interest that in both C. ruficollis and C. edithae the basal half to two-thirds of the feathers from chest to breast and on the back of the neck and upper mantle are white or whitish, whereas the remaining body feathers have very little white at the base. These areas of white-based feathers correspond with the areas of wholly white feathers in C. albus. In addition, the apical half of these feathers was brown, not black, in four of the ten specimens of edithae. In ruficollis the feathers of these areas, as well as of the head,

502 c. M. G . BLAIR : HYBRIDIZATION OF CORVUS ALBUS AND CORVUS EDITHAE IBIS 103a

are always more or less brown. These observations and the evidence of hybridization give some justification for my earlier remark that there is a close affinity between the three African crows, C. edithae, C. albus and C. ruficollis.

I wish to record my gratitude to Mr. J. D. Macdonald for his interest and help in the preparation of this paper, and to Dr. J. F. Monk for improvements to the draft.

CONCLUSIONS AND SUMMARY

It appears that hybridization between Comus albus and Corwus edithae takes place in south- eastern Ethiopia where the two species meet, and this is a more likely explanation than that they are forms of albus as suggested by Kleinschmidt, or edithae. It would be interesting to know if there is any evidence of hybridization between C. alhus and C. ruficollis in the Sudan, where these species meet.

Hybridization between the Hooded Crow Corwus cornix and the Carrion Crow Corwus corone is well known. Kleinschmidt suggested that C . albus is the African representative of the Hooded Crow. If this was the case its hybridization with C. edithae might suggest, by analogy, that C. edithae and C . rujicollis are really the African representatives of the Carrion Crow C. corone rather than of the Raven.

REFERENCES

FRIEDMA", H. 1937. Birds collected by the Childs Frick Expedition to Ethiopia and Kenya Colonv. 2. Passeres. Bull. U.S. Nat. Mus. 153: 1-506.

KLEINSCHMI~T, 0. 1906. Beitrage zur Vogelfauna Nordostafrikas mit besonderer Beriicksichtigung

VAURIE, C. 1954. Systematic notes on Palaearctic birds. No. 5. Corvidae. Amer. Mus. Novit. der Zoogeographie. J. Om. 54 : 78-99.

1668 : 1-23.

C. M . G. Blair, P.O. Box 1089, Addis Ababa, Ethiopia.