On the Birds of North and Central Darfur. Taxo-nomic Appendix –Part III-X
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346 Admiral H. Lynes on the [Ibis,
Brattta hutchinsi. 10 adult males. Wing 390-455 (419); culinen 34-45 (39.4) ; tarsus 68-86 (77 ) ; mid-toe and
Branta catiodensis canadensis. 10 adult males. Wing 418-527 (500.6) ; culmen 47-58 (52.4) ; tarsus 76-98 (92.3) ; mid-toe and claw 77-106 (97.3).
Branta canadensis occidentalis. 4 adult males. Wing 433-495 (465.7) ; culmen 48-51 (48.7) j tarsus 86-99 (92.2) : niid-toe and cli~w 83-95 (87.2).
claw 67-85 (73.5).
P1. VII. illustrates typical skins of adults of : 1. Branta canadensis occidentalis. 2. Branta hutcliinsi. 3. Branta minima. 4. h a n t a bernicla.
The last is introduced to show its size relative to Branta miriinaa.
XIV.--On the Birds of North and Central Darfur. Tax+ By ADMIRAL HUBERT LYNES, nomic Appendix.-Part I.
C.B., C.M.G., M.B.O.IJ.
IN my account of the birds of North and Central Darfur, I promised* to explain in an Appendix my reasons for having published determinations of a few of our specimens some- what out of' line with what had hitherto been in general acceptance. This I now do for all the species concerned except the Uisticolae.
Seeing that little useful could be done by a small incursion into it, I am now engaged in an attempt to review the whole of that group. Thanks to cordial help from our colleagues abroad, nearly all of whom have been able to send me the type-specimens out of their museums, from Lord Rothschild and Dr. Hartert, who have given me the whole of the Tring
* Ibis, 1924, p. 649.
1926.J Bird.$ o j North untl Central llarfur. 347
collection to put nlongsidr. :hat of tlie British Muwuni, iind from our Editor and others, this rather formidable venture progresses, I think, well, and I hope to be able to offer the first part oE the review for our Ju ly ' Ibis.'
The contents of the present contribution are as follows :-
Prefatory Remarks .................................................. 347 Clessifiaation of Ge 369
(Map 13.) ...................................................... 376
.................................... 392 15.) . . . . . . . . . . . . . . . . . . . . . . . . . . . 387
,, ,, African Grey-headed S p a ~ o w s (Passer g r i s e u ~ etc.).
Note on Genus Hypochera. ... ,; Pyte l ia melba citerior .............................................. 399 ,, Pyromelana hordacea . . . . . . . . . . . . . . . . . . . . . . ............ 401 ,, Muscicapa (Aleeonax) qa3nbag.z .............................. 401 ,, Crag-Martins (Ptyonoprogne) ........................................ 402
Map 8. Africa. Avifaunal subdivieions. 7 ,, 9. Africa. Physical. ,, 10. Africa. Political. Plate VIII. I ,, 11. Africa. Vegetation. J
1 Plate IX. Map 12. Genus Umginth.us. Distribution, Map 14. African Grey-headed Sparrows.
,, 13. African House-Sparrows. Distribution.
,, 15. Genus Cercontsla. Distribution in Africa. }Plate X. Distribution.
The classifications are offered with the idea OF their helping to make the groups of birds concerned, their affinities and distribution better understood than hitherto ; except in one or two respects, which I will esplain, there is nothing very novel in the inode of treatment, the plan Eollowed being merely the custoinary and necessary one of bringing up to date older classifications by meails of recently acquired knowledge.
SVBSIWXES. I n discriminating between species and suhspecies I have
endeavoured to follow tlie general principles of Mr. F. M. Chapman's excellent " Criteria for tlie Determination of Sub- species ...... (Auk, xli. 1924, pp. 17-29); that is, treating
348 Admiral H. Lyiies on the [Ibis,
.each case on its merits, basing conclusions on due con- sideration of all Rvailable pertinent evidence rather than following either of the I two general rules in more or less current use.
Mr. Chapmans thesis is costnopolitan, but as the examples he selects to mike his points itre of American birds, 1 should like to mention a f e w aspects of the case drawn from a study of soint! Arican birds, i n order to illustrate in a general way soine of the cases concerned in this paper. For repeti- tion wliich cannot be avoided I can only ask to be forgiven, and plead that, there is very little in thet pitper that is not well worth repetition.
The following are prominent among the cases that hxve to be provided for with a suitahle mode of treatment *, and refer to resident birds only :-
(a) The very cominon one of intergradation of external characters, little by little. Geographical variation in its most obvious form ; this touche9 several of the subjects in m y classifications- UrRginthus, Passer griseus, for example. No further remarks are necessary, except to explain the slight novelty of treat>meiit which I have adopted in order to show proportion ; this follows.
(6) Not greatly different, and also easy of recognition as nothing more than eiinple geographical variation, is that in which two very slightly different forms occur near one another ; but tho transition is more or less abrupt t. Whether, if there is a small gap between their respective ranges, it may be ascribed to the intervention of some obvious natural barrier, or no such reason is apparent, or the two forms are found to occur somewhat indiscriminately over a narrow neutral zone $ ; from their strong reselnL1:ince to one another, That is, suppasinK there to be enough material to ~ ~ p p l y the facts.
Of course it is often quite a different proposition when it comes t o I placing a newly-discovered bird, or birdrr, from an iaolated or new locality, or when the birds themselves and their distribution are very little known.
t Some examples for the Sudanese arid belt were named on p. 766, Ibis, 1926, under (6).
3 Not at all uncommon; Cisticola rwficeps is one, the ne~rrtl zone being R t the Nile.
I 926.1 Birds OJ North and Central Ilarjiir. 349
and other considerations, such as noling the style of chnnge in the species in other parts of it$ raiige, their sub,p s ecific relationship may be called practically obvioue. In present practice a case even more common than (u) ; but it is safe to guess only so, because in many cases exploratioti and colleating have so far been insufficient to supply the inter- mediate forms that probably exist. For the latter reason alone no review of' the changrs in a species ranging over most of the Continelit can well be expected to be free at all its poiiits from a case of this sort for inany a long clay. I t recurs niore or less througliout the present classifications.
(c) That in which t w o obviously riearly related forms occur quite close to one another, or even with ranges that on the map overlap one another (whicli is not always the same thing as the t w o forms being actually alongside one another), and present differences wlicli, though no greater than tha t which cumulative effect of variation often produces in species a t the opposite ends of a wide range, are con- siderably greater than what one would expect to be due merely to the causcs-whatever they may be-promoting geographical variation, judging from other species in a cotnparatively sinall district.
Tllnstrations from among my present subjects are the House-Sparrows and Passer gongon~nsix, which seetii to m e decidedly difficult of treatment.
(d) Also difficult of' treatment, assuming, of course, that in classifying such birds the aim is x higher one than merely to group them up i n a convenient way for reference ; that in which two slightly tliferent kinds occur in widely separated places with nothing like them in between. The large pap in distribution, say of half the Continent, may be diic either obviously to lack of sdtable environment in i t or to no apparent cause ; the ground in between h n s been well worked and no connecting links have been found. The case of Passer naotitensis and Passer c*ordofanicus furnishes an illustration among my present subjects, and, inter alia, it is very pertinent to certain other '' arid " bird-forms inhabiting tlie widely eeparated Sudaneae and the south-west arid districts of Africa. Mr. Chapman ( t o m cit .) gives his
350 Admiral H. Lynes on the [Ibis
opinion as to how some cases analogous to this are properly treated as subspecies, illustrating it Iiy the Horned Larks (Otocoyys etc.), but, as he stiys, each case must be treated on its merits.
'l'lia '; Formenkreise " of our German colleagues, I believe, presents such matters from another point of view, tmt I have not yet breii able to study i t proprArly ; however, 131.. Stiese- Inann teile me that lie will read :L paper on it at the forth- coniing Ornithological Congress, and I am sure that too will greatly help townrds putting us more in line in these difficulties of classification.
How SUBSPECTER HAVE BEEN TREATED IN TEE CLASSIFICATION.
The classifications are those comidered suit:rble for general ornithology, i. e . for all ordinary purposes, for i t check-list like the ' Systems Arium Etiriopicarum,' and so forth : that is their purpose. Greater subspecific refiiienient is necessary for the complete study oi' certain special problenis, but for all ordinary purposes wonld, I t h i i i l i , defeat the purpose of the classifications for grner.:il use, by niaking thuni too corn pl ex.
I n any case, no matter what the end in view, when it, comes to classifying the geographical races of a species with an uiibrolren are:: ot' diJtribut>ion, consistent treatment deinands the creation o some arbitrary standard of recog- nition ; or, to put it in other words, when the transition t'rom one form to others i n other districts is gradrml, a i d every sort of intermediate is f ~ u n d , tlie selection of the subspecific units in a c:lassification cannot but be a rnntter of convention. The standard itdopted niust suit the purpose ot' tlie claesifi- cat,ion : if the standard is not considered acceptable, then the classificritioii itself must be modifid 01. rejected.
I believe tliat the study of geographical i 'orm, compara- tively new :IS it is, is suHiciently atlvnnced to show tile desirability of having some sort of generally accepted standard for this phase of classification ; but however tliiit may be i n other parts of t h e world, in North Tropical
1926. J Birds of Nortlr and Central Dwfur. 35 E
Africa iE not throughout the whole Ethiopian Region,. where ecology is so largely the key to the dibtribution of its- geographical forms, one is constantly finding the need of' it.
This is the nature of the ever-recurring problem ; rexders of Part 11. of my paper will already have reinarireti how it pervades the relationships of the birds of DsrEur mitb other parts of North Tropical Africa.
In a series of sprciinens f'roin districts A and 13, any person of' averiige perception, wi th no other aid t1r:tn tlie eye to gauge the colour-tints i l t i t l :I millimetre measure f o r the size, can correctly separate '30 p9r cent. or more of them on the table according to their respective districts. Everyone agrees that the two are good geographical races and iiiust be given two different subspecific names. Specimens from between districts A and 3 are found to be hterniediate in every degree ; froin here most of' thein nearer the A race, froiii there nearer the S ; from elsewhere about Iralf-way between the two ; from almost anywhere in the intermediate territory occasional examples are to be found inseparable from the A or B foriris ; and from no localit,y in i t m e more than about 50 per cent. clearly sep:mhle froin either oiie or the other. But while everyone agrees to tlie facts, every sort of contrwversy arises over the taxonomy, culminating in natural consequence over the nonienclatnIe, whether inore races have been named than ciili be recognized o r accepted, and so forth-taxonomic discussions not always constructive, and which often leave one in doubt which opinion to follow, and to wonder whether the diH'erence of opinion is not due rather to difference of' treatment of the subject than to any doubt about the observed facts.
For illustration take Passw giiwzis, and refer to the classitication proposed on p. 382.
Fourteen years ago three races, eritrew, nruwia,rni, and swainsoni *, were described as occurring i n a part of Eritrea about the size of Oxfordshire.
On the one hand, there could be 110 doubt about the * J. f . 0. 1911, pp. 33 etc. (the no nclatnre lins latterly been
352 Admiral H. Lynes on the [Ibis,
existence uf differences which caused so expert an ornitho- logist as Count Zedlitz to separate the three forms; on the other, it was difficult to understand how three different sub- species could occur in so circumscribed an rirea.
Increiised knowledge and study of the birds and geography sf this and the surrounding countries now shows that in Erit,rea the forms of Posser grisezts and a number of other species are intermediate between those of the Abyssinian Plateau arid the British Sndan, and that fha pliysical geography of Eritrea is also of ;in intermediate character.
I n the light of this knowledge the difficiilty is explained : ,just us one might have expected, t;il;en as :,L whole (i. e. as shown by series of specimens), the mount:iin birds are nearer to, so in^ inseparable from, the grey-breasted bird dominant in Abyssinia, those on the Sudan side of the mountains inore like t lie white-broasted bird dominant in the Sudan, :md on the Red Sea side rather niore like the Abyssinian ; hnt froin almost any part of Eritrea come .occasional examples inseparable ~ O I I I one or otlier of the two dominant forms, and nowliere are more than about .50 per cent. quite like one another. Any person of average perception can separate the two dominant forins correctly by their colour-differences ; and their separate identity has ,never been questioned since the study of geographical races began, whereas the validity, appropriateness, distribution,
.and everything .else to do with intermediate nettmami have always been controversial.
And the case is clearly typical of what occurs with many .other continuous ranging species in Eritrea, in North Tropical and other sufficiently worked parts of Africa, and probably all over the world.
I n the hope of not adding to what has been non-construc- tive in sonie of these discussions about subspecies, I have aelected three main principles a s the governing factors of my classifications ; they :ire as follows :-
Factor I. postulates t,hat one single classificiition cannot he sufficiently refined lor t h e study of every special subject
~ 9 2 6 . 1 Birds ofiYorth anti Central Darfur. 353
without making i t too involved to fulfil its main function, which is certainly that of facilitating the study of general ornithology ; and that when special subjects are to be studied, a inucli more refined classification inay often be required.
For illustration refer ag...