8 ETNAR LÖNNBERG, BIRDS. 



nunmehr eine Landverbindung zwischen den einstigen Inseln hergestellt war. Jedoch 

 erscheinen solche Hypothesen bei dem gegenwärtigen Stande imserer faunistischen Kennt- 

 niss Afrikas noch verfriiht. »* 



It appears to the present writer that any such theory about tlie possibility of the 

 mountains in question having once been islands in a former sea is not needed for the ex- 

 planation of the facts quoted above. From a biological point of view they really are a 

 kind of islands, because the conditions of life on them are different from those prevailing 

 in the surrounding country. They are thus isolated spöts in that respect just as well as 

 an island outside a continent is. But on the other hand the isolation between some of 

 these mountains is not fully as great as it formerly was believed to be. The mountains 

 in tropical Africa are generally covered more or less with forests in consequence of the cli- 

 matic conditions prevailing on them. The birds enumerated by Reichenow as examples 

 of nearly related forms occurring on distant and isolated mountains, viz. members of 

 the genera Cryptospiza, Linurgus and Alcippe (or Turdinus) , are all of them forest birds. 

 The first and last of these genera are now known from so many places in Africa where fo- 

 rests are to be found that their being represented on the Cameroon mountain, and on Kili- 

 manjaro no longer is apt to create much wonder, and it is rather to be expected that Li- 

 nurgus will be found in intermediate localities 2 as well. A somewhat analogous example 

 may be offered. The genus Alethe is enumerated by Reichenow 3 among those which, 

 when he wrote his great work, were known only from the western forest-region and thus 

 characteristic of the same. Not long time ago, however, a typical member of this genus 

 was described by Dearborn, then by Jackson from Kenia and Kikuyu forest, and finally 

 also collected by the present author in the forests on eastern Kenia, and at Meru borna. 4 

 This Alethe from Kenia is undoubtedly only a geographic race of a species originally de- 

 scribed from Cameroon and Fernando Po. By the study of a rich material which could 

 allow an extensive comparison of specimens from different parts of Africa I am convinced 

 that many similar examples would be found, and the resemblance of the birds of the dif- 

 ferent mountains of tropical Africa would then fully be explained. 



It is, of course, almost impossible to express the distribution of a species of bird with 

 some single letters signifying a certain region, province, or district, because there are very 

 few birds which have identically the same range. Nevertheless I have tried to make 

 some arrangements in this respect to facilitate a general review of the geographical distri- 

 bution of the species known by this Expedition. It must therefore be emphasized that 

 in the following tables the letters signifying the range of the different species are only an 

 attem.pt of approximate valuation of the zoogeographical facts. It is hoped, however, 

 that it may be a contribution to a correct valuation, even if alterations are needed here 

 and there, and necessarily will come with the increase of our knowledge about the African 

 ornis. The general range of the birds in relation to their occurrence in the country visited 



1 Vögel Afrikas I, p. I -XX XIX. 



2 I almost suspect that I saw a pair of Linurgus in the mixed forest- and bamboo-region, but as I did 

 not succeed in shooting any of them I do not dåre to make any statement. 



• ! i. c. i, p. Lxxxvin. 



4 Conf. about this further below. 



