168 BIRDS OF TUNISIA 



specimeu of doubtful Grey Shrike obtained from South Tunisia with 

 examples of L. fallax in the British Museum, I found it agree so 

 closely with some of them that I determined to refer it to this species. 

 Having, however, now obtained similarly plumaged birds from a 

 district in Central Tunisia which may be considered the meeting 

 ground of the two, L. algeriensis and L. elegans, I am inclined to look 

 upon these birds as being either hybrids between the two species, 

 or else as belonging to intermediate forms, modified according to the 

 natural characteristics of the localities where they may occur ; in any 

 case, I think it evident that they should not be referred to L. fallax, 

 admitting this to be a good species, which is perhaps open to doubt. 



"Which of the two theories I have just mentioned may be the 

 correct one I am not prepared to say, although the balance of evidence 

 is perhaps somewhat in favour of the former. The theory of hybridism, 

 unentertainable as it might be in certain cases, is certainly not 

 improbable in a case like the present, where the two species in question 

 are so closely allied, and where no sufdcient natural boundary or 

 division exists to keep them apart, for the Atlas Mountains in Tunisia 

 do not form the same unbroken barrier that they do further west. 



" In favour of this theory, moreover, are the following facts : firstly, 

 that, so far at any rate as I have been able to ascertain, there does not 

 seem to be a gradual continuity of intermediate forms connecting 

 or uniting the two species ; and secondly, that in the particular 

 district where these nondescript birds occur we do not find one 

 constant type, but individuals which vary in plumage among them- 

 selves, some resembling more L. algeriensis and some L. elegans, and 

 others, again, standing halfway between the two. 



" On the other hand, in support of the alternative theory of 

 intermediate forms may be adduced the argument that the difference 

 between the two Shrikes, L. algeriensis and L. elegans, although 

 sufdciently pronounced in typical examples, isj after all merely one of 

 plumage-colouring, or, to be more precise, I should say a difference 

 in the shade of plumage-colouring, and in the proportion of black and 

 white markings, this difference being subject to modification according 

 to the locality inhabited. Structurally there would appear to be 

 no difference whatever between the two species. In the case of 

 typically plumaged birds, besides the very marked difference in the 

 shade of the general grey colouring, both above and below, we have 

 that of the markings of the wings and tail-feathers, there being. 



