137 [Vol. XXXV. 



" The Bustard case may be of the same kind, and, if so, 

 one would expect a darkening of the plumage in the damper* 

 island climate. If this were so, oue would have to regard 

 the apparent protective resemblance as merely a coincidence. 



" By the way, are there enemies f on the island which 

 could theoretically eliminate the lighter forms ? 



"It would be a pretty experiment to transfer the con- 

 tinental form to the island climate and observe whether it 

 got darker with successive moults.^' 



Dr. Hartert : I think it is very clear, from what Mr. Ban- 

 nerman has said_, that it is the wish of Nature that the bird 

 should assume the colour of the soil on which it lives. 

 In the Sahara — at least, where I have seen it — there are 

 certainly no black lava-blocks, and therefore, because the 

 black lava-stones cover the plains of Faerteventura^ the 

 Bustards have become black-spotted, so as to accord with 

 these lava-strewn plains. If the rainfall is not much 

 greater, and the air not more moist in Fuerteventura than 

 in Morocco, which I thought was the case, I think it is a 

 very clear instance of the actual adaptation of a bird to 

 the surrounding soil, and has a wonderful bearing on 

 Lord Rothschild's remarks. The same may be said of the 

 Crested Larks. 



The Chairman : I think Dr. Hartert's meaning is that 

 the birds which do not resemble the soil die out through 

 their inability to contend with certain factors which produce 

 the variation. 



Before calling on Mr. Baker, who has some remarks to 

 make, I should like to point out that in the case of those 

 Galapagan Finches where the males are very black instead 

 of blue, and the females have become light grey instead of 

 dark brown, that the climate of the Galapagos Islands is 

 extremely dry, while the climate of British Guiana and 



* [In my letter to Professor Pimnett I had not laid sufficient stress 

 on the fact that the island in question possessed an exceptionally dry 

 climate. — D. A. B.] 



t [The only enemy of the Bustard in Fuerteventura is Man. No 

 mammals or reptiles exist in the island in a wild state, and hardly any 

 dangerous Birds of Prey. — D. A. B.] 



