82 A HISTORY OF BIRDS 



roughly speaking, the birds frequenting the mountainous and 

 more humid regions of the north are dark in colour, those 

 found in the lower lying and drier central districts, paler, while 

 those inhabiting the arid desert country of the south are 

 isabelline or sand-coloured." 



Captain Boyd .Alexander, on his return in 1907 from his 

 remarkable journey across Africa, showed me a particularly 

 interesting case of bleaching. This was furnished by a Night- 

 jar {Capri iiiii/gHS cUmdi) which presented two phases — a light 

 and a dark phase. The former is found only in open country 

 away from the forest region — by Lake Albert — on ironstone 

 rocks. The birds which exhibit this pallid hue are never found 

 among grass or other vegetation, but pass their whole lives amid 

 the rocks, which they so closely resemble in colour that they 

 are invisible until approached within a couple of feet or less. 

 The darker phase of this bird occurs towards the Gold Coast, 

 on the borders of the forest, where there is a heavy rainfall. 



Since desert conditions beget bleached forms it is not sur- 

 prising to find that the opposite — a moist atmosphere — should 

 produce dark-coloured types. A case in point we have just 

 referred to, in the Night-jar. White-throated Sparrows and 

 Wood-thrushes are said by Mr. Beebe to become "almost like 

 Blackbirds in colour when confined in a bird-house where the 

 air was constantly moist". "A South x^merican Pipit," he 

 continues, " the individuals of which passed their lives on very 

 circumscribed plots of earth, exhibit two colour forms entirely 

 different, and thought to be due solely to the amount of moisture 

 in the ground on which it lives. Very dark coloured and very 

 pale individuals live within a few hundred yards of each other, 

 in dry and swampy stations re.spectively, each, it is said, keeping 

 entirely to its own little beat ! " 



Mr. Whitaker has drawn attention to the fact that the 

 Skylark {Alauda arvensis), which is found in the marshy 

 Roman Campagna, is exceedingly dark in colour, so much so 

 as to foi'm a distinct race. 



Similarly in the Galapagos Islands, where the climate is 

 damp, the birds are remarkable for their dark coloration. That 

 this is due to the humidity of the climate is clearly demon- 

 strated in the case of two species — a Short-eared Owl {Asio 

 galapagooisis) and a Night-heron {Nycticorax pauper), inasmuch 



