6 THE BIRDS OF THE BRITISH ISLES. 



the Holarctic Region. The remainder of Africa and southern 

 Arabia is the Ethiopian, whilst the Oriental or Indian Region 

 includes southern Asia and the Malays. Australia, New Guinea 

 and the southern Pacific form the Australasian Region, from 

 which Huxley separated the New Zealand area. South and 

 Central America are the Neotropical Region. The British Isles 

 lie on the western boundary of the Palaearctic, and are influenced 

 by that region, the Nearctic, and in summer by the Ethiopian. 



The chart, mapping the topography of a typical bird, will 

 explain the terms used in descriptions ; technicalities are 

 avoided wherever possible. I have endeavoured to point out 

 salient characters, noticeable in birds in the field, rather than 

 complicated descriptions of plumage. The illustrations of birds 

 which vary so greatly in size cannot all be on the same scale ; 

 I have therefore endeavoured to depict them on the plates to 

 show as much detail as space permitted. The measurements 

 supplied at the end of each description are merely to indicate 

 size ; birds of one species vary greatly in size as well as plumage ; 

 only by giving extremes of a large number of specimens can we 

 arrive at anything like accuracy. The length, measured from 

 the tip of the bill to the tip of the longest tail feather, is always 

 a rough, uncertain measurement, utterly unreliable if taken from 

 a dry skin. Although millimetres are now usual for scientific 

 measurement, I believe that for the general reader inches and 

 tenths are preferable. 



There is one point which the town-dweller must remember. 

 The illustrations are of birds at their best, bright and clean, and 

 do not represent the soot-soiled specimens that are met with in 

 manufacturing districts or near large cities. 



The songs and calls of birds are a great difficulty to the 

 novice, and, often enough, to the expert. In many cases it is 

 impossible to give a correct impression by any combination of 

 letters, with some even instruments utterly fail to provide an 

 imitation which can be recognised. 



