CONTINENTAL RACIAL FORMS, ETC. 99 



CONTINENTAL RACIAL FORMS OF SCOTTISH 

 BREEDING BIRDS AND THEIR OCCUR- 

 RENCES IN SCOTLAND. 



By Leonora Jeffrey Rintoul, H.M.B.O.U., and 

 Evelyn V. Baxter, H.M.B.O.U. 



Each year more interest is being taken in the study of 

 geographical races of birds, their importance is becoming 

 more generally recognised, and their value more appreciated. 

 There are, of course, many species which do not vary in any 

 particular throughout the whole extent of their geographical 

 range, and with these there is no question of subspecies. On 

 the other hand there are also many species which vary 

 according to the localities in which the birds breed. In 

 some cases the difference is striking and the differentiation 

 is therefore easy ; in others the differences, though constant, 

 are small, and need careful study and comparison. These 

 differences, if constant in birds breeding in a given area, 

 entitle such bird to subspecific rank. The breeding quarters 

 of the various races of a species are, therefore, always dis- 

 tinct, though the winter quarters of the various forms may 

 be identical. There is a certain amount of intergrading 

 between the races, where the ranges meet, as in the case of 

 the Barn Owl, of which the dark-breasted and light-breasted 

 forms intergrade in France, and this may also be observed 

 in other cases. In this paper we shall only include those 

 which have occurred in Scotland, and of which we have a 

 resident race. 



The identification of these racial forms is not by any 

 means an easy matter ; in many cases they differ in such 

 small particulars that it is impossible to identify them unless 

 the specimen be available for comparison and measurement. 

 Field identifications are, therefore, usually of little value ; 

 the comparative thickness of bill, length of wing, shades of 

 colour, etc., cannot be determined at a glance ; in fact, until 

 the worker is thoroughly familiar with the various races, 

 identification should only be attempted when a large series 



