GEOGRAPHICAL GROUPS 171 



GEOGRAPHICAL GROUPS 



Tables I and II contain the numerical data for each of the seven groups, which are 

 arranged in order from east to west. 



New Zealand and Falkland Islands. The differences in average measurements are 

 greatest between the New Zealand and the Falkland Islands groups, which are also the 

 farthest apart, and if these, the extremes, are compared first the positions of the inter- 

 mediate groups will be easier to define. 



Measurements from forty-one Falkland birds are available, and of them thirty-four 

 are in the British Museum, while the New Zealand specimens are twenty-nine in 

 number with sixteen in the British Museum. 



One New Zealand specimen has a tarsal length which is altogether exceptional, 95 mm., 

 the next highest being 84 mm. ; the isolation of the larger measurement suggests that it 

 may be the result of development which is not quite normal. Between the two series 

 the wing measurements do not overlap ; but the difference is only 7 mm., less than 2 per 

 cent of the maximum for the Falkland Islands (400 mm.), and this 7 mm. is quite 

 possibly within the error of measurement (p. 165). There is a noticeable overlapping 

 in bill measurements, and in tarsal length there is a difference of only 1 mm. (Fig. 1). 



In spite of this close approximation the New Zealand birds are on the whole larger 

 than those from the Falklands and they often have rather duller plumage and a less 

 developed yellow collar. But, since there are no real plumage differences and no abrupt 

 hiatus between the series of measurements, the two forms cannot be regarded as being 

 more than subspecies of Catharacta skua, as is suggested by Lowe and Kinnear, and the 

 names used by these authors should be retained, namely C. s. antarctica (Lesson) for the 

 Falkland Islands form and C. s. lonnbergi (Mathews) for that of the New Zealand region. 



Kerguelen and Crozets. The other groups of Brown Skua may now be considered 

 in accordance with their distribution. 



Nearest in space to lonnbergi is the race from the Crozets and Kerguelen : it has been 

 distinguished as C. s. intercedens by Mathews. An examination of the eight specimens 

 in the British Museum shows that there is no difference between them and the New 

 Zealand birds so far as plumage is concerned. 



It will further be observed that the measurements of eight out of the ten specimens 

 from which the data were taken fall within the limits of the dimensions of lonnbergi, in 

 spite of the fact that the average of the wing lengths is 20 mm. less than the corresponding 

 figure for that race (Fig. 1). In the other measurements there is a difference of 1 mm. 

 in the depth of the bill, of 1 mm. in the length of the tarsus of one specimen, and of 

 2-5 mm. in the length of the tarsus of another. It appears, then, that the distinction 

 between these two races rests on the possession of a wing which may be, but is by no 

 means always, shorter in the Kerguelen bird, and in the occasional occurrence of a 

 slightly shorter tarsus. Since it is known that the range of measurements in the Brown 

 Skuas is considerable it cannot be considered that such slight differences are grounds 

 for separating the Kerguelen group as a subspecies. 



