5^ , Introduction: Variation. 



be attained when each specimen is compared with the type — the first-described 

 individual — of its species, and a formula representing the difference appended 

 to the binomial name. Such a method is however impossible at present for 

 practical reasons; there is no means of measuring the differences in question. 

 Another reason why individual variation finds so little mention from those who 

 have most experience of it is that for a long time a strong effort has been 

 made to enforce the recognition of subspecies; the effect of this has been to 

 give undue prominence to geogi'aphical variation and to divert attention from 

 individual and other phases of variation, which form exceedingly difficult factors 

 in the study of local races, and are for that very reason disregarded by careless 

 or ignorant writers. 



Range of individual variation. — Compared with some other animal forms, 

 for instance, certain Beetles, individual variation in birds (other than domesticated 

 racesl keeps within somewhat narrow limits. The maximum as regards variation 

 of plumage is seen in the male Ruff (Machetes pugnax). The extinct Solitaire 

 (Pezophaps) of Rodriguez was also extremely variable; its osteological remains 

 show that "the variability of colour he (Leguat) had noticed in the females 

 — some fair, some brown — was paralleled by the marvellous variability dis- 

 ])layed by almost every bone of the skeleton" (Newton, D. B., S90). Other 

 familiar examples of high individual variability among birds are furnished by 

 the Honey Buzzard [Pernis apivorus), the Common Partridge (Perdia; cinerea), and 

 the Common Crossbill (Loxia airvirostra). The minimum of individual variation 

 is perhaps found among certain highly local species of Pigeons, such as those 

 of the genera Ptilopns and Osmotreron ; also many Sunbirds, Kingfishers, Parrots, etc., 

 seem to be very stable in this respect. The differences separating many species 

 of Pigeons are so small that it creates a feeling of surprise to find that large 

 series of specimens do not present every sort of intermediate form and other 

 modification. Under domestication, on the other hand, the Blue Rock Dove 

 has displayed a most remarkable variability. A high degree of individual 

 variability is sometimes found among s^iecies of birds in which the sexes are 

 dissimilar (e. g. Machetes, Macropygia, Galliis), but the sexes are dissimilar also 

 in Ptilopiis, Osmotreron, the Sunbirds, and other stable forms, so that this factor 

 evidently has no dii-ect influence in the matter. 



Some species vary much in the measurements of various parts of the body, 

 but little in coloration (e. g. Streptocitta, Amaurornis moluccana); others vary much 

 both in size of parts and in coloration (e. g. Halcyon chloris, Xanthocnus Jlavicollis). 

 Highly specialized features are generally very variable: for instance, the long 

 tails of Streptocitta, Phocnicophaes and Fregata, the long hind claws of Centro- 

 coccifx and Ilydralector, the long bills of Linwsa and Numenius, the long tarsus 

 of Himautopits; but age also plays an important role in this connection. 



Psychological differences of individuals. — Persons who have closely observed 

 or have kept wild species in confinement have often noticed differences of 



