Vol. XI 

 1902 



^1 DwiGHT, Variations of the American GoUfinch. I5I 



length, the loss being greatest in young birds. These facts are 

 true of other species than the Goldfinch, and their importance is 

 obvious if races are to be established on minute differences of 

 dimension; for if by any chance a series of young birds, for 

 instance, should be compared with adults of a supposed new form, 

 the differences in the new form would be magnified out of propor- 

 tion to their value. Furthermore the element of wear complicates 

 the question unless absolutely comparable series of equally worn 

 birds are available. True, these differences are extremely small 

 and only to be made out by average measurements of series, but 

 it is on just such small variations that races are now founded, 

 hence the need for a better understanding of seasonal variation in 

 dimension. 



Seasonal variation in color is due to moult and subsequent fading 

 of the plumage. Probably no colors are more susceptible to fad- 

 ing than the browns and the buffs, and therefore the Goldfinch, 

 particularly in winter dress, varies between wide extremes on the 

 Atlantic coast, but fades less on the Pacific. Specimens show that 

 tristis and salicamans are equally brown after the postnuptial moult, 

 the drier, brighter climate in the East fading tristis quite rapidly 

 in the subsequent months, while salicamans remains dark. This 

 may well raise the interesting question whether geographical races 

 may be separated on mere fading. It seems to me they should be 

 independent of accidents of moisture and sunlight, otherwise an 

 unusually wet or dry season anywhere would produce temporarily 

 a dark or a light race, as the case might be. The evidences of 

 climatic influences ought to be found in fresh plumages if they are 

 to be of any value. It is unfortunate that the type of salicamans, 

 taken December 21, should be a more or less faded winter bird, 

 for individual differences in plumage are greater in the brown 

 winter dress than in the more stable yellow of the summer months. 

 The earlier moult of western birds is a matter that has never 

 been considered in its possible bearing upon the fading of plum- 

 age. The series of salicamans shows that the moults of the Cali- 

 fornia bird take place a month or two earlier than in eastern tristis. 

 Comparable birds in fresh plumage are therefore naturally Septem- 

 ber salicamans with November tristis and, except for the evidences 

 of fading which survive the prenuptial moult, average March sali- 



