28 SUGGESTIOXS AND DIRECTIONS FOR FIELD-WORK. 



this matter under several heads, a. Your own "series" of 

 skins of any species is incomplete until it contains at least one 

 example of each sex, of every normal state of plumage, and 

 every normal transition stage of plumage, and further illus- 

 trates at least the principal abnormal variations in size, form 

 and color to wliich the species may be subject ; I will even add 

 that every different faunal area the bird is known to inhabit 

 should be represented by a specimen, particularly if there be 

 anything exceptional in the geographical distribution of the 

 species. Any additional specimens to all such are your only 

 "duplicates," properly speaking, b. Birds vary so much in 

 their size, form and coloring, that a "specific character" can 

 only be precisely determined from examination of a large num- 

 ber of specimens, shot at different times, in different places ; 

 still less can the "limits of variation" in these respects be 

 settled without ample materials, c. The rarity of any bird is 

 necessarily an arbitrary and fluctuating consideration, because 

 in the nature of the case there can be no natural unit of com- 

 parison, nor standard of appreciation. It may be said, in 

 general terms, no bird is actually " rare." With a few possible 

 exceptions, as in the cases of birds occupying extraordinarily 

 limited areas, like some of the birds of paradise, or about to 

 become extinct, like the great auk, enough birds of all kinds 

 exist to overstock every public and private collection in the 

 world, Avithout sensible diminution of their numbers. " Rar- 

 ity" or the reverse is only predicable upon the accidental (so 

 to speak) circumstances that throw, or tend to throw, specimens 

 into naturalists' hands. Accessibility is the variable element in 

 every case. The fulmar petrel is said (on what authority I 

 know not) to exceed any other bird in its aggregate of indi- 

 viduals ; how do the skins of that bird you have handled com- 

 pare in number with specimens you have seen of the "rare" 

 warbler of your own vicinity ? All birds are common somewhere 

 at some season ; the point is, have collectors been there at the 

 time? Moreover, even the arbitrary appreciation of "rarity" 

 is fluctuating, and may change at any time ; long sought and 

 highly prized birds are liable to appear suddenly in great num- 



