
28 SUGGESTIONS 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 which 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. 0. 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, without 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- 

