SUGGESTIONS AND DIRECTIONS FOR FIELD-WORK. 13 
medium of exchange among ornithologists the world over; they represent value, —money value 
and scientific value. If you have more of one kind than you can use, exchange with some 
one for species you lack; both parties to the transaction are equally benefited. Let me bring* 
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 illustrates 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. (b.) Birds 
vary so much in their size, form, and coloring, that a ‘ specific character” can only be pre- 
cisely determined from examination of a large number of specimens, shot at different times, in 
different places ; still less can the “ limits of variation” in these respects be settled without 
ample materials. (¢.) The rarity of any bird is necessarily an arbitrary and fluctuating con- 
sideration, because in the nature of the case there can be no natural unit of comparison, 
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 pied duck, 
enough birds of all kinds exist to overstock every public and private collection in the world, 
without sensible diminution of their numbers. ‘‘ Rarity” 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 individuals ; 
how do the skins of that bird you have handled compare 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 numbers in places that knew them not 
before ; a single heavy ‘‘ invoice” of a bird from some distant or little-explored region may at 
once stock the market, and depreciate the current value of the species to almost nothing. 
For example, Baird’s bunting and Sprague’s lark remained for thirty years among our special 
desiderata, only one specimen of the former and two or three of the latter beng known. Yet 
they are two of the most abundant birds of Dakota, where in 1873 I took as many of both as 
I desired; and specimens enough have lately been secured to stock all the leading museums 
of this country and Europe. (d.) Some practical deductions are to be made from these 
premises. Your object is to make yourself acquainted with all the birds of your vicinity, and 
to preserve a complete suite of specimens of every species. Begin by shooting every bird you 
can, coupling this sad destruction, however, with the closest observations upon habits. You 
will very soon fill your series of a few kinds, that you find almost everywhere, almost daily. 
Then if you are in a region the ornithology of which is well known to the profession, at once 
stop killing these common birds—they are in every collection. You should uot, as a rule, 
destroy any more robins, bluebirds, song-sparrows, and the like, than you want for yourself. 
Keep an eye on them, studying them always, but turn your actual pursuit into other channels, 
until in this way, gradually eliminating the undesirables, you exhaust the bird fauna as far as 
possible (you will not quite exhaust it—at least for many years). But if you are in a new 
or little-known locality, I had almost said the very reverse course is the best. The chances 
are that the most abundant and characteristic birds are ‘‘ rare” in collections. Many a bird’s 
range is quite restricted: you may happen to be just at its metropolis ; seize the opportunity. 
and get good store, — yes, up to fifty or a hundred; all you ean spare will be thankfully 
received by those who have none. Quite as likely, birds that are scarce just where you happen 
