84 BIRDS'-NESTING. 



In the first place you must study the geographical 

 distribution of the birds of North America in order 

 to know what species never will breed in your neigh- 

 borhood, and which consequently you never can hope 

 to find wild ; and, second, what ones that do breed 

 w^ith you are rarest elsewhere, and therefore would 

 be most in demand. 



The latter consideration will of course change 

 according to the region where your correspondent 

 of that moment happens to live.- Some birds have 

 a special "local distribution, " as it is termed, that is, 

 they are to be found only in spots ; I do not know, 

 for example, that the blue warbler {Dendroeca coe- 

 rulea) breeds plentifully anywhere except in southern 

 Illinois. These are especially to be prized, and if 

 from some peculiarity of geographical position or 

 by accident, you have one or two such species as 

 common summer residents, you will do well to 

 gather many duplicates of their nests, since you can 

 always exchange them to advantage, fc^^ Mark all 

 your duplicates as exactly as you do the eggs in your 

 own cabinet-series. 



Though sometimes impossible, yet generally you 

 ought to know something about the person with whom 

 you propose an exchange of eggs ; and you ought to 

 be willing to give a guarantee in return. Even 

 personal honesty you will find of value in this matter 



