Are those birds at my feeder House or Purple Finches?

Folks with feeders in New Orleans are likely to see brown finches eating seed, some of them with red breasts and rumps*.   The all-brown individuals can be distinguished from the similar female House Sparrows most easily by the finches' streaked undersides. 

If you look in a book, you will see three similar finches.    One, the Cassin's Finch, is only found from the Rockies westward- easy to rule that one out.

But the House and Purple Finches both occur in Louisiana.  They look hard to tell apart in the book.

Fortunately for us, House is so much more common than Purple in southeast Louisiana, that birds can safely be assumed House unless you have a reason to think otherwise. 

If you do see one that looks suspicious, have a closer look- you may be lucky.  Purple males are a more purplish red, and have unstreaked sides.  Purple females have bold white stripes over the eye and under the cheek.  

*the "rump" is the lowermost back in birds