I'm no expert (honestly stated up front) but I have had catbirds regularly 
coming to my deck and particularly a window feeder on my sliding glass 
door. I never thought twice about it (except to enjoy them) but do think 
they are eating some sort of seed from there. It is a mix I bought at 
Target that has both millet and cracked corn in it, also sunflower seeds 
and nuts. 

peace-
emily wilberg
germantown