I will list things in order.
Corn. It is good feed but not a complete nutrition. Add it to their diet especially during winter so they generate additional body warmth from the carbohydrate calories. If they consume too much, the results may be decreased egg production due to low protein intake. Use only cracked corn for best result. Whole corn can possibly get lodged in smaller birds throats.
Scratch . Is a mixture of about 4 or 5 grains that corn is usually a large portion of. This is also not a complete feed which may result in decreased egg production if given in too large of amounts. It does provide a variety for the chickens to eat and enjoy. Chickens do have taste buds by the way. They do have their favorite foods. Processed feed seems to be at the bottom of their preference compared to other things.
Bird seed. I do give my chickens wild bird seeds as a treat. They will eat all of it up first. Again, I do not feed it exclusively. I also kept pigeons, and their feed is seeds only. I go thru a lot of bird seeds. Look thru my pix and you will see I feed all the neighborhood song birds as well as squirrels. Chickens get a portion, as well as pigeons. There are about 15 different grains in the mix I get. Just so that you are assured.. I have been keeping my chickens for about 19 years and have been feeding them this way. THEY ALL LIVE LONG LIVES. (I don't eat my chickens, only as pets) Do eat the eggs. My current oldest is 10 now. and my longest living went to the other side after 13 years. I must be doing it right.
All the kitchen scraps of veggies and fruit never go to waste ether.