Omega, not every yeast infection is caused by antibiotics. Antibiotics can indeed cause an imbalance that sets up the situation for a yeast infection. But yeast infections also occur for other reasons. So it is perfectly reasonable to expect that your chickens are capable of having a yeast infection, even though you don't use antibiotics.

My first reaction is that at some point the bird had a sinus/nasal infection and this is the last bit of evidence, crud coming out the ears. I don't know if a chicken's head is built the same way ours are, but a sinus infection in a human can indeed lead to ear discharge.

I have never seen anything like this in my birds. But if I did my first reaction would be to dribble some peroxide in the ear to see if it would bubble out the goo. Then, if I thought it was infection, I'd glob some antibiotic ointment into the ear OR if I thought it was a yeast infection I'd use some lady meds on it, like Monistat, and glob some of that into the ears.

The only way to find out what it is is to see what cures it. I mean, if you're going to cull the bird anyway, may as well do some deductive experimenting, providing you are not causing pain and the bird is not suffering.