Didn't make any difference at first but now the birds are using copper & non copper feeders.
One of the reasons I changed feeders was that, although they were starting to corrode away, I caught a rat feeding from seed in the middle of the day. It was climbing the pole.
Having replaced the 4 pole-mounted feeders with just one pole with all feeders and water on it I could have a squirrel Baffle: https://m.media-amazon.com/images/I/61pCDvxnwtL._AC_SL1500_.jpg
This would also thwart the rat(s)
I decided to review the trail cam footage for the previous month and my suspicions were well founded, a rat had visited a feeder virtually every day during March, at night.☹️
Hopefully no more.