don't know about your woodpeckers but i have a pair of lewis's woodpeckers who have nested here last 3 years. i also have lots of orioles and i put out fruit and jelly and watermelon for the orioles, the young Lewis's love the jelly and watermelon and eat lots of fruit and they come back every year. i also have downeys and hairys and flickers that use the same feeders as the Lewis's

i had five fledgling lewis's woodpeckers this spring and when the parents brought them to the feeders the young ones tried every feeder i had including the nyjer and the necter feeders and the jelly dishes. but it did not take them long to pick their favorites most of them prefer the nuts and sunflower seeds and the cracked corn and suet blocks. but there are a couple that still eat the grape jelly and drink the sugar water and love to peck on watermelon rinds. but none of them did more than try the nyjer sock.

oh you should post a video!! My feeder came with "bee guards" It limits the size of the hole for just hummers. It works great for the bees. But then I found a different kind of feeder and nothing gets in it but the birds, not even tiny nats.

I don’t know much about elderberry eating birds, but I do have quite a bit of beauty berry, coral honeysuckle and woodbine that produce berries. The birds I see munching on berries are as you mentioned, mockingbirds, tufted titmouse, cardinals and the #1 berry munching bird are the robins that come through late winter/early spring. They descend upon my yard in huge flocks, strip the beauty berries and then they all pile in the 3 bird baths and get their Saturday baths in! I love the robins and always let my northern friends know that the robins are on the way! I think just about any bird will eat berries. Woodpeckers too. Do you get cedar waxwings? They also are berry eaters and will arrive in flocks like the robins. They don’t stay long but what beautiful hungry birds!