my parents experienced the same thing at their house, after years of bird
feeding, suddenly no birds... then they discovered they did have one
bird... a great big hawk. The song birds found safer feeders until the
hawk moved on.

Here, at our house, we have several resident red tail hawks, they surf the
feeders in the morning, looking and sometimes finding a hapless victim, but
usually they move on to the meadow for the field mice and the birds come
right back.