have you had any trees or shrubs removed that used to provide cover for them? or perhaps there is a new cat in the area.

Sometimes they just move on for no apparent reason. we had a 6 months of very little visitation then it changed back to many and often. though we hadn't changed anything.

I live in a similar sort of area & it's dominated by the greedy magpies completely. I have been attracting a growing number of blue tits with dried mealworms though. Maybe they still have young that can't deal with peanuts, etc?
Hope your cats wear bells?

My garden is like Grand Central Station. I only put a pan of water out for them. However, when the Blue Jays show up, all the other birds flee like there was no tomorrow. The Blue Jays bully the smaller birds. Also, I have a pair of Mockingbirds building a nest up in my juniper trees - they don't like to share. They will dive-bomb anything the comes near the nest (except for me). All the other birds get the message and instinctively stay away.

I have the opposite "problem". A robin has decided to nest in the greenhouse this year and gets quite upset if I go in there as well

I live on the edge of open countryside and the birds seem to have migrated into the fields and there are few birds in my garden. During the winter I was plagued with Magpies and Wood Pigeons and lots of Gold Finches (they just love sunflower hearts). Up until a few weeks ago, I had loads of Blackbirds but even they have left though I'm not sorry to see the back of the Parakeets.