Some of mine were eaten by Coopers or Sharpshin hawks.

I have noticed a lot of red tail hawks in my area recently. Some are larger, so they may be golden eagles. But either way, there have been a large increase in their numbers.

pinwheel,

Is there a housing development going up nearby, or a has someone knocked down some trees? It is possible that their habitat has been disrupted and they relocated.

It is a shame that all these houses are going up everywhere. Developers clear the land to make a buck and not think about the habitats they are destroying. Why don't they knock down existing abandoned homes and re-develop those areas?

Last week I found a fluff of red feathers that seemed to spell the end of one of the resident cardinals here (probably also due to hawks)...

but also early this spring there was a sick cardinal at the bird feeder. Kind of listless, no energy. A few days later I found the body not too far away. I only mention this because I almost NEVER find bird bodies around here, so I thought a sick bird was unusual.

(but I also saw a healthy one this afternoon, so they're still around)

I have lots of Cardinals at my place in Centre County. This is the time of year when a lot of cardinals are busy nesting or raising young, which eat bugs, not seeds. So, your cardinals may be spending a lot of time on the nest, so you aren't seeing them, or spending a lot of time catching bugs for the young, so they don't visit feeders. They may also move to a nearby spot that is brushier than your yard, where they have found a more suitable place to nest. Also, with the abundant bugs around this time of the year, they simply might bother to visit feeders. I see lots of cardinals in the neighborhood, so I don't think there is any widespread decline of the Cardinal population going on.