Where have the Siskins gone?

Up until a couple of weeks ago I had heaps of Siskins, Blue Tits, Great Tits and Chaffinches at my bird feeders, along with a few sparrows The Siskins have disappeared altogether, I've seen the odd Great Tit, no Finches and I'm now over-run with Sparrows. Explanation please from a knowledgeable birdy person.

Our Siskins have all but disappeared from the garden as well but the local wood is usually heaving with them as they feast on the cone seeds this time of year.