Where have my goldfinches gone?

Hi

I've been feeding goldfinches for several years and in summer I can have up to about 15 sitting round the feeders and bringing their young to feed.  I feed them all year round but there seems to be less through the winter but they always appear in the spring.  This year I have had only maybe five or six and recently maybe only two or three.  Usually they get thorugh about four feeders a day but this week they have been eating very little and finally today none have been at all.  

Have they found another food source (maybe they're bored with my nyger seeds!) or has something bad happened to them?  We live on the Somerset Levels and it is extremely wet at the moment, so maybe they can't feed?  A sparrowhawk has been hanging around for a couple of weeks but it hasn't scared off the various tits / sparrows/ chaffinch etc etc even though she has been giving them a bit a scare a few times (the little birds hide in the wild rose bush next to the feeders 'til she's gone!).

Any advice greatly appreciated, Alison - Worried of the Levels.