Goldfinches tend to move around a lot every year. Eg. I have them in good numbers every autumn and winter- yet come mid spring and early summer they vanish but our sparrows take over till they return in late summer. Something I now expect year in year out. It can work out vice versa depending on the area and food supplies. Another possible reason is the quality of the food in the feeders- if the seeds get wet, this can put them off, sometimes this means the seeds will go stale. I've put rain guards on my main feeder and regularly clean them out when I can to sift out the uneatable bits that tend to clog the feeders up etc. All depends on the circumstances. Anyway, hope this info helps. ..