Adding Yellow Rumped Warbler and American Robin.

I wondered why I was seeing the Yellow Rumped Warbler - then changed my suet feeder out for a caged one. Still no pine warbler spotted - could be just because I have missed it or could be because I have had to take down a couple of tall white pines in the past year.

Robins are a mystery to me. Many of them stay here year-round according to what I read on local birding sites, but generally speaking, I don't see them from late November until mid January - not in my yard or anywhere else locally that I travel, and when I start seeing them in January, is on warm days when the soil is damp and probably some earthworms are stirring. Where are they lurking in the meantime?