I find it is always a treat to spot a ruby-crowned kinglet in my backyard. Although a handful of these petite birds winter in my backyard each winter, they only occasionally visit my feeders.
Most of the time, I spot ruby-crowned kinglets looking for tiny insects, spiders, and their eggs among on twigs and on the undersides of the leaves of the shrubs and trees that are scattered across my yard.
When they do decide to visit my bird feeding area, they always dine on suet laced with peanut butter offered in a rectangular metal cage. I never see more than one ruby-crowned kinglet dining at a time. When I do spot one feeding at a feeder I cannot help but wonder whether I am hosting one or several kinglets. 
Among the other foods ruby-crowned kinglets have been known to consume at feeders are cornbread, peanut hearts, peanut butter, hulled sunflower seeds, tiny chips of nuts such as pecans and even cake doughnuts.
Chances are ruby-crowned kinglets are hiding in plain sight in your backyard this winter. They are easy to overlook since they are just a bit larger than a ruby-throated hummingbird, olive-green in color, and sport two white wing bars. This male also flashes a bright ruby crowned when it is agitated.
I have at least one male Ruby kinglet coming to my windowsill. I haven’t seen him at a suet feeder yet; there was a brown creeper on a suet feeder when the kinglet came to nectar this morning. It and my mob of bushtits were trying to drink from the hummingbird feeder, a few days ago, but I don’t think their beaks are long enough to reach down the tubes to the nectar. I wonder if their tongues are long enough? Anyway, I put some nectar (Winter mix, 3/1) in a red plastic jar lid, and put it out on the wide glass feeding platform on the kitchen window sill, and the kinglet is coming to it several times a day. I just added some hulled sunflower seeds, but I didn’t see him take one just now. Any idea how I can feed him and the hummers some protein in the winter?