albert, I have Goldfinches on my Goldfinch tube feeder and am keeping sunflower HEARTS in it constantly so they don't think of going elsewhere. I mean, in this terribly frigid winter, I wouldn't dream of leaving it empty. Same in summer, spring, fall, but at these times I keep regular Black Oiled Sunflower Seeds in their feeder. I don't know that I've ever had a Lesser Goldfinch, however.

Lessers are birds of the west. We had both lessers and American goldfinches (as well as pine siskins, another Spinus species) in Colorado, though the lessers were by far more common. Here in Arizona I have yet to see any American goldfinches. California, and to a smaller extent, Arizona, has the fourth and final American Spinus finch, the Lawrence's goldfinch, which I have been searching for in vain all winter.

Albert, where are you located? In the northern part of their range lesser goldfinches tend to be much less common in winter and to see a flock of 25 is not only very neat at this time of year, but something that I would report to places like Cornell Lab (via ebird) so they can either get a better picture of this species range and migration habits or see how it may be changing over time.