Most of these birds will become quite tame with a little care on our part, and will soon come to look to us for their daily food. Especially if the ground is covered with snow, they will learn to become clamorous for their food, even alighting on the window-sills and striking the glass, apparently to attract attention to their wants. In summer the same species are much more shy, so winter gives us a better opportunity to study the habits and dispositions of the various birds that remain with us.
Mary Treat, "Our Winter Birds," The Atlantic Monthly, vol. 49, March 1882.
I'm not sure how the phrase "eats like a bird" came to imply something dainty and delicate. Birds, at least the little birds around my house, eat like starving high school linebackers. Every time we fill the feeders, Sean and I watch in amazement as gangs of chickadees, titmice and finches eat and eat and eat, dropping the levels of seed in the tube by the inch before our bewildered eyes. Pounds of thistle and mixed seed disappear at alarming rates, and we can't blame the squirrels, because we can see the birds at work. And if we let the levels start getting low, they let us know, flying bang into the window, and lining up on the porch rail when we step outside, watching intently, which is a little unnerving. But turnabout is fair play. Sean and I can sit for hours watching them go about their bird business, and they've become our favorite neighbors.