Why do we see cardinals at our feeders at early and late? Why do some sparrows prefer to feed in the shade?
First, the male's red plumage is bright and distinct in daylight, but looks darker in dim light. Light at a low level makes male cardinals inconspicuous early and late in the day. Female cardinals, browning birds, have built-in protection. The birds are less likely to be seen by common urban/suburtban predators, like cats. And, the major local avian predator, Cooper's Hawk, is inactive at dawn and dusk.
Animals feeding early and late in the day, favoring less light, are called crepuscular.
Migrant sparrows will soon be in the neighborhood, if not already. We have Song Sparrows singing in the swampy brush behind the house. I saw Tree Sparrows on a Friday walk. I spread seed on the ground near brush cover to attract these birds to the yard. White-throated and White-crowned, and Lincoln's sparrows have been fairly regular spring visitors. These birds seem to prefer to feed in shade. They will first take seeds in any bit of shade, even areas as narrow as the shade from the feeder post. My guess is that, as with cardinals, dimmer light makes them less conspicuous, less vulnerable to predation.
This White-throated Sparrow is on the edge of a shade.