One of the challenges of understanding the color patterns of birds is that we only see the tips of their feathers, and feathers are flexible. This means that longer feathers on the body can move around a lot relative to their neighbors, and the color patterns formed by the tips of the feathers can change depending on where the feathers go.
We see this a lot in the streaked patterns on the breast and flanks of many species. These feathers are particularly long and flexible, and the dark streaks on the tips of the feathers end up forming irregular wavy lines rather than consistent neat and even streaks.
Shorter and stiffer feathers — for example, around the face and on the wings — move a lot less and form much more consistent and reliable patterns, which is one of the reasons we end up focusing on those feathers for identification.
Another aspect of this is that head feathers move with the head, while the “breast” feathers (which, in fact, grow from the front of the neck) mostly stay with the body. The upper breast feathers (from the upper part of the neck) do rotate a little when the head turns, but their length and flexibility tend to keep the tips of the feathers in line with the body feathers lower down, and feathers on the lower breast don’t rotate at all.
I saw this in action recently while watching a Blue Jay, and I made the sketches above to show the changes as the bird’s head turned. The dark frame around the face and throat of a Blue Jay is an unusual plumage pattern that includes fairly inflexible head feathers at the back of the cheek and quite flexible feathers across the breast.
Notice how the dark frame behind the cheeks moves with the head and doesn’t change shape while the head turns, a narrow ring of feathers between head and body turns partially with the head, and most of the dark breastband stays in line with the body.
Watch for these differences in a bird’s appearance as feathers move. You’ll boost your understanding of feather patterns and your identification skills.