Linguists call it alef, but then they call all A's alef. I think of it as a sound.
In Japanese calligraphy the brush strokes for each character are ritualized. There is a definite starting point and for a reason, the way the ink trails off by the brush stroke is of crucial importance, the brush strokes themselves impart a visual energy.
I expect the same thing is true for these. The characters did endure a long time. You don't just go sketching birds willy-nilly, and you don't build them up from scritchty-scratchy scribbles either finding your lines. The lines are known, codified, because they've been drawn a million times. It seems to me you establish the central-ness of the breast first and the weight of the bird by by its back. Either the back or the breast first. Then everything follows. The breast and the back established by the beak and the shape of the head. So not actually first, but of first interest, having the weight at the center of the block.
Birds can be a bit frustrating too. The tiniest line makes all the difference as the space between lines. This Egyptian vulture in hieroglyphics is hardly distinguishable from another long-legged vulture and when the work is worn or the copy damaged then it becomes impossible to distinguish between them. Flat head is the key.
They are drawn with flat heads but not horizontal to the ground. That's one way to tell them apart. G1 and G4 on the signs list.