To make sense of immature gulls, ignore how pale or dark the birds look

Know when to concentrate on bill shape, posture, movements, and contrasting markings, not color

To get to know streaked ­sparrows, focus first on a few key features of the face

Why a duck’s head shape might vary from the picture in your field guide

How your line of sight can change how dark or pale a bird’s feathers appear

To learn bird songs, listen carefully while watching the accompanying behavior

How to use body shape to identify songbirds whose field marks aren’t visible

How the Red-winged Blackbird makes its patches obvious one minute and almost invisible the next

Why you should be cautious about judging color based on fleeting views

How the way a bird holds its legs in flight can change its ­appearance

Why bill color remains an important field mark for identifying Caspian and Royal Terns