As a bird photographer you quickly learn which birds are approachable and which will fly off to the horizon if you glance sideways at them. Two very nervous species that spring immediately to mind are grey heron and curlew. Another very difficult species to approach are linnet. I found a flock on a local field busy feeding on dandelion seeds and the presence of a road along side allowed the use of the car as a hide. Even so they where still nervous although the situation was not helped by numerous dogwalkers.