These young robins—if I am not mistaken with my identification—were in the backyard late one afternoon last week*. Although they could fly, at least between the branches of the trees they were on, their chief defense against would-be predators seemed to be their ability to stand almost completely motionless for long periods. Certain predators, for example, cats may be more likely to detect a prey when the latter is moving. Thus, a prey that can sit still escapes detection as long as the predator is not too close. I remember one summer day several years ago when I put a chair out on the grass and sat down to read a book and then several minutes later noticed that there was a little baby rabbit among the grass blades next to my foot; it was watching me with wide open eyes while making not one move.
This defensive behavior, of course, provides opportunities for the photographer to get very close to its subject as long as he doesn't mind the increased risk of getting his camera or face splattered with fresh bird poop.
*Strictly speaking American Robin (Turdus migratorius).