Is this a common thing - feeding birds to get photographs?
It is something that doesn't sit comfortably with me at all. I notice that in some of the galleries that there a remarkable number of different birds photographed from the same perch, or with lenses way shorter than you would expect.
Photographing birds without 'influence' in their natural habitats, going about natural behaviours is for the most part hard work, and requires lots of dedication. Also lots of knowledge about behaviours and how likely encounters would fit in with proximity, lighting direction, speed, length of time of opportunity etc, This along with familiarity of suitable gear that works in those circumstances, such that it is an automatic extension of yourself. This takes quite a bit of practice, and then regular use and maintenance of those skills.
I'm all for camo and ghillie suits etc, but I really prefer to keep my distance ....