I am new to the photography world. I purchased myself a D7000 a week ago that came with the 18mm-105mm lens kit. I've become really interested in photos of birds and would like to get into taking pictures of them. The lens that came with the camera doesn't seem to do justice. My budget is $400 dollars. Are there lens out there that does a good job at capturing birds with that budget and also does good bokeh? Any recommendations? Thanks!