Here's an additional idea. Combine any long lens on any camera with increased woodsmanship which is the ability to 1. spot birds and 2. the ability to approach birds without spooking them.
And or rig up a blind to conceal yourself. A folding chair with a canopy, covered with some sunscreen material with a lens port cut, is a very inexpensive, comfortable and handy portable blind for you, your camera and, if desired, a tripod. Some bait strategically placed might also help. Baiting animals for photo purposes is not unsportsmanlike like it would be if you werehunting them
Folding chairs with canopies can be found on the Internet for as low as $25.00. However, this chair seems like it would really suit a photographer and it runs about $60.00. I have the cheaper model and wish I had seen this one. By the way, it will also screen you from the hot sun
http://www.brylanehome.com/product.a...=scplp12488062
Just clip on the netting to the top of the canopy. Shade screen netting can be purchased by the yard at any home improvement center.