Recently got a Nikon D5000 with a kit 18-55 lens and a 55-200 lens which seems too short a range for birding. I used the 200 zoom a bit on a recent vacation and found it a bit short... I have an option to switch to the 70-300 f4-5.6 lens if I pony up a several more hundred. I would return the 55-200 lens.

Question: What is the minimum lens for birding do you think? Would the 70-300 f4-5.6 do it or is that a lens with which I would be frustrated?

I am new to digital and having worked with film until now but have not had a birding lens at all to this point. Since I just got the camera, money is an issue in terms of the longer reach lens. I am trying to get into birding pictures and to do it economically. What do you recommend?