I would add that, since I don't do wildlife photography on a regular basis, I would tend to rent one of those expensive exotic long lenses to fit the purpose.

BUT IF I were to consider buying, this is an option that comes in at a reasonable price, with reasonably good reviews, and if you can live with the slower f6.3 at the long end.

http://www.sigmaphoto.com/lenses/len...07&navigator=3