Reddit mentions of Sigma 150mm f/2.8 AF APO EX DG OS HSM Macro Lens for Nikon Digital SLRs

I think most of the people hree are taking the wrong approach. These guys are MILLIMETERS long, and the zoom on your camera is already huge, so please ignore people telling you to get 200 or 400 mm lenses, as another commenter says, your current camera equals about 800mm. What you need is huge resolution, so you can crop a ton, and macro with a high enough focal length that the guys wont scurry away. so I'm getting a little radical here, but your situation is unusual, so what about the sigma SD1 and sigma 150mm f/2.8? Here's the body I see no reason to buy it, since it's a niche camera, why not just rent it and save a ton of money? It comes with a lens, but you don't need to use it.If you do want to though, it's 1900 on amazon. now i recommend the 150mm lens, it focuses up to 15 inches, but with that resolution you could probably be more that two feet away and still get acceptable pictures, I know you said that it's hard getting that close to them, but I truly think that it's the best way.The lens is here, on amazon, it's not available to rent.

Edit: I forgot to include the actual reason I reccomended the SD1: it's 46 megapixels, aka HUGE resolution, one of the biggest I believe.

Now for a tripod, which i assume you will need, cuz these guys must be hard to find. I recommend something simple, and tall. I don't know much about tripods, but what about a manfrotto? typically very reliable, well within your price range. not sure which one, hopefully someone else who knows more about it can tell you (i almost never use a tripod.)