>>3282669Define "birding." Do you want to publish these images? Is photographing birds in flight a priority? Do you care how sharply defined the feathers are, or is it good enough to resolve the bird clear enough to identify it?
There are special techniques and aspects of a birding camera and lens which are important to people who really get into bird photography.
-Cameras with high megapixel counts allow the photographer to crop into the image even if the lens isn't long enough to get a properly magnified image of the bird, so the recent Nikon crop cameras with 24 MP sensors would be a good choice.
-An effective autofocus drive in the lens is required to quickly and reliably nail focus, so screwdrive lenses, like many of Pentax's cheapest telephoto zooms or older Nikon lenses, are out.
-Effective autofocus tracking technology is also important to keep the bird in focus when it moves around on the branch or takes flight. That means both the tracking algorithms and the number and spread of autofocus points are important. Many of the cheaper or entry-level camera bodies only have basic 9 point AF implementations that will limit you.
-The lens should be optically fast and the camera sensor should have good high ISO performance so that when you have to use >1/1000 sec shutter speeds in less-than-ideal lighting, the sensor noise doesn't smooth out all the fine details in the birds' feathers. An f/4 lens is much more desirable than an f/6.3 lens, but a 300mm f/4 prime will tend to cost three times more than a 300mm f/6.3 zoom.
-Burst rate is also important because in spite of your best technique, sometimes you can only get a sharp, clear, well positioned shot of a bird if you're shooting burts as soon as it comes into view.
My quick and dirty recommendation to stay in your price range is a used Nikon D7100, which you should be able to get for around $450 in minty condition on ebay and the 70-300mm f/4.5-5.6 AF-S VR, which you should be able to find for $250.
