Unless you’re shooting very large birds, or large flocks of birds, there is just no getting around the fact that you’re going to have to have a long lens to photograph them well. Even if your chosen subject is very tame, or if you are in a hide that is very close, you'll struggle to get frame filling shots with anything shorter than a 300mm and even at that you are going to have your work cut out for you. If you still do not have a long lens, well.. that’s the bad news.. but the good news is you really do not have to spend a fortune to get the reach you need. One way is to buy a teleconverter. Teleconverters, which fit between the camera body and the lens, increase the length of any compatible lens by either 1.4x or 2x. This for example would make a 200 mm lens either a 280mm or 400mm lens.
And if you add in a crop factor of 1.3x or even 1.5x or 1.6x (if you have a APC sensor) you will be able to get frame filling shots at a fraction of the cost of a telephoto lens. A teleconverter will cost you a few hundred dollars which is considerably less than all but the most basic lenses of an equivalent reach. In addition to a long lens and/or a teleconverter, here are a few other accessories that may just come in handy depending on the subject you’re shooting and the type of shot you are after.
1) Monopod- Long lenses can be heavy. A monopod will not help steady the camera but will take the weight of the lens. This will help you to concentrate on taking the shot as opposed to trying to keep the camera steady