As Donald mentioned, an f/5.6 aperture is "a bit slow for bird photography" except... if you are shooting with a lens that provides top-notch IQ at its widest aperture.
Canon shooters are blessed to have the 400mm f/5.6L lens which is "slow" at f/5.6 but, which also produces as good image quality at that f/stop as it does stopped down a few stops.
It doesn't have any stabilizaton which can be a PITA but, it only weighs 44 ounces which is pretty light weight for a 400mm lens. It is also often available (in the USA) on the used market for under $1,000 USD.
I often either use mine with a monopod and a swivel head or with the rig that I fabricated, using hand tools, with less than twenty dollars worth of material. The rig is absolutely great for following birds in flight. Resting on both shoulders, it provides a very stable platform. It could be modified for any camera and any long lens. IMO, the double shoulder rest beats the heck out of the Bushhawk for stability. And, of course, the price is no comparison
An equipment list and directions for fabrication are available at my smugmug site:
http://rpcrowe.smugmug.com/Photograp...822870&k=3vQ4W