You have sparked a really informative thread. I have been practicing with birds for about two years, and still have a long way to go. Using the Canon 6D and Sigma 150-500 has produced a few good photos, but I agree that technical knowledge, and the best gear you can afford will improve your success ratio. All of you that go handheld are obviously much more skilled than I, as my success ratio with my setup is pretty low handheld. Best results have come from tripod, and remote shutter release. Many bird photographers also recommend Aperture priority which allows for quicker exposure selection, which is what I use exclusively. It sure is fun, no matter how you go about it. Now if I could come up with the $7500 for that 500 f4 lens just think how good I could become.

You have sparked a really informative thread. I have been practicing with birds for about two years, and still have a long way to go. Using the Canon 6D and Sigma 150-500 has produced a few good photos, but I agree that technical knowledge, and the best gear you can afford will improve your success ratio. All of you that go handheld are obviously much more skilled than I, as my success ratio with my setup is pretty low handheld. Best results have come from tripod, and remote shutter release. Many bird photographers also recommend Aperture priority which allows for quicker exposure selection, which is what I use exclusively. It sure is fun, no matter how you go about it. Now if I could come up with the $7500 for that 500 f4 lens just think how good I could become.

A couple of tips I have picked up over the years.
Put your camera on manual and set the ISO to auto.
One of the biggest hurdles to overcome when shooting with a telephoto lens is camera shake – softness introduced by not being able to hold the camera steady for the duration of the exposure. One of the easiest ways to overcome this is to make sure that the shutter speed you select is faster than the reciprocal of the focal length. For example, in order to minimize the effect of camera shake with a 300 mm lens, a shutter speed faster than 1/300th second is recommended.
Don't forget to take the crop factor of your sensor into consideration.

Shutter speed selection, as mentioned above, was all about considering shutter speed in relation to freezing motion. Aperture selection, however, is two-fold:

a) Image softness wide open – this is generally a rule for all but the top of the range telephoto lenses, but shooting at the widest aperture (smallest f/ number) your lens allows will often result in image softness. Therefore, if you choose a slightly smaller aperture, e.g. from f/5.6 to 6.3 or 7.1 (known as stopping down) you will minimize this effect and see an increase in the sharpness of the resulting images.

b) Ensuring you have enough depth of field – a key component of wildlife and action photography is depth of field. Often, you shoot as wide an aperture (small f/ number) as possible, to try and isolate the subject and give a soft diffuse background. However, at long focal lengths, with a close subject, the depth of field (i.e. the region of the image which will be captured in sharp focus) can be as small as a few millimetres, meaning that tiny errors in focusing accuracy will mean that the crucial part of your wildlife shot that needed to be in focus, will be soft. There are plenty of mobile apps or websites that help you calculate the depth of field for your given camera, aperture and focal length, so make sure you have an awareness how small an aperture you actually need in order have enough depth of field.
Praying helps also.