Why I shoot in 'aperture priority'
If you read almost any guide or forum on the internet you'll most likely hear it said that many people, and most professionals, shoot in full manual mode (M mode on Nikon/Canon). This is usually for the control it provides over the exposure in certain scenarios, and this is a completely true and justifiable reason. All cameras, regardless of the make or style, will aim for an exposure of 18% grey, and this often leads to photos looking flat or having their highlights or shadows blown out by a 'middle ground' exposure in especially harsh lighting. Having full control over your aperture, shutter speed and ISO gives you the right speed and depth of field to get the image that you want, but I, and indeed many other wildlife photographers, rarely use manual exposure.
Now you may be wondering why I hyped up the benefits of manual exposure and then don't use it, and put simply it all comes down to speed. When working with wildlife you're often dealing with a subject that is constantly moving, with constantly changing backgrounds, lighting and angles, and in this situation trying to keep up with the correct exposure for many situations is a feat very few have the ability to do. My camera is always set to aperture priority (A on Nikon and AV on Canon) with spot metering mode enabled. I use my rear control dial to move my focus point to where I want it, focus, and take the shot. Yes, the resulting image may be a little flat straight from the camera, but most importantly the exposure on the subject will be ok. It's the worst thing in the world to take a shot only to find the subject over or underexposed! My mind cannot register the precise exposure changes needed when trying to follow and compose a flying bird in my viewfinder, and so I let technology take over to let me get the shot I want. I guess you could say it's not 'pure', but I'd rather do that than miss images from poor judgement.
That being said, shooting in any of the 'auto' manual modes (shutter priority and aperture priority) does not tie you to one exposure. The exposure compensation tool (usually a box with a + and - in it) is a fantastic way to control exposure around a constantly changing point. It gives the needed control, but still keeps the compensation of such changing lighting conditions. For a full blog of exposure compensation - specifically how you can use it to create unusual images, please see by previous blog post HERE