thekiwi:The answer is YES and quite often it is called fill flash used in extreme close up work it is used where lets say you have a bird sitting up in a tree and there are light areas and shaded areas using fill flash (your flash) that will even all that out. If you have a TTL flash then you can vary the intensity of the flash.
A bit late to the party, I know, but...
Flash is one of the tools that pro wildlife photographers use all the time, and the best ones get so good at it, that you don't even know that they're using it when you look at their photos.
Flash adds light to your scene, but it's not only good for lighting up a dark room. When the sun is high in the sky, you get really contrasty lighting (really bright highlights next to really dark shadows). You can use flash to fill in the shadows and preserve some of the detail, rather than shooting with natural light and having those areas go pure black. If you apply flash naively, you'll eliminate the shadows completely, which looks OK, but it's not very natural. If you carefully control the flash and the exposure, you can leave the shadow areas there, but just add a bit of light to them to keep them from going all the way dark.
One of the best uses for flash in bird photography is to bring out the colors. Have you ever gotten a photo of a bird that you know has brilliant plumage, but it looks kind of drab in your shot? Feathers are designed to catch sunlight and reflect it back. When a bird is in full direct sunlight, you get the full effect in your photo. However, birds are known to sit in trees where the sunlight is blocked, and as a result, their plumage is muted and shows up drab. To fix this, you can apply just enough flash to bring out the plumage, without completely replacing the natural light.
There's a great book about using flash, called The Hot Shoe Diaries by Joe McNally, if you really want to know how the pros do it.
