The Problem of Backgrounds

Limpkin
I set my f/stop to f/5.6 to put the bird and some of the flowers in focus,
but I wanted to blur the background to obscure the trail and separate it from the bird

One of the constant challenges faced by wildlife photographers is getting a pleasing background.  Photographers often covet finding a scene in which they can make the background completely blurred.  This is achieved by a combination of factors:

1. Distance between the subject and background.  The more distance you can put between your subject and the background behind it, the more you can blur the background.
2. Small f/stop.  By using a smaller f/stop (=wider aperture) you can decrease the depth of field in your photograph, making it easier to blur the background.
3. Focal Length of Lens.  The longer the focal length of the lens, the easier it is to make the background appear less cluttered, more uniform, and more blurry.  In other words, with a longer focal length lens, you can isolate one part of the background you'd have to include with a wider lens, and you can choose a part that has a more even coloration farther away from the subject.  With longer focal length lenses, what's in the background is proportionately larger when compared the the background of a wider angle lens.  So if the background is somewhat blurred, it will appear even more blurred with a longer focal length lens.

Cedar Waxwing
the sky often can make for a nice, "blurry" background

You have only limited control over the distance between the subject and background in the field.  You can sometimes move yourself to a good position to maximize this distance, but as wildlife photographers we have to deal with the reality that wildlife tends to move, and our movements tend to increase the likelihood that that our subjects will move.  So most wildlife photographers often desire shoot with long lenses with large maximum apertures.

Gray Kingbird
I like this photo only for its subject (the first one I've ever seen);
the background is cluttered and distracting, but it's the best the bird gave me

But here's the problem.  Those lenses are expensive and heavy.  They are beyond the price many can afford, and bigger, bulkier lenses are also more cumbersome to use in the field--it's easy to miss a great shot because it takes too long to get the big lens focused on the subject.  So while I confess I do envy those with these wonderful big lenses, there's something to be said for a "smaller" setup you can hand hold.

Blue-gray Gnatcatcher
for me, the leaves in the background do not clutter the composition;
they complement the bird's environment

Using a setup like this (Canon 40D with 400mm f/5.6 lens), it's not always possible to achieve the perfect, blurry background (and that's true even with the best equipment).  So I try to look for other ways to make photographic backgrounds more pleasing.  Here are a few things I try to achieve in my backgrounds:

1. Softness. I want to be able to separate the subject from the background through a sharp subject and soft background.
2. Uniformity.  I try to make the background as uniform as possible, and it's even better if this uniform background contrasts in some way with the subject.
3. Interpretation.  I try to allow the background to complement the subject.  Birds live in environments, so including it in the background of your photo can improve the interpretive qualities of the photograph.

Black-bellied Whistling Duck
spanish moss improves just about any composition

Over time, I've come to appreciate photographs that can put all three of these elements together.  And while I still like the "bird on a stick" photos that blur all the bird's surroundings besides the stick it's perched on, there's a great sense of satisfaction I get when I can find a way to let the background complement the subject and help interpret its environment.

American Bittern
the bittern's surroundings here help to interpret the way the bittern hunts for food,
so I was glad to have much of it in focus.

Blue Jay
there are some things in the background here I'd probably want to change,
but overall, I think the blurred leaves are more pleasing than distracting