Back lighting is one of my favorite “tricks” to use to get a slight rim of light around the subject to separate it from the background. This rim light effect is easily seen on the top of the bird’s beak and around the feathers to the right of his head.
However using ambient outdoor light is kind of tricky especially when you don’t have reflectors, flashes or strobes to fill and you’ve got to do it on the fly. The key is to set your exposure to be slightly over exposed - this will overexpose (lighten) the background where the light is coming from but your subject should be properly exposed and not left in the dark! Give it a try and send me what you’ve created!
I was staking out a spot in the park next to our condo for a portrait session and heard this little guy singing his happy hour song. He let me get pretty close. This was taken with my D300 + AF Nikkor 85mm f/1.4 @ 1/125s at f/4.0, ISO 400.