Mary Oliver's poems are remarkably consistent in their approach. She experiments with several styles in terms of line breaks and structure and length, and takes on the big themes of life and death and desire, but she usually approaches them through the observation and celebration of the natural world.
Her body of work is like a long, varied, and beautiful treatise, arguing that most important work is to notice and sing the glory of the world, in all its aspects. Or perhaps in all its natural aspects (she doesn't write much about cars and cities). So when you see lines that are all about looking or observing, about being full of curiosity, about being full of amazement – well, there's a good chance you've got your hands on a Mary Oliver poem.