As a phrase, 'solitary circles' doesn't mean anything in particular. It's just telling us two things about the goose: 1. It's swimming in circles 2. It's doing this on its own. NB Free bonus punctuation lesson for anyone who isn't sure about the difference between 'it's and 'it's' . Take another look at sentence number two if you want some examples of how to use these words. 'It's' = it is. Its = referring or belonging to the animal.