Guessing this is a little out of date now, what with the question being about a month old... but my understanding of the HTTParty docs is that it should automatically follow redirects, unless you set the no_follow flag. I haven't successfully tested it though (I'm a total HTTParty n00b and stumbled on this trying to find an answer to my own problem, d'oh...)
If that doesn't work, you could always read the header directly and parse the redirect manually. I've done that in Javascript AJAX requests before, it is not difficult. But you shouldn't have to do that with HTTParty.