No, I'm afraid there's currently no way to make the link in the navigation default to the month view.
One thing you can do though is to make a link in a page which takes people straight to the month view of your calendar.
e.g., if the default calendar view you want people to see is http://e-voice.org.uk/ellertonandaughton/calendar/view?view=month then you could add that as a link on your site homepage (or wherever).
Hope that helps
Joe - Voice Admin