From what I have seen a group of allied Barbarius ships makes a beeline from their system to one of my colonies from time to time. It seemed different groups may be aiming for different colonies at the same time. Once they get to one of my colonies they soon turn around and go back from where they have come.
The amount and types of ships differ each time but while it seemed like a (suspected) laser destroyer or two at first, now the visiting group can consists of over dozen missile ships with suite of few more (laser?) classes. The gravsurvey and geosurvey classes seem to hardly show up, being busy in other systems.
Maybe NPRs are patrolling their trade routes even when there is no trade occuring on that route.
