For retrieving the activities we just send the request:
and then we filter on the basis of objectType of the particular activity. If we get objectType as jive:level,jive:project,jive:group or jive:connected for any activity then we render that activity as social news.
At the moment, there are no verb filters available on any of the activity stream APIs. That would be a useful enhancement, and has been filed. In the mean time, you can just keep following the pagination links to retrieve all available activity, and then do the filtering yourself.
Note that the activity URI you are calling retrieves all possible activity visible to the requesting user. In some use cases, you can reduce the amount of information by requesting the activity for a particular person (/people/####/activities) or place (/places/####/activities), or perhaps just the activities visible on a particular custom stream of the requesting user. For the present, you'll still have to filter yourself to grab just the social news, but you might be able to reduce the amount of information that you need to wade through to find it.