Oracle Database Discussions

So we have over 1,000 db_links and want to clean up the old ones that are never used, but we are not sure which are being used and which are not.

Is there any way to check Oracle to see when the last time or last day that a db_link was used? If there is not a way to check the database for this information, is there anyway to create a trigger or pl/sql code or anything that could track or log when the db_link is used?
(Perhaps there is some info deep inside the data dictionary that keeps track of this in real time, so that I could see which db_links have recently been used in the last 30 minutes or something.)

Any insight on this would be great thanks!!!

Ryan