Dunadans have a natural sensitivity to evil, and have a natural passive ability like the Detect Evil spell.
Dunadans are friends of the Elves. They can pray to Rivendell without previously visiting it and will be welcomed in Lorien with considerably less effort than other men.
Dunadans are master swordsmen, and are able to defend themselves better with bladed weapons.
Dunadans have a natural affinity for Leadership. This does not affect practising the skill.
Dunadans are natural teachers. They will share a portion of their knowledge in ranger skills with their f ollowers who are not as proficient as they are.
Dunadans are excellent trackers. They will get a bonus to their ability to track as they become more well-rounded rangers. This does not affect practising the skill.