Firstly, they switch between melee and ranged attacks which is signified by their stance. When attacking with melee, they will stand on their hind legs and when attacking with ranged, they stand on all fours. They switch between the two based on the damage being dealt to them - if damaged most by magic attacks, they will switch to ranged, and if being damaged by melee or ranged attacks, they will switch to a melee.
Secondly, Airuts have a special attack in both stances which is very powerful and hits rapidly. Both specials are signalled by an animation in which the Airut beats its chest and can be prevented by either using the Flurry ability against the melee special or Rapid-fire against the ranged special.
Finally, Airut have the unique ability to increase their defence as their lifepoints decrease. This is where your equipment becomes vital as you will need at least level 80 weaponry to deal any significant damage when their defence is boosted. The use of level 90 weaponry, Extreme/Overload potions and stat-boosting prayers such as Turmoil make fighting Airuts much easier.
*Only dropped in Kuradal's dungeon.