关于卢恩骑士的职业介绍没提到不能骑
只说可以骑龙
http://i.imgur.com/gaWtT9q.jpg
游侠也只说可以有狼没说不能用鸟啊！
卢恩骑士转职全剧情中也没有提到任何有关于大嘴鸟的部分
http://ciconia.lofter.com/post/1e0185_efc3d8
反倒是国外网站介绍卢恩骑士有提到
http://ragnarok.wikia.com/wiki/Rune_Knight
以下是节录 (在background)
No longer could the Rune Knights rideeco Pecosecause ordinary animals are intimidated by Rune Knights' fearsome mana, but the dragons are true creatures of magic and acknowledge the Rune Knights as their masters. Together, the Rune Knights and dragons marched to the front lines of battle to terrorize their enemies.
简单讲就是卢恩魔力强，大嘴鸟这种普通魔物会怕，无法骑乘，所以改骑龙。
不过呢，原始职业设定上到底有没有这种东西就不清楚了。