Rystil,
I am in the process of leveling up Abdiel. Since he is now third level, Selar gains two 2HD (from 1-3). In the Monster Manual, it states that an Eagle that has 2-3 HD changes size to Medium - does this happen to Selar? If so, what happens when he gains more HD, and goes off the chart for HD for Eagles? My thought is that his size does not change, but I just wanted to confirm.
Abdiel and Selar have both taken the Weapon Focus(natural attacks) feat.
Here are the Hit Dice rolls for Abdiel
9, and Selar
7 & 4