[buserror]

Or perhaps it makes sense to practice the skill as much as they can, so they are better at it when it comes to defend their own young?

[MrMullen]

To me, this is what it is. If young Humpbacks are vulnerable for a certain amount of time, being good at protecting them would a good idea. They can't risk losing that skill since every time they fail, a young Humpback dies.