Do pigeons have external fertilisation external?

Yes, They Do.

There has not been any huge advantage but they can produce a number of the eggs.

The advantages in external fertilization is that there are lots of egg cells produce but the disadvantages are that a small number survive because if you are using a frog, the egg cells get eaten or...

internal duhh they are mammals

It depends. Are you talking about humans? 8DHumans use internal fertilization but the disadvantages in external fertilization is that a small number of eggs survive.