Everyone else has said so many things I love about the prologue - the wonderful scene, the slight sense of snark about the weather, Ewen being such a happy lad, the tension introduced by Lachlan, and above all the scenery descriptions. What a wonderfully visual writer.

I've searched and searched for information about the role of the heron in folklore, and the only thing I can find is that it's a denizen of three worlds - earth, air and water. So I suppose it's a fit messenger between those worlds.