Well, it turns out (via the modern research paper I just linked to, in my second edit) that the shepherds in Isreal right about now are likely in fact, to be watching over their ewes and lambs.

But it seems such a simple way to answer the "We have no way of knowing Jesus's real birthday!"

Of course, since Luke's version of the birth story was nothing more than a massive retcon, and Jesus was likely born very happily at home, we still have no way of knowing the historical fact.

But the lambing season is a concrete, real-world, way of putting some internal logic into the story, and puts some humanity into it. And as a storyteller, that's what I care about.