Thanks. Very interesting. Do you mean to infer that pasture grazing is necessarily done during lambing?
Yes, since lambing is done during the time of the best grazing (when the grass is new) due to the nutritional requirements of lactating. When I looked into the rainy season around Jerusalem/Bethlehem and found it started in November, it was easy to infer that shepherds would be in the area in December and that it would be lambing season.