My alpacas are incredibly protective over the lambs, they're all 4 boys so not a maternal thing! In fact they were the same when my big pig farrowed in their field last summer, they were fascinated by piglets. They actively chase my dogs away even though the lambs love the dogs (one thinks he is a dog) and their mums don't mind the dogs being close either.
However with just chickens to guard in a large/free range area they have let me down - I would have the birds in a smaller area and them patrolling around it if I were to do it again and this works well for other people I know with alpacas and chickens. I suspect they will remain more protective of all the sheep now, they were a bit stand-offish before lambs came along.