Jacob is the Hurley Bird and Flies to the Lighthouse by Dave LeClair

Jacob keeps track of everyone everywhere because he can take the form of a bird. He called for Hurley in this shape in the seasons 1 & 2 finales. Of anyone we know, Jacob has the closest relationship with Hurley, and the bird was calling Hurley's name...

Why a bird? It's probably an Egyptian mythology thing. There are a few bird gods to choose from, but the best fit is Benu. Benu, which means "rise in brilliance" or "shine", flew over the waters of Nun before creation, and came to rest on a rock. Here his cry broke the silence of the waters and this determined what was and what would not be in the creation. Benu was thought to be the soul of Ra, the sun god - both of which are attributed to self generation. Benu is thought to be the prototype for the phoenix, the bird that rises from its own ashes. Jacob and Benu have a bit in common!

Flying would make spying on the whole island easy, and Jacob can easily swoop up to the top of his lighthouse or into a cave this way. Jacob would see off-island happenings through the lighthouse mirror before he leaves for the mainland.

With our first view of the top of the lighthouse, we hear and then see a group of birds fly by. Birds are also shown from a scene at the bottom of the lighthouse. The appearance of these birds are new hints.