It is a psychic ability, so it would respond the same as it would to anyone else seeing him. He’d get a general sense of unease, the strength of it depending if he’ll be in any danger from the person seeing him, and know to duck instantly out of sight, hopefully leaving the birdwatcher to assume they’re seeing things. Range doesn’t matter for this ability, only the act of being seen

February 26th excerpt:

Jacob hesitated before taking that last step and leaning on SEND; up until now, he’d merely had a view of trees and birds and squirrels at his new (hopefully not permanent) size. Calling Dean meant he’d be asking someone over six feet tall to come to his aid.