Could you leave his door ajar and a light on in the hallway?

I think fears are very common around this age. My daughter is 28 months too, and is scared of all sorts of things, ranging from moths to vacuum cleaners. Her fears are usually connected to a fascination with the objects (she recently got up the courage to hug the vacuum cleaner!) Yesterday she claimed to be scared of the sand in the sandpit... today she said 'nana is scary', then changed her mind a few moments later. Maybe if you tell your son a story about the birds at night and how they look after him and are friendly (or something like that!) he will get over his fear. Good luck!