odd feeding behavior

Blackie (a half-feral of 7-months age) has of late, one to two weeks, been terminating his meals early, after a couple of minutes--while the two other cats we care for continue to eat--walks away from the dish, commences grooming himself, and doesn't return to the dish until the other two cats have left nothing but scraps.  He doesn't look unhealthy, and seems to behave normally.  Any ideas?  Should I take him to the vet (he'll tolerate this)?

Cats will often leave and return to a meal.  My Paige does this.  She considers herself 3rd in line and will often wait until my Persians are done.  She'll start and walk away and return when they walk away.  Especially if they are not "top" cat or commonly known as alpha.  Cats when living with other cats, form a pride like mentality and there is a higherarchy, an alpha, a beta and so on.  If he is getting enough to eat, and he keeps his weight on him, he should be fine.  If you are concerned, you might try separating them as they eat.