Complex sentence: Like the Old World vultures, they are scavengers; however, unlike Old World vultures, which find carcasses by sight, New World vultures have a good sense of smell with which they locate carcasses.
Split into simpler sentences: Like the Old World vultures, they are scavengers. Unlike Old World vultures, which find carcasses by sight, New World vultures have a good sense of smell with which they locate carcasses.