Complex sentence: Ratite chicks tend to be more omnivorous or insectivorous; similarities in adults end with feeding, as they all vary in diet and length of digestive tract, which is indicative of diet.
Split into simpler sentences: Ratite chicks tend to be more omnivorous or insectivorous. That is where the similarities end with feeding as they all vary in diet and length of digestive tract, which is indicative of diet.