Many of these are then eaten by birds such as saddlebacks and robins. In the case of the saddlebacks, they are a vivid red in colour. Fledgling saddlebacks are often seen until March and April. The diet of North Island saddlebacks mostly consists of insects, berries, invertebrates, and nectar. North Island saddlebacks are monogamous and usually mate for life. North Island saddlebacks have an average length of 25 cm. Some saddlebacks have since started breeding outside of the predator-proof sanctuary. Adult males develop a light grey area on their backs, thus are called "saddlebacks". The saddlebacks () are two species of New Zealand bird of the family Callaeidae. Before the arrival of humans, North Island saddlebacks were widespread on mainland North Island. Saddlebacks have also been introduced at several other mainland sanctuaries. Saddlebacks vary their calls so that even individuals from different areas can be identified. Saddlebacks will nest in epiphytes, tree fern crowns, or holes in tree trunks.