do dominate females, and thus will aggressively exclude females from food, such that females will only access food sources when unattended by the males. During breeding season, the female is solely responsible for nest building and incubation, and the male will provide the female and the hatchlings with food. South Island robins become sexually mature between six and 12 months of age. They begin their breeding season fairly early in August or September (Southern Hemisphere spring) and thus can make use of the winter's remaining food stores during this time. They build open-cup nests in tree-forks or inside tree cavities. Incubation lasts 18 days, and chicks leave the nest after 21 days. Five to 25 days after fledglings leave the nest, the pair may breed again. Modal clutch size is two eggs, with the expected inverse correlation between dimensions and number of eggs. Replacement clutches, in the case of loss of eggs or nestlings to predation, can be produced relatively rapidly, within 3–10 days. Feeding Invertebrates, including earthworms, beetles, and other arthropods foraged from the leaf litter comprise most of the South Island robins' diet. Invertebrate prey may be cached whole or in portions. Single items are cached at separate sites. Prey is typically stored within 10 metres of where it was procured, even if the bird is outside its own territory. In the winter the primary cache is earthworms, while during the summer the trend is toward cicadas. South Island robins have a very good memory of their storage sites; a male was observed to empty as many as five consecutive caches before returning the stores to his mate during incubation. The birds have demonstrated an ability to differentiate and prioritise caches of varying sizes, up to 12 total items, without any training, which appears to be the highest recorded numerical competency of any wild animal. Because of its high metabolic rate, a robin might spend as much as 90% of its day foraging or storing during the winter. South Island robins have also been observed to eat berries on occasion; however, these are not cached. Vocalisation A male's call during non-breeding season is a series of loud notes with descending frequency, which start in rapid succession and finish slowly. During breeding season, the males resort to full song to court the females. Full song is a loud, clear, and continuous song, which can last for more than 30