Timing and duration of primary moult in New Zealand's silvereye (tauhou, Zosterops lateralis)

Across all bird species, latitude plays an important role in determining patterns in timing, duration, and synchronisation of primary moult but, apart from Africa, moult studies at the southernmost limits of the continents and islands in the southern hemisphere are lacking. The focus of this study is the self-introduced silvereye (tauhou, Zosterops lateralis) in New Zealand, one of the most southern countries in the world. Moult data collected by bird banders during the period 1978-2022 were analysed using the Underhill-Zucchini moult model. Silvereyes had an estimated primary moult duration of 74 days, with a mean population start date of 3 February and a mean completion date of 19 April. Post-breeding primary moult in adult silvereyes starts soon after the breeding season and ends shortly before some of the more southern birds embark on their seasonal northward migratory movements. Juvenile primary moult is estimated to start approximately two weeks after the start of post-breeding moult in adults. A literature review suggested that primary moult duration for Zosterops species is similar regardless of latitude, but the timing of moult is variable and adjusted to local conditions.