Breeding of the Australasian Bittern (Botaurus poiciloptilus) in New Zealand

Abstract

In Australasia, wetlands and the birds that inhabit them are under considerable threat. Australasian Bitterns (Botaurus poiciloptilus) are a potential indicator of wetland health but there is an urgent need to collect baseline ecological data and understand processes threatening the species so that conservation actions aimed at reversing apparent declines can be implemented. I collated nest records from New Zealand to determine breeding parameters and highlight areas requiring further research. Nests were recorded throughout the country, and all except one were in wetlands. Booming calls were recorded in most months but peaked between September and November. Breeding was observed from August to May, with most activity in November and December. Nests were in a wide variety of vegetation types, frequently Typha orientalis, and sites were usually surrounded by deep water. Breeding parameters appear similar to those of northern hemisphere species of Botaurus. Australasian Bitterns appear to have a high potential breeding capacity, with large clutches, fairly short incubation periods, and a long breeding season but there are no quantifiable data on nesting success. There are major gaps in our knowledge, and research on breeding should focus on assessing the fate of breeding attempts, potential influence of habitat loss and fragmentation on breeding success, vulnerability to predation by introduced mammals, the interaction between predation risk and water levels, and the roles of food and habitat in sustaining populations.