The ecology, behaviour and management of New Zealand brown teal, or pateke (Anas aucklandica chlorotis)

Abstract

The brown teal, or pateke, (Anas aucklandica chlorotis) is a small dabbling duck endemic to New Zealand. After being widespread last century it is largely confined to two areas in northern New Zealand. Numbers are still declining in Northland, but are stable on Great Barrier Island. The species is one of the world's rarest waterfowl yet its conservation and management has been hampered by a lack of ecological information. This thesis is an empirical, field oriented approach to brown teal biology concentrating on the bird's population demography, habitat use and social organisation on Great Barrier Island. Surveys established that approximately 1500 brown teal are present on Great Barrier Island. The birds are divided into several functionally discrete populations and each is confined to one of the island's major valleys. Migration between valleys is very low. Annual fluctuations in population size do occur but the main study population was stable over three years, as indicated by both direct counts and the estimated lifetime productivity of each bird. Adult survivorship was high, relative to other waterfowl, while the largest single factor against population growth was low duckling survivorship. Brown teal have traditional roost sites where large numbers of birds congregate seasonally. These are often sited on quiet coastal streams which are tidal. The largest roosts characteristically have adjacent pasture areas which are used by the birds for nocturnal feeding. They also have collapsed banks and bankside vegetation which provide both perches and escape cover. Pasture areas are used by the birds throughout the year for feeding and they show preferences for large areas that have short, wet vegetation. The size of the flock using each roost site peaks in summer. It then reaches a minimum in late winter, or early spring, when most birds are away from the roost breeding. At this time some roosts are completely vacated while others contain small groups of non-breeding birds. Breeding occurs in thick vegetation away from the roost, but close to water. Each pair defends an exclusive area around the nest and the male takes an active role in maintaining this area as well as defending the brood. Male parental care is unusual among dabbling ducks and consequently, the pair bond is long relative to the breeding season. Pairs form at the roost site before the birds disperse into the surrounding area to establish their exclusive areas, however, the level of courtship at the roost was very low. It is suggested that the birds sedentary nature has promoted the establishment of stable dominance relationship and that status is important in pair formation. Traditional courtship displays appear to be ritualised aggressive behaviours. While brown teal fit the generalisation of waterfowl monogamy it is also suggested that waterfowl mating systems could be better understood if conceptualised as examples of male dominance polygamy. Also included is a review of the literature concerning brown teal; discussions of the overall approach to avifaunal conservation in New Zealand and the future direction of brown teal management; and assessment of the success of the trapping, and sexing techniques developed.