Breeding season behaviour, reproductive success, and dispersal after translocation in tūturuatu (Thinornis novaeseelandiae) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Conservation Biology at Te Kunenga ki Pūrehuroa, Tāmaki Makaurau, Aotearoa (Massey University, Auckland, New Zealand)
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Date
2022
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Massey University
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Abstract
The tūturuatu (tchūriwat’, shore plover, Thinornis novaeseelandiae) is an endangered shorebird endemic to Aotearoa (New Zealand). The remnant wild population of approximately 45 breeding pairs appears stable but is confined to Hokorereoro (Rangatira, South East Island), a small island in the Chatham Islands group. Since 1994 efforts to translocate captive-bred juvenile birds to other island sanctuaries free of introduced mammalian predators have met with mixed success. This study investigated the behavioural ecology of a population of eighteen tūturuatu on Motutapu, an island in the Hauraki Gulf near Tāmaki Makaurau (Auckland), which were either survivors of or descended from 92 captive-bred juveniles released between 2012 and 2017. The behaviour of each breeding pair, and their chicks once hatched, was recorded every two minutes at their nest site or territory for two hours each day until the last chick had fledged, a total of almost 20,000 observations. Trail camera recordings of the nest site and surrounding area augmented my direct observations. Behavioural time budgets were constructed for adults and chicks allowing comparison between sexes, phases of the breeding season, and between the Motutapu population and published reports on the Hokorereoro population. Display activity was observed and circa-tidal effects on behaviour were investigated. Comparison of foraging time budgets with published reports on tūturuatu and other plover species suggested that adequate food resources were available for both adults and chicks. Display activity was primarily directed at competitive species; and increased in frequency and intensity during the chick-rearing phase compared with the earlier phases of the breeding season. I suggest that this behaviour is linked to the sudden increase in vulnerability of tūturuatu chicks after hatching rather than the gradual increase in “reproductive value” through the season. Patterns of foraging and inactive behaviour in tūturuatu appeared to be affected by circa-tidal rhythms. Reproductive success was investigated, with an emphasis on egg survival, and chick survival to fledging. Egg survival rates were high, which I suggest is at least partly attributable to the unusual covered nest of this species. Chick mortality rates were high, with avian predation and female desertion identified as the primary causes. Female desertion is a common sequel to a male-biased adult sex ratio in other plover species but has not been observed previously in tūturuatu. Deleterious outcomes were observed both for chicks and deserted male partners, prompting wildlife management recommendations. Thirty-six captive-bred juveniles were closely monitored after translocation to the island with the aim of distinguishing between mortality and dispersal in those that disappeared. Subsequently the records of all 128 birds translocated to the island between 2012 and 2019 were investigated to compare the effects of various predictors of detection probability. The timing of release with respect to the summer solstice was identified as a key predictor of detection probability with the most successful outcomes aligning with the timing of juvenile independence in the wild population.