No evidence that dietary nutrient deficiency is related to poor reproductive success of translocated takahe

The aim of the study was to identify from the existing literature the essential nutrients that are known to affect egg fertility and hatching success in birds, and compare the concentrations of these between source and translocated populations of the endangered New Zealand takahe. Takahe are herbivorous, and those that have been translocated to highly modified island sites with pasture grasses have higher rates of egg infertility and low hatching success compared to takahe that breed in native tussock grasslands in Fiordland. Nine essential nutrients were analysed from infertile eggs collected from Fiordland and four island sites over a 4-year period. Only manganese showed any evidence of being in low concentrations in island takahe relative to Fiordland takahe, a result consistent with earlier analysis that showed low concentrations of manganese in takahe plant-foods on islands. However, manganese was in lowest concentrations on Kapiti Island where takahe consistently have the highest reproductive success of the four island sites, with 10 of the 15 samples from the other three islands falling within the range of the Fiordland samples. Therefore neither manganese nor any of the other eight essential nutrients appear to be widely deficient in island birds. Based on the results of this study, a supplementary feeding programme to improve egg fertility in takahe is not recommended.