The consequences of early- and adult-life nutrition for the colour and conservation of hihi Notiomystis cincta
Nutrition is profoundly important for practically all aspects of life. Getting enough of the right kind of food affects cellular function and energy acquisition, disease avoidance, mate attraction, trophic interactions and hence ecosystem structure. When nutritional needs are inadequately met, fecundity and survival can be adversely affected. However, the severity of these effects, and the importance of the particular life history stage when they were experienced, is incompletely understood. Understanding how and when nutritional conditions affect fitness is particularly important for the conservation of endangered species, especially when food supplementation is a key part of managing the few populations that remain. In this thesis, I explore the importance of nutrition during early- and adult-life for the hihi (Notiomystis cincta), a colourful, sexually dichromatic endangered New Zealand passerine. I begin by investigating the importance of nestling nutritional environment for the expression of colourful plumage in adulthood. By experimentally supplementing nestlings with alternative dietary treatments, I demonstrate that early life nutritional conditions have long-term consequences for the expression of both carotenoid-based and structurally produced plumage features. Next I investigate whether these colourful plumage traits are sexually selected. I show that different components of a male’s colourful plumage, including yellow carotenoid-based, black melanin-based and white structurally-based colour, are relevant for different aspects of reproductive success. Using the dietary supplementation experiment, I also consider the impact of alternative supplementary foods on the growth and subsequent survival of hihi. I show that directly supplementing nestlings with protein has a negligible long-term survival benefit over supplementing carbohydrates, and present evidence that males and females have divergent nutritional needs during development – an important consideration for any supplementary feeding program. Finally, I consider whether moulting male hihi selectively forage for carotenoid-rich foods in the wild, as would be expected in a species that requires these pigments for sexual display. I present evidence that adult male hihi do indeed target carotenoid-rich foods during moult, which is consistent with the suggestion that dietary carotenoid access maintains signal honesty. In short, by addressing evolutionary questions from a nutritional perspective, I discover how and when investment in key life history traits is prioritised, how this differs between the sexes and show how this knowledge might be used in supplementary feeding programs to the benefit of endangered species.
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