Testing for food limitation in reintroduced Hihi populations: contrasting results for two islands

Abstract

The Hihi Notiomystis cincta, a New Zealand honeyeater (Aves: Meliphagidae), became extinct everywhere except one offshore island following European colonization, Attempts to establish Hihi on additional islands in the 1980s had poor success, and this was attributed to food limitation. These islands had all been modified by human use, and had a lower diversity of natural carbohydrate (fruit and nectar) sources than the source island, particularly in winter. When Hihi were released on two additional islands, Mokoia and Tiritiri Matangi, we used supplementation experiments to test whether condition and survival of birds were limited by availability of carbohydrate food. Sugar water was provided on an on-off basis from autumn through spring in the year after the release. Birds were weighed at the beginning and end of fed periods, and survival for fed and unfed periods was estimated using mark-recapture analysis on sighting data. Armstrong and Perrott (2000) reported that supplementary feeding had no effect on condition or survival on Mokoia, and annual survival was about 40%, both in the year of the experiment and in subsequent years when food was supplied continuously. This paper reports contrasting results for Tiritiri Matangi. Supplementary feeding on Tiritiri Matangi increased both condition and survival, and overall survival was substantially higher than on Mokoia - 66% in the year of the experiment and 76% the following year when food was supplied continuously. It therefore appears that supplementary feeding can be used to improve survival of Hihi on Tiritiri Matangi, whereas survival is constrained to a low level by other factors on Mokoia. These results emphasize the value of habitat manipulation experiments for developing appropriate management strategies for reintroduced populations.