We will track WTSH breeding at the Freeman Seabird Preserve on Oʻahu, Hawaiʻi by deploying 30 British Antarctic Survey Lotek MK 4093 (weight 1.5 g) GLS loggers on breeding adults during early chick-rearing in October 2023 (El Niño year) and October 2024 (likely “normal” year). Tags will be retrieved shortly after individuals have returned to the breeding colony prior to the pre-laying exodus (April 2024 and April 2025).
To optimize success of GLS deployment and retrieval, single-entrance burrows known to have successfully fledged chicks in previous years will be chosen. Total deployment weight (2.5 g) represents less than 1% of an adult bird’s weight, well below the 3%-5% recommended maximum weight for device deployment (Barron et al. 2010). We have previously used these methods working with this species at this site.
Feather barbs (~ 0.5 mg) from the first, fifth, and tenth primary will be trimmed and collected to examine δ15N and δ13C isotope ratios. Isotopic values of carbon and nitrogen will be used as proxies of foraging habitat and trophic level of the diet. Because the molt of WTSH feathers takes place during the non-breeding season, feather isotopic values reflect diet at the time of growth. Sampling three primaries (P1, P5, P10) will cover the entire winter molting period.
This project has not yet shared any protocols.