Despite being one of the most widespread seabird species in the main Hawaiian Islands, little is known about the breeding phenology of the White-tailed Tropicbird Phaethon lepturus dorotheae. This is presumably due to its low conservation concern, coupled with the inaccessibility of most of its nesting sites, meaning that there are an extremely limited number of known nest sites where birds could be monitored directly. To better understand the breeding phenology of this species on Kaua‘i, we reviewed data from the Save Our Shearwaters (SOS) program (a Kaua‘i-based seabird rescue and rehabilitation program) to analyze when fledgling tropicbirds were recovered. We discovered 313 records of hatch-year birds in the database. Using breeding data from other populations of this species and back-dating the phenology based on these fledging records from the SOS database, we conclude that this species breeds year-round on Kaua‘i. However, typically, eggs are laid between March and September, with a peak in June. Chicks hatch between April and October (with a peak in July) and birds fledge between July and January (with a peak in October). The number of tropicbird fledglings handed over to SOS has increased significantly since the program's inception in 1979, to a high of 31 fledglings received in 2016. It is not clear whether this indicates an increase in the population of this species on Kaua‘i, an increase in public awareness of seabird conservation on the island, or both. Data from rescue and rehabilitation projects can be an important data resource for studying rare, cryptic, or difficult-to-access seabird species.
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