Breeding phenology of Hawaiian petrels (Pterodroma sandwichensis) and Newell's shearwaters (Puffinus auricularis newelli) on Kaua'i, Hawai'i, using ornithological radar, auditory, and visual surveys

Hawaiian petrels (Pterodroma sandwichensis) and Newell's shearwaters (Puffinus auricularis newelli) are seabirds endemic to Hawai'i (Harrison 1990), and U.S. federally listed as endangered and threatened, respectively (U.S. Fish and Wildlife Service 1983). Recovery relies upon management efforts to study and monitor known populations. Traditionally, population size and productivity of seabirds is determined by direct counts in colonies of breeding birds with eggs or chicks (Walsh, Halley et al. 1995). However, colony-based methods of study are often impractical on Kaua`i Island at many of the steep, densely vegetated nesting locations. To date, efforts to study and monitor these species has relied upon indirect measures of activity, such as movement and calling rates (Day, Cooper and Telfer 2003; Kaua'i Endangered Seabird Recovery Project 2009a unpubl.). Interpretation of these results and informed decision making about survey design can be improved with an understanding of how such indirect measures correspond with breeding activity.;In 2008, a project was undertaken on Kaua'i to investigate the intra-seasonal variation of Hawaiian petrel and Newell's shearwater passage and calling rates when measured with ornithological radar, auditory and visual surveys, against current best knowledge of breeding phenology. Overall aims of the project were to provide managers with contextual information when using current radar monitoring protocol, and contribute relevant information on the breeding phenology of these species. Surveys were designed to accomplish the following: (1) quantify intra-seasonal variation in activity levels using these proxy measures, (2) compare how these proxy measures correspond with breeding phenology, and (3) give assessment on the protocol of the current monitoring regime that uses ornithological radar.;Project results showed that indirect measures of breeding activity using ornithological radar, auditory, and visual survey methods can provide a reasonable indication of the timing of breeding tasks. In all measures, variation was consistent with aspects of breeding activities, including increased detection rates during arrival and following egg-laying and hatching, and decreased rates during exodus, departure of non-breeders, and fledging. Radar consistently showed the lowest night-to-night variability amongst survey weeks, making it a reliable measure for estimating population size and productivity in annual monitoring efforts. Factors that influenced survey counts were moonlight on calling activity and cloud cover on visual observations, both of which would need to be considered in interpreting survey results.;This project has produced beneficial management information on monitoring efforts currently used to track populations of Hawaiian petrels and Newell's shearwaters on Kaua'i. This information can be applied to the monitoring of these species elsewhere in Hawai'i, and may be used by management programs employing proxy monitoring methods on other species with cryptic breeding habits that are difficult to study using traditional methods.