5. Survey plot locations, nest counts, and habitat characteristics for Wedge-tailed Shearwaters (Ardenna pacifica) at Kīlauea Point National Wildlife Refuge, Kauaʻi, in 2019
Dates
Publication Date
2020-12-08
Start Date
2019-07-01
End Date
2019-07-07
Citation
Felis, J.J., Kelsey, E.C., Adams, J., Stenske, J.G., and White, L.M., 2020, Population estimates for selected breeding seabirds at Kīlauea Point National Wildlife Refuge, Kauaʻi, in 2019: U.S. Geological Survey data release, https://doi.org/10.5066/P93MPDR1.
Summary
We used a stratified-random sampling approach to estimate the total abundance of Wedge-tailed Shearwater (Ardenna pacifica) nest sites across Kīlauea Point National Wildlife Refuge (KPNWR), Kauaʻi, in 2019. To estimate stratum-specific nest site abundance, we generated randomly located, non-overlapping circular plots within several sampling strata. We set plot radius to 5 m in most strata, except for some portions of Kīlauea Point where a 3-m radius was used to accommodate narrow strips of habitat. We generated enough plots to survey 10 percent of total stratum area where we expected high nest site abundance, and 5 percent of stratum area where expected nest site abundance was low or minimal. This data table contains all plot locations [...]
Summary
We used a stratified-random sampling approach to estimate the total abundance of Wedge-tailed Shearwater (Ardenna pacifica) nest sites across Kīlauea Point National Wildlife Refuge (KPNWR), Kauaʻi, in 2019. To estimate stratum-specific nest site abundance, we generated randomly located, non-overlapping circular plots within several sampling strata. We set plot radius to 5 m in most strata, except for some portions of Kīlauea Point where a 3-m radius was used to accommodate narrow strips of habitat. We generated enough plots to survey 10 percent of total stratum area where we expected high nest site abundance, and 5 percent of stratum area where expected nest site abundance was low or minimal. This data table contains all plot locations and data collected in the field. We surveyed plots for nesting Wedge-tailed Shearwaters during 1-7 July 2019 at KPNWR. We navigated to plot locations on the ground using a handheld GPS. We occasionally moved plots in the field when part of the plot fell on either inaccessible habitat (e.g., cliffs) or on non-habitat (e.g., paved surfaces). To preserve randomness, we moved plots the shortest distance possible away from these features and updated location coordinates. If a plot could not be moved (e.g., it was located within a narrow strip of accessible habitat), it was reduced in size and we recalculated plot area accordingly. Once at the plot, we staked a rope with 3-m and 5-m markings at the plot center to accurately determine the plot boundary. We counted all active and potential Wedge-tailed Shearwater nest sites in each plot’s designated radius, including soil burrows, natural rock alcoves/crevices, vegetative shelters (vegetation burrows), and surface nest sites. A nest site was counted if any portion of the radius made contact with the nest site. We measured occupancy in a subset of nest sites identified in plots using a systematic design that randomized site selection with a periodic interval. Beginning with the first nest site identified in the first plot of the day, we checked the occupancy of every fifth nest site encountered-cumulatively-across consecutive plots. For example, if plot P1 had 12 nest sites, we checked the occupancy of the 5th and 10th sites. If plot P2 then had 7 nest sites, we checked the occupancy of the 3rd site, and so on. This sampling design scaled occupancy to the number of burrows in a plot and was achievable given time restraints. We defined six occupancy categories: 1) Occupied Bird, bird present (presence of egg not confirmed); 2) Occupied Egg, an unattended egg was present; 3) Unoccupied Sign, no bird or egg present but sign present; 4) Unoccupied No Sign, no signs of presence; 5) Unknown Sign, unable to determine occupancy but sign present; and 6) Unknown No Sign, unable to determine occupancy and no sign present. In addition to counting shearwater nesting sites and evaluating occupancy, we collected information on several habitat parameters associated with each plot. We categorized the percent cover of bare soil, exposed rock, leaf litter, grass cover, shrub cover, and tree cover (0, 1-33, 34-66, and 67-100 percent). We estimated cover types on the ground surface (bare soil, exposed rock, and leaf litter) in the same plane and their sum could not exceed 100 percent. Cover types above the ground surface (grass, shrub, and tree cover) were estimated in independent planes and their sum could be greater than 100 percent. We also categorized maximum tree height (less than 2m, 2-4m, and greater than 4m) and shrub height (less than 1m, 1-3m, and greater than 3m). When possible, we identified the dominant tree species and the first and second most dominant shrub species in plots. We measured plot slope and aspect with an inclinometer and compass, respectively.
These data were collected to estimate the population size of Wedge-tailed Shearwaters (Ardenna pacifica) breeding at Kīlauea Point National Wildlife Refuge, Kauaʻi, in 2019. Counts of nest sites and occupancy values in survey plots can be used with appropriate statistical methods to generate breeding population estimates for this species.
