Characteristics Associated with Newell's Shearwater (Puffinus newelli) and Hawaiian Petrel (Pterodroma sandwichensis) Burrows on Kauai, Hawaii, USA

Small-scale environmental characteristics associated with nesting burrows of the Newell's Shearwater (Puffinus newelli) and Hawaiian Petrel (Pterodroma sandwichensis) were documented in mesic and wet montane forest on the island of Kauai, Hawaii, USA. Most plots containing burrows were located on steep slopes, ranging from 28° to 48° (median = 39°) for the Newell's Shearwater and 0° to 67° (median = 34.5°) for the Hawaiian Petrel. Plots generally contained > 20% to 40% up to > 80% to 100% estimated vegetation cover 0–1 m above ground and > 0% to 20% up to > 60% to 80% cover 1–2 m above ground. Plots were also associated with estimated canopy cover from > 0% to 10% up to > 80% to 90% for the Newell's Shearwater and 0% up to > 70% to 80% for the Hawaiian Petrel. Soil in Newell's Shearwater plots tended to be harder 7.62–22.86 cm below ground, which might provide increased burrow stability. Additionally, maximum vegetation height tended to be greater above Newell's Shearwater plots (median = 6.00 m) than Hawaiian Petrel plots (median = 3.25 m). Taller trees may serve as climbing structures helping Newell's Shearwaters become airborne in thickly vegetated regions that are farther from ridgelines and associated with lighter wind speeds aloft.