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Comparison of Managed and Unmanaged Wedge-Tailed Shearwater Colonies on O'ahu: Effects of Predation

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Title:Comparison of Managed and Unmanaged Wedge-Tailed Shearwater Colonies on O'ahu: Effects of Predation
Authors:Smith, David G.
Polhemus, John T.
VanderWerf, Eric A.
Date Issued:Oct 2002
Publisher:University of Hawai'i Press
Citation:Smith DG, Polhemus JT, VanderWerf EA. 2002. Comparison of managed and unmanaged Wedge-Tailed Shearwater colonies on O'ahu: effects of predation. Pac Sci 56(4): 451-457.
Abstract:On O'ahu, Wedge-tailed Shearwaters (Puffinus pacifieus) and other
seabirds nest primarily on small offshore islets, but fossil evidence shows that
many seabirds formerly bred on O'ahu itself. Predation by introduced mammals
is suspected to be the primary factor preventing shearwaters and other seabirds
from reestablishing large nesting colonies on O'ahu. We investigated the effects
of predation on Wedge-tailed Shearwaters by comparing three small unmanaged
colonies at Malaekahana State Recreation Area on O'ahu, where feral
cats are fed by the public, with a large managed colony at nearby Moku'auia
Island State Seabird Sanctuary, where predators are absent. During three visits
on 19 April, 16 June, and 23 October 2000, we located 69 occupied burrows in
three colonies at Malaekahana and 85 occupied burrows in four monitoring
plots at Moku'auia. Many more nests produced chicks at Moku'auia (62 %) than
at Malaekahana (20%). Among plots at Malaekahana, reproductive success was
lowest (zero) at the colony closest to the cat feeding site. In addition, 44 adult
shearwater carcasses were found at Malaekahana near the cat feeding site. Predation,
most likely by cats attracted to supplemental food, had a devastating
impact on shearwaters at Malaekahana. At one colony there was complete reproductive
failure and almost all adults were killed. Populations of long-lived
species like seabirds are sensitive to adult mortality, and Malaekahana may act as
a sink, draining birds away from other areas.
Appears in Collections: Pacific Science Volume 56, Number 4, 2002

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