New study provides first direct evidence of feral cats in Hawaii killing endangered Hawaiian petrel
Hawaiian petrel existence threatened by cats
April 2013. A new study by federal and university scientists has provided the first direct videographic evidence of depredation of the endangered Hawaiian Petrel by feral cats. The study affirms large amounts of earlier anecdotal evidence that feral cats are an important factor in population declines of the species and provides important additional information on the behaviour of cats at petrel burrows.
Petrel burrows video surveillance
The study, which was prepared by scientists from the University of Hawaiʻi, National Park Service, and U.S. Geological Survey, involved the monitoring of 14 Hawaiian Petrel burrows with digital infrared video cameras that produced 819 videos and 89 still photographs during 2007 and 2008 at petrel nesting areas on Mauna Loa on Hawaiʻi Island. The study confirmed the presence of feral cats at eight burrows.
The report says that the effects of feral cats on endangered birds are poorly understood because many endangered species are rare and therefore observed infrequently. In addition, some endangered species are nocturnal and occur only seasonally in remote and inaccessible environments.
Numbers reduced drastically
All that is true in the case of the Hawaiian Petrel. This species was once numerous and widespread throughout the entire Hawaiian archipelago but now numbers only about 15,000 birds distributed in isolated breeding colonies on Kauaʻi, Lanaʻi, Maui, and Hawaiʻi Island. The birds spend most of their time at sea, and return to land only to breed in barren alpine areas and steep forested slopes, where they come and go from underground burrows nocturnally. Usually, confirmation of breeding is determined by a variety of indirect signs such as the presence of droppings, feathers, footprints, or vocalizations.
Depredation of Hawaiian Petrel adults and chicks at colonies has been frequently documented and attributed to cats based on the condition of bird carcasses and the presence of nearby cat scat. Analysis of cat scat and stomach contents of feral cats also suggest that cat depredation is occurring. However, the technology does not currently exist to differentiate whether petrel remains came from consumption of live prey or scavenged dead animals.
One feral cat depredation event was recorded on video in 2008 and showed a feral cat waiting near the entrance of a burrow for over one hour. When the petrel chick emerged, the cat quickly grabbed it. The remains of the chick were found 10 meters from the burrow. Evidence from an additional depredation event was documented in 2008 during a field visit by researchers, while eight other depredation events were documented during field visits in 2007.
The report says that the video data should prove useful in studying both the bird’s nesting behaviour and predator interactions. “This information may prove to be beneficial for developing more targeted management strategies for a suite of endangered bird species in Hawaii,” said Dr. Steven Hess of the U.S. Geological Survey.
Endangered Palila and Hawaiian goose also targeted
Video evidence already exists for feral cat depredation of another endangered Hawaiian bird, the Palila, while another video shows a feral cat trying to take the egg of a Nēnē, the endangered Hawaiian Goose. According to the study, other strong evidence for the negative effects of feral cats on native Hawaiian seabirds comes from the positive response of bird populations where feral cats have been controlled and from comparisons of Wedge-tailed Shearwater reproduction in the presence and absence of feral cats.
The authors point out that while the depredation of Hawaiian Petrel chicks may limit the recruitment of chicks into the population, the killing of adults by cats may have even more severe consequences.
Slow reproduction rate
“This species has delayed sexual maturity, low reproductive potential and extended nestling development, all of which place a premium on survivorship of the adult birds. Further, the birds also have a high degree of mate fidelity and may have difficulty replacing mates that have been depredated,” said Dr. Darcy Hu of the National Park Service.
She pointed out that the majority of numerous depredated Hawaiian Petrel carcasses found in the study area were adult birds, presumably ones that were actively breeding or seeking mates.
Cat based extinction
“These data provide yet more evidence that feral cats are having an impact on many wildlife species, but especially on birds,” said George Wallace, ABC’s Vice President for Oceans and Islands. “Feral cats are believed to have been at least partially, if not fully, responsible for the extinction of several dozen wildlife species, including the Stephens Island Wren of New Zealand and Mexico’s Guadalupe Storm-Petrel. Management controls, such as predator control and predator-proof fencing are urgently needed to prevent that from happening to the Hawaiian Petrel.”
One such effort is underway to protect Mauna Loa’s Hawaiian Petrels. The National Park Service with support from the US Fish and Wildlife Service, National Fish and Wildlife Foundation, and the American Bird Conservancy, is constructing a fence specifically designed to keep feral cats and mongooses out of important Hawaiian Petrel nesting habitat in Hawaiʻi Volcanoes National Park. Once completed, the fence will protect an estimated 45 active petrel nesting sites and enclose 640 acres of prime nesting habitat.