U.S. Department of the Interior U.S. Geological Survey
USGS FS 2006-3006
January 2006
Printed on recycled paper
Background
Domestic cats (Felis catus ) were first brought to Hawai‘i aboard sailing ships of European explorers and colonists. The job of the predators was to control mice and rats on the ships during the long voyages. As in other places, cats were taken in and adopted by the families of Hawai‘i and soon became hou-hold pets known as popoki . But cats have always been very well equipped to live and hunt on their own. On tropical archipelagos like the Hawaiian Islands where no other predatory mammals of comparable size existed, abundant and naïve prey were particu-larly easy game, and cats soon thrived in the wild.
Although the details of when cats first came to live in the wild remain little known, adventurers, writers, and naturalists of the day recorded some important obrvations. Feral cats were obrved in remote
wilderness around Kˉılauea volcano on Hawai‘i Island as early as 1840 by explorer William Brack-enridge. Mark Twain was so impresd by the great abundance of cats when he visited Honolulu in 1866 that he reported his obrvations in the Sacramento Union newspaper, which were later reprinted in his book Roughing It :
I saw… tame cats, wild cats, singed cats, individual cats, groups of cats, platoons of cats, companies of cats, regiments of cats, armies of cats, multitudes of cats, millions of cats…
Cats Prey on Native Birds in a Variety of Habitats
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Cats were also common in remote and isolated communities,
as noted by the famous traveler, Isabella Bird, during her visit to Waimanu Valley on Hawai‘i Island in 1873. By that time, a dis-turbing but little known phenomenon was beginning to happen to the unique birds of Hawai‘i. At least 30 species or subspecies
of endemic forest birds were either greatly reduced in number or became extinct between 1870 and 1930. One of the earli-est naturalists to implicate feral cats as a causal factor in the loss was R.C.L. Perkins, who wrote in 1903:
On Lanai, in walking up a single ravine, I counted the re-mains of no less than twenty-two native birds killed by cats, and the must all have been destroyed within two days, as previously the whole gulch had been washed out by a heavy flood. Two cats were actually shot on this occasion as they were devouring their prey, and veral others en, but, owing to the fact that they are extremely shy and mostly nocturnal in habits, few people who have not lived much in the woods have any idea of their numbers.
In Hawai‘i today, cats range from relatively high densi-ties near a level where abandoned pets are frequently fed by well-meaning animal-lovers, to spar isolated populations in remote rain forests and even alpine areas on the islands of Maui and Hawai‘i. Cats kill songbirds, which nest, feed, and roost in trees, and ground nesting birds, such as quail and other intro-duced game birds. Native a birds and other species that nest on the ground or in burrows are particularly vulnerable to preda-tion by cats. For example, endangered ‘ua‘u (Hawaiian Petrel; Pterodroma sandwichensis ) are particularly vulnerable becau they rai their single chicks in lava crevices and nestlings can-not fly for more than 15 weeks after hatching. Adult ‘ua‘u are also often killed by cats, causing rious population declines becau it takes each bird five to
recognition
six years to reach
Feral Cats: Too Long a Threat to Hawaiian Wildlife
This feral cat was photographed by a remote camera in Hawai‘i Volca-noes National Park (e page 3).
wedsLeft. ‘Ua‘u are rare and endangered long-lived
abirds that feed on fish and squid offshore but nest in
lava crevices at high elevation on volcanoes. (Photo by W. Banko ) Right. This adult ‘ua‘u was killed by a cat high on the slopes of Mauna Loa in Hawai‘i Volcanoes National Park. (Photo by F. R. Warshauer, USGS )
feral cats using various tools in-cluding remote cameras and telemetry.
Remote Cameras Capture Images of Feral Cats
Surveillance cameras installed at nests of the palila revealed
that cats reduce palila nest success. Cats mainly kill palila chicks, although adult females may be ki
lled while sitting on the nest. Cat kills at nests not being monitored by cameras are identified by hair, claw marks, and tracks around the nest. Up to 11% of palila nests are depredated by feral cats each year. The loss may threaten the survival of the species, which lays few eggs each year and takes a long time to develop to adulthood. In contrast, mainland songbirds have much larger clutches and rai nestlings much more quickly, decreasing
maturity. Even birds that nest and feed in wetlands are killed by cats, demonstrating that no bird in any habitat is safe from the stealthy, wide-ranging, introduced predators.Cats Carry and Transmit Dias to Other Wildlife Not only do cats prey on vulnerable endangered birds, but
they also carry dias that may infect endangered birds and other wildlife. Cats are the definitive host of a potentially fatal dia called toxoplasmosis. In Hawai‘i, toxoplasmosis has killed native Hawaiian birds such as the critically endangered ‘alalˉa (Corvus hawaiiensis ), the endangered ne ˉne ˉ (Hawaiian goo; Branta sandvicensis ), and even abirds such as the red-footed booby (Sula sula ). Becau the protozoan organism that caus toxoplasmosis (Toxoplasma gondii ) can complete an important part of its life cycle in awater, this dia also pos a threat to marine mammals. Fatal toxoplasmosis was recently confirmed in an endangered Hawaiian monk al (Mo-nachus schauinslandi ), and may possibly threaten other marine mammals in Hawai‘i such as the spi
nner dolphin (Stenella lon-girostris ). In addition to threatening wildlife, toxoplasmosis is zoonotic and pos a significant health risk to pregnant women. Feral cats are also known to carry bacteria that have killed pueo (Hawaiian Short-eared Owls; Asio flammeus sandwichensis ) and ‘alalˉa .
USGS Studies Ecology of Feral Cats in Subalpine Hawai‘i Island
importdataFeral cats now live throughout the dry subalpine and alpine shrublands of Mauna Kea and Mauna Loa on the island of Hawai‘i. Being completely isolated from human ttlements, the cats live entirely off the land under extreme conditions, enduring freezing temperatures, battling lethal dias, and relying entirely on hunting wildlife. Although feral cats exist in small numbers in the rugged ecosystems, they can be very damaging to endangered birds, such as the palila (Loxioides bailleui ) and the ‘ua‘u . Understanding how feral cats live, move, and feed will allow us to formulate better strategies to protect endangered birds. The USGS has been investigating
The death of adults has very vere conquences for populations
of long-lived birds, becau their reproductive rates are low and parental investment in raising young is high. (Photo by J. Jeffrey
)
Feral cats are difficult to study becau of their nocturnal habits and wariness of people. Infrared-triggered cameras are ud to determine the prence of cats in the vicinity of endangered birds.
T h i s
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m a l e n ¯e n ¯e w a s k i l l e d b y a c a t w h i l e s i t t i n g o n h e r n
e s t i n t h e K a ‘u
D e s e r t o n K ¯ıl a u e a v o l c a n o i n H a w a i ‘i V o l c a n o e s N a t i o n a l P a r k . C a t
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a r e i d e n t i fie d
b y
c a t h a i r , c l a w m a r k s a n
d t r a c k s a r
o u n d t h e r e m a i n s . (P h o t o b y K a t h l e e n M i s a j o n , N P S )
threaten nesting birds from great distances. In addition, veral cats may hunt in the same area, exposing birds to threats from a host of different cats over a short period of
time. In the ca of palila occupying only about 140 km 2 (54 mi 2), the home range of each male cat reprents more than 10% of this area. Cats are most active at night, when birds have ttled on their nests and are particularly vulnerable.Diet
Stomach contents from feral cats captured at two sites were examined in order to characterize the diet of the introduced predators (Figure 1). Feral cats on Mauna Kea subsist to a great extent on invertebrates and birds, including both songbirds
their exposure to predators dramatically. In addition, many
Hawaiian birds exhibit little fear of potential predators and often lack avoidance behaviors. Telemetry
Radio transmitters were attached to a sample of cats captured on Mauna Kea in order to describe their home ranges, move-ments and activity patterns. On Mauna Kea, some male cats can range up to 20 km 2 (8 mi 2) and this rivals the largest reported home range for a feral cat from anywhere in the world. In contrast, the home ranges of three females averaged less than 8 km 2 (3 mi 2).
The significance of the large home ranges and daily
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movements is that cats
Palila chicks are highly vulnerable to predators becau their nestling development period is approximately twice as long as that of continen-
tal songbirds.
In order to track the movements of feral cats in endangered palila terri-tory, cats were trapped and fitted with radio collars before relea back
to the wild.
The home ranges of a male (orange ) and a female (blue ) feral cat within the critical habitat of the endangered palila (red lines ) on the West Slope of Mauna Kea. The home range of the male was 20.1 km 2, and the home range of the female was 6.1 km 2. Smaller shapes inside the home
ranges are areas that the cats ud more intensively.
T h i s p a l i l a n e s t w a s d i s c o v e r e d o n M数百
a u n a K e a (H a w a i ‘i I s l a n d ) a
f t e r t h e c h i c k s
h a d b e e n k i l l e d b y a c a t . P r e d a t i o n c a n h a v e s i g
n i fic a n t i m
p a c t s o n t h
e p o p u l a
t i o n o f t h i s e n d a n g e r e d b i r d .
and game birds. Some stomachs contained leg bands from both native and introduced songbirds that had previously been captured and banded at the site. Incts are also common prey items. Surprisingly, rodents are less important than birds and incts despite the great abundance of mice in this environment. In contrast, in Hawai‘i V olcanoes National Park (HA VO), the most common prey items are mice and invertebrates, including grasshoppers and flies. While no gamebirds were found; one stomach contained remains of a young ‘ua‘u , identified by a complete mandible t, feathers, and bones. Most of the rodent remains were mice; rats were rarely found. The diet of cats in
HA VO suggests that cats may subsist on common
prey such as mice and incts, but then
turn to birds when they are more
accessible during nest-ing periods.
Since their introduction to Hawai‘i in灵通英语
the 1800s, cats have adapted to life on their own in
resistorHawaiian ecosystems, where they are now abundant. Their suc-cess in the habitats has been at the expen of native animals, which evolved in the abnce of mammalian predators. Native birds are particularly vulnerable. In addition to predation, cats also impact native wildlife by transmitting lethal dias. For the ‘alalˉa , ne ˉne ˉ, palila , and ‘ua‘u , unnatural predation, in addi-tion to other factors, continues to threaten the survival of the endangered species. Given enough time, feral cats may even cau the extirpation of some populations of the birds. USGS is currently collaborating with NPS to reduce the threat of the introduced predators to endangered species in parks throughout Hawai‘i. The findings will help protect native birds whether they occur in areas managed by USFWS, State of Hawai‘i, or on privately-owned lands.
Suggested Reading
Banko, P.C. et al. 2002. Availability of food resources, distribu-tion of invasive species, and conrvation of a Hawaiian bird along a gradient of elevation. Journal of Biogeography 29: 789–808.Perkins, R.C.L. 1903. Vertebrata (Aves). Pp. 368-465 in Fauna
Hawaiiensis, Vol. I, part IV (D. Sharpe, ed.). The Univer-sity Press, Cambridge, England.Simons, T.R., and C.N. Hodges. 1998. Dark-rumped Petrel
(Pterodroma phaeopygia ). Birds of North America, No. America, Inc. Philadelphia, PA.Tomich, P.Q. 1986. Mammals in Hawaii, 2nd Ed. Bishop Mu-um Press, Honolulu, HI.Winter, L. 2003. Popoki and Hawai‘i’s native birds.
‘Elepaio 63: 43–46.
For more information contact:
Station Leader, Kilauea Field Station Email:**************
Fact sheet written by:
Steven C. Hess and Paul C. Banko,
USGS Pacific Island Ecosystems Rearch Center
Photo credits:
Background image this page by Rex Williams. Other photos by USGS, except where noted.
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Figure 1. Stomach contents of cats captured at two subalpine sites on Hawai‘i Island.
What the Public Can Do
• Be a responsible pet owner by keeping your cat indoors as much as possible, especially at night; keeping track of its whereabouts; and making sure your cat is well-fed at all times.• Cats that are properly cared-for and kept indoors have been shown to live longer, healthier lives than do feral cats. Plea do not relea cats into the wild becau it is inhumane to both the cats and to the wildlife on which they prey.
• Plea help to reduce the population of feral cats by taking them to the Humane Society rather than feeding them. Feeding feral ani-mals only increas their numbers. • Have your cats spayed or neutered. ”If you feed it, fix it.”
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