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Reducing feral cat threats to native wildlife in Hawai`i

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Title: Reducing feral cat threats to native wildlife in Hawai`i
Authors: Hess, Steven C.
Hansen, Heidi
Banko, Paul C.
Keywords: Endangered species
Feral cat
predator control
bait preference
Issue Date: Jul 2008
Series/Report no.: TR-HCSU;010
Related To:
Abstract: We documented the diet of feral cats (Felis catus) on Kīlauea and Mauna Loa within Hawai`i Volcanoes National Park (HAVO), determined the incidence of three feline diseases on Mauna Kea, studied feral cat home range, developed and tested trap-signaling devices, tested food-based baits and attractants, analyzed feral cat population dynamics using genetic techniques, and developed an adaptive strategy for reducing predation on endangered Hawaiian birds.
We documented the diet of feral cats by analyzing the contents of 42 digestive tracts from Kīlauea and Mauna Loa in Hawai`i Volcanoes National Park. Small mammals, invertebrates, and birds were the most common prey types consumed by feral cats. Birds occurred in 27.8–29.2% of digestive tracts. The total number of bird, small mammal, and
invertebrate prey differed between Kīlauea and Mauna Loa. On Mauna Loa, significantly more (89%) feral cats consumed small mammals, primarily rodents, than on Kīlauea Volcano (50%). Mice (Mus musculus) were the major component of the feral cat diet on Mauna Loa, whereas
Orthoptera were the major component of the diet on Kīlauea. We recovered a mandible set, feathers, and bones of an endangered Hawaiian Petrel (Pterodroma sandwichensis) from a digestive tract from Mauna Loa. This specimen represents the first well-documented endangered seabird to be recovered from the digestive tract of a feral cat in Hawai`i and suggests that feral cats prey on this species.
We determined prevalence to feline immunodeficiency virus (FIV) antibodies, feline leukemia virus (FeLV) antigen, and Toxoplasma gondii antibodies in feral cats on Mauna Kea Hawai`i from April 2002 to May 2004. Six of 68 (8.8%) and 11/68 (16.2%) were antibody positive to FIV and antigen positive for FeLV, respectively; 25/67 (37.3%) were seropositive to T. gondii. Antibodies to FeLV and T. gondii occurred in all age and sex classes, but FIV occurred only in adult males. Evidence of previous or current infections with two of these infectious agents was detected in eight of 64 cats (12.5%). Despite exposure to these infectious agents, feral cats remain abundant throughout the Hawaiian Islands.
Feral cats in dry subalpine woodland of Mauna Kea, Hawai`i, live in low density and exhibit some of the largest reported home ranges in the literature. While 95% fixed kernel home range estimates for three females averaged 772 ha, four males averaged 1,418 ha, and one male maintained a home range of 2,050 ha. Mean daily movement rates between sexes overlapped widely and did not differ significantly (P = 0.083). Log-transformed 95% kernel 2 home ranges for males were significantly larger than those of females (P = 0.024), but 25%
kernel home ranges for females were larger than those of males (P = 0.017). Moreover, logtransformed home ranges of males were also significantly larger than those of females in this and seven other studies from the Pacific region (P = 0.044). Feral cats present a major threat
to endangered Hawaiian birds, but knowledge of their ecology can be used for management by optimizing trap spacing and creating buffer zones around conservation areas.
Frequent checks of live traps require enormous amounts of labor and add human scents associated with repeated monitoring which may reduce capture efficiency. To reduce efforts and increase efficiency, we developed a trap-signaling device with long-distance reception, durability in adverse weather, and ease of transport, deployment, and use. Modifications from
previous designs include a normally-open magnetic switch and a mounting configuration to maximize reception. The system weighed < 225 g, was effective ≤ 17.1 km, and failed in < 1% of trap-nights. Employing this system, researchers and wildlife managers may reduce the
amount of effort checking traps while improving the welfare of trapped animals.
Successful feral cat control programs require effective baits and lures. Non-targets may interfere with trapping efforts by rapidly consuming bait before feral cats encounter traps, necessitating frequent bait replacement. We compared the effectiveness of baits and lures by analyzing capture rates of feral cats and non-targets and monitoring animal visits to bait
stations with remotely-triggered cameras. We tested four different baits and attractants: canned cat food, sardines, catnip, and a bait sausage that we formulated from pork and fat. We trapped for a total of 3,389 trap nights and captured 35 feral cats. There were 323 incidences
of trap interferences, reducing the effective trap nights (ETN) to 3,225. The primary cause of trap interference was feral pigs rolling over traps (n = 185, 57.3% of interferences). The primary non-target species captured were small Indian mongooses (n = 74, 22.9% of interferences). Overall, more cats and mongooses were captured using sardines, although the
catch frequencies were not dependent on the bait type used. We obtained photographs of 1,476 small mammals at the bait stations. Mongooses were the principal mammals photographed (n = 939, 69.5% of pictures). We also obtained 398 photographs of rats (29.5%) and 9 (0.7%) of mice. Feral cats were photographed only 5 (0.4%) times. We found strong
differences between mongooses, rodents, and cats photographed at the four bait types. Sardines were the most visited bait type (n = 641, 47.4% of photographs). Pork sausage and cat food accounted for 383 (28.3%) and 322 (23.8%) visits while catnip had only 67 (5.0%) 3 visits. Feral cats were photographed only at sardine bait. Mongooses were attracted primarily to sardines (49.3%). Pork sausage was the most attractive bait to rats, accounting for 44.5% of photographs. Due to the high rate of non-target interference, other attractants need to be tested for successful feral cat control programs.
Population genetics can provide information about the demographics and dynamics of invasive species that is beneficial for developing effective control strategies. We studied the population genetics of feral cats on Hawai`i Island by microsatellite analysis to evaluate genetic diversity and population structure, assess gene flow and connectivity among three populations, identify potential source populations, characterize population dynamics, and evaluate sex-biased dispersal. High genetic diversity, low structure, and high number of migrants per generation supported high gene flow that was not limited spatially. Migration rates revealed that most migration occurred out of West Mauna Kea. Effective population size estimates indicated increasing cat populations despite control efforts. Despite high gene flow, relatedness estimates declined significantly with increased geographic distance and Bayesian assignment tests revealed the presence of three population clusters. Genetic structure and relatedness estimates indicated male-biased dispersal. Mauna Kea may be a source population that can be targeted for control. However, recolonization seems likely given the great dispersal ability that may not
be inhibited by barriers such as lava flows. Genetic monitoring will be necessary to assess the effectiveness of future control efforts.
Despite the long history of feral cats in Hawai`i, there has been little research to provide strategies to improve control programs and reduce depredation on endangered species. Our objective was to develop a predictive model to determine how landscape features on Mauna Kea such as habitat, elevation, and proximity to roads affect the number of feral cats captured at each trap. We used log-link generalized linear models and QAICc model ranking criteria to determine the effect of these factors. We found that the number of cats captured per trap was related to trapping effort, habitat type, and whether traps were located on the West or North Slope of Mauna Kea. We recommend an adaptive management strategy to minimize trapping interference by non-target small Indian mongoose (Herpestes auropunctatus) with toxicants, to focus trapping efforts in māmane (Sophora chrysophylla) habitat on the West slope of Mauna Kea, and to cluster traps near others that have previously captured multiple cats.
Pages/Duration: 116
Appears in Collections:Hawaii Cooperative Studies Unit (HCSU)

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