The Removal of Feral Cats from San Nicolas Island: Methodology

Abstract

Feral cats are considered one of the most detrimental invasive species within island ecosystems. Non-native feral cats have been on San Nicolas Island (5,896 ha, or 14,562 acres) since at least 1952. In an effort to counter the negative impacts of feral cats on marine and terrestrial birds, the San Nicolas seabird restoration project, with the goal of eradicating cats, was initiated in June 2009. Although aimed at seabird restoration, feral cat eradication is expected to aid in the protection of endemic terrestrial species, including the federally threatened island night lizard, federally threatened western snowy plover, a subspecies of deer mouse, and the state threatened island fox. Methods including the use of altered padded leg-hold live traps, detection dogs, and hunting are being utilized to deliver a successful eradication within a short window of opportunity. In addition, a trap monitoring system, operated in tandem with field PCs and GIS, has proven effective in managing large numbers of traps. Since initiation, a rotation of staff has provided an average of 6 field personnel on-island at any one time to staff the project continuously over 10 months. Eradication was complicated by the similarly sized island fox, rugged topography, restricted access to parts of the island by Navy activities, marine mammal presence on the beaches, and sea and shore birds nesting and roosting. Island eradications require multiple methods to effectively remove all cats, and operations on larger islands benefit from the intensive use of management tools such as GIS. The systems developed on the San Nicolas Seabird Restoration Project will advance the global effort to reduce the threats of invasive species, particularly feral cats.

Drivers and facilitators of hunting behaviour in domestic cats and options for management

“…With intense effort and favourable terrain, trapping may facilitate eradication from small islands. Otherwise, cage traps are used in capture for euthanasia, sterilisation or live removal (Hanson et al 2010), or when non-target casualties, including of owned cats, are unacceptable. Captured feral cats may be killed by shooting, lethal injection or carbon dioxide gas (Rocamora & Henriette 2015), though the latter is associated with welfare concerns (Simonsen et al 1981).…”

Removal and eradication of introduced species in a fenced reserve: Quantifying effort, costs and results

“…Whilst not undertaken in the current study, such data could also be used as input into detection probability models, which determine the probability of eradication (e.g. Ramsey et al ; Hanson et al ). These balance managers' perceptions of risk with probability values (Ramsey et al ), in turn decreasing financial and human inputs.…”

Outdoor Cats: An Animal Welfare and Protection Perspective

“…The San Nicolas Island cat removal project exemplifies a multi-organization, multi-agency effort to restore an island ecosystem to meet wildlife conservation goals held mutually between the participants. The program itself, as described by Hanson et al (2010), involved the trapping and live removal and relocation of cats that had been feral on the island since at least the 1950s. In the draft environmental plan, lethal removal had been identified as the preferred alternative, but this changed after The Humane Society of the United States (HSUS) and other cat advocacy groups complained that non-lethal alternatives had not been sufficiently examined.…”