Survival of Feral Cats, Felis catus (Carnivora: Felidae), on Mauna Kea,Hawaiâ•Ÿi, Based on Tooth Cementum Lines

Feral cats (Felis catus) have spread throughout anthropogenic and insular environments of the world. They now threaten many species of native wildlife with chronic depredation. Knowledge of feral cat population dynamics is necessary to understand their ecological effects and to develop effective control strategies. However, there are few studies worldwide regarding annual or lifetime survival rates in remote systems, and none on Pacific islands. We constructed the age distribution and estimated survival of feral cats in a remote area of Hawai‘i Island using cementum lines present in lower canine teeth. Our data suggest annual cementum line formation. A log-linear model estimated annual survivalb 1 yr of age to be 0.647. Relatively high survival coupled with high reproductive output allows individual cats to affect native wildlife for many years and cat populations to rebound quickly after control efforts. Feral cats (Felis catus) are considered by the World Conservation Union (IUCN) as one of the ‘‘100 of the world’s worst invasive alien species’’ (Lowe et al. 2000). They have been specifically implicated in at least 33 bird extinctions, primarily on islands, making them one of the most important causes of bird extinctions worldwide (Nogales et al. 2004). To develop more effective control strategies for feral cats, knowledge of their population dynamics based on survival, reproduction, and movements is required. There are some data on immigration and emigration (Edwards et al. 2001, Devillard et al. 2003, Hansen et al. 2007, Schmidt et al. 2007), as well as reproduction (van Aarde 1983, Pascal 1980), but survival is relatively unknown worldwide. Most studies of feral cat survival rates are from anthropogenic landscapes (Devillard et al. 2003, Schmidt et al. 2007) where the mortality factors tend to be human-related (e.g., cars) or as part of eradication programs (Short et al. 1997, Bester et al. 2002, Rodrı́guez et al. 2006). There are few studies of natural mortality in remote systems (van Aarde 1983, 1984, Pascal 1980) and none on Pacific islands. Feral cats became abundant in forests of the Hawaiian Islands soon after their introduction in the late 1700s (Rothschild 1893, Perkins 1903). They were subsequently reported to be notorious and harmful predators that contributed to the decline and extinction of some Hawaiian bird species (Perkins 1903, Ralph and van Riper 1985, Stone 1985, Pacific Science (2010), vol. 64, no. 3:381–389 doi: 10.2984/64.3.381 : 2010 by University of Hawai‘i Press All rights reserved 1 This research was funded by the Federal Highway Administration, the Natural Resources Partnership Program of the U.S. Geological Survey and the National Park Service, and the U.S. Geological Survey Wildlife and Terrestrial Resources Program and Invasive Species Programs. Portions of this research were performed under Cooperative Agreement 00003HS025 to the University of Hawai‘i at Mānoa and Cooperative Agreement 3036WS0012 to the University of Hawai‘i at Hilo. Manuscript accepted 18 August 2009. 2 Hawai‘i Cooperative Studies Unit, Pacific Aquaculture and Coastal Resources Center, University of Hawai‘i, Hilo, P.O. Box 44, Hawai‘i National Park, Hawai‘i 96718. 3 Current address: Department of Biological Sciences, Virginia Polytechnic Institute and State University, 2125 Derring Hall, Blacksburg, Virginia 24061. 4 Pacific Island Ecosystems Research Center, U.S. Geological Survey, Kı̄lauea Field Station, P.O. Box 44, Hawai‘i National Park, Hawai‘i 96718. 5 Department of Land and Natural Resources, Division of Forestry and Wildlife, 19 East Kāwili Street, Hilo, Hawai‘i 96720. 6 Corresponding author (e-mail: [email protected]). Smucker et al. 2000). Feral cats in Hawai‘i prey upon endangered forest birds (Laut et al. 2003, Hess et al. 2004) and terrestrial birds that nest near the ground (Kowalsky et al. 2002), as well as colonial nesting seabirds (Hu et al. 2001, Smith et al. 2002, Hess et al. 2007). In addition, cats are the definitive host of Toxoplasma gondii, a parasite that has killed individuals of several native and introduced wildlife species (Work et al. 2000, 2002, Honnold et al. 2005). Feral cats range throughout the Hawaiian Islands from high-density colonies near coastal areas where pets are frequently abandoned and fed by people (Winter 2003), to remote, lowdensity populations in montane forests and subalpine areas of Maui (Simons 1983) and Hawai‘i Island (Tomich 1986, Hu et al. 2001, Hansen et al. 2007). Feral cats, particularly males, occupy large home ranges and disperse long distances in Hawai‘i (Hansen et al. 2007, Goltz et al. 2008). Tooth cementum lines are ideal for studies of wild mammal population dynamics because they may provide more precise age estimates, especially for older individuals, than methods that rely on pelage, dentition, or eye lens weight (Dimmick and Pelton 1996). This method is effective for many mammal species (Crowe 1972, Spinage 1976, Grue and Jensen 1979), including F. catus (Pascal and Castanet 1978, Grue and Jensen 1979, van Aarde 1983, Daniels et al. 1998), but as yet has not been widely used. Our objectives were to construct the age distribution and estimate the survival rate of feral cats on Mauna Kea, Hawai‘i Island, based on the number of tooth cementum lines.