Feral cat potential as an invasive alien species
Recently, studies about invasive mammal species in the urban wildlife publications across the globe were predominantly represented by free-roaming domesticated cats, Felis catus (Collins et al. 2021). Feral cats have been considered as the invasive species which threaten numerous endemic vertebrates on the islands. Trouwborst et al. (2020) summarized the growing evidence of negative impacts from free ranging domestic cats on wildlife.
Previous study on the fecal analysis and isotopic mixing method (Maeda et al. 2019) revealed that both feral and stray cats were able to move from forest area and village to residential area, and vice versa. Although the free-ranging cats have impacted on the population of endemic mammal species in Tokunoshima Island, they actually depend on the human-derived food resources. The link between the free ranging cats and the population of native species could be differed by case or depends on many factors, such as the population density of the feral cats on the island, size of the area where the native species live in, the border between the forest and residential area/village, and the availability of the prey (i.e., farm animals) close to the residential area.
There are many legal obligations already exist, such as Convention on Biological Diversity (CBD), which require governments or authorities to prevent and mitigate the threat of invasive alien species on native or endemic biodiversity (Trouwborst et al. 2020). However, the adoption of this international level regulation would be really depended on the policy issued by each national authority.
In order to prevent, mitigate, or eliminate the negative impact of the feral cats on native and endangered species on the island, some strategies below should be adopted and applied. First, prohibition for the introduction of domestic cats on the island where the native species live. Numerous islands worldwide might still ‘sterile’ from the domestic cats which potentially increased the density of the stray and feral cats’ population, especially on the island that has been designated as a conservation area of endangered species. As the negative impacts of introduced cats have been recorded (Russel et al. 2018), the prohibition of any domestic species, including cats, introduction can be an early low-cost prevention strategy to conserve the native species on the island.
Second, prohibition for cat owners let their cats to roam free. Study in Tokunoshima Island (Maeda et al. 2019) showed that there are both types of free roaming cats, stray and feral cats on the island. When domestic cats have introduced into the island, strict regulation of cat ownership is important for the community on the island where the native species live. Registration, vaccination, and not allowing their cats to roam free could prevent the increasing of new stray and feral cats’ number on the island (Trouwborst et al. 2020).
Third, trapping and sterilization of free ranging (both feral and stray) cats. In the area of island where the feral cats’ population has existed, a trap, neuter, and release (TNR) program could be one of the management programs for feral cats on island where the native species live. As described in the previous study (Maeda et al. 2019), endemic species conservation and management program conducted by Local Government in Tokunoshima Island and Ministry of Environment since 2014 have successfully decreased the population of free-ranging cats and increased three endangered mammals on the island. Mitigation of feral cats might be focused on sterilisation depends on the local or national norms as reported in some states in Brazil, where the lethal control of cats was forbidden (Russel et al. 2018). However, from my personal communication with Dr. Makoto Asano (Laboratory of Zoo and Wildlife Medicine, Faculty of Applied Biological Sciences, Gifu University), this method takes a very long time to reach the goal so that it is not the best choice for the endangered species conservation, as the number of the feral cats will relatively stable and the predation will continue for "long time".
Fourth, eradication of the feral cats. Depopulation or eradication of the feral cats which included in wildlife management program might have high conservation impact. Successful stories of feral cats’ eradication with various methods were reported in previous studies (Campbell et al. 2011; Dilley et al. 2017). However, a detailed data on which native island species are threatened by feral cats-resulting population declines will be required to help the authority to manage the ecosystem stability, especially for native and endangered species population (Nogales et al. 2013). Moreover, these data will be very useful to understand whether feral cat eradication program will have the significant conservation impact. Also, these data will help the authority to avoid the misguided depopulation program, which might face animal welfare issue. In addition of the classical “lethal” (and highly cost as well) action by eradication of feral cats, the action should be prioritized based on the geographical areas which have supporting facilities and the areas where the native species are mostly affected by the predation of feral cats. In the term of geographical area, the first target of action should be area with manageable size, in order to get the reasonable (rational) conservation impact.
|Photo by Антон Злобин (www.pexels.com)|
Current status and issues of feral cat management in Indonesia
As international level obligations require authority to prevent and mitigate the threat of invasive alien species, Indonesia has the Ministry of Environment and Forestry as the National Focal Points (NFP) according to the list issued by the CBD Secretariat in 2013. Regarding the invasive species, Indonesia has ministerial regulation which is Decree of the Minister of Environment and Forestry No. P94 of 2016 on Invasive Species. In general, eradication or depopulation should be addressed for invasive species according to the risk analysis result (Ministry of Environment and Forestry 2016). Recently, according to the ministerial regulation, free-ranging cats (Felis catus) have not included into the list of invasive species yet.
Fact that feral cats are not included on the list of invasive species on the national law in Indonesia does not mean that there is no potential threat of feral cats on the native species. It might be due to the lack of studies of the feral cats’ impact on the native endangered species on numerous islands in the world (Medina et al. 2011). Feral cats’ predation was reported as one of many potentially threats for many species’ nest in forest margin area in Sulawesi (Pangau-Adam et al. 2006). Shekelle and Salim (2009) reported the additional threat of predation of feral cats in Sangihe Island, North Sulawesi, Indonesia as an associated consequence of the high human population density threatens tarsier (endemic species) populations. Another report about the endemic birds (Bali starlings) in Nusa Penida, Bali, Indonesia which faced few predators including feral cats (Abrantes 2018). Further comprehensive studies are needed to assess the feral cats’ impacts specifically on native species on islands in Indonesia.
The article in this blog post was an assignment for the basic special lecture for wildlife, as part of my PhD course. Thanks for reading, and let me know your thought.
- Abrantes A. 2018. Avifaunal Biodiversity and Land Use on Indonesia's Palau Penida Archipelago. Master’s Theses. New York (US): State University of New York at Fredonia. [http://hdl.handle.net/1951/71099].
- Campbell KJ, Harper G, Algar D, Hanson CC, Keitt BS, Robinson S. 2011. Review of feral cat eradications on islands. In CR Veitch, MN Clout, DR Towns, Editors. 2011. Island invasives: eradication and management (pp. 37–46). Gland (CH): IUCN.
- Collins MK, Magle SB, Gallo T. 2021. Global trends in urban wildlife ecology and conservation. Biological Conservation 248(108635):1-9. DOI: 10.1016/j.biocon.2021.109236
- Dilley BJ, Schramm M, Ryan PG. 2017. Modest increases in densities of burrow-nesting petrels following the removal of cats (Felis catus) from Marion Island. Polar Biology 40:625–637. DOI: 10.1007/s00300-016-1985-z.
- Maeda T, Nakashita R, Shionosaki K, Yamada F, Watari Y. 2019. Predation on endangered species by human-subsidized domestic cats on Tokunoshima Island. Scientific Reports 9:16200. DOI: 10.1038/s41598-019-52472-3.
- Medina FM, Bonnaud E, Vidal E, Tershy BR, Zavaleta ES, Donlan CJ, Keitt BS, Corre ML, Horwarth SH, Nogales M. 2011. A global review of the impacts of invasive cats on island endangered vertebrates. Global Change Biology 17:3503–3510. DOI: 10.1111/j.1365-2486.2011.02464.x.
- Ministry of Environment and Forestry. 2016. Decree of the Minister of Environment and Forestry Republic of Indonesia No. P94/2016 on Invasive Species. Jakarta, Indonesia.
- Nogales M, Vidal E, Medina FM, Bonnaud E, Tershy BR, Campbell KJ, Zavaleta ES. 2013. Feral cats and biodiversity conservation: the urgent prioritization of island management. BioScience 63(10): 804-810.
- Pangau-Adam MZ, Waltert M, Muhlenberg M. 2006. Nest predation risk on ground and shrub nests in forest margin areas of Sulawesi, Indonesia. Biodiversity and Conservation 15:4143–4158. DOI: 10.1007/s10531-005-3370-z.
- Russell JC, Abrahão CR, Silva JCR, Dias RA, 2018. Management of cats and rodents on inhabited islands: an overview and case study of Fernando de Noronha, Brazil. Perspectives in Ecology and Conservation 16 (4): 193-200. DOI: 10.1016/j.pecon.2018.10.005.
- Shakelle M and Salim A. 2009. An acute conservation threat to two tarsier species in the Sangihe Island chain, North Sulawesi, Indonesia. Oryx 43(3): 419–426. DOI:10.1017/S0030605309000337.
- Trouwborst A, McCormack PC, Camacho EM. 2020. Domestic cats and their impacts on biodiversity: A blind spot in the application of nature conservation law. People and Nature 2:235–250. DOI:10.1002/pan3.10073.