April 2020 Student of the Month – Hannah Lockwood
The domestic cat (Felis silvestris catus) is one of the most ubiquitous predators in the world, having established populations in six continents, from the Outback of Australia to remote oceanic islands. First domesticated in the Near East, cats were found to be useful in controlling rodent populations and were transported around the world by whalers and sealers (Driscoll et al. 2007).
Cats are now cited as contributing to the decline and extinction of 367 and 63 species, respectively (Doherty et al. 2016). These effects are particularly apparent on oceanic islands, where high species endemism and poorly developed predator defence strategies can lead to severe declines and extinctions of native species (Medina et al. 2011). However, in the UK, prey species have evolved alongside the European wildcat (F. s. silvestris) and mustelid species, exerting similar pressure on populations. Therefore, prey present in the UK are better adapted to either avoid predation (through crypsis, escape, or defence), or able to cope with losses (through high productivity rates) than on remote islands where prey species have not faced such predation pressures previously.
Cats in the UK are mostly owned, having regular access to anthropogenic food sources including commercial cat food. In contrast, island populations are often made up of feral individuals, relying solely on wild food sources and therefore killing a far greater number of wild prey animals. Since pet cat populations are not limited by the same factors as wild predators (habitat and food resource availability, disease), they occur in far greater densities. This has led to concern regarding the predation rates of individuals and the impacts of this on native wildlife.
‘What the Cat Dragged in’ is a citizen science project which I set up around two years ago in order to find out exactly what cats are bringing home. Any cat owner in the UK can sign their cat(s) up to this programme and submit data each month for 12 months. Since cats are known to eat their prey or discard it, I am using collar-mounted cameras to find out the proportion of prey returned home, along with GPS units to monitor activity. This will ultimately allow me to estimate the number of prey killed by cats per year in the UK.
So far, our study cats have caught a wide variety of prey from stoats to grass snakes, but wood mice are the top prey source. We have had a fantastic response from the public, registering cats from Orkney to Cornwall, but new participants are needed to improve the accuracy of data. If you or someone you know has an outdoor-going cat, please go to the website to sign up (www.whatthecatdraggedin.org).
Later in my PhD I will be looking into the impacts of domestic cats on wildlife populations in the UK. There are a number of ways to do this, such as looking at life stage and breeding status of prey to see whether predation is additive or compensatory. The situation with cats is very complicated, as their population density is directly related to that of humans, and therefore it can be unclear whether impacts are directly related to cats or some other form of anthropogenic disturbance (i.e noise, light, or air pollution). I plan to use mapping software to see whether areas of high cat density may be causing lower prey density. I will then compare changes in prey density with changes in land use and climate to identify whether these may have a larger impact.
Doherty, T.S., Glen, A.S., Nimmo, D.G., Ritchie, E.G., Dickman, C.R., 2016. Invasive predators and global biodiversity loss. PNAS, 113(40), pp. 11261-11265.
Driscoll, C.A., Menotti-Raymond, M., Roca, A.L., Hupe, K., Johnson, W.E., Geffen, E., Harley, E., Delibes, M., Pontier, D., Kitchene, A.C., Yamaguchi, N., O’Brien, S.J., Macdonald, D., 2007. The Near Eastern origin of cat domestication. Science, 317(5837), pp. 519-523.
Medina, F.M., Bonnaud, E., Vidal, E., Tershy, B.R., Zavaleta, E.S., Donlan, C.J., Keitt, B.S., Le Corre, M., Horwath, S.V., Nogales, M., 2011. A global review of the impacts of invasive cats on island endangered vertebrates. Global Change Biology, 17(11), pp. 3503-3510.
Blog by Hannah Lockwood, PhD researcher from the University of Derby.