Les hommes ont oublié cette vérité. Mais tu ne dois pas l'oublier, dit le renard. Tu deviens responsable pour toujours de ce que tu as apprivoisé.
Le Petit Prince, chap. 21

Wednesday, 2 March 2016

Spatial ecology and prey choice of tagged feral cats

van der Ende, J. M. (2015). Spatial ecology and prey choice of tagged feral cats on Schiermonnikoog. M.Sc. Dissertation.  Master of Science in Geographical Information Systems (UNIGIS) Faculty of Economics and Business Administration Vrije Universiteit Amsterdam
The Netherlands

Feral cats (Felis catus) inhabiting the island Schiermonnikoog, The Netherlands, are a potential threat for local prey species populations. To improve the understanding and retrieve more insight in the spatial ecology of this invasive predator, ten feral cats (5 male : 5 female; 5 adult : 5 subadult) were equipped with GPS tags and followed from May till July 2014. Spatio-temporal analyses were used. The home ranges we calculated using Minimum Convex Polygon and Kernel density estimators and tested for differences in sex, age and time. The displacement distance and habitat use was compared between day and night. Locomotive behaviour was compared between subjects using a pre-defined dimension dyad with daily movement variables. In addition, scats were collected and analysed on prey remains and compared with the prey present in the area.
Average 3-month home ranges were found to be 81 and 158ha using Kernel density 95% and Minimum Convex Polygon 95% home ranges respectively. Home range sizes were not significantly different between sexes or age classes. However, nocturnal home range sizes were bigger than the diurnal ones. The nocturnal habitat use did differ from the diurnal use, suggesting a small preference for short salt marsh vegetation during the night. The cats showed a higher nightly displacement (M=45m/15min) compared to during the day (M=22m/15min). The cats were very variable in their daily migration (range M=198-528m) and cumulative daily displacement (range M=1.5-4.1km). A new visualisation technique was proposed to identify differences and similarities between the feral cats and seemed to work well. Hares (Lepus europaeus) contributed the most to the diet in terms of relative prey volume, but Common vole (Microtus arvalis) was the most numerous prey item found in the scats.
In conclusion this study describes the spatial ecology of feral cats and give new insights in the behaviour of feral cats in a natural part of a Dutch Waddensea island. The home ranges of males are not necessarily bigger than female ones. They tend to use short salt marsh vegetation more during the night which could indicate they hunt on the nocturnal species foraging there like hares and rabbits. Bird remains are found in the scats which indicate a potential threat for the bird population by this invasive introduced predator. However in this research no indication is found they actively search and hunt on birds. Further research using acceleration data might be useful to better quantify their hunting behaviour.

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