Abstract
Feral cats (Felis catus) are predators that cause widespread loss of native wildlife in urban ecosystems. Despite these risks, cats are commonly released as control agents for city rats (Rattus spp.). Cats can influence their prey directly by killing or indirectly through changes to feeding or space-use. However, cats prefer defenseless prey, and there are no data suggesting that cats influence large (>300g) urban rats. We used a pre-existing radiofrequency identification assay (microchipped rats and field cameras) and ethograms to assess the impact of cats, including temporal and space use patterns, on an active rat colony. From Dec 27, 2017 through May 28, 2018 we captured 306 videos of pre-identified cats and/or rats that shared the same space. There were three instances of predation and 20 stalking events. Logistic regression showed the likelihood of a rat being seen on a particular day is associated with the number of cats seen on the same day (OR=0.1, p<0.001) or previous day (OR=0.15, p<0.001). Space-use was also impacted. For every additional cat sighting, a rat is 1.19 times more likely to move in the direction of shelter. Our findings of low levels of predation support why ecologists believe the risks to native wildlife outweighs any benefits of releasing cats. Even though rats were less likely to be seen, they simply shifted their movements and remained present in the system. Our findings that cat presence led to fewer rat sightings may explain the common perception of their value as rat-predators despite the associated risks.
Highlights
Cat predation on rodents, mice (Mus, Peromyscus spp.), is among the most recognized models of predator: prey interactions, inspiring nursery rhymes, cartoons and public perceptions
This study is the first research to document the direct and indirect influences of identifiable feral cats on a partially-identified population of city rats. This partly-enclosed urban ecosystem was under heavy pressure from cats, as evidenced by the number of cats present and the number of staking attempts from each cat throughout the study
These events occurred during all hours of the day and evening
Summary
Mice (Mus, Peromyscus spp.), is among the most recognized models of predator: prey interactions, inspiring nursery rhymes, cartoons and public perceptions. Many non-trained observers, cannot tell the difference between mice which weigh 20–35 g (Zielinski et al, 1992) and city rats which often weigh 10 times as much (Parsons et al, 2017; Combs et al, 2018). This misconception may be partly responsible for cats being widely considered. The domestication of cats, and abundance of easier to obtain alternative foods cast doubts on cats’ inclination to prey on city rats and suppress their numbers
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