Abstract
Shortly after the enactment of restrictions aimed at limiting the spread of COVID-19, various local government and public health authorities around the world reported an increased sighting of rats. Such reports have yet to be empirically validated. Here we combined data from multi-catch rodent stations (providing data on rodent captures), rodent bait stations (providing data on rodent activity) and residents’ complaints to explore the effects of a six week lockdown period on rodent populations within the City of Sydney, Australia. The sampling interval encompassed October 2019 to July 2020 with lockdown defined as the interval from April 1st to May 15th, 2020. Rodent captures and activity (visits to bait stations) were stable prior to lockdown. Captures showed a rapid increase and then decline during the lockdown, while rodent visits to bait stations declined throughout this period. There were no changes in the frequency of complaints during lockdown relative to before and after lockdown. There was a non-directional change in the geographical distribution of indices of rodent abundance suggesting that rodents redistributed in response to resource scarcity. We hypothesize that lockdown measures initially resulted in increased rodent captures due to sudden shortage of human-derived food resources. Rodent visits to bait stations might not show this pattern due to the nature of the binary data collected, namely the presence or absence of a visit. Relocation of bait stations driven by pest management goals may also have affected the detection of any directional spatial effect. We conclude that the onset of COVID-19 may have disrupted commensal rodent populations, with possible implications for the future management of these ubiquitous urban indicator species.
Highlights
After the enactment of restrictions aimed at limiting the spread of COVID-19, various local government and public health authorities around the world reported an increased sighting of rats
Some of these reports described rodents engaging in atypical behaviors, such as rats being active during the day and in close proximity to h umans[35,36,37], as well as rats consuming conspecifics[31,38]
There can be a reliable relationship between public complaints and rodent abundance[42], this has not been validated during abnormal times such as COVID-19
Summary
After the enactment of restrictions aimed at limiting the spread of COVID-19, various local government and public health authorities around the world reported an increased sighting of rats. Shortly after restrictions were enacted, reports from various local governments and public health authorities linked the closures of restaurants and food-related venues to increased sightings of rats[28,29,30,31,32,33,34] Some of these reports described rodents engaging in atypical behaviors, such as rats being active during the day and in close proximity to h umans[35,36,37], as well as rats consuming conspecifics (e.g. muricide or cannibalism)[31,38]. Parsons et al released a preprint in which they investigated how stay-at-home measures affected rat sightings in various urbanized environments They analyzed rat-related public complaints in New York City and Tokyo and surveyed pest control companies in the United States, Canada, Japan and Poland[41]. For example, that public perceptions of rodent abundance are affected by cognitive and observational biases potentiated by COVID-19 restrictions and the increased use of social m edia[39,43,44]
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