Abstract
Understanding the local ecology of urban Norway rats (Rattus norevgicus) is necessary to inform effective rat mitigation strategies. While Capture-Mark-Recapture (CMR) methods can be used to acquire such ecological information (e.g., abundance, movement patterns, and habitat use), these techniques assume that all individuals of the study population are equally trappable. To test whether urban rats adhere to this assumption, we conducted a four-week CMR study in an urban neighborhood of Vancouver, Canada, to evaluate whether rat characteristics (i.e., age, sex, size, wound status, and infection with the pathogen Leptospira spp.) were associated with trappability. We found that the majority of rats entered traps in the first two weeks of trapping, and that larger rats were caught earlier in the trapping period. However, smaller, sexually immature rats were recaught more often than were larger, sexually mature rats, suggesting that prior capture affects the ability to recapture urban Norway rats. This highlights the need for CMR studies to account for size and sexual maturity when interpreting data.
Highlights
Norway rats (Rattus norvegicus) are infamous urban exploiters, thriving in cities worldwide (Feng and Himsworth, 2014)
580 individual Norway rats were captured over 20 trap days with an overall trap success of 14%
We found that the number of rats captured decreased over the trapping period and that larger rats were more likely to enter traps earlier in the trapping period and were less likely to be recaught than were smaller rats. These results suggest that urban Norway rats do not follow the assumption of equal trappability, and that CMR studies may be biased toward obtaining more robust capture histories for smaller individuals than larger individuals
Summary
Norway rats (Rattus norvegicus) are infamous urban exploiters, thriving in cities worldwide (Feng and Himsworth, 2014). They are economically costly, estimated to account for over 19 billion dollars in damages annually in the United States through their consumption and contamination of food products alone (Pimentel et al, 2000). An estimate by the province of Alberta, Canada projected that rats would cost up to 42.5 million dollars annually in the absence of their current rodent control program (McClay et al, 2004). Rats pose a health risk to human populations, harboring numerous zoonotic pathogens (those transmissible between animals and people) responsible for human morbidity and mortality in cities globally (Himsworth et al, 2013b)
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