Notes on the population of the brown rat, Rattus norvegicus in a laboratory-animal shed : Studies on the ecology and control of rats, Part I

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  • Osada Yasuhiro
    Department of Parasitology, Institute for Infectious Diseases, University of Tokyo
  • Sato Kinsaku
    Department of Parasitology, Institute for Infectious Diseases, University of Tokyo
  • Tanaka Hidehumi
    Department of Parasitology, Institute for Infectious Diseases, University of Tokyo

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Other Title
  • ある小動物舍のドブネズミ Rattus norvegicus の棲息状況について : ネズミの生態と駆除に関する研究第 1 報
  • ある小動物舎のドブネズミのRattus norvegicusの棲息状況について
  • アル ショウドウブツシャ ノ ドブネズミ ノ Rattus norvegicus ノ セイソク ジョウキョウ ニ ツイテ

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Abstract

For the purpose of estimating the population size and home ranges of the house rat Rattus norvegicus, an investigation was made in a laboratory animal shed. The effects of snap-traps as the control measure on the rat were also observed after the above stated experiments. The mark and release operation were carried on for successive 8 days, untill no unmarked rats could be recovered. The number of total marked rats attained was 41. Estimation of the population size by the graphic method using the linear equation (E)Y=(N-x)P resulted in 40, thus showing a coincidence between the theoretical and actial sizes. (Y : the ratio of marked individuals to the total number captured in a single operation. N : the number captured. x : the cumulated number of captured rats. p : probability of capturing a rat) The real population size, however, was estimated to be larger, because of the presence of individuals not exposed to the cage-traps. During course of the snap-trap collections made later, 13 unmarked rats were trapped besides 19 marked individuals. The probabilities of capture for unmarked (P) and the marked (π) were calculated as 0.357 and 0.196, respectively. It was presumed in this case that rats, once captured, showed the behaviour to be less easily trapped than the unmarked. The average distance between the localities of the successive captures in each individual was calculated as 6.53m for a male and 4.96m for a female. Home ranges of 50% of the males were estimated as less than 36.1 square meters, and as 33.5 square meters in the females. The males seemed to cover more areas than the females.

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