SREL Reprint #0266




Use of Radioactively Tagged Bait to Study Movement Patterns in Small Mammal Populations

John B. Gentry, Michael H. Smith and Robert J. Breyers



Small mammal movement patterns were studied on a 14.1 ha grid with 26 lines and rows 676 trap stations) with 15 m intervals between stations. The study area was located in a  lowland mesic-hardwood forest in the southeastern United States. All stations were prebaited with radioactive peanut butter for five days prior to the initiation of snap-trapping. The radioactive isotopes 59Fe, 65Zn and 131I were mixed with the peanut butter.  After the five-day prebaiting period, two traps were set at each of 256 stations on the centrally located 16 x 16 (256 station) grid for a period of 18 days.  At that time, traps were also set on the remaining 420 stations arranged in a band around the 16 x 16 grid.  Traps were set on the entire 26 x 26 grid for the last 18 days.  Animals were taken to the laboratory and checked for the presence of isotopes using a multi-channel pulse-height analyzer.

Most of the animals, consisting mainly of Blarina brevicauda, were removed within 4 - 8 days. However, certain animals were difficult to capture.  Isotope-labeled animals were captured on days 21, 25, 30 and 36.  Removal trapping caused animals to move into the grid from the border zone.  Also, many animals captured on the inner 16 x 16 grid were double isotope-labeled (65Zn-131I).  Many animals captured on the surrounding outer bend were single-isotope-labeled (I).  Also, a huge proportion of animals captured on the surrounding outer bend wore unlabeled.

Mean minimum distances traveled were calculated to set a lower limit on movement distances.  The results indicated that the absolute minimum width of the border zone affected by small mammal removal was about 15 m.


SREL Reprint #0266

Gentry, J.B., M.H. Smith, and R.J. Beyers. 1971. Use of radioactively tagged bait to study movement patterns in small mammal populations. Annales Zoologici Fennici 8:17-21.

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