Cooperative Fish and Wildlife Research Units Program: Iowa
Education, Research and Technical Assistance for Managing Our Natural Resources

Smith, J.B., S.K. Windels, T. Wolf, R.W. Klaver, J.L. Belant. 2016. Do transmitters affect fitness of American beavers (Castor Canadensis)? Wildlife Biology 22:117 - 123


One key assumption often inferred with using radio-equipped individuals is that the transmitter has no effect on the metric of interest. To evaluate this assumption, we used a known fate model to assess the effect of transmitter type (i.e. tail-mounted or peritoneal implant) on short-term (one year) survival and a joint live–dead recovery model and results from a mark–recapture study to compare long-term (eight years) survival and body condition of ear-tagged only Ameri-can beavers Castor canadensis to those equipped with radio transmitters in Voyageurs National Park, Minnesota, USA. Short-term (1-year) survival was not influenced by transmitter type (wi  0.64). Over the 8-year study period, annual survival was similar between transmitter-equipped beavers (tail-mounted and implant transmitters combined; 0.76; 95% CI  0.45–0.91) versus ear-tagged only (0.78; 95% CI  0.45–0.93). Additionally, we found no difference in weight gain (t9  0.25, p  0.80) or tail area (t11  1.25, p  0.24) from spring to summer between the two groups. In contrast, winter weight loss (t22   2.03, p  0.05) and tail area decrease (t30   3.04, p  0.01) was greater for transmitter-equipped (weight   3.09 kg, SE  0.55; tail area   33.71 cm2, SE  4.80) than ear-tagged only (weight   1.80 kg, SE  0.33; tail area   12.38 cm2, SE  5.13) beavers. Our results generally support the continued use of transmitters on beavers for estimating demographic parameters, although we recommend additional assessments of transmitter effects under different environmental conditions.