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

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.