Do radio-collars increase the predation risk of small rodents?

Abstract

Small radio-collars are useful for the to study of movements and predation risk in cryptic small rodents. The results may be biased, however, if collars alter the behaviour or vulnerability of tagged individuals. We measured the effects of radio-collars (1.5 g) on the behaviour of voles [Microtus agrestis (body mass 33 g), M. epiroticus (27 g) and Clethrionomys glareolus (18 g)] in two aviary experiments. First, the mobility of collared and non-collared voles was studied 1 to 4 days after the attachment. On the 1st day after attachment but not later, collared voles moved less than non-collared voles. Second, the risk of predation by Tengmalm's owls (Aegolius funereus) was estimated on the 4th day after attachment. Owls captured 5 of 13 collared voles and 8 of 13 non-collared voles. The results suggest that radio-collars do not markedly alter the behaviour or increase the risk from avian predation in these small rodents.