Effects of radio-collars on European badgers (Meles meles) F. A. M. Tuyttens 1 *, D. W. Macdonald 1 and A. W. Roddam 2 1 Wildlife Conservation Research Unit, Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, U.K. 2 Wellcome Trust Centre for the Epidemiology of Infectious Disease, Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3FY, U.K. (Accepted 24 April 2001) Abstract The relationships between radio-collaring/tracking and 12 biometric parameters in a population of badgers (Meles meles) that were live-trapped in south-west England were investigated. The length of time for which a badger had worn a radio-collar was selected as an explanatory variable in generalized linear models of three biometric parameters (body condition, body weight and testes volume) irrespective of whether or not age class was included as a variable in the analyses. There was evidence that badgers that had been carrying a radio-collar for 1±100 days had lower body condition scores both when compared to badgers that had not been collared and with those that had been collared for longer than 100 days, suggesting a post- collaring acclimation period. In addition, the time period between ®rst and last capture was longer for radio-collared than non-collared badgers. It is unlikely that this was due to an effect of collaring on trappability or to non-random selection of badgers for collaring. Although testes size differed between non-collared badgers and badgers that had been tagged for > 100 days, the relationship between radio- collaring and reproductive output remained unproven. These results highlight not only the need to assess the welfare aspects of radio-collaring but also the potential intricacy of corollaries of collaring. Explora- tions such as that reported here are important to the validity of studies that make use of radio-telemetry. Key words: body condition, mortality, radio-telemetry, reproduction, survival, Meles meles INTRODUCTION Radio-telemetry is a commonly used technique to study the behaviour, physiology and movement patterns of animals. An inherent assumption in these studies is that radio-tagged animals are representative of the entire study population. Two mechanisms may invalidate this assumption. First, animals ®tted with radio-tags may be a biased sub-sample of the population. Second, tagging and/or tracking may affect the health, condition and behaviour of the animals. Except for obvious injury or behavioural changes, the effects of attaching a radio-tag are dif®cult to quantify in wild animals. Radio-telemetry has commonly been used to provide data on locations and activities of European badgers Meles meles (Cheeseman & Mallinson, 1980; Cresswell & Harris, 1988; Roper et al., 1993; Woodroffe, Macdonald & da Silva, 1993; Butler & Roper, 1994; Rodriguez, Martin & Delibes, 1996; Bro Èseth, Knutsen & Bevanger, 1997). Very little has been published about the effect of radio-tagging and/or radio-tracking on the welfare, health and behaviour of this species. Brown (1993) reported that the emergence times and time away from the main sett did not differ between radio-collared badgers that had been captured, sedated and ®tted with a spool-and-line and radio- collared badgers that had not been handled recently. Tuyttens, Macdonald, Swait et al. (1999) did not ®nd an effect of radio-collaring/tracking on the probability of subsequently capturing badgers in cage-traps. Apart from these reports, little relevant data have been pub- lished about the existence or the extent of either or both potential sources of bias. We compared several potential indicators of health and body condition between live-trapped European badgers that had not been radio-collared and badgers that had been radio-collared for a short (< 100 days) or long (> 100 days) time. In addition, we investigated whether collaring affects population dynamics (mor- tality and reproduction). *All correspondence to present address: F. A. M. Tuyttens, Department Mechanisation ± Labour ± Buildings ± Animal Welfare and Environmental Protection, Van Gansberghelaan 115, 9820 Merelbeke, Belgium. E-mail: frank.tuyttens@clo.fgov.be J. Zool., Lond. (2002) 257, 37±42 # 2002 The Zoological Society of London Printed in the United Kingdom DOI:10.1017/S0952836902000638