Herpetological Review 42(4), 2011 522 TECHNIQUES Tracking animals provides a detailed picture of their be- haviour and can be important in understanding their ecology. Tracking is especially useful for elucidating the ecology of ani- mals that are cryptic during all or parts of their life cycle (Heyer et al. 1994; Langkilde and Alford 2002; Reynolds and Riley 2002). Amphibians, for example, can be hard to study outside breed- ing aggregations, and wildlife telemetry can provide insight on otherwise unknown aspects of their biology (Heyer et al. 1994; Naef-Daenzer 1993; Naef-Daenzer et al. 2005; Rowley and Alford 2007a, b, c; Rowley et al. 2007). Tracking devices should be small and unobtrusive (Hamley and Falls 1975; Heyer et al. 1994; Korpimaki et al. 1996; Ormings- ton 1985). Many guidelines recommend that the mass of tracking devices should not exceed between 5% (Wilson and McMahon 2006) and 10% (Blomquist and Hunter 2007; Gursky 1998; Rich- ards et al. 1994) of the animal’s body mass, particularly when tracking vertebrates. Package shape is also an important con- sideration; devices must not impede the tracked animal’s move- ment (Blomquist and Hunter 2007; Greenwood and Sargeant 1973; Wilson and McMahon 2006). Finally, devices should have long useful lifespans, reducing the frequency of capture, han- dling, and other potentially stressful procedures (Langkilde and Alford 2002; Pereira et al. 2009). Tracking devices, therefore, typi- cally reflect compromises among the needs for small size, low mass, long life, and high durability. Two main approaches can be taken to track animals using ra- dio signals. Tracking using tags containing active radio transmit- ters allows researchers to locate subjects and identify them indi- vidually (Heyer et al. 1994; Indermaur et al. 2008; Naef-Daenzer 1993; Naef-Daenzer et al. 2005; Rowley et al. 2007), and may en- able the retrieval of additional information, such as the subject’s physiological status and local environmental conditions (Reyn- olds et al. 2002), but the method is restricted to larger species or individuals, due to the relatively high weight of the battery, harness, and transmitter package (Langkilde and Alford 2002; Naef-Daenzer 1993; Naef-Daenzer et al. 2005; Rowley and Alford 2007c). Currently, minimum body mass of animals tracked using radio-transmitters is 2–4 g, based on a minimum package plus harness mass of 0.2 g for the smallest available transmitters and limitations to 5–10% of the body mass (Naef-Daenzer et al. 2005). These extremely light tags have extremely short battery lives, measured in days; this further restricts their usefulness in field studies, where animals may require some time to return to nor- mal behaviour following tag attachment (Langkilde and Alford 2002; Rowley et al. 2007). It is also possible to use tags that do not contain their own power sources. These tags fall into two categories: PIT (Passive Integrated Transponder) tags and harmonic radar tags. PIT tags, pattern recognition exclusively can still be a useful aid to indi- vidual identification. Acknowledgments.—We are grateful to Barley Van Clief and the Pennsylvania Resource Council, Tri-State Bird Rescue and Research, Fred and Cindy von Czoernig, and Michael and Angie Riska for al- lowing us access to their property and springhouse. We especially thank Kevin Fryberger for coordinating site visits and Jim White for assistance with photography and field work. We also thank P. Adkins, L. Allison, G. Colligan, K. J. 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