Behaviour 151 (2014) 421–434 brill.com/beh It takes two to tango: female movement facilitates male mate location in wild northern watersnakes (Nerodia sipedon) Benjamin C. Jellen ∗ and Robert D. Aldridge Department of Biology, Saint Louis University, 3507 Laclede Avenue, St. Louis, MO 63103, USA * Corresponding author’s current address: Department of Mathematics & Science, McKendree University, 701 College Road, Lebanon, IL 62254, USA, e-mail: ben.jellen@gmail.com Accepted 30 August 2013; published online 2 October 2013 Abstract To facilitate location of mating partners, females of many taxa emit chemical signals (i.e., sex pheromones) to inform male conspecifics of their location and reproductive status. Males subse- quently alter their movements to increase their likelihood of encountering females and this move- ment has been historically viewed as a primary determinant of mate location. However, because of the method of female sex pheromone release, particularly via terrestrial trails, female movement likely contributes to mate location; however, information on this topic is lacking. We monitored the movements of 27 free-ranging radio-equipped adult female northern watersnakes (Nerodia sipedon) during the 2007–2009 mating seasons to determine if females employed movement tac- tics to facilitate location by males. For a limited period following shedding, female movement increased. During this period, they were approximately five times more likely to be located by a male than during the remainder of the mating period. Further, females experienced maximum male mate location following shedding. Because increased movement is associated with increased costs, females may minimise these costs by restricting this risky behavior to a limited period of time when their attractiveness and/or receptiveness is presumed to peak. Keywords mate location, movement, sex, shedding. 1. Introduction For internally-fertilising taxa to mate, members of the opposite sex must first locate one another. This can be problematic for species that are widely  2014 Koninklijke Brill NV, Leiden DOI:10.1163/1568539X-00003128