The use of low-cost, advanced global positioning system (GPS) telemetry devices for wildlife tracking is growing in popularity, especially use of systems that can communicate with each other to track contacts or transfer data. We evaluated the communication and data-transfer capabilities of a low-cost, custom-built GPS telemetry system with an on-board wireless sensor network using human subjects and captive bighorn sheep (Ovis canadensis) as an experimental model. We conducted tests in July 2010, at 2 facilities in Colorado, USA. Wireless sensor networks use a collection of nodes to ferry data from one destination to another. We tested data-transfer capabilities at several transmission strengths (−25 decibel-milliwatts (dBm), −15 dBm, −10 dBm, −5 dBm, and 0 dBm) and with several types of bodily obstruction (unobstructed, human, bighorn sheep). Under conditions of high transmission strength and low obstruction, a log-logistic decay curve was the best model for data-transfer success. Contrastingly, under conditions of low transmission strength and high obstruction, data transfer was noisier, and was best represented by a linear model. Obstruction resulting from the placement of the collar in relation to the subject's body adversely affected the communication abilities of our system, with bighorn sheep lowering baseline data-transfer success to <50% at low transmission strengths. Obstruction also affected the distance of data transfer for each transmission strength, but bighorn sheep had less of an impact than did humans. Wireless sensor node manufacturers recommend an optimum communications distance for each possible transmission strength, but we suggest that managers calibrate the communications systems of their in-house-constructed GPS telemetry systems, preferably by using the target animal subject, in order to optimize operation in field conditions. © 2012 The Wildlife Society.