Tools and Technology Why Camera Traps Fail to Detect a Semi-Aquatic Mammal? Activation Devices as Possible Cause LAURA LERONE, 1,2 Department of Biology, University of Roma Tre, I-00146, Rome, Italy GIUSEPPE M. CARPANETO, Department of Biology, University of Roma Tre, I-00146, Rome, Italy ANNA LOY, Environmetrics Laboratory, University of Molise, I-86090, Pesche, Italy ABSTRACT Camera-trapping represents a powerful tool in wildlife research, particularly when dealing with elusive and rare species such as otters (Lutra spp.). Nevertheless, detection problems arise when trying to detect otters with camera traps. We hypothesized that the temperature difference between the otter emerging from the water and the environment was too low to be detected by the standard passive infrared sensors (PIR). During June–September of 2010 and 2011 in the Sangro River basin in central Italy, we designed and tested a new pressure trigger and compared its effectiveness with that of the standard PIR. Results are encouraging and suggest that the new trigger could be able to detect otters and other semi-aquatic mammals. Ó 2015 The Wildlife Society. KEY WORDS camera-trapping, infrared sensor, Lutra lutra, semi-aquatic mammals, thermoregulation. Remote photography in wildlife research increased in the 1990 s when commercial digital and low-cost cameras became available (Swann et al. 2011). Detecting elusive and rare species, recording activity patterns, and estimating population parameters are among the challenges of this technology (Karanth and Nichols., 1998, Maffei et al. 2005, O’Connell et al. 2006, Nichols et al. 2008). The Eurasian otter (Lutra lutra) represents a suitable potential target for camera traps because its elusiveness, marking behavior, and nocturnal habits (Kruuk 2006) make direct observation of individuals difficult. Nevertheless, data on otters obtained by remote cameras are still very scanty and high incidence of missing data characterize most studies (Stevens et al. 2004, Garcia de Leaniz et al. 2006, Guter et al. 2008, Ho ¨nigsfeld and Smole 2011). We hypothesized that detection problems could be due to otter thermoregulation and hair structure (Tarasoff 1974, Kuhn and Meyer 2010). Using a FLIR ThermaCam B20 (FLIR Systems Boston, North Billerica, MA), Kuhn and Meyer (2009) observed 2 layers of hairs providing a high thermal insulation and demonstrated that, after swimming bouts, the temperatures of otters’ surface and water were similar, and a period of activity on land is necessary to increase the otter body temperature (Kuhn and Meyer., 2009). According to Kuhn and Meyer (2009), the foot is the most important thermoregulatory surface for the Eurasian otter and foot temperature decreases while the animal is in the water. Thermograms demonstrated also that the foot temperature was the same as that of the water when otters emerged after a swimming bout. The ears, the vibrissal pads, and the peripalpebral region appeared usually warm also after swimming bouts; nevertheless, these small warm areas could be too small to trigger a camera trap. The low surface temperature of otters emerging from water may prevent the activation of the standard passive infrared sensors (PIR). Based on these considerations, we tested a camera trap with a modified trigger specifically designed to overcome this problem and to increase the detection probability of otters. STUDY AREA The study area was the Sangro River basin in central Italy. The main course of the Sangro River flowed for approximately 122 km from the Abruzzo, Lazio, and Molise National Park (1,441 m above sea level) to the Adriatic Sea. The Sangro basin was recently re-colonized by otters and represented the current northernmost limit of the species range in southern Italy. MATERIALS AND METHODS We detected Eurasian otters frequently marking sites during a pilot study performed for a non-invasive genetic sampling of the Sangro’s otter population (Lerone et al. 2011). Almost no otter signs were found under bridges. Nor was it possible to locate proper latrines containing large amounts of feces; rather, the marking sites were located on rocks emerging in the middle of the water course. We initially set 2 passive triggered camera traps (ScoutGuard SG550; HCO Outdoor Products, Norcross, GA), equipped with a PIR sensor, on the riverbanks associated with rocks where fresh marking signs (spraints and/or anal jellies) were found. We set Received: 11 April 2014; Accepted: 11 August 2014 1 E-mail: laura.lerone@gmail.com 2 Present address: Via dei Biancospini 2, 00040 Lariano (RM), Italy Wildlife Society Bulletin 9999:1–4; 2015; DOI: 10.1002/wsb.508 Lerone et al.  Camera-Trapping of Eurasian Otter 1