The Efficacy of Camera Traps and Acoustic Recorders to Detect Mexican Wolves (Canis lupus baileyi)

Autonomous recording units (hereafter, recorders) have been studied as a non-invasive method for surveying wild wolves and collecting pack composition data via detection of and analyzing wolf howls. Their efficacy has been compared to other non-invasive survey methods such as camera traps and scat collection. Several researchers have measured a 1.6-3.2 kilometer detection range of wolf howls in mountainous and forested areas, but the detection decay from high wolf activity sites is largely unknown. Comparing the efficacy of recorders and other non-invasive devices near homesites (e.g., den and rendezvous sites) has been understudied as most studies focus on a larger portion of their territory. The use of recorders to detect uncollared wolf packs has also been understudied. We compared the detection rates and number of detections of two non-invasive methods (camera traps and recorders) to detect Mexican wolves at concentric distances from known homesites and at suitable pup rearing habitat using an existing Resource Selection Function model from July 1st, 2024, through October 27th, 2024 for a total of 17 survey weeks. Camera traps were set to motion-trigger 24/7 and recorders were set to record the first 30 minutes of each hour from 2100 to 0500 (during the times of known wolf howling activity). We found that the detection rates of camera traps decreased significantly from 1.6 km to 4.8 km from homesites. Detection rates and number of detections from both device types experienced a downward trend as distance from a homesite increased. Detection rates between camera traps and recorders did not differ significantly, but camera traps had significantly more detections than recorders during the denning season (July through mid-August). The number of recorder detections were significantly higher during the rendezvous season than during the denning season. Elk detection rate did not significantly influence wolf detection rate because Mexican wolves will choose den and rendezvous locations based on a high presence of elk. Camera trap detections were highest between the hours of 1900 and 0800, and recorder detections occurred throughout 2100 and 0500 with peak activity at 2100 and 0500. Two uncollared wolves were detected on a camera trap at a high pup rearing suitability site. Camera traps are a more effective method of detection during the denning/early rendezvous season when howling activity is low. When howling activity increases, primarily being influenced by the late rendezvous season when wolf pups are more mobile, recorders are just as effective at detecting wolves as camera traps, however camera traps are a consistent detection method across the pup-rearing season.