# Non-Invasive Methods to Assess Co-Occurrence of Mammalian Carnivores > Which works best for finding carnivores: walking for tracks and scats, cameras, hair traps or track plates? On the rims of Grand Canyon, searching for tracks and signs gave the most detections, cameras and track plates were best at catching common species, and hair traps mostly failed. Along the way the study found that coyotes and bobcats never shared a site on the North Rim. Summary by Kersey Lawrence, Original Wisdom. Updated 9 November 2026. Page: https://www.originalwisdom.com/tracking-literature/2011-reed-non-invasive-methods-assess/ ## Citation and access - **Authors:** Sarah E. Reed - **Year published:** 2011 - **Journal or source:** The Southwestern Naturalist - **Full citation:** Reed, S. E. 2011. Non-invasive methods to assess co-occurrence of mammalian carnivores. The Southwestern Naturalist 56(2): 231–240. - **DOI:** 10.1894/F13-JKF-14.1 - **Access status:** Publisher link only - **Where to find it:** https://doi.org/10.1894/F13-JKF-14.1 ## Tags - **Species:** Mammals > American badger; Mammals > Bobcat; Mammals > Coyote; Mammals > Grey fox; Mammals > Long-tailed weasel; Mammals > Mountain lion; Mammals > Raccoon; Mammals > Striped skunk; Mammals > Western spotted skunk - **Region:** North America > United States - **Tracking:** Burrows; Scat; Sign surveys; Track measurements; Tracking; Tracks; Tracks and signs identification - **Behaviour and ecology:** Behaviour; Carnivore coexistence; Habitat selection; Interspecific competition - **Methods and technology:** Akaike Information Criterion (AIC); Camera traps; Detectability; DNA; Geographic Information System (GIS); Hair sampling; Occupancy models - **Data type:** New field data - **Observer qualification:** Not reported - **Discipline:** Behaviour and ecology; Wildlife tracking - **Year published:** 2011 ## Detailed keywords - **Species:** Studied: mammalian carnivores. Nine species detected: cougar (Puma concolor), coyote (Canis latrans), bobcat (Lynx rufus), American badger (Taxidea taxus), raccoon (Procyon lotor), gray fox (Urocyon cinereoargenteus), striped skunk (Mephitis mephitis), western spotted skunk (Spilogale gracilis) and long-tailed weasel (Mustela frenata). Co-occurrence was modelled for coyote, bobcat, American badger and gray fox. Believed present in the park but not detected: American black bear (Ursus americanus) and ringtail (Bassariscus astutus). Extirpated from the park: brown bear (Ursus arctos), jaguar (Panthera onca) and gray wolf (Canis lupus). Discussed from other studies: cougars and jaguars in Venezuela; bobcats and coyotes in northern California. - **Location and habitat:** North Rim (Kaibab Plateau) and South Rim (Coconino Plateau) of Grand Canyon, Grand Canyon National Park, Coconino County, Arizona, United States. North Rim: ponderosa pine and mixed conifer forest of Douglas fir and white fir, the largest continuous unharvested and ungrazed forest in Arizona. South Rim: ponderosa pine forest and woodlands of Colorado pinyon and juniper, not harvested or grazed for over 100 years. Mean site elevation about 2,505 m (North Rim) and 2,163 m (South Rim). - **Topics:** non-invasive survey methods; comparing detection methods; species co-occurrence; spatial avoidance between carnivores; imperfect detection and false absences; use of habitat; distance to public roads, park boundary and water; canopy cover; elevation; scat DNA identification; survey design for carnivore communities; scat-detection dogs (suggested). - **Statistics or models:** Single-season occupancy models and two-species co-occurrence models (alternate parameterization) in the program PRESENCE 3.0; species-interaction factor (phi); Akaike’s Information Criterion corrected for small samples (AICc) and model averaging; t-test comparing the species-interaction factor to one. Laboratory: polymerase chain reaction (PCR) and restriction-fragment-length polymorphisms (RFLP) of the mitochondrial cytochrome-b gene to identify scats and hairs to species. Inconsistencies: the text says elevation was related positively to use of habitat by American badgers on the North Rim and negatively by gray foxes on the South Rim, but Table 2 gives the opposite signs (badger coefficient -1.56; gray fox coefficient 2.86). The Results give 77 detections from scats on transects as the greatest number, while the Discussion gives 114 detections from transects in total (most of them scats). In Figure 1 the camera bar for coyotes appears higher than the 0.200 given in the text. - **Data type:** New field data. North Rim surveyed 2003 and 2004 (20 sites each season); South Rim 2004 and 2005 (18 and 24 sites); 82 sites in all, each visited three times between June and September. DNA analysis July to August 2006. ## Synopsis ### 1. What they did Carnivores are wide-ranging and hard to see, so researchers often rely on methods that do not need the animals to be caught or seen. Most models of where species live also look at one species at a time and ignore how species affect each other. The author set out to compare four such non-invasive methods and to see whether pairs of carnivore species avoid each other. - Sites. 82 sites of 4 hectares (200 by 200 m) in forest on the North and South rims of Grand Canyon, at least 2 km apart, surveyed for two seasons on each rim between 2003 and 2005. Each site was visited three times per season, about 14 days apart. - Transect searches. One observer walked four 200 m transects (800 m in all) per site, looking for scats, tracks, burrows and other evidence of carnivores. All evidence was measured, photographed and identified to species by size and appearance, using two field guides. Scats were collected. - Cameras. One baited, infrared-triggered film camera per site. - Hair traps. Baited with a scented lure, with an aluminium pie tin hung nearby to draw animals in. - Track plates (from 2004). Aluminium plates with sticky shelf paper in the centre and a chalk and ethanol mixture on the ends, inside a plywood box, baited with cat food, added to pick up smaller carnivores. Each track was measured with calipers and matched to a published key. - DNA. Scats and hairs were identified to species in the laboratory (cougar, coyote, bobcat and gray fox). - Analysis. Occupancy models estimated how likely each method was to detect each species on one visit, how likely each species was to use a site, and whether pairs of species were found together more or less often than expected by chance. ### 2. What they found Species detected - Nine of the 11 carnivore species thought to live in the park’s forests were detected. American black bears and ringtails were not. - All nine were detected by at least two methods, but raccoon, striped skunk, western spotted skunk and long-tailed weasel were each detected on five or fewer visits. The four methods - Transect searches gave the most detections; most were scats (77 scat detections). Only 65% of scats (50) were identified to species in the laboratory, and 62% of those were coyote. - Transects and track plates detected the greatest number of species, especially smaller carnivores. - Cameras detected coyotes most often and also recorded rarer species, including American badgers and both skunks. Photos gave unequivocal identifications. - Hair traps gave the second-highest number of detections (38), but DNA failed for 61% of hair samples. The hair identified came from coyote (47%), gray fox (47%) and bobcat (7%), even though the lure was meant to attract cats. - Per visit, cameras were the most likely method to detect coyotes (0.200) and gray foxes (0.240); track plates were most likely to detect bobcats (0.152). - Using all four methods over eight sampling occasions, the chance of detecting a species at a site where it was present was 0.589 for bobcats, 0.623 for coyotes and 0.633 for gray foxes. Use of habitat - Modelled use of habitat was on average 71.5% higher than the observed detection rate on the North Rim and 64.6% higher on the South Rim. - Bobcats and American badgers were detected more often on the North Rim; coyotes and gray foxes on the South Rim. - Distance to a public road mattered most: coyotes and bobcats were more likely to use sites farther from roads, and gray foxes sites closer to roads. Distance to water mattered for no species. Who avoided whom - North Rim: coyotes and bobcats never occurred at the same site (species-interaction factor of zero), suggesting complete avoidance or exclusion. - South Rim: coyotes and gray foxes occurred together less than half as often as expected if they were independent (factor 0.401). - No avoidance was found for the other pairs, though the uncertainty around those estimates was high. ### 3. What they concluded - No single non-invasive method is enough to survey a whole carnivore community. Pairing transect searches with more cameras and track-plate stations may be the most reliable and efficient approach in western North America. Scat-detection dogs could make transect searches more efficient. - Hair traps were ineffective compared with the other methods. - Results based only on detections underestimate the area a species uses, so imperfect detection needs to be accounted for. - Co-occurrence and habitat should be modelled together, because responses to things like roads can make species seem to meet more or less often. - Surveys should identify pairs of species likely to interact before fieldwork, collect data on co-occurring species in the same way as habitat data, and keep differences between sites small. ### 4. How tracking was or was not used Tracks and signs were central to one of the four methods. On each transect, one observer searched for scats, tracks, burrows and other carnivore evidence, and measured, photographed and identified each sign to species from its size and appearance, using Murie (1975) and Halfpenny (1986). Scats of black bears, raccoons and skunks were assumed to be identifiable by appearance; scats of the four DNA-target species were confirmed in the laboratory. Track-plate prints were measured with dial calipers and matched to a published key (Taylor and Raphael 1988). No trailing was reported. ### 5. Tracker or observer certification Not reported. The paper says one observer walked each transect and that one to two field technicians helped, but gives no information on their tracking experience. Sign identifications other than DNA-confirmed scats depend on this observer’s skill. ### 6. Other technologies, skills or innovations - Infrared-triggered 35 mm film cameras, baited with a pork rib or chicken leg - Hair traps with a scented lure (beaver castoreum, catnip oil and cougar or bobcat urine) - Track plates (aluminium, sticky shelf paper and carpenter chalk) in a plywood box - Species identification from scat and hair DNA (PCR and RFLP) - Occupancy and two-species co-occurrence models in PRESENCE 3.0 ### 7. Implications for conservation (from the paper) - Measuring where species do and do not occur together matters for biodiversity monitoring and conservation. - Surveys designed around the whole carnivore community, rather than one species, give more accurate estimates for every species. - The survey was not intensive enough to show whether undetected species (black bears, ringtails) are truly absent; the author calls for more research on these species and for inventory data to help manage Grand Canyon National Park. ### 8. Implications for tracking (Original Wisdom's observations) _These are Original Wisdom's observations, not the authors'._ - Searching transects for tracks and signs gave the most detections of any method, and across eight species, which shows how much information sign surveys can collect. - The study did not test the observer’s identifications, and only 65% of scats could be confirmed by DNA, so the accuracy of sign identifications in the field is unknown. A tested observer would make this kind of result easier to rely on. ## Cite this summary Lawrence, K. 2026. Summary of: Non-Invasive Methods to Assess Co-Occurrence of Mammalian Carnivores (Reed, 2011). Original Wisdom, Tracking Literature. https://www.originalwisdom.com/tracking-literature/2011-reed-non-invasive-methods-assess/