Mexican gray wolves (Canis lupus baileyi) are the smallest subspecies of North American gray wolves (Canis lupus), and identification of Mexican wolf scats could be confused with those of sympatric coyotes (Canis latrans). We used DNA analysis (molecular scatology) to differentiate scats (n = 203) of free‐ranging Mexican gray wolves and coyotes and compared the results to traditional field methods (i.e., diameter, location, and sign) and odor used for identifying scats of the 2 species. We then used the scats whose species identifications were confirmed with DNA analysis to evaluate discriminant analysis for classifying scats using 3 measurements—diameter, mass, and length. Forty‐nine (24%) of the field‐collected scats (n = 203) tested provided amplifiable DNA and were determined to comprise 28 scats deposited by Mexican wolves and 21 deposited by coyotes. Scats identified with DNA analysis to the 2 species had a 79% diameter overlap (Mexican wolf 16.3–35.8 mm; coyote 17.4–27.8 mm), and scats ≥28 mm in diameter were Mexican wolf scats. There was a significant difference (t = −2.28; P < 0.05) between diameter means for the 2 species (Mexican wolf r̄x = 26.0 mm; coyote r̄x = 22.8 mm). Of 45 scats that would have been field‐identified as deposited by Mexican wolves based on location and odor criteria, DNA analysis indicated that 19 (42%) were deposited by coyotes; of 41 scats that would have been field‐identified as deposited by coyotes based on diameter < 30 mm criterion, 20 (49%) were deposited by Mexican wolves. Halfpenny's (1986) suggested diameter criterion for field identification of scats identified 3 of the scats as gray (Urocyon cinereoargenteus) or red fox (Vulpes vulpes; 0% correct), 24 as coyote (62% correct), and 20 as Mexican wolf (75% correct). Discriminant analysis indicated that diameter and mass of scats offered the best results for accurately classifying coyote scats (86%) but provided relatively low accuracy for classifying Mexican wolf scats (65%). Our results suggest that previous diet studies using traditional identification methods may have misrepresented the diets of both the North American gray wolf and the coyote when the 2 species were sympatric. Molecular scatology appears to be a more definitive scat‐identification technique than traditional field methods or odor for these canids.

Systematic diet studies of Mexican gray wolves (Canis lupus baileyi) were not conducted before wolves were extirpated by the late 1960s from the southwestern United States. We collected carnivore scats (n = 1,682) from the Apache and Gila national forests in Arizona and New Mexico, USA, from April 1998 through October 2001 and identified scats to species using traditional field methods, of which 251 were identified as Mexican wolf scats. We found the diet consisted of large‐sized food items (92.8% percent frequency of occurrence [PFO]), primarily elk (Cervus elaphus) adults (36.6% PFO) and calves (36.2% PFO). Biomass calculations indicated that Mexican wolves consumed 414 kg of prey as represented by the scats, with elk representing 76.7% of the biomass. When comparing PFO with percent biomass, PFO calculations may have underrepresented larger food items and percent biomass may have overrepresented smaller food items. We compared the diet composition of Mexican wolf scats (n = 251) to the diets reported in previous North American gray wolf (C. lupus) studies (n = 7). The high proportion of elk in Mexican wolf diets in our study area may reflect the low‐density, early colonizing stage of the wolf population and elk probably being the most numerous ungulate in our study area. Our results suggested that free‐ranging Mexican wolves consumed a higher proportion of large‐sized prey than other North American gray wolves. Our results provide baseline diet information for a newly reestablished wolf population.