Abstract
Pellet counts are widely used to monitor ungulates but rely on the assumption that pellets of different species are correctly identified in the field. Recent studies question this assumption using DNA barcoding techniques to check field identification rates. For Europe, which is undergoing a rapid shift towards more diverse ungulate assemblages, such an assessment is still missing. Using DNA barcoding on 3889 fecal samples from nine ungulate species in four European countries, we found average field misidentification rates varied from 0.6% for horse (Equus ferus) to 41.1% for roe deer (Capreolus capreolus). Most identification errors occurred between similar-sized species from the same taxonomic family. For a subset of samples from Sweden, we looked at the effect of dung morphometry, observer experience, and season on species identification success. Dung morphometry clearly distinguished moose (Alces alces) but not red (Cervus elaphus), roe, and fallow deer (Dama dama). Experienced observers performed better than novices for red and fallow deer although still making significant identification errors (26% and 17% incorrectly identified). Identification success was higher during spring and winter ( overline{x} = 86%) than summer and autumn ( overline{x} = 74%). We question pellet counts as an accurate monitoring tool where similar-sized species coexist and monitoring relates to the whole community. For this increasingly common situation across Europe, DNA testing or camera traps may be a better alternative. Pellet counts remain useful where only few species with clearly different dung morphology coexist (e.g., moose and roe deer) or when focused on species with distinctive dung morphology (e.g., moose).
Highlights
The sustainable management of wild ungulate populations is of high priority in many European countries but is becoming increasingly challenging (Apollonio et al 2017)
Several studies have shown that morphometric measurements can work well for distinguishing ungulate pellet groups at the intraspecific level, especially if pellet size scales with body size
In cases of misidentification in the field, the correct species generally corresponded. Experience, and their interaction had significant effects on species identification success
Summary
The sustainable management of wild ungulate populations is of high priority in many European countries but is becoming increasingly challenging (Apollonio et al 2017). The use of feces is a common monitoring approach for the study of many terrestrial mammals (Chame 2003; Rouco et al 2009; Lonsinger et al 2015), including ungulates (Cromsigt et al 2009). Fecal pellets can be collected non-invasively in large numbers and with relative ease. This opens numerous avenues of investigation, including diet, disease, stress level, habitat use, and population dynamics (Kohn and Wayne 1997). Species-level identification of fecal pellets has traditionally relied upon assessment of morphometric variables like length, width, weight, the number of pellets per group, and various derivatives, e.g., the length/width ratio and volume. MacCracken and Van Ballenberge (1987) were able to correctly identify 91% of moose pellet groups as originating from adult males, adult females, and yearlings based on pellet volume. Ball (2010) successfully used pellet length to distinguish calf and yearling age-classes from adults in caribou (Rangifer tarandus caribou), and Woodruff et al (2016) found a 98% probability of correctly classifying fawns versus adult Sonoran pronghorn (Antilocapra americana sonoriensis) using pellet width
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