Isotopic ecology of coyotes from scat and road kill carcasses: A complementary approach to feeding experiments

Abstract

Scat is frequently used to study animal diets because it is easy to find and collect, but one concern is that gross fecal analysis (GFA) techniques exaggerate the importance of small-bodied prey to mammalian mesopredator diets. To capitalize on the benefits of scat, we suggest the analysis of scat carbon and nitrogen isotope values (δ13C and δ15N). This technique offers researchers a non-invasive method to gather short-term dietary information. We conducted three interrelated studies to validate the use of isotopic values from coyote scat: 1) we determined tissue-to-tissue apparent C and N isotope enrichment factors (ε13* and ε15*) for coyotes from road kill animals (n = 4); 2) we derived diet-to-scat isotope discrimination factors for coyotes; and 3) we used field collected coyote scats (n = 12) to compare estimates of coyote dietary proportions from stable isotope mixing models with estimates from two GFA techniques. Scat consistently had the lowest δ13C and δ15N values among the tissues sampled. We derived a diet-to-scat Δ13C value of -1.5‰ ± 1.6‰ and Δ15N value of 2.3‰ ± 1.3‰ for coyotes. Coyote scat δ13C and δ15N values adjusted for discrimination consistently plot within the isotopic mixing space created by known dietary items. In comparison with GFA results, we found that mixing model estimates of coyote dietary proportions de-emphasize the importance of small-bodied prey. Coyote scat δ13C and δ15N values therefore offer a relatively quick and non-invasive way to gain accurate dietary information.

Changes to vertebrate tissue stable isotope (δ15N) composition during decomposition

“…Because the goal of this study was to identify if tissues exhibit stable isotopic changes during decay, which may be partly due to changes to the lipid fraction, no tissues were chemically treated prior to freeze-drying and analyses. This includes retaining all lipids within samples, unlike some prior studies, which removed lipids prior to analyses 5,33 .…”

“…Vertebrate tissue isotopic composition is widely used by ecologists to address questions related to broader ecosystem functioning, including population dynamics, animal migrations or ranges, provenance, age, and diet, which can be used to infer trophic-level interactions 1–5 . For animals that are difficult to observe directly in nature or for archaeological communities, these types of chemical fingerprints are invaluable for understanding ecosystems 6,7 .…”

“…For animals that are difficult to track or with low population densities, found samples are the only viable materials available. For example, the coyote diet was reconstructed using stable isotopic composition of road kill and scat 5 . The use of archived specimens, often collected over decades and potentially from difficult to access localities or from endangered species, may represent the only viable sample source for reconstructing past environments.…”

Coyote (Canis latrans) use of marine resources in coastal California: A new behavior relative to their recent ancestors

“…We used the results of our previous work on coyote scat contents (Reid and Koch, 2017) to identify coyote food sources for isotopic characterization, including marine mammals, deer, small mammals, berries, arthropods, reptiles, birds, anthropogenic foods, and other mammalian mesopredators. When possible, we sourced local isotopic data for these food items from the literature, but we also opportunistically collected berry and insect samples along the transects and sampled hair from live-trapped small mammals at Año Nuevo.…”

Parasites in Myodes glareolus and their association with diet assessed by stable isotope analysis

“…Diet composition can be monitored through a number of methods; they range from visual analyses of stomach content ( Andreasen et al, 2017 ), molecular analysis of faecal samples ( Deagle et al, 2009 ), to assessment of stable isotopes ( Panarello and Fernández, 2002 ; Hobbie et al, 2017 ; Reid and Koch, 2017 ). The latter can be used to trace the transfer of energy and matter through the foodweb because heavy isotopes accumulate at increasing trophic levels ( Vaughan et al, 2011 ; Galetti et al, 2016 ).…”