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Severe environmental conditions create severe conflicts? A novel ecological pathway to extreme coyote attacks on humans

Citation

Newsome, Seth (2022), Severe environmental conditions create severe conflicts? A novel ecological pathway to extreme coyote attacks on humans, Dryad, Dataset, https://doi.org/10.5061/dryad.d51c5b06t

Abstract

1) Identifying the circumstances and causes of carnivore attacks on humans is important for prevention of future incidents as well as employing effective wildlife management strategies. Cape Breton Highlands National Park (CBHNP) in Nova Scotia has experienced multiple attacks by coyotes (Canis latrans) on humans, including a fatal attack on an adult in 2009.

2) Here we use a combination of data on space use and diet collected from 2011–2013 to reveal that limited resources and a reliance on a large ungulate (moose, Alces americanus) as the mechanism leading to aggression by coyotes in CBHNP.

3) Resident coyotes exhibited large home range sizes (mean=77.5 km2) indicative of limited resources and spatiotemporal avoidance of human activity. Carbon (d13C) and nitrogen (d15N) isotope values of sub-sampled coyote whiskers (n=32), which provide a longitudinal record of diet over the months before collection, revealed little intra- and inter-individual variation with nearly all individuals specializing on moose, a pattern that agrees with indices of natural resource availability. Specifically, stable isotope mixing models show that moose was the most important prey for most coyotes (25/32), representing between 41% and 78% of dietary inputs. Only four coyotes exhibited use of anthropogenic resources (food), and only one of seven coyotes involved in attacks on people had been consuming human foods before the attacks.

4) Synthesis and Applications: We have described a unique ecological system in which a generalist carnivore has expanded its niche to specialize on a large prey species, with the unfortunate consequence of also expanding pathways to conflicts with people. Our results suggest extreme unprovoked predatory attacks by coyotes on people are likely to be quite rare and associated with unique ecological characteristics. Extreme management actions such as bounties are unnecessary, but managers may need to employ hazing or lethal removal earlier in the conflict process than under normal circumstances. Also, users of these areas should be made aware of the risks coyotes pose and encouraged to take precautions. 

Methods

We analyzed vibrissae from 32 (17 F, 15 M) coyotes (Table S3), including 19 whiskers from coyotes that were live-captured and radiocollared, 5 from the 2009 lethal attack including 2 that were confirmed to be involved in the attack, 4 from coyotes lethally removed following human-coyote incidents including attacks, and 4 from unmarked individuals captured during trapping or recovered as roadkill. We also opportunistically collected hair from potential coyote prey items that occur in the study area during 2012–2014 for stable isotope analysis (Table S4), including southern red-backed voles (Myodes gapperi; n=27), shrews (Sorex spp.; n=49), snowshoe hare (Lepus americanus; n=17), white-tailed deer (Odocoileus virginianus; n=20), and moose (Alces americanus; n=21).  Red-backed voles and shrews were grouped as small mammals because they had statistically indistinguishable δ13C and δ15N values. Samples were collected during unrelated small mammal surveys or from roadkill animals within the study area. We also analyzed the isotopic composition of local human residents to serve as a proxy for a consumer of anthropogenic resources that could be directly compared to measured coyote isotope values; human hair samples were collected opportunistically from local barbershops.

Keratin samples from coyotes (vibrissa), potential prey (hair), and humans (hair) were rinsed in 2:1 chloroform:methanol solution to remove surface contaminants. Hair samples were homogenized with surgical scissors and vibrissa were sub-sampled into 0.2–0.3mg segments using nail clippers; this weight range represents the lowest weight for which we can reliably generate δ13C and δ15N data for keratin. δ13C and δ15N values were measured with a Costech 4010 elemental analyzer (Valencia, CA) coupled to a Finnegan Delta Plus XL isotope ratio mass spectrometer at the University of Wyoming Stable Isotope Facility (Laramie, WY). Isotopic results are expressed as d values: δ13C or δ15N = 1000* [(Rsample - Rstandard / Rstandard) – 1], where Rsample and Rstandard are the 13C/12C or 15N/14N ratios of the sample and standard, respectively; units are parts per thousand or per mil (‰). Analytical precision was determined via repeated analysis of internal reference materials calibrated to international standards; within-run standard deviation of an acetanilide standard was ≤0.2‰ for both δ13C and δ15N values. We applied tissue-specific δ13C and δ15N trophic discrimination factors (TDF) of 2‰ and 3‰ (Fig. 3) respectively reported for captive wolves (Canis lupus; Derbridge et al. 2015) to directly compare isotope values of keratin tissues from coyotes (vibrissae) to that of potential prey (hair); we also used these TDFs in the mixing model analysis (see below). Lastly, experiments on captive canids and other mammalian carnivores show that vibrissae growth rates likely scale with body mass (Hirons et al. 2001, Robertson et al. 2013, Tyrrell et al. 2013, Stanek 2014). Based on these studies, we assume that coyotes (15–20kg) will have mean vibrissae growth rates in the range of 8–12 cm/year. Since the mean (±SD) length of a vibrissa collected from the CBHNP was 6.2±0.5 cm, we estimate that our sub-sampling approach produces a ~6- to 9-month longitudinal record of dietary information for each individual coyote but acknowledge that seasonal variation in vibrissae growth rates (McLaren et al. 2015) could impact this estimate.

Funding

Parks Canada

Nova Scotia Department of Lands and Forestry

Max McGraw Wildlife Foundation