64thE CanaDian FiElD-natUraliSt

Vol. 127

Encounter Competition between a Cougar, Puma concolor, and aWestern Spotted Skunk, Spilogale gracilis
MaxiMilian l. allEn1,4, l. Mark ElbroCh2,3, and hEiko U. WittMEr1,3

1School of biological Sciences, Victoria University of Wellington, P.o. box 600, Wellington 6140, new Zealand
2Panthera, 8 West 40th Street, 18th Floor, new York, new York 10018 USa

3Department of Wildlife, Fish and Conservation biology, University of California at Davis, 1 Shields avenue, Davis, California

95616 USa

4Corresponding author; email: Maximilian.allen@vuw.ac.nz

allen, Maximilian l., l. Mark Elbroch, and heiko U. Wittmer. 2013. Encounter competition between a Cougar, Puma concolor,and a Western Spotted Skunk, Spilogale gracilis. Canadian Field-naturalist 127(1): 64–66.

Encounter competition occurs frequently over food resources and may include kleptoparasitism, where scavengers usurp preykilled by carnivores. Scavenging may have important adverse effects on carnivores and may result in higher than expectedkill rates by predators. Using camera traps placed on a black-tailed Deer (Odocoileus hemionus columbianus) carcass killed bya Cougar (Puma concolor) in California, we observed a series of encounters in which a Western Spotted Skunk (Spilogalegracilis) temporally usurped the carcass from the Cougar. the Western Spotted Skunk also successfully defended the carcass
when the Cougar returned and attempted to feed. the Spotted Skunk was about 1% of the mass of the Cougar. our observationis the largest reported size differential of a mammalian species engaging in successful encounter competition.
key Words: Cougar, Mountain lion, Puma concolor, Western Spotted Skunk, Spilogale gracilis, encounter competition, kleptoparasitism, competition, California.

Encounter competition describes non-territorial interand intra-specific competition for resources, including
access to food and mates (Schoener 1983). Encountercompetition, which includes kleptoparasitism (when anindividual attempts to usurp or feed on prey killed byanother) (Cooper 1991; Murphy et al. 1995; trinkel
and kastberger 2005; hebblewhite and Smith 2010),
is likely common but is not well reported in the literature. in interspecific encounter competition, smaller
species generally avoid larger species (Dickman 1991);
however, when species directly interact, the group orindividual of the species with more biomass typicallywins access to the contested resource (Johnson et al.
1985; Cooper 1991; Gorman et al.1998; berger andGese 2007).
kleptoparasitism increases in frequency when foodresources are scarce, search time for food is high, or, as
in other forms of encounter competition, there is asymmetry between the two competitors—meaning thatlarger, more powerful kleptoparasites more easily andmore often steal from physically inferior species orconspecifics (van der Meer et al. 2011; broom andruxton 2003). Scavengers directly decrease carnivore
energetic intake and fitness, are responsible for an increase in kill rates, and indirectly alter predator–preydynamics of ecosystems (Gorman et al. 1998; krofelet al. 2012; Elbroch and Wittmer 2013a). For example, kleptoparasitism has been noted in kills made byGray Wolves (Canis lupus) (hebblewhite and Smith
2010), Coyotes (Canis latrans) (Jung et al. 2009), andCougars (Puma concolor) (ruth and Murphy 2010;
Elbroch and Wittmer 2012).
Cougars are large, solitary carnivores that frequently kill ungulates. Cougars also provide a significant
food subsidy to scavengers, in comparison with othercarnivores (ruth and Murphy 2010; Elbroch and Wittmer 2012). Gray Wolves, brown bears (Grizzly bears)(Ursus arctos), and american black bears (Ursusamericanus) usurp Cougars kills (ruth and Murphy2010). Mesocarnivores, such as Coyotes, bobcats (Lynxrufus), and Gray Foxes (Urocyon cinereoargenteus),
have also been documented scavenging from Cougar
kills without displacing them (koehler and hornocker
1991; boyd and o’Gara 1995; logan and Sweanor2001). the numerous species scavenging from Cougar
kills may lead to significant food losses, especiallywhen Cougars are displaced from their kills. here, wedescribe a series of encounters between a Cougar anda Western Spotted Skunk (Spilogale gracilis) feedingfrom a black-tailed Deer (Odocoileus hemionus columbianus) killed by the Cougar.

Methods

our observations were made as part of a study on
the influence of Cougar predation on a declining blacktailed Deer population in Mendocino national Forest,
California (39.7°n, 122.9°W). We captured Cougars
using trained hounds and box traps, chemically immobilized the Cougars, and then fitted them with argos
GPS collars (7000SaW, lotek Engineering inc.,newmarket, ontario). based on Elbroch and Wittmer(2013b), GPS collars were programmed to acquire
GPS locations at 2-hour intervals, and location data
were downloaded via satellite connection every threedays. We conducted field investigations of ≥3 points,
including a night-time location, within 150 m of eachother to locate potential kill sites. When we discovered
active kill sites at which the Cougar was still feeding,we placed motion-triggered video-cameras (bushnell
trophyCam, overland Park, kansas) programmed to2013notE

collect 60-second videos with a 1-second delay between
triggers over the carcass for 20 days to document thediversity of scavengers that fed on it.

Results

on 22 november 2011, we discovered a black-tailed
Deer killed by Cougar F23 approximately 10 hours previously. F23 was an adult female originally captured inJune 2011 and estimated to be 4.4 years of age, basedon gumline recession (laundre et al. 2000). During capture, we noted the Cougar as being in very good health(based on fat deposits, pelage condition, and lack of
external parasites). She was a large female, weighing
49.5 kg.
the carcass was in a small drainage within a montane hardwood habitat underneath a cluster of scrub
oaks (Quercus spp.). the carcass was very fresh; theCougar had removed only minimal organs and had
not yet cached it. the black-tailed Deer was a female
and was 3.5 years of age based on molar wear patterns(heffelfinger 2010*). the video-camera was placed ona tree 2.5 m away, and the carcass was anchored to atree with a wire cable.
before the encounter, the Cougar returned and fed
from the carcass for three days. During this time, shevisited the carcass seven times, with visits lasting amean of 34.3 minutes (SD 6.7). on 25 november 2011,a Western Spotted Skunk was detected at the carcass
at 21:54. the Western Spotted Skunk investigated thecarcass and left 1 minute later. the Cougar returned tothe carcass 4.3 hours later and fed on the carcass for
24 minutes, at which point she noticed the WesternSpotted Skunk arriving from a distance. as the Western
Spotted Skunk approached, the Cougar backed awayfrom the carcass. the Western Spotted Skunk then approached the carcass and began feeding. after feeding for 3 minutes, the Western Spotted Skunk moved
aggressively towards the Cougar, causing her to hissand quickly leave the area. based on the pattern ofmarkings on the coat of the Western Spotted Skunk,
we believed it to be the same individual that originallyinvestigated the carcass.
the Cougar returned 20 minutes later and cautiously approached the carcass. the Cougar spent 1 minutealternating between smelling the carcass and visually
searching the area. the Western Spotted Skunk thencame out from beneath a nearby rock and rushed
toward the Cougar, causing her to growl and jump backout of the way. the Cougar moved about 4 m awayfrom the Western Spotted Skunk, up the bank from thecarcass. the Western Spotted Skunk spent 18 seconds
inspecting the carcass and then moved uphill directly
towards the Cougar. When the Western Spotted Skunk
approached within 1 m of the Cougar, she retreated andagain moved off. the Western Spotted Skunk returnedto the carcass and spent 3 minutes feeding before leaving.

65

the Cougar returned once again at 5:04 (3 hours later) and slowly approached the carcass. She smelled andinvestigated around the carcass for 3 minutes before she
began to feed. the Western Spotted Skunk approached
the carcass 12 minutes later. Upon arrival, the Western
Spotted Skunk quickly approached the carcass. insteadof retreating, the Cougar hissed and bared her teeth atthe Western Spotted Skunk, causing the Western Spotted Skunk to back up, away from the carcass. the Western Spotted Skunk then circled around the bottom sideof the carcass before cautiously approaching the carcass again. the Western Spotted Skunk then began
feeding on the downhill side of the carcass while theCougar continued to feed on the uphill side. the Western Spotted Skunk fed actively on the carcass for 2 minutes before leaving the carcass, and the Cougar fed foranother 51 minutes before leaving.
the Cougar returned once more on the evening of
26 november 2011 for a 9-minute visit before abandoning the carcass. there were little edible remains
left on the carcass at this point. it was monitored for
15 more days, and visits by a bobcat and a Fisher(Martes pennanti) were recorded, but neither theCougar nor the Western Spotted Skunk were detectedagain.

Discussion

During these encounters, the Western Spotted Skunk
appeared to initially rely upon tail-lifting in order tothreaten to spray the Cougar, while also appearing tocommunicate its aggressiveness to the Cougar throughbody language. after the initial encounter, the Western Spotted Skunk appeared to rely less on threats ofspraying and instead just used aggressive body language in its direct encounters with the Cougar. hunter(2009) found evidence that potential Striped Skunk(Mephitis mephitis) predators learn from experience
not to engage skunks and that, through experience,
predators learn the implied threat in aposematic coloration. it may be that this Cougar had had past encounters with either Western Spotted Skunks or Striped
Skunks and had learned to avoid, rather than confront,them.
Western Spotted Skunks typically weigh about 0.5 kg(Jameson and Peeters 2004). in this series of encounters, a Western Spotted Skunk temporarily usurped acarcass from a Cougar weighing about 99 times morethan the Western Spotted Skunk. our observation is incontrast to most published information on encountercompetition, where the larger species displaces thesmaller species. We believe that this is the largest
reported size differential for the smaller mammalian
species winning such an encounter against a larger
species. there have been unsubstantiated anecdotalreports of relatively small-bodied Wolverines (Gulogulo) usurping prey from larger-bodied carnivores,
but the body size differential is likely not as great as

66

thE CanaDian FiElD-natUraliSt

we observed between a Western Spotted Skunk and aCougar. our observations, along with those describedfor challenge commonly held beliefs about which species will win encounter competition events and should
lead us to consider factors other than the size or biomass of the competing species.

Acknowledgements

Funding for the project was provided by the California Department of Fish and Game, the University ofCalifornia, Davis, and Victoria University of Wellington. all animal captures were approved by the independent institutional animal Care and Use Committee at the University of California, Davis. We would
like to thank k. t. Everatt and t. S. Jung for comments
on earlier drafts that greatly improved the quality ofthis manuscript.

Documents Cited (marked * in text)

Heffelfinger, J. 2010. age criteria for southwestern game animals. arizona Game and Fish Department Special report#19. 40 pages.

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Supplementary video available at:
http://www.canadianfieldnaturalist.ca
received 18 January 2013
accepted 25 February 2013