Carnivore interactions are a game of risk and reward

Date:
August 26, 2021
Source:
Oregon State University
Summary:
Coyotes can eat by scavenging cougars' prey but it's a risky
proposition as coyotes often end up killed by cougars too, a new
study of predator interactions shows.



FULL STORY ========================================================================== Coyotes can eat by scavenging cougars' prey but it's a risky proposition
as coyotes often end up killed by cougars too, a new study of predator interactions by Oregon State University shows.


========================================================================== Researchers in the OSU College of Agricultural Sciences also looked at
black bears and bobcats and found the interplay within the four-species
"guild" of predators defied simplistic description.

Findings, published today in the Proceedings of the National Academy
of Sciences, challenge the traditional model for carnivore interactions
among species: that dominant predators suppress the other ones.

The study, one of the first to quantify rates of both scavenging and
intraguild predation, is important because understanding the influence of dominant predators is necessary for anticipating the ecological effects
of changes in carnivore populations.

Factoring in the study area's cougar and coyote density, the findings
suggest nearly one-quarter of the area's coyote population is killed by
cougars each year, although in many cases, coyotes did not appear to be
killed while scavenging.

"That kill percentage estimate implies a strong suppressive effect counteracting the benefit to coyotes provided by the cougars," said
Oregon State Ph.D. student Joel Ruprecht. "Overall, the issue of whether subordinate species incur a net fitness cost or benefit from dominant
predators is far from resolved." Coyotes seem to readily accept the risk
of being near a cougar if a food reward is available, possibly because
they can manage the risk by being extra vigilant, he added. Also, if a
dominant predator becomes satiated after feeding on a kill, it may not
be motivated to kill other carnivores.



========================================================================== "Learning whether dominant carnivores kill subordinate carnivores for
food or for the long-term benefit of removing a competitor needs to be
the focus of further research," said OSU associate professor Taal Levi.

Ruprecht, Levi and Ph.D. student Charlotte Eriksson led the study, which
also involved scientists from the Oregon Department of Fish and Wildlife,
the U.S.

Forest Service and the University of California, Santa Cruz.

Between 2016 and 2020 in the Blue Mountains of northeastern Oregon,
researchers tagged a "guild" of predators -- 17 cougars, 17 coyotes,
11 black bears and six bobcats -- with GPS collars that recorded their
location every few hours.

Scientists also tested the animals' scat to see what they were eating.

"How often elk turns up in the scats of the subordinate predators is
a proxy for how much scavenging they're doing because it's unlikely
any of them are killing adult elk," Levi said. "That means if they're
eating elk it's probably either via scavenging or preying on calves,
but in the Blue Mountains coyotes and bobcats rarely kill elk calves;
black bears are somewhat more likely to." To further zero in on what
the predators were eating, the scientists did ground searches based
on clusters of cougar GPS locations -- indicating potential kills --
and set up cameras at 28 of the 128 confirmed kill sites. The cameras
allowed for a daily tally of site visits by bears, bobcats and coyotes
and thus enabled an estimate of scavenging rates.



==========================================================================
"The traditional paradigm for species interactions among carnivores has stressed hierarchies: Dominant predators curb the efforts of the next
level, the mesopredators," Levi said. "We found evidence of that but also evidence of facilitation. The coyotes we studied had a strong attraction
to kill sites, frequent carrion in their diet and high scavenging rates, compared to two indicators of suppression: They avoided cougars and
also were preyed on by them." There was no evidence to suggest coyotes' attraction to kill sites was lessened if a cougar was around, he added, indicating coyotes' willingness to disregard cougar risk if a food reward
was present.

Bears had moderate scavenging rates and ate moderate levels of carrion
but showed a statistically significant aversion to being around
cougars. Nothing suggested bears were particularly attracted to kill
sites or suffered predation at the hands of cougars, or that cougars
had any effect at all on bobcats.

"Bobcats were indifferent to both cougars and their kill sites,"
Ruprecht said.

"And bobcats weren't avoiding coyotes in general, meaning coyote presence
was probably not a primary reason bobcats didn't feed on cougar kills."
There were coyotes on the scene at 89% of carcasses, bears at 50% of
carcasses outside the hibernation period and bobcats at none of them.

Scat analyses showed elk in 58% of coyote scats and deer in 12%,
comparable to the percentages for cougar scats (61% and 22%). Bear scats contained elk 29% of the time and deer 8% of the time. No bobcat scats
provided evidence they had eaten elk, and 8% of bobcat scats contained
deer.

"Investigations of the cougar kill sites showed that elk
represented 64% and deer 16% of the prey items killed by cougars,"
Levi said. "Investigations also showed that coyotes represented 7%
of cougar kills. In eight cases coyotes were the only prey item found,
and in one case a dead coyote was found along with another prey item."
The bobcat findings were particularly surprising, he noted, because
bobcats are known to scavenge from and be eaten by cougars in other
locations, and also because it's usually more likely for a wild cat like
a cougar to kill another species of cat than a predator from outside
their taxonomic family.

"By foregoing the energy benefits they could gain from eating on cougar
kills, and in doing so reducing mortality risk, bobcats in our study
area approached the risk-reward tradeoff quite differently than the
coyotes," he said. "But scavenging is only optimal under a specific
set of conditions that also includes the probability of finding
other food sources, and the energy required to search for them. The
coyotes we studied faced little risk except from cougars and scavenged profusely; they're probably less likely to scavenge when there are lots
of competitors for each carcass." Oregon State, the ODFW, the Forest
Service's Pacific Northwest Research Station and the Wildlife Restoration
Act supported this research.

Video: https://www.youtube.com/watch?v=Lb5cT8M-GxM ========================================================================== Story Source: Materials provided by Oregon_State_University. Original
written by Steve Lundeberg. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Joel Ruprecht, Charlotte E. Eriksson, Tavis D. Forrester, Derek
B. Spitz,
Darren A. Clark, Michael J. Wisdom, Marcus Bianco, Mary M. Rowland,
Joshua B. Smith, Bruce K. Johnson, Taal Levi. Variable strategies to
solve risk-reward tradeoffs in carnivore communities. Proceedings
of the National Academy of Sciences, 2021; 118 (35): e2101614118
DOI: 10.1073/ pnas.2101614118 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210826095038.htm

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