Volume 192, December 2015, Pages 11–19
Highlights
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- One of the most endangered species is the red wolf.
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- To reduce introgression, coyotes and hybrids were sterilized and released as “placeholders”.
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- Thirty-seven percent of placeholders were displaced leading to occupancy by a wolf.
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- More placeholders displaced from larger home ranges.
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- More placeholders were displaced from home ranges with lower road density.
Abstract
One of the most endangered species is the red wolf, Canis rufus. Reintroduction of the red wolf began in 1987, but in 1993 hybridization between coyotes (Canis latrans)
and wolves was documented. To reduce genetic introgression, coyotes and
coyote–wolf hybrids were captured, sterilized, and released as
“placeholders”. Placeholders held territories until either displaced or
killed by a wolf, or management personnel removed them before releasing a
wolf. We evaluated the placeholder concept by examining the number of
animals sterilized and released, likelihood of displacement by a wolf,
factors influencing displacements, territory fidelity of placeholders,
and survival rates and causes of mortality of placeholders and wolves.
Of the 182 placeholders, 125 were coyotes and 57 were hybrids. From 1999
to 2013, 51 placeholders were displaced or killed by wolves, and 16
were removed by management personnel. Thus, 37% of the placeholders were
displaced leading to occupancy by a wolf. Most displacements occurred
in winter (43%) and were always by the same sex. Males were more likely
to be displaced than females. Home range characteristics influencing the
probability of displacement included home-range size (i.e., more
placeholders displaced from larger home ranges) and road density (i.e.,
more placeholders displaced from home ranges with lower road density).
Annual survival of placeholders was higher than wolves in 12 of
14 years, with cause-specific mortality similar among wolves and
placeholders. Placeholders provided territories for wolves to colonize,
yet reduced the production of hybrid litters, thereby limiting genetic
introgression to < 4% coyote ancestry in the wolf population.
Keywords
- Coyote;
- Hybrid;
- Introgression;
- Placeholder;
- Red wolf;
- Sterilization