Friday, May 9, 2014

Research indicates coyote predation on deer in East manageable

IMAGE: This is an Eastern coyote.

Coyotes are a major predator of white-tailed deer across the East, especially fawns born each spring, but wildlife managers nonetheless are able to stabilize and even grow deer herds, according to researchers in Penn State's College of Agricultural Sciences.

Coyotes -- Canis latrans -- are a relatively recent arrival to eastern North America, appearing first in the region in noticeable numbers in the 1970s. They are a significant source of deer mortality and most often prey on whitetails in the earliest months of their lives. Coyotes have long inhabited the American West.

With the range expansion of coyotes eastward, and their crossbreeding with gray wolves (Canis lupus) along the way, Eastern coyotes are larger than their Western counterparts. Many people are concerned that their predation may be adversely affecting Eastern deer populations. Recently, lawmakers in Pennsylvania proposed placing a bounty on coyotes to incentivize their destruction for the sake of deer.
In response to those concerns, researchers initiated a study to look at deer and coyote populations from southeastern Canada through the mid-Atlantic region to the Southeast. Using published study data from throughout eastern North America that included fawn mortality, adult doe survival and reproductive rates -- and even the effects of severe winter weather on deer survival and predation -- researchers studied how deer populations responded to changes in predation and hunter harvest.
The research, published in the May issue of the Journal of Wildlife Management, aimed to determine whether managers can compensate for coyote predation of white-tailed deer.
IMAGE: This is an Eastern coyote.

"The concern is that coyotes may be changing the established population dynamics of white-tailed deer herds through increased predation on fawns," said Duane Diefenbach, adjunct professor of wildlife ecology and leader of the Pennsylvania Cooperative Fish and Wildlife Research Unit based at Penn State. "If that's true, then deer managers need to adjust how they make harvest-management decisions, because manipulating doe harvests is typically how wildlife agencies maintain, increase or decrease deer populations."
The study showed that coyote predation -- even at the highest levels reported -- is not significant enough to cause deer populations to decline if doe harvests are reduced. In fact, in most places in North America, continued doe harvest is required to stabilize deer populations.
Diefenbach said the only place in which that might not be true is the Southeast, where wildlife managers have found the highest predation rates on fawns by coyotes. In that region, an average of only one in four fawns survives to three months of age. But that is only in combination with extremely low doe-survival rates.
"However, we couldn't find any published research on adult-doe-survival rates in the Southeast, so it is possible that if doe hunting were stopped, deer populations would stabilize despite the heavy predation."
Mortality of white-tailed deer fawns is significant across the East, Diefenbach noted. Only an average of one in two survives its first three months of life, which is when most mortality occurs. Predation by coyotes, black bears and bobcats accounts for most mortality. Regardless, the number of fawns that survive generally is adequate to sustain nearly all populations.
"Besides predators, the other major source of mortality in fawns is hunting," said Diefenbach. "Thus, reduced hunting can be used to offset mortality from natural predators. Enough fawns survive all sources of mortality that we still need to harvest antlerless deer to maintain stable deer populations. There is little evidence to date that the increase in coyote predation could create a crisis that could not be solved by wildlife managers simply responding with reductions in antlerless deer harvests."

Monday, May 5, 2014

Inbred wolves struggle, moose proliferate at Isle Royale National Park

During their annual Winter Study at Isle Royale National Park, scientists from Michigan Technological University counted nine wolves organized into one breeding pack and a second small group that is a remnant of a formerly breeding pack. 

In the Isle Royale Wolf-Moose Study’s annual report released today, the researchers say that over the past three years, they have tallied the lowest numbers of wolves ever:  nine in 2011–12, eight in 2012–13 and nine in 2013–14.  During the same period, predation rates—the proportion of the moose population killed by wolves—also dropped to the lowest ever recorded, while the number of moose doubled, to approximately 1,050 moose.

Wolves are the only predators of moose on the remote island national park in northwestern Lake Superior.  The moose population has been increasing because wolf predation has been so low.

Wolves are Inbred

 “The poor condition of wolf predation on Isle Royale appears to be caused by inbreeding,” said John Vucetich, director of Michigan Tech’s study of the wolves and moose of Isle Royale. In its 56th year, the research project is the longest continuous predator-prey study in the world.

In the annual report, Vucetich and Rolf Peterson, research professor in Michigan Tech’s School of Forest Resources and Environmental Science and a codirector of the wolf-moose study, document analysis of the DNA of more than 1,000 fecal samples collected from wolves over the past 15 years.  Doing so allowed them to construct a family tree from 1999 to 2013.

That pedigree enabled them to monitor the rate of inbreeding among the wolves.  They found that an immigrant wolf, who eventually came to be known as the Old Gray Guy, came to the island across an ice bridge from Canada in 1997.  He brought a fresh infusion of genes that so dominated the Isle Royale wolves’ weakened gene pool that, by 2008, most of the wolves on the island were descended from the Old Gray Guy.

“This represents a very high standard of evidence that Isle Royale wolves had been suffering from inbreeding prior to the immigrant’s arrival,” says Vucetich.

In the 1960s, ice bridges between Isle Royale and the mainland formed seven out of every 10 winters, the scientists note.  In the past 17 years since the immigrant’s arrival, only two ice bridges have occurred, so the Old Gray Guy’s descendants soon became highly inbred as well. In particular, a large portion of the Old Gray Guy’s descendants were the result of two consecutive generations of close inbreeding.  Of those wolves, all lived short lives, all were dead by 2011, and only one reproduced in this case, a single pup.

“Their short, unproductive lives appear to mark the waning benefits of the genetic rescue event that occurred with the immigrant’s arrival in 1997,” the scientists say in the annual report.

The wolves of Isle Royale were not there when the national park was established in 1940. They are believed to have crossed an ice bridge from Canada in the late 1940s.

Vucetich and Peterson have analyzed data from decades of scientists’ field notes, trying to determine whether the Isle Royale wolves might have benefited from infusions of new genetic material from wolves crossing ice bridges on other occasions in the past.  They found, for example, that a pack of seven or eight wolves, including four black ones, crossed an ice bridge to the island in 1967.  Many of these wolves were still present a year later and may have rejuvenated the population, genetically speaking, about two decades after its founding.

In a paper just published in the journal Conservation Genetics, Peterson, Vucetich, Philip Hedrick of Arizona State University, Jennifer Adams of the University of Idaho and Michigan Tech’s Leah Vucetich report on their study of the effects of this new genetic input.  The Isle Royale study is significant, they write, because “few documented instances of genetic rescue have been observed long enough or in sufficient detail to understand how long one can expect the beneficial effects of genetic rescue to persist.”

But ice bridges are two-way streets. In 1977, researchers observed a pack of wolves chase a pack mate half way to the mainland across an ice bridge. In 2008, the last time an ice bridge formed before this winter, two radio-collared wolves disappeared shortly after the ice bridge formed.  And in late January 2014, an Isle Royale wolf crossed to the mainland on an ice bridge and was found dead as a result of an air pellet wound  near Grand Portage, Minn.

Moose are Proliferating 

Not limited by predation, moose are thriving on Isle Royale. In the past three years, their numbers have doubled; the vegetation that they eat is still plentiful, and the primary factor limiting their growth has probably been the severity of the past two winters, the researchers report.

Unless the next five winters are especially harsh, the moose population is likely to increase dramatically, the researchers say.  Their concern is that, “the likely result would be significant and long-lasting harm to Isle Royale’s forest.”

No Genetic Rescue for Now

The scientists have recommended genetic rescue: bringing a few new wolves to Isle Royale to mitigate the effects of inbreeding. In their new Conservation Genetics paper, the researchers say, “Past gene flow also suggests that human-assisted gene flow is necessary to conserve the ecosystem services associated with predation, since climate warming has reduced the frequency of ice bridges and with it the only opportunity for unassisted gene flow.

Isle Royale National Park recently affirmed that as long as a breeding population of wolves exists on the island there would be no intervention in the near term.

However, the Park Service will begin an expanded planning effort and environmental impact analysis for ecosystem management, focusing on moose and their impacts to the forest, as well as the dynamics between predator and prey.

 “There is time to fully explore all the consequences of such an action,” said Isle Royale National Park Superintendent Phyllis Green.  “Bringing wolves to the island remains an option, however the final decision will be based on the best available sound science, accurate fidelity to the law and long-term public interest.

The annual report is available at