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Can Coyotes Stifle Deer Herds?

The Coyote's impact on deer herds can vary, here are the factors to look for.

When deer hunters use binoculars and scouting cameras to evaluate bucks roaming their hunting grounds from late summer through early fall, they should also pay attention to the herd's fawn-to-doe ratio if the herd seems to be shrinking.

If twin fawns with mature does are rare sights, and instead you see one fawn for every two or more does, it might mean coyotes or other predators are devouring much of the "fawn crop" each summer. In fact, if deer densities fall below management goals, it might be time to add coyote hunting and trapping to your hobbies. That's because scientific research from eastern Canada to the southeastern U.S. shows coyote predation on fawns kill more deer than herds can replace in some areas.

Coyote impacts vary, however, depending on their population, their habitat and food options and the deer herd's size. In some ways, science is just beginning to analyze the East's coyote/whitetail relationship. These cagy, highly adaptable predators weren't found east of a line from central Texas to southern Wisconsin before the late 1800s. During the past 100 years, however, coyotes colonized North America's eastern corridor after gray wolves and red wolves were exterminated.

The Coyote Connection
Likewise, as coyotes increased in the East during recent decades, whitetail numbers declined in some areas. These shifts are prompting more researchers at universities and wildlife agencies to assess the connection.

Three recent University of Georgia research projects examined properties in Georgia, Alabama and South Carolina. All three studies found coyotes can be tough on fawns, especially during the fawns' first six weeks.

In southwestern Georgia, researchers used trail cameras to survey fawn-to-doe ratios in two study areas 2.5 miles apart. They removed 23 coyotes and three bobcats from January to August in an 11,000-acre area, but removed no predators from a nearby 7,000-acre block.

Shortly before hunting season, their camera census estimated 0.72 fawns per doe where predators were killed, and 0.07 fawns per doe where no predators were killed. Translation: Two fawns were present for every three does in the predator-removal area, and two fawns were present for every 28 does where no predators were killed.

In South Carolina, a 3-year study at the U.S. Forest Service's Southern Research Station on the 300-square-mile Savannah River Site found only 16 of 60 radio-collared fawns lived past nine weeks, a 27 percent survival rate. Most deaths occurred within five to six weeks of birth. Specifically, 16 (36 percent) died the first week; 26 (59 percent) died between week two and week six; one died in week seven; and one died in week nine. In other words, if two does gave birth to twins, by Labor Day they had one fawn between them.

Researchers attributed only 13 percent (five) of those 44 deaths to bobcats. They confirmed coyotes as the predator in 65 percent of the deaths, the probable predator in 15 percent of the deaths and the most likely predator in 5 percent of the deaths. Therefore, coyotes were likely responsible for about 38 (85 percent) of the 44 dead fawns.

Using swabs to collect DNA samples at kill sites, the researchers also concluded all coyotes kill fawns, not just dominant, experienced breeders. Of 15 kill sites used to identify individual coyotes and bobcats, researchers recorded only two individual coyotes at more than one site.

In northeastern Alabama, a two-year study on 2,000 acres convinced researchers that coyotes were a limiting factor in the number of fawns "recruited" into the herd. Two findings guided their conclusion: First, laboratory analysis of coyote scat and stomach contents showed fawns made up 27.3 percent of the coyotes' July-to-September diet, the region's peak fawning months. Although small mammals (rabbits and rodents) also formed 27.3 percent of the summer diet, fawn meat was found more important because of its higher nutritional value. Second, the researchers documented a staggering jump in fawn abundance after trappers removed 22 coyotes and 10 bobcats between February and July 2007.

Data from experienced-hunter observations showed a fawn/doe ratio of 0.52 before the trapping program, and 1.1 after the removals. Similarly, a network of Web-equipped cameras showed 0.52 fawns per doe before removal and 1.33 afterward. Combined, that's a 190 percent increase in fawn-to-doe ratios.

Coyote predation is as natural as human predation on deer. And, as such, it's not necessarily bad thing when deer herds are at or exceeding habitat limits; after all, when deer herds overpopulate they can be destructive to ecosystems. It is time to pay attention, however, if deer herds crash in your local area.

 

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1 Response to Can Coyotes Stifle Deer Herds?

Reed Wilson wrote:
September 21, 2010

Our local deer population in North Central Kansas peaked about 10 years ago. I had thought the decline was due to hunting pressure and extended doe seasons. However I now recall that there were very few coyotes due to a stiff bout of mange. Our coyote population has now come back healthy. But the deer population has declined. Makes me wonder...