Only about half of all white-tailed fawns survive to the first year, but in some landscapes the young deer fare much better.
A study conducted by Penn State researchers and Pennsylvania Game Commission deer biologists found that fawns survive at a greater rate in landscapes with mixed forest and agricultural cover as opposed to those areas comprised mainly of woods. Also, predators such as coyotes and black bears were responsible for most of the fawn mortality.
Researchers estimated fawn survival in four different study areas in Pennsylvania. In addition, they combined fawn-survival estimates from published data from 29 deer populations in 16 states throughout North America to look at landscape patterns in fawn survival. Adjunct professor of wildlife ecology Duane Diefenbach’s research group in the College of Agricultural Sciences conducted the work. He noted that it is the first large-scale study to link predation of fawns to habitat characteristics.
Researchers modeled fawn survival relative to percentage of agricultural land cover. The estimated average survival to six months of age was about 41 percent in contiguous forest landscapes with no agriculture. For every 10 percent increase in land area in agriculture, fawn survival increased by almost 5 percent.
“Coyote predation was a greater source of mortality than black bear or bobcat predation, especially in the southeastern U.S,” said Diefenbach, who is leader of the Pennsylvania Cooperative Fish and Wildlife Research Unit at Penn State. “But black bears accounted for similar, or greater, proportions of mortality compared to coyotes in several studies we reviewed.”
From 2015 to 2016, researchers radio-collared 98 fawns in two study areas in Pennsylvania. They monitored fawn survival and cause-specific mortality in part of the Susquehannock State Forest in Potter County, and in parts of the Rothrock and Bald Eagle state forests in Centre, Mifflin and Huntingdon counties.
Researchers classified mortality as human-caused — killed by agricultural machinery and vehicle collisions; natural — excluding predation; and predation. They used the categories of agriculturally dominated, forested, and mixed farmland and forest landscapes. Predation was the greatest source of mortality in all landscapes.
Although landscapes with agricultural cover and mixed agriculture and forest cover had lower proportions and rates of mortality due to predators compared to forested landscapes, the ag-influenced areas had greater proportions and rates of human‐caused mortalities, noted lead researcher Tess Gingery, who recently graduated with a master’s degree in wildlife and fisheries science.
“Natural sources of mortality such as starvation and abandonment occurred in similar proportions across all landscapes, and human causes were the smallest source of mortality,” she said. “We failed to detect any relationship between fawn survival and deer density.”
Kevin Wenner, a biologist supervisor with the PGC’s Northeast Region, said even though the study didn’t focus on the northeast the findings can be applied to the area.
“There are benefits to having that mixed forest and agriculture landscape, as it provides more suitable cover — such as hay fields — for fawns at a crucial time of year,” Wenner said. “Some of the big woods without a heavy understory doesn’t offer that escape cover for fawns.”
To accomplish the study, which was published recently in the Journal of Wildlife Management, researchers had to closely track pregnant does and fawns, Gingery noted. They monitored survival of radio-collared fawns via ground-based telemetry twice daily from capture until mid-August, one to seven times weekly from mid-August through early December, and one to three times weekly thereafter until mortality or collar failure.
The findings likely explain some of the movement researchers see with female deer, when a few leave forested areas and go to farmland habitat to have fawns, Diefenbach pointed out. The animals seem to sense they have greater success rearing fawns in agricultural areas, he believes.
“It seems that predators are not as efficient at finding fawns in grasslands or croplands,” he said. “And, in a camera-trapping research project we have in progress now, we are seeing fewer predators in farmland habitat than in forests.”
Wenner said the findings confirm what previous fawn mortality work has shown. One difference, he said, is the amount of impact bears and coyotes have on fawn mortality. While coyote predation in the southeast United States is a major issue affecting deer populations, black bears are as much if not a greater culprit in parts of Pennsylvania.
But Wenner added that no matter what cover exists on the landscape, there is another element that contributes to fawn survival: A healthy deer population with a good buck-to-doe ratio.
The proper ratio, Wenner said, allows fawns to be born in a timely manner.
“When you’re flooding the landscape with fawns all at once, it minimizes the amount of predation that can occur,” he said. “When the fawns are born over a larger time span, predation tends to have a greater impact as opposed to a lot of fawns all at once overwhelming predators.”
Noting that the Pennsylvania component of the study showed fawn survival is slightly higher in the Keystone State than similar landscapes in other parts of North America, Diefenbach suggested the research’s findings are important because they will help wildlife managers across the country understand why fawn survival varies.
The findings have management implications, he believes, because the results of the meta-analysis indicate that efforts to alter fawn survival to increase overall deer numbers will be challenging. Although predation is the largest source of mortality and occurred at the greatest rates, predator control efforts are difficult and often unsuccessful.
“Managers looking to influence fawn mortality by increasing habitat diversity and maintaining a landscape structure with a mix of agriculture and forest may observe less fawn predation,” he said. “However, reduced antlerless harvests may be more effective at achieving deer population objectives than attempts to manipulate the factors that influence fawn mortality.”
Wenner said PGC staff monitors the amount of 6-month-old deer in the harvest each hunting season when they visit processors to age deer. If a large decrease in 6-month-old deer is noted, it’s an issue that can be addressed, he said.
“If there was an issue associated with predation on the six month age class, we’d look to decrease the antlerless license allocation for that management unit,” Wenner said.
Reach Tom Venesky at 570-991-6395 or on Twitter @TomVenesky