White-tailed deer fawns fare better in farmland than forests — in Pennsylvania and across North America
The cruel truth is that throughout the white-tailed deer range, only about half of all fawns live to see their first birthday — most are killed by predators. However, they have a much better chance of surviving if they are born in farmland rather than in forest.
That’s the conclusion of Penn State researchers, who collaborated with Pennsylvania Game Commission deer biologists to estimate 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.
Landscapes with mixed forest and agricultural cover had lower rates of mortality due to predators, when compared to forested landscapes, according to adjunct professor of wildlife ecology Duane Diefenbach, whose research group 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 the 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.
The findings have management implications, Diefenbach 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.
“Because of the difficulty in controlling predators, and the fact that many deer hunters do not support reducing bear populations for the benefit of deer populations, we would reduce antlerless harvests if predators impacted deer population too much,” said Chris Rosenberry, chief of the Game Commission’s deer and elk section.
“In Pennsylvania, we have demonstrated that reducing the antlerless harvest is an easy and effective way to increase deer numbers.”