LAST UPDATED: May 1st, 2015
Two surprises emerged during Wisconsin’s research into deer predation and fawn survival the past three springs: Wolves were not linked to any fawn deaths in the Northern Forest study area near Winter, and starvation was the top fawn-killer in the Eastern farmlands study area near Shawano. Of those two 2011 through 2013 surprises reported by the Department of Natural Resources, we should be most intrigued that many newborn fawns in east-central Wisconsin’s farming region died of disease or malnourishment soon after their births. The fawn study, which began in 2010-11, ended last year. No fawns were collared and monitored this spring. The DNR is still monitoring adult deer collared since 2010-11. Its researchers have collared roughly 500 deer in each study area since the program began.
A doe runs back into the woods after being fitted with a radio-collar by DNR researchers.
Researchers attached radio-collars to 139 newborn fawns over the past three springs at the Eastern site, and monitored them throughout summer. Roughly 31 percent died each year, with most succumbing soon after birth. Of fawns monitored, 14 percent (20) died of starvation/disease, 7 percent fell to coyotes, 3 percent were road-kills, 2 percent died of unknown causes, 1 percent fell to bobcats, 1 percent fell to bears and 2 percent fell to predators that couldn’t be identified by tracks, bites, scat and other evidence at kill sites. “We didn’t expect to see starvation as the Eastern site’s top killer,” said Daniel Storm, the project’s lead researcher. “Winters there are less harsh than at the Northern site, and there’s more food. And yet some does – probably yearlings and 2-year-olds that are still growing – apparently couldn’t produce milk after giving birth. They just walked away.” That suggests many woodlots in Eastern farmland have become too mature and lack the understory to feed deer, which can’t find enough standing crops or waste-grain on surrounding farms during winter, leaving does weak in spring.
DNR researchers hold down a deer and cover its eyes to calm it while attaching a radio-collar.
At the Northern site, the DNR collared 89 fawns over the past three springs, and annual death rates varied from 37 percent to 63 percent. Predators were the leading cause of death during those years. Of the monitored fawns, nearly 15 percent were killed by predators that couldn’t be identified, 10 percent fell to black bears, 7 percent fell to bobcats, 6 percent fell to coyotes, 3.5 percent fell to disease or starvation, and 6 percent fell to unknown causes. Although wolves weren’t linked by physical evidence to any fawn deaths, it’s possible they caused some of the “unknown-predator” deaths. Even so, most unknowns occurred soon after the fawns’ births, which is when bears are most deadly on deer. “The ‘unknowns’ dropped right off after the first month, which is when bear predation really drops,” Storm said. “Fawns are large enough to outrun bears by then.” Storm said disease/starvation could have played a greater role than numbers show in the Northern site, because predators could have picked off starving fawns before they died on their own. The Northern site has more predators than the Eastern site, and they likely key on hungry fawns bleating for food.
Fawns are most vulnerable to predators in the first month of life.
Although wolves didn’t show up as fawn predators the past three years, they were linked to some adult-deer deaths. In the Northern site, the DNR radio-collared 372 mature deer over the 2010-11, 2011-12 and 2012-13 winters, and recorded annual death rates from 7 percent to 41 percent. Of the site’s 372 collared adult deer, wolves and coyotes each killed about 2.5 percent of them, while bobcats killed about 0.5 percent and bears about 0.25 percent. “Unknown predators” accounted for 4 percent of the deaths those years, followed by starvation, 3 percent; road-kills, 1.75 percent, poaching, 1.5 percent; and unknown, 1 percent. Of the 373 collared adults in the Eastern study area, road-kills claimed 5 percent of the group, with coyotes, starvation, poaching and unknowns each claiming about 1 percent or less.
After fawns are about one month old, they can often outrun black bears and other predators.
Meanwhile, the 2013-14 winter – the most severe on record since the DNR began tracking conditions in 1960 with a winter severity index – killed 43 percent of collared juvenile deer and 10 percent of collared adult deer in the Northern site. The brutal winter also claimed 14 percent of juveniles and 9 percent of adults in the Eastern site. Storm said the Northern Forest’s herd typically begins winter with 40 percent juveniles and 60 percent adults, so its overall death rate this winter was 23 percent. The Eastern Farmland’s herd typically starts winter with 46 percent juveniles and 54 percent adults, so it’s overall winter death rate was 11 percent.
For the moment, hunting was the leading cause of death in both study areas the past three years. Of the collared deer, roughly 15 percent of antlerless deer and 40 percent of bucks fell each year to hunters. Because these results don’t implicate wolves, the study will disappoint critics who pushed hard for it five years ago. But the research has been transparent from the start, and included more than 1,000 citizen-volunteers during its first 18 months alone.
And true, the study won’t end until after this fall’s hunts, but Storm doesn’t expect startling upticks in wolf predation the next six months. The study’s results suggest declining habitat quality and increasing disease rates remain the whitetail’s most dire challenges.
What do you think is threatening the deer in your area? Is it lack of food or something else?