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Study: fawn survival

Deer fawn
Photo Credit: Getty Images

South Dakota Game, Fish and Parks biologists are studying deer fawn mortality as part of an effort to better determine the number of deer licenses issued.

For the last 15 years, the status of the deer population has been quite tumultuous. In the early 2000s, deer numbers skyrocketed and biologists launched a record breaking program geared at shrinking the herd. States issued an enormous number of deer tags, often allowing licenses with three tags. The annual deer harvest record was broken a number of times. 

“We’ve all gotten kind of used to a high number of tags,” Andy Lindbloom, GF&P’s senior big game biologist, told the Capital Journal. “The availability of licenses has just been incredible.”

Then everything changed. Starting in 2009 a series of harsh winters and severe drought-laden summers had a profound impact on deer populations. In each of the last three years the number of deer tags has been reduced substantially. 

From 2013 to 2014 the number of deer licenses dropped by 22% in east river hunting units, while west river licenses dropped by 17% and tags by a staggering 56%. 

“What we’re seeing is its getting back to the norm now,” Lindbloom said. 

While experts cannot stop nor predict ill weather, they can find better ways to manage how it, along with other factors like predation and disease, impact the deer. This is where research studies, such as those that explore fawn mortality, become crucial. 

The fawns will be momentarily captured, weighed and measured, then fit with a VHF (expandable radio-collar). For the next year, if the fawn survives that long, experts will track the animal along with all the other collared fawns in the study area to determine how many survive their first six months and how many survive their first year. 

If a hunter kills one of the fawns once it is grown, they will be able to call the phone number on the collar to report their harvest and return the collar to appropriate officials. If the fawn dies from other reasons, experts will attempt to understand what caused the death. 

Research has shown that a fawn’s first several weeks and months are by far its most dangerous. In a 2003 study of fawn survival, the Pennsylvania Game Commission captured and collared 110 fawns from an agricultural area and 108 from a heavily forested region. Just nine weeks after the capture, 28% of the farmland fawns, and 43% of the forest fawns were dead. And 26 weeks after capture, mortality rates rose to 42% and 55% respectively. 

Though determining the cause of death is difficult, predation is probably the most common cause of death for fawns. Black bears and coyotes top the list, depending on the region, with bobcats playing a role as well. Natural causes, like starvation, are also problematic, followed by vehicle accidents and finally, hunting.

“It’s not really obvious unless you see it,” said Nathan Baker, a South Dakota GF&P biologist.

The data from this study will enable experts to estimate the mortality rates of fawns occupying agricultural landscapes. These numbers will then be used to construct population and harvest models, and ultimately, to determine the number of deer licenses that will be issued every year. 

As of this point, biologists have captured 271 fawns, including 181 whitetail deer and 89 mule deer. Whitetail deer constitute the majority of the study as they account for roughly 85% of the state’s deer harvest. 

“It’s going to be some of the best information we’ve had,” said Lindbloom.

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