June 14, 2016
By Dr. Grant Woods
Several states reported a decreased deer harvest during the 2015-16 season. When we think of statewide deer-harvest totals, most of us think about mature bucks and does.
But those folks who hunt in areas where the number of deer have been decreasing during the past few years should be concerned about fawns.
Why should they be concerned about fawns? It is because fawn survival is a huge factor in deer populations and eventual harvest totals. In fact, a lot of deer-population management is fawn management, although we rarely talk about fawns.
Let's start with the basics. "Fawn recruitment" is a term often used to describe the number of fawns per 100 does that survive to at least six months of age. A recruitment rate of 50 percent means that, on average, for each 100 does, 50 fawns survived to at least six months of age.
That does not mean 50 percent of the does that had a fawn all survived. There could have been 25 does that had twin fawns that survived, but on average, it took 100 does to produce 50 fawns that survived to six months of age. It is important to note that fawns are considered "recruited" into the herd once they are six months old. That is because fawns often have a very high rate of mortality until they are approximately six months old.
Some folks make the mistake of basing fawn recruitment rates on the average number of fetuses found in does harvested during the late season. This always leads to a gross overestimate of the number of fawns recruited into the herd. Many things can happen to a pregnant doe that affect fetal survival, such as low-quality nutrition during late winter, accidents, predation, etc.
I am writing this during mid-February, and there is a record-breaking cold front passing through many Eastern states. No doubt these conditions will reduce fawn recruitment in some areas.
There is rarely an abundance of natural food available during the late winter. A pregnant doe requires a huge amount of quality nutrition for the fetuses to develop properly. I suspect many does will lose some fetuses during this extremely stressful period, especially those living where the habitat is low quality during the late winter.
"During the past decade in many areas, deer populations were high and predator populations were low."
There's no doubt the winter of 2016 will result in decreased fawn recruitment in some areas, and if deer managers don't adjust other sources of mortality — such as reducing the number of deer-hunting permits available — then the overall deer population in those areas will decrease.
Of course, even fetuses carried to full term are not guaranteed to survive. Several researchers use VITs (vaginal implant transmitters) to monitor when and where fawns are born. These GPS transmitters are placed in a doe's birth canal, often before the rut.
The transmitter is pushed out when the fawns are born. The transmitter signal changes upon expulsion and tells researchers exactly where and when fawns are born.
Researchers were shocked at how many fawns were killed by predators within a few hours of being born! Many times, the only thing researchers would find is the transmitter and maybe a piece of the hoof. Technicians would then swab the site and use genetics to determine what species killed and consumed the fawn.
In many study areas, coyotes were the leading fawn predators. However, bobcats and black bears killed the majority of fawns in other areas. Researchers have documented fawns killed by domestic dogs, raccoons, eagles and other predators. Almost all predators will enjoy a six-pound protein package that does not run or fight.
During the past decade in many areas, deer populations were high and predator populations were low. No one worried about predators taking some fawns. In fact, many ranches in Texas counted on predators to keep the overall deer population in check so they would not have to harvest so many does each year.
Even some Midwest states such as Iowa, where deer have thrived, now report that the population and hunter harvest levels are down by up to 40 percent. That will get hunters' attention! Many Midwest states were hit very hard by EHD (epizootic hemorrhagic disease, often called blue tongue) during 2012, and a substantial portion of adult deer were killed or impacted by this disease. A substantial number of does either were killed or were so sick that they did not have a successful pregnancy.
During this same time, corn and soybean prices were extremely high and many acres of CRP were converted back to production crops. CRP is the primary source of cover in many agricultural areas, and without this escape cover fawns became easy targets for predators.
This resulted in a double whammy — reduced adults and reduced fawns to replace the adult deer that died due to the disease outbreak. A herd with a fawn recruitment rate of less than the overall death rate will decrease in size. This has happened recently in many areas due to a variety of reasons.
This summer, take notice of how many fawns you observe in your hunting area — both on the hoof and on your trail cameras. If you are not seeing as many fawns as you used to, or you believe the number of deer has substantially decreased, it may be time to determine what the actual fawn recruitment rate is where you hunt. If the rate is low, it will be necessary to change the deer herd and/or habitat management to increase the local deer population.