What Biologists Learn from Following Fawns

By Jon Rachael, Regional Wildlife Manager Idaho Department of Fish and Game - Southwest Region The Idaho Department of Fish and Game has been intensively monitoring survival of mule deer fawns on a dozen study areas across southern Idaho for the last six winters. Three of these study areas are in the Southwest Region. Two of these, the Boise foothills northeast of town and a site north of Emmett, have been monitored since the program began. A new study area was added this year east of Garden Valley along the South Fork Payette River. At each study area, crews have captured and radio-collared 20 to 30 fawns during early winter when they are six to seven months old. After capture, the radio-collared fawns are monitored three times per week so biologists can quickly investigate the cause of death of any that die. Because of their smaller bodies and lower fat reserves, fawns are usually the first deer to succumb to difficult winter conditions. By monitoring their survival, we get a sensitive and measurable indicator of how the entire deer herd is faring. When survival of fawns is evaluated in conjunction with population surveys, doe:fawn ratios, and hunter harvest estimates, biologists can assess whether enough fawns are surviving to replace the number of adults that died during the year and make adjustments to antlerless deer seasons and permit levels if necessary. What has been learned? Not surprisingly, each study area in the state is a little different and every winter is different. Harsh conditions vary in duration and intensity and these conditions come and go at different times during the winter. Deer either adjust and survive, or suffer accordingly. Between 40 and 70 percent of fawns survive a typical winter. In general, the smaller the fawn is at the beginning of the winter, the more likely it is to die before the end of spring. However, all else being equal, female fawns tend to have a slightly better chance of surviving than male fawns. So how did the deer do last winter? Hot and dry conditions during summer and fall 2003 left fawns in less than ideal condition going into winter in the southwest region. Although winter was relatively mild only 25 percent of fawns captured north of Emmett survived, and only 40 percent of the radio-collared fawns captured in the Boise foothills survived the winter. The natural knee-jerk reaction to high over-winter losses of fawns might suggest that the deer population is headed for trouble. However, going into last winter total deer numbers in these two southwest region study areas were probably at or near their highest level in more than a decade. With good weather and good habitat conditions, deer birth rates and fawn survival can increase dramatically. Conditions this last summer and fall were cooler and wetter than the previous several years. As a result, deer had more -and better quality- forage available and went into this winter in excellent condition. This winter has been mild with little snow and few fawns have died. Survival through the winter and physical condition of adult deer should also be higher this year, and excellent production of new fawns this June can be expected. In addition to monitoring survival of fawns, much has been learned about the movements of deer and how far they migrate between winter and summer range. Some of the fawns that were captured just north of Emmett have traveled more than 60 miles to spend the summer in the Upper Payette Lake area north of McCall. Fawns captured on the Boise Front winter range have been found as far as 60 miles northeast in the Sawtooth National Recreation Area. Winter is not over yet, but things are looking pretty good so far. In the years ahead, the fawn monitoring program will continue to give Fish and Game first indicator of the impacts of winter severity on deer populations in the southwest region and throughout the rest of southern Idaho.