In the last Kip's Korner I discussed fawn recruitment rates, their impact on a deer management program, and nationwide trends in this statistic.  These data were obtained in a QDMA survey of deer project leaders from each state wildlife agency for the periods 1998 and 2008.  In that survey we also collected information on three other variables, and this article will continue with the herd monitoring cornerstone and focus on doe fawn breeding rates. 

Doe fawn breeding rates are the percentage of doe fawns that conceive during their first year (generally six to eight months of age).  This is governed by nutrition, and doe fawns attain sexual maturity when they reach a specific weight threshold.  In general, southern fawns reach it at approximately 70 pounds and northern fawns at approximately 80 pounds live weight.  Fawns hitting this threshold tend to do so in December and January, and are one reason for an apparent "second" rut in many areas.   

Since the percentage of doe fawns that breed is based on weight, not age, it is a good indicator of herd health, and you can monitor this index by checking the lactation status of all yearling does that are harvested (obviously if they're lactating at 1.5 years, they were bred as fawns).  Deer herds with access to abundant high-quality forage and light to moderate winters can have breeding in over 50 percent of their doe fawns.  Conversely, deer herds exposed to poor habitat or severe winters often have less than 5 percent of their doe fawns reach the threshold weight and breed. 

Doe fawn breeding rates vary widely across states.  Less than 10 percent of doe fawns breed in Delaware, Idaho and South Carolina, while 70 percent of them breed in Iowa.  This is testament to the mineral-rich soils and volume of agriculture in Iowa that provides abundant high-quality forage, and allows fawns to grow rapidly.  Amazingly, 10 percent of the doe fawns that breed in Iowa give birth to twins.  Even more amazing is that 21 percent of the doe fawns that breed in the farmland region of Ohio have twins!

Nationwide, 26 percent of doe fawns bred in 1998, and that average dropped slightly to 23 percent in 2008.  However, since this index is so closely tied to a region's habitat quality, it is difficult to lump the breeding rates across a region or even a state together.  For example, in my home state of Pennsylvania an average of 25 percent of the doe fawns bred in 2008, but that percentage varied from 0 to 38 percent across the state's wildlife management units (WMU).  Similar ranges occurred in Alabama (0 to 33 percent), New Hampshire (0 to 25 percent), South Dakota (0 to 58 percent), and Virginia (3 to 49 percent).  These rates likely varied even more across specific properties within any WMU.  This is one reason why collecting data from your location and using that to make site-specific harvest recommendations can benefit your deer management program.  Also, you can compare your data to WMU or state averages and assess how your management program measures up, and whether you have realistic expectations for what you can accomplish. 

As mentioned briefly in the last Kip's Korner, the percentage of doe fawns that breed can have a major impact on your management program, especially regarding the number of deer you can harvest annually.  Let's use the following hypothetical data as an example:

 Deer Herd A
 

            No. Does     Age (yr.)               No. Fawns Recruited          Deer Eligible for Harvest
                 40            1.5                                         0                                          40 + 0 = 40
                 60            2.5 and older                        60                                      60 + 60 = 120
               100            All does                                60                                          160 deer
 

Deer Herd A has no fawn breeding (0 fawns for 1.5 year-olds), and 2.5+ year-olds recruited 1 fawn each. 

 Deer Herd B
 

            No. Does     Age (yr.)               No. Fawns Recruited          Deer Eligible for Harvest
                 40            1.5                                       10                                        40 + 10 = 50
                 60            2.5 and older                        60                                      60 + 60 = 120
               100            All does                                70                                          170 deer
 

Deer Herd B has the same number of does as Herd A, but it is from an area where half of the fawns will breed and have fawns as yearlings (n=20 fawns).  We'll estimate that only half of those newborn fawns will survive to be eligible for harvest (half of 20 is 10; the other half will be lost to predation, vehicles, etc.).  Notice the only difference between Herds A and B is Herd B had some fawn breeding, and thus additional deer eligible for harvest.

In this realistic example of only 100 does, by having half of the fawns breed in Deer Herd B (and being conservative with the number that survived) we increased the number of deer available for harvest by 10 individuals.  Generally speaking, fawns are born at approximately a 1:1 buck:doe ratio, so this property would have five more doe fawns and five more buck fawns on the ground.  Those doe fawns that survive would breed either their first or second fall, and the buck fawns that survive would have antlers next year.  This directly relates to how quickly a deer herd can grow and how many bucks and does are available for harvest or merely for viewing each year.  

This is a simple example, but it clearly shows the impact that doe fawn breeding can have on a deer population and its corresponding management program.  It also partly explains why highly-productive states like Illinois, Iowa and Ohio can have so many bucks in their herds.  Restricting the buck harvest clearly plays a key role, but the fact that a sizable percentage of doe fawns contribute their own fawns at one year of age can"t be overlooked.

Kip's Korner is written by Kip Adams, a Certified Wildlife Biologist and Northern Director of Education and Outreach for the Quality Deer Management Association (QDMA).  The QDMA is an international nonprofit wildlife conservation organization dedicated to ethical hunting, sound deer management and preservation of the deer-hunting heritage.  The QDMA can be reached at 1-800-209-DEER or www.QDMA.com.

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