Study Examines Reproductive Success in Female White-Tailed Deer
I have discussed "breeding success" of male white-tailed deer in past NF Ag News & Views articles, and now, thanks to our collaborative efforts with Mississippi State University (Dr. Steve Demarais and Dr. Randy DeYoung) and Texas A&M University (Dr. Rodney Honeycutt), we are beginning to look at the female side of the equation. Results are preliminary, but very interesting.
For purposes of this article, "reproductive success" is defined as producing and raising at least one fawn to about 6 months of age. Thus far, data from the Noble Research Institute Wildlife Unit (NFWU) for 1991 through 2001 has been analyzed. An estimated 40 percent to 60 percent of the deer population was marked and identifiable during this time frame. Three hundred twelve deer have been accurately assigned birth years. DNA analysis was used to determine that 93 individual females were responsible for producing 161 of these deer (52 percent assignment rate). The dams of the other 151 deer were not part of the marked population.
Reproductive success was addressed from short- and long-term perspectives. On a single year basis, 85 percent of the does that were successful raising a fawn raised only one fawn (Figure 1). Relatively few deer successfully raised two fawns. It appears that even though the norm was for mature does to give birth to twins, it was not the norm for them to successfully raise both of them.
From the long-term perspective, most does (52 percent) that were successful reproducers were documented to raise only one fawn from 1991-2001 (Figure 2). Twenty-nine percent and 14 percent were documented to successfully raise two and three fawns, respectively, over the course of the study. Only 5 percent were documented to successfully raise four or more fawns. The data indicate that the average successful doe raised about 1.7 fawns over the 11-year study period.
And, finally, we looked at female reproductive success by age class (Figure 3). In the NFWU population, over 80 percent of the successful reproduction was accomplished by does three years or older at breeding. Very few does bred as yearlings were successful raising a fawn.
Physiological and experiential factors may play a role in success differences among age classes.
In summary, raising fawns appears to be hard work. Out of 161 fawns, we documented only 24 sets of twins being raised to at least 6 months of age. This is in spite of the fact that the NFWU adult female population was comprised of more than 70 percent of 2.5-year-olds or older, and that deer in these age classes usually give birth to twins. Additionally, raising fawns in successive years was not all that common. An individual raising at least one fawn in two successive years occurred only 26 times three successive years occurred only three times.
Many questions remain, but our data indicate that because of the different reproductive potential among age classes, doe harvest and the resulting age-structure can affect potential fawn recruitment. This could positively or negatively affect different management strategies or goals.
A word of caution about extrapolating information from these results it is important to remember that information reported here is preliminary and site specific. Additional data analysis as well as study replication on other areas are in order to gain a better understanding of female reproductive success.