Fawn Survival—It Depends on Your Mama—Her Age and Experience
Photos by Chris Young.
For a fawn white-tailed deer, whether you survive to a year of age or not seems to depend mostly on the age and experience of your mother. This experience includes a doe’s selection of a birth place and how well she protects her fawn from predation and also from interacting too soon with other deer, which can prevent the fawn from imprinting on his or her mother.
Selection of a predator-resistant birth site, and her position within the social structure surrounding her home range, were important contributors to fawn survival. To determine the effects of these factors on Illinois deer, we examined fawn survival on three sites in Piatt, Brown-Adams and DeKalb counties.
Research in other states has found that younger females usually lose more fawns prior to weaning age (at four months or so) than older females. So, we were surprised to find that yearling females, or those that bred as fawns (N = 31 mothers), were the most successful mothers, losing less than 10 percent of their fawns before age 1. However, 2-year-old mothers lost significantly more fawns (24 percent) compared to any other female age class. Females aged 3 years or more averaged about 15 percent fawn loss.
Yearling females usually give birth close to their mother and likely benefit from her presence and experience. Two-year-old females usually move away from their mother’s influence, selecting a site without much experience as to what is needed for fawn protection. This represents her first birthing experience away from her mother’s influence. Yearlings, because they give birth close to their mother, benefit from her selection of a more secure birth site, a benefit not available to the 2-year-old mother. Except when close to their fawns, yearlings interact with their mothers daily during feeding bouts.
The reason for more fawn losses for 2-year-old females may also relate to the selection of a birth site. These mothers tended to select areas with a more open understory such as in older oak-hickory forests or in frequently flooded bottomlands. Females older than two years selected younger forests with more understory cover making predator searches more difficult. The mother’s selection of habitat with better fawn protection also benefited their yearling offspring that breed, as these pregnant yearlings selected birth sites having the same understory characteristics as their mothers. While 2-year-old females may have given birth close to their mothers as yearlings, by moving away to a new birth site at age 2 they lose the day-to-day influence of her nearby presence.
The loss of one or more fawns in any year did not affect fawn survival in subsequent years. Of 33 females monitored on the Piatt area only three lost a fawn in consecutive years. For 33 females on the Brown-Adams site, only five lost a fawn two years in a row, while only two of 13 females observed in northern Illinois lost fawns in consecutive years. Two-year-old females learn how to improve fawn survival as they grow older, improving from age three on.
Based on Illinois studies, fawn mortality rates appear to depend on maternal experience as reflected in selection of a birth site.
Charles M. Nixon retired as a Wildlife Ecologist with the Illinois Natural History Survey.
Dwayne R. Etter is a Research Specialist with the Michigan Department of Natural Resources and Environment.