Is It Possible to Kill Too Many Does?

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John Ozoga | 2007

Young Does Seek Companionship In this study, doe groups typically consisted of genetically related animals, but even young individuals deprived of close kin seemed compelled to band together. All females younger than 2 years of age, for example, sought adult doe leadership and readily accepted subordinate roles within female groups by October. Social animals reunited with their respective families, whereas isolates linked with an older tolerant animal and shared its range.

In contrast, isolated 21/2-year-old does commonly became group leaders, whereas socials of the same age normally reunited with their matriarch and assumed subordinate family roles.

Stress from Isolation
Despite these findings, blood tests taken from deer each March revealed certain physiological differences related to doe treatment. Compared to social does, isolated individuals exhibited higher plasma progesterone levels indicative of stress. This trend was consistent within an age class.

During other studies, for example, we learned that the adrenal gland can secrete significant amounts of progesterone when deer are stressed due to handling. As a result, we theorized high progesterone among isolate does quite likely reflected difficulty in achieving compatible associations with other deer during winter, when sociability among whitetails reaches its peak and can be vital to an individual’s well-being and ultimate survival.

Progeny Quality
Surprisingly, although the herd was supplementally fed, buck fawns raised by social does exhibited superior growth rates as compared to those raised by isolate does. In March, when we livetrapped the herd, social buck fawns weighed, on average, 91.3 pounds compared to 84.4 pounds for isolate buck fawns. But we saw no such difference among social versus isolate doe fawns, which weighed 71.1 pounds and 71.7 pounds, respectively.

Deer The most plausible explanation for the difference noted in the growth rate is that buck fawns experienced certain nutritional benefits related to family living, a situation scientists refer to as “social facilitation.”

Presumably, the compatible association demonstrated by members of a cohesive clan enable buck fawns to obtain more (or perhaps better quality) forage in grazing over a larger ancestral range. Because males also are more independently active than females, buck fawns more frequently accompanied close kin to feeders independent of the mother’s schedule. By comparison, males reared by isolate does were entirely dependent upon maternal guidance.

Effects of Orphaning
Given the opportunity — and an antlerless permit — most hunters will choose to shot a large-bodied doe rather than a small fawn, which often results in orphaned fawns.

A review of the literature concerning the effects of orphaning reveals contradictory findings — as I discussed in the January 2001 issue of Deer & Deer Hunting. Some studies show orphaning to be detrimental. Others studies show it to be beneficial. Still others show no effects at all.

Based on studies he conducted in South Texas, D&DH Southern Field Editor Bob Zaiglin warned, “There is the potential drawback of prematurely removing does that have fawns.”

According to Zaiglin, “Early orphaning can reduce a fawn’s home range. Although fawn movements were unaffected by orphaning, orphaned fawns occupied smaller home ranges (383 acres) than did unorphaned fawns (713 acres).More importantly, without a doe, the orphaned fawns could have experienced a disadvantage, particularly in search for food, water and, more critically, escape cover from predators.”

Probably as a result, in South Texas, orphaned doe fawns weighed an average of 9.1 pounds less than unorphaned doe fawns when killed about a year later. The orphans were also more likely to die from natural causes.

On the positive side, two of four orphaned doe fawns bred, whereas none of the five unorphaned females bred. This suggests that orphaning might increase breeding rates in young does, at least in mild environments.

Although researchers in Virginia determined that orphaning had no influence on fawn survival, they found considerable differences in orphan behavior, depending on whether they had a sibling companion. Orphaned fawns without siblings more readily associated with adult deer and learned the location of seasonal food and shelter. By comparison, orphans with siblings occupied smaller ranges and seldom associated with adult deer.

As a result, the Virginia researchers warned that if some orphaned fawns on Northern range fail to achieve compatible adult associations, they might not learn lengthy migratory routes to winter habitat.

Effects on Dispersal
Social pressure from older female relatives — especially the mother — is believed to be the primary stimulus prompting yearling bucks to leave their birth range.

Studies conducted in Virginia by Stefan Holzenbein and Larry Marchinton demonstrated the importance of maternal domination in prompting dispersal among bucks.

When comparing the movements of young bucks raised with their mothers versus those of buck fawns orphaned several months after being weaned, the investigators found few orphaned males dispersed from their natal home range as yearlings. Meanwhile, most doe-raised males dispersed as expected.

As a group, the orphans also exhibited a higher 2-year survival rate (46.2 percent) compared to nonorphans (6.7 percent), which reflects the dangers involved in trying to establish a new home range. Despite these findings, the researchers warned, “Orphaning may be harmful in migratory deer populations, because fawns must learn traditional migration patterns between summer ranges and winter ranges from their dams.”

Contrasting Evidence
Other investigators have reported contrasting results. In a 2000-acre Virginia enclosure, for example, researchers found a higher dispersal rate among orphans, 24 percent, compared to nonorphans, 6 percent.

Researchers led by Charles Nixon also produced results different from Holzenbein and Marchinton. They found no significant difference in dispersal behavior between orphans and nonorphans on the intensively farmed lands of Illinois.

In another study, however, the Illinois researchers reported higher dispersal rates for orphan females (69 percent) versus nonorphan females (37 percent). Survival rates were high for orphans and nonorphans, as only eight of 107 doe fawns died from natural causes.

Clearly, the response of fawns to orphaning is highly variable, depending upon their sex, age and a host of environmental factors. Predator Defense Few failings are as unforgiving — or as abruptly terminal — as a deer’s failure to avoid a predator. Logically, then predation has been a strong selective force in the evolution of the whitetail’s behavioral traits — especially during the precarious fawning season and during harsh winter weather on Northern range.