Poor nutrition during spring and early summer negatively affects the well-being of all deer. Invariably, an inadequate diet during this critical period contributes to poor growth of young deer and poor reproductive performance among does, and yields physically smaller-than normal bucks carrying inferior antlers at maturity.
Most importantly, the quality and amount of deer nutrition during late pregnancy and early stages of fawn nursing will determine deer reproductive success, population growth rates and, ultimately, deer hunting success and harvest rates. If a pregnant doe’s diet is inadequate, she draws on her bones and body tissues to nourish her fetuses. If she survives, when severely malnourished, she tends to give birth to weak, undersized fawns, most of which die in a few days. In addition, nursing her fawns is the most energy-demanding time for female whitetails. The malnourished mother might not produce milk and might behave abnormally by not defending her newborn, or she might even abandon them. Life for a young fawn is precarious. Even those healthy enough to survive the first day or two might later succumb to malnutrition, predation, accident, disease, abandonment, adverse weather or many other maladies we don’t fully understand. In some environments, the consequences might be relatively minor, but sometimes, almost an entire age class of deer can be lost.Fetal
Failure Investigations conducted by Louis Verme at the Cusino
Wildlife Research Station in Michigan revealed that the doe’s nutrition during the
final one-third of pregnancy (April through early June) is by far the most
crucial factor determining the newborn fawn’s fate. Based on controlled
studies, Verme found 92 percent of fawns born to does malnourished throughout
pregnancy died within 48 hours of birth. Some were born dead or died at birth. All
died from nutritive failure. That is, most were small and weak, the mothers did
not produce milk, or the doe abandoned them and the fawns starved. When winter
diets were poor, as they commonly are on Northern whitetail range, and spring
diets were good, does still lost 35 percent of their fawns. In contrast, about
95 percent of the fawns survived if their mothers were well fed throughout
pregnancy. Fawn birth weights ranged from 2 to more than 10 pounds. Survivors, on
average, weighed about 8 pounds at birth, but those that died weighed about 4
pounds. Five pounds seemed to be the cut-off point. Using his research
experience, Verme predicted newborn fawn mortality rates in Upper Michigan
based on examination of fetuses from 1,000 road-killed deer during a five-year
period. Predicted average annual fawn birth weights ranged from 5 pounds to
more than 7 pounds. Predicted newborn fawn mortality, attributed only to
nutritive failure, ranged from 10 percent to 68 percent, averaging 34 percent
annually. Newborn fawn mortality rates have been equally variable in the arid
Southwest, where drought can reduce the quality and quantity of deer foods and
fawn-hiding cover. In one study, fawn losses ranged from 10 percent during
years of heavy rainfall to as much as 90 percent during years of drought.
Protein
Effects Earlier studies conducted at the Cusino Wildlife
Research Station demonstrated that food stress causes a reduction in the amount
of milk a doe produces, but milk quality did not change. Several years later, other
researchers reported the amount of protein in the diet of the pregnant doe
greatly influenced newborn fawn survival. When fed a 13 percent crude-protein
ration, does didn’t lose any fawns after birth. By comparison, a group of does
fed a 10.4 percent crude-protein diet lost 25 percent of their fawns, and
another group receiving 7.4 percent had 42 percent fawn mortality. Because no
dead fawns had milk in their stomachs, delayed or inadequate milk production
was considered the primary cause of mortality. These results clearly indicate
that pregnancy increases the need for dietary protein.
Fawn
Bedding Cover Healthy newborn fawns cared for by healthy
mothers are well endowed with inherent strategies that help minimize detection
and increase their chances of surviving early life, provided they have favorable
ground-level hiding cover. Unfortunately, researchers are finding examples
where poor hiding cover contributes to excessive predator kill or
weather-related stress. As noted, drought in southern Texas often causes scant
low-level vegetation, poor maternal nutrition and a resultant increase in fawn mortality
rates largely because of coyote predation. The latest studies in that area indicate
heat stress can cause poor fawn growth rates and make small, weak fawns more
prone to disease and predation. Likewise, on the prairie grasslands of South
Dakota, researchers found that most fawns bedded in tall grass providing
superior overhead vegetative cover, better concealment and great thermal
insulation fared better as compared to surrounding cultivated cropland.
Conversion of grassland to wheat production increased fawn mortality because of
coyote predation and hypothermia. Researchers in Illinois found the best
newborn fawn survival habitat was large forest patches bordering open areas,
with more irregular edge habitat as compared to “mortality habitat.” In other
words, coyotes seem to be more successful hunting small patches of cover and
straight-line edges.
Lactation
Crisis Given nutritional shortage during early stages of fawn
growth, Canadian researchers suggest that a doe’s immense resource needs might
no longer be sufficient to cope with energy needs of lactation, growth and
replenishment of body reserves. If so, they theorize lactating does would adopt
a conservation strategy, ensuring their own future reproduction and survival at
the expense of their newborn offspring. Accordingly, they said, “This trade-off
in energy allocation could be expressed through changes in behavior. For
example, females may decrease nursing activities and increase time foraging
when food resources decrease.” Using captive deer, the Canadian researchers
manipulated food availability to simulate nursing doe food shortage during
summer. At the same time, they monitored maternal care traits and fawn behavior
when fawns were five to 80 days old. All does used in the study were fed
unlimited feed except from May through August, when half were fed full rations
and the other food restricted group was fed 20 percent less. In a nutshell,
this study demonstrated that a mere 20 percent shortage in the mother’s
nutritional needs during peak lactation caused a change in maternal behavior
and resulted in the death of 88 percent of their newborn. Fourteen of 16 fawns
died after 16 days of age, long after formation of the doe-fawn bond. By
comparison, well-fed mothers lost only 13 percent of their fawns. The most
striking differences in lactation behavior between the two groups occurred
during the first 30 days. Thereafter, time spent suckling decreased sharply. Fawns
from the food-restricted group spent more time suckling and soliciting
attention from their mothers than fawns from well-fed mothers, suggesting they
tried harder to get milk. Even so, fawns from food-restricted mothers grew
slower and suffered higher mortality. Food-restricted mothers also spent 21
percent more time foraging than well-fed does, in an apparent attempt to
compensate for energy shortage. Hence, study results support the energy
conservation theory that given nutritional stress, does will sacrifice their
newborn for their own benefit.
Conclusions
The
primary goal of deer management must be to maintain healthy deer via
diversified habitat management that best meets the whitetail’s seasonally
changing food and cover requirements. Understandably, those basic needs and
management strategies will vary depending upon the environment and require
proper herd control. There is no doubt that predation of newborn fawns can be a
serious factor causing high newborn fawn mortality, thereby curbing annual deer
recruitment rates in some parts of the whitetail range. Unfortunately, only
controlling predator numbers does not seem to be a reasonable solution to the
problem. Further, I believe the real problem in many areas is poor maternal nutrition,
and that excessive loss of newborn fawns is compensatory because many fawns
would die anyway. If newborn fawn mortality is judged to be excessive, as it
commonly is in the North, I see no logical solution other than providing better
food and cover conditions for pregnant and lactating does as well as for young
fawns. Regardless of environmental conditions, I believe opening management can
play a critical role in satisfying these basic needs. Because the duration of
cold weather and snow cover partly governs deer health, reproductive success
and survival prospects in the North, top priority must be given to maintaining
mature conifers as deer wintering shelter, interlaced with early successional
stages of deciduous vegetation as a winter food source. Remember, the
combination of poor deer wintering habitat and a long, severe winter can
eliminate 30 to 40 percent of a wintering deer herd. As a result, throughout
their Northern range, many deer populations are currently below carrying
capacity of the summer range. Even in the North, creating and maintaining
openings within deer winter complexes is important, because snow tends to melt
from open habitat at least two weeks earlier than in adjacent forest cover. It
is recommended these open areas be cut, mowed, planted and burned as necessary
to maintain them in cool-season clover mixes for maximum spring benefit. Obviously,
in the South and Midwest plains, limiting factors are much different, and sometimes
might deal with drought, deer overpopulation, improper land use or various
other factors. There’s good evidence that heat stress in the South should be
taken in account when managing fawn-rearing habitat. For example, because areas
with moist soil are cooler than dry areas, it is recommended that wetlands,
riparian areas and even low spots should be maintained with quality fawn
bedding cover. Likewise, on the Midwestern plains, researchers report increased
fawn mortality because of predation and cold stress, since changing farming
practices have eliminated vast areas of prime fawn bedding cover. It seems
rectifying that problem will be difficult. Food plots can no doubt play an
important role in improving deer maternal nutrition and softening the predator
effect. When carefully planned, food plots can target specific seasonal dietary
needs for whitetails, such as high-protein-content forage superior to that
typically available in native plants during spring and early summer. If you’re
seeing fewer fawns per doe than expected on your property, review the reasons
I’ve discussed here. Timely killing a few coyotes might help some, but it won’t
cure the problem of poor-quality food and cover just before and during the
fawning season. If you determine that inadequate nutrition during the critical
pre-and post-fawning period is at least partially responsible for fewer fawns
than expected on your property, consider food plot management as a remedy. And,
above all, have the expert staff at the Whitetail Institute help you formulate
a management program that best meets the environmental constraints of your
area.
