Deer populations in North America are declining, probably most noticeably in the Upper Great Lakes region, Northeast and Southeast. Many factors are involved, but the primary reason is steadily decreasing newborn fawn survival rates and resultant lower annual deer recruitment… contributing to a decrease in deer harvest rates.
Needless to say, this is in sharp contrast to circumstances only a few decades ago when wildlife managers were struggling to find a solution to the widespread problem of “too many deer.”
My how fast things can change — especially when dealing with adaptable critters such as white-tailed deer and coyotes.
In the eastern United States, predation by coyotes (especially of newborn fawns) has clearly been identified as being one of the most important reasons for reduced recruitment of deer.
Also, some studies have shown that a reduction in coyote numbers improves fawn survival rates — hence recruitment — but that continued coyote control over large areas is difficult, if not impossible.
Likewise, habitat modification, such as providing better fawn hiding cover and/or more alternate prey for coyotes, designed to improve newborn fawn survival rates, have not produced encouraging results. To my knowledge, there have been no studies to investigate the value of improving nutrition for pregnant does, especially during late-term gestation.
This current problem is magnified by the fact that deer management strategies have not kept pace with changing times.
South Carolina researcher John Kilgo points out the following: “Antlerless harvest programs in many states were designed during the 1980s and 1990s to control deer populations that were increasingly overabundant at the time. These liberal harvest limits were largely set prior to the widespread establishment of coyotes in the region and prior to the knowledge that coyotes could substantially affect recruitment.”
The decline in deer numbers has fueled controversy among members of the public, as well as politicians, wildlife managers, and even deer researchers. Most arguments revolve around the merits of coyote control (some even advocate bounties) and reducing antlerless deer harvest rates as a means of increasing annual deer recruitment for hunting purposes. Others suggest that coyotes in residential areas benefit management, because they help control deer numbers when other methods such as hunter harvest fail.
Two recently published studies, one conducted in the lower Northeast, the other in the Southeast, used population modeling data for their respective regions to generate various deer population scenarios to investigate the interaction effects associated with declining deer numbers, coyote control, and reductions in antlerless deer harvest.
It’s not particularly surprising that these researchers reached somewhat different conclusions and management implications, as is often the case when dealing with a behaviorally “plastic” species such as the white-tailed deer — not to mention the clever coyote.
“Can managers compensate for coyote predation of white-tailed deer?” That’s a question recently addressed by researchers in New York and Pennsylvania.
Investigators involved in the study speculated that predator control was not necessary, in order to curb declining deer populations caused by low newborn survival rates. Instead, they offered the following: “Declining recruitment, regardless of the cause, simply needs to be offset by increased adult survival of the breeding population, which potentially can be addressed via reduced antlerless harvest rates. Second, reproductive rates and adult female survival rates (excluding mortalities from hunting or winter weather conditions in the Northern range) are relatively stable across space and time. Therefore, the effects of management actions should be relatively predictable when trying to offset reduced recruitment with increased adult female survival through reduced antlerless harvest.”
Specifically, the researchers used population simulation models to evaluate combinations of low newborn fawn survival rates, severe winters and low adult deer survival rates to determine the effectiveness of altering antlerless deer harvest rates to stabilize deer populations.
These investigators concluded the following: “Our results suggest increased deer mortality from coyotes can be addressed through reduced hunting harvest of adult female deer in most circumstances throughout eastern North America. However, specific knowledge of adult female survival rates is important for making management decisions in areas where both neonate and adult survival may be affected by predation and other mortality factors.”
The authors also suggest that increasing the proportion of pregnant females will result in more fawns and a “swamping effect,” overwhelming coyotes with potential prey and resulting in increased fawn survival rates.
These researchers acknowledged that their deer population models are not valid in the extreme Northern range. Certainly, in those areas, winter deer mortality could limit the ability of reduced antlerless harvest to compensate for increased newborn fawn mortality due to any cause.
It’s important to note, for example, that the Northeast model will not apply to the Upper Peninsula (UP) of Michigan, where prolonged winters of deteriorated deer wintering habitat have not only contributed to heavy winter deer kill but also to excessive newborn fawn mortality. During the past 20 years, UP deer populations have declined from an average of more than 40 deer per square mile to around 10 deer per square mile, even though antlerless deer harvest rates have been extremely low.
In this northern Michigan region, forest and wildlife managers have finally recognized the need for serious management of deer wintering complexes in order to curb this downward spiral in regional deer numbers. Currently, the UP deer population is as low as it’s been in the past 50 years, and undoubtedly will continue to decline during the next decade, even in the absence of antlerless deer harvest, and even following winters of only moderate severity.
In contrast to the Northeast report, studies conducted under the direction of Michael Chitwood in central North Carolina indicate the following: “Our results indicate that for low-density deer populations with heavy predation pressure on neonates, protecting adult females from harvest may not be a magic bullet.”
Chitwood and his cohorts conducted their study at Fort Bragg Military Installation, where monitored deer density and deer hunting success declined sharply commensurate with coyote density increase. Given the lack of data for the region, one of their primary objectives was to determine the importance of natural of natural mortality factors of adult females, They employed population modeling, using deer reproductive/survival statistics for the area, to evaluate various management options (i.e., “what if scenarios”) that include predator removal strategies.
These researchers concluded, given that hunter-harvest at Fort Bragg is now minimal, adult female survival should be at its maximum — but it is not. Instead, they found that coyote predation of adult female deer can represent a greater percentage of mortality than either hunter-harvest or vehicle collisions. Likewise, even though adult female harvest was low, newborn fawn mortality remained high.
In fact, quite by accident, they verified the killing of four radio-collared adult females by coyotes during a study of newborn fawn survival. All four does were pregnant and carried vaginal implant transmitters, designed to signal birth of fawns. Instead, when checking the anticipated fawning sites, they found that all four does had been killed by coyotes within less than four hours prior. These observations indicated that coyotes could be a significant source of mortality for adult female deer in the areas, but they could not determine if any of the does were killed while in the process of giving birth.
They also determined that estimates of newborn fawn predation by coyotes might be inflated due to other factors. For example, abandonment. This type of behavior, and resultant mortality, has been observed in other studies of nutritionally stressed pregnant does. As a result, Chitwood believes that estimates of newborn fawn predation could be inflated because of abandonment — which in my view is often the result of nutritional shortage.
In areas with greater deer density and heavier female harvest quotas, Chitwood and his co-workers suggest it is more likely that reduction in female harvest could have a greater impact on adult female survival rates and might contribute to deer population stabilization or even growth. However, their findings clearly demonstrate that population modeling data in any given region might not apply equally to all areas even within that region.
Authors of the Southeast study conclude the following: “Coyote removal may need to be implemented in conjunction with the protection of adult females because of the possibility of increasing fawn survival, which appears to be the most important vital rate in the Fort Bragg deer population. Because of the trade-off between cost and effectiveness of coyote trapping, reducing female harvest is the most cost-efficient and logical strategy for managers to implement.”
It’s important to recognize that those involved in the studies voice the same associated concerns:
“…management will need to consider the possibility that some deer populations might be so sensitive to hunter antlerless harvest that antlerless seasons should be suspended, which could have important implications on hunter satisfaction, retention and recruitment.”
This problem of declining deer density must be more intensively studied. And as is usually the case, further study will likely yield a host of differing proposed solutions
geared to meet specific effects and concerns that vary from one area to the next.
Meanwhile, in Michigan’s UP, winter weather and quality of deer wintering habitat govern deer welfare and abundance reducing or eliminating the antlerless deer harvest will have minimal impact on deer population size.