White-tailed deer are still overabundant in many sections of the nation, especially where hunter harvest is the only important source of deer mortality. Meanwhile, some areas are experiencing a disturbing decline in deer abundance, primarily because of poorly understood natural mortality factors.
By John Ozoga
As I discussed in the December 2010 Deer & Deer Hunting, whitetail numbers in the Upper Peninsula of Michigan are at their lowest level since 1979 — in my view because of the poor condition of deer wintering habitat and resultant poor reproductive performance. Further, I contend this pattern probably extends across the Upper Great Lakes region, where quality of winter habitat and severity of winter weather still determine deer welfare.
A commentary by John Kilgo and other biologists from South Carolina and Georgia, published in The Journal of Wildlife Management, indicates that whitetail numbers are also declining in the Southeast — coincident with a corresponding increase in coyotes.
Kilgo and his group admit the evidence “does not establish cause and effect between coyotes and observed declines in deer recruitment.” However, they present a convincing argument that coyote-induced newborn-fawn mortality is seriously lowering annual deer herd recruitment rates. If so, that tends to invalidate deer population models commonly used in Eastern states that consider hunting the only important mortality factor for deer.
More important, despite the apparent lack of concern among “wildlife professionals” in the region, if deer recruitment is reduced because of coyote predation on fawns, as the authors of the commentary propose, “Management strategies may need to be altered.”
Coyotes are relatively new arrivals in much of the Southeast, and the importance of their predatory effects on deer have not been thoroughly researched. So currently, there are probably many more questions than answers concerning coyote-deer relationships in the Southeast. Here is what the experts know about the situation, based largely upon data gathered in South Carolina.
Whitetails in the Southeast
Whitetails were nearly gone from the Southeast by 1900. Protection of remnant deer populations, trapping and translocation programs, improved habitat conditions, and law enforcement in the 1940s and 1950s brought quick results. Deer populations increased dramatically during the 1970s and 1980s.
In South Carolina, the deer population peaked at about 1.1 million from 1992 to 1997. Since then, it has decreased to about 750,000 — a 31 percent decline (see Figure 1). According to University of Georgia professor Karl Miller, that deer population pattern has occurred throughout the Southeast.
A deer population model developed for the Savannah River Site, a 301-square-mile tract in western South Carolina, indicated that hunter harvest was the primary deer mortality source from 1965 through the mid-1990s. Nonhunting mortality accounted for about 26 percent of the annual mortality across all sex and age classes.
Beginning in the early 2000s, deer spotlight surveys revealed that model estimates were no longer accurate. From 2003 through 2005, model estimates continued to increase, but spotlight indices showed a decline. Low hunter harvest rates also reflected decreasing deer numbers, suggesting that nonhunting mortality factors were involved.
Kilgo and his group acknowledge that many factors, such as changing forest management practices and extensive land development, might have played a role in the recent deer decline. However, as noted in Figure 1, the timing of the deer decline occurred coincidentally with the increase in coyotes.
Coyotes in the Southeast
Coyotes are not native to the Southeast. Historically, the region was home to the red wolf. Habitat change and disappearance of the red wolf undoubtedly helped the establishment of coyotes, but human activity was probably more important. Apparently, many coyotes were intentionally or accidentally translocated and released by humans.
According to Kilgo and his coworkers, coyotes colonized much of the Southeast only recently and are abundant where they did not occur 20 to 30 years ago. For example, in South Carolina, the first coyote was reported in 1978, but coyotes were found throughout the state by the mid-1990s. Based on harvest records by trappers and incidental shooting of coyotes by deer hunters, most of the coyote population growth has occurred since the mid-1990s.
The first sighting of a coyote on the Savannah River Site was in 1986. By 2005, a population survey estimated 1,177 coyotes in the area, or almost four coyotes per square mile. That’s a lot of coyotes. This density is higher than the average reported for Texas, which has less than one coyote per square mile. Also, this suggests the Savannah River Site coyote population increased from almost zero in the early to mid-1980s to being well-established by 2000, a pattern that has probably prevailed throughout the Southeast.
The decline in whitetail abundance and sharp decrease in the number of fawns per doe occurred concurrently with the rapid increase in coyote numbers. Kilgo and his group asked the obvious question: “Could coyotes be the unknown new source of mortality to fawns in the population?”
Coyotes are one of the most effective predators of newborn fawns. They’re at least as efficient as black bears and far better than gray wolves. Certainly, given their current densities, coyotes are potentially a critical player in whitetail population dynamics throughout the Southeast.
According to Karl Miller, there is no reason to believe that in-utero productivity among whitetails in the Southeast has decreased. To the contrary, the best evidence indicates that almost all adult does (1 year and older) conceive and, on average, carry about 1.7 fetuses per doe. The major reason for the decrease in the number of fawns observed per doe is high newborn fawn mortality rates — and it appears coyotes are responsible.
Interestingly, Miller noted that lactation rates — which are indicative of fawn rearing success — for does 2 years old and older have decreased from almost 100 percent to 70 percent. That is, about 30 percent of the adult does currently don’t raise fawns.
The ratio of fawns per adult female in the harvest, shown in Figure 2, also indicates that fawn survival has decreased in recent years. Using an average conception rate of 1.7 fawns per doe, these data show that newborn fawn mortality rates from 1965 to 1990 ranged from 26 percent to 53 percent, annually.
However, from 1999 to 2006, 67 percent to 87 percent of the fawns died before the hunting season each year.
Study of coyote food habits conducted on the Savannah River Site during 2005 and 2006 provided firm evidence that coyotes are eating fawns. During the peak of the fawning season (May), 31 percent to 38 percent of the coyote scats examined contained deer fawn remains. Fawn remains were also identified in 15 percent to 23 percent of the June-collected scats and with lesser frequency through August. In some Southeastern states, evidence of fawns has been found in more than 70 percent of the coyote scats examined during the primary fawning period. As a result, investigators agree that coyote-induced fawn mortality is probably significant.
Studies conducted in Alabama provide supporting evidence that coyotes have a major effect on deer populations. For example, University of Georgia student Cory Vangilder used camera surveys to determine fawn-to-doe ratios before and after experimental predator removal. Before predator removal, the fawn-to-doe ratio was 0.41 fawns per doe. After the removal of 22 coyotes and 10 bobcats, the ratio increased to 1.2 fawns per doe.
Another study conducted by Sarah Saalfeld and Stephen Ditchkoff in Alabama also revealed high newborn fawn mortality rates, primarily because of coyote predation. During a two-year study, conducted in 2004 and 2005, 36 fawns were captured, transmitter-equipped and monitored daily in an exurban setting. Only 12 of the 36 fawns (33 percent) survived longer than eight weeks, with coyotes being responsible for 42 percent to 63 percent of the mortality.
Saalfeld and Ditchkoff concluded this: “Coyotes and their predation on neonatal deer should be considered an integral part of any [deer] population control strategy in the exurban landscape.” That is, in certain situations, where overabundant deer are not controlled by hunting, coyote-induced fawn mortality might be considered beneficial.
Granted, the data linking coyotes to low deer productivity in the Southeast tends to be circumstantial. Obviously, more research is needed. Other factors, such as disease and accidents, might also periodically contribute to increased fawn mortality, as could malnutrition in some cases. Nonetheless, there is reason to believe that coyote predation of newborn fawns is responsible for the recent poor whitetail reproduction and is the primary factor in the decline in deer numbers throughout the Southeast.
The authors of this commentary call attention to several questions about the relationship between coyotes and whitetails. Aside from a need for more research on the subject, they also warn that changes in deer management strategies might be required.
First and foremost, they ask “What is the level of coyote-induced mortality, and is it additive?”
As I discussed in the June 2010 Deer & Deer Hunting (“Maternal Defense: When is it Worth it?”), in the North, malnourished pregnant does produce stunted fawns that die soon after birth, often because they are abandoned or not defended by the mother and are killed by predators. So, the killing of small, weak newborn fawns by predators is largely compensatory because the fawns would have died anyway.
By comparison, in the South, does are less likely to be malnourished during pregnancy (unless deer populations are extremely high), so coyote predation of newborn fawns is more likely additive and must be considered when setting deer harvest rates to avoid overharvest.
Miller pointed out that deer population size is also important when considering the potential significance of coyote predation. High-density deer populations might avoid high levels of predation through so-called predator swamping (overwhelming predators with potential prey). In contrast, if a deer population has been reduced to a low level by disease or high harvest, each fawn is important, and coyote predation can slow population recovery.
Although specific fawn habitat requirements in the densely vegetated Southeast are unknown, habitat quality might also be important in determining the vulnerability of newborn fawns to predation. Some managers have suggested that landowners can minimize coyote predation by managing to provide favorable fawn hiding cover. Also, habitat might be manipulated to increase alternative food items for coyotes, such as soft mast and small mammals, thereby decreasing coyote predation of fawns.
Clearly, if coyote-induced fawn mortality is causing the deer population to decrease to less than favorable levels for hunting, managers must increase deer productivity or reduce fawn mortality. In some cases, this might call for limiting the harvest of female deer — which might not sit well with Southern hunters accustomed to extremely liberal deer harvest regulations.
— John Ozoga is D&DH’s research editor.
Kilgo, J.C., H.S. Ray, C. Ruth, and K.V. Miller. 2010. “Can Coyotes Affect Deer Populations in Southeastern North America?” Journal of Wildlife Management 74:929-933.
Ozoga, J.J. 2010. “Maternal Defense: When is it Worth It?” Deer & Deer Hunting 33(9):42-46.
Saalfeld, S.T., and S.S. Ditchkoff. 2007. “Survival of Neonatal White-Tailed Deer in an Exurban Population.” Journal of Wildlife Management 71:940-944.