A Cooper’s hawk snatches a young squirrel from the side of a tree, a red fox finds a nest of newborn rabbits in an overgrown field, and a largemouth bass ambushes an unsuspecting school of minnows.
These are all examples of predation, the drama of predator versus prey, that plays out everyday in Kentucky’s woods, fields and waterways. Many species of wildlife prey on (eat) other animals to survive — one animal dies that another may live.
But predation, and animals taken by hunting, called harvest mortality by biologists, are just two of several mortality factors that affect wildlife. There are also a number of natural causes for wildlife deaths, including old age, diseases, parasites, and injuries.
There’s also the issue of wildlife-vehicle collisions. The slaughter of wildlife on America’s highway is year-round, but seems to peak in the spring and fall. Turtles, squirrels, rabbits, birds of prey, furbearers (mostly opossums and raccoons), songbirds, foxes and coyotes frequently become roadkill on busy highways.
Wildlife numbers fluctuate with the amount and quality of habitat available, especially for nesting, and rearing young. The best example might be migratory waterfowl. Duck production in the northern U.S. and Canadian prairie pothole region is severely impacted by drought.
But some wildlife-vehicle collisions result in more than animal deaths.
According to the Insurance Information Institute there are an estimated 1.6 million deer-vehicle collisions in the U.S. each year, resulting in about 150 human deaths, tens of thousands of injuries and an estimated $4.6 billion in total cost, including vehicle damage repair and medical expenses to drivers and occupants of vehicles.
The total number of deer killed by motor vehicles in Kentucky is unknown because not all collisions are reported, but the Kentucky State Police (KSP) tracks reported deer-vehicle collisions, and resulting human injuries and deaths. About 47 percent of all deer-vehicle collisions in Kentucky occur in the months of October through November, during the deer mating season (rut), when deer are most active.
In the four year period between 2012 and 2015, the number of reported collisions increased from 2,798 to 3,283, according to KSP. In 2015, the number of human injuries reported was 163, with three fatalities.
Diseases and Poisonings
Outbreaks of disease are often cyclic, or dependent on specific environmental conditions, or can be linked to population numbers that are higher than can be supported by the habitat. For example, in extremely dense deer herds, individual animals may succumb to parasitic, viral or bacterial infections, and severe tick infestations.
But sometimes wildlife die-offs can be traced to poisonings.
Baiting wild turkeys with shelled corn during the spring hunting season is not only illegal and unethical, but it can expose all the birds in the area to aflatoxin, which has proven to be especially harmful to young turkeys. Produced by common molds that contaminates grain in wet conditions, aflatoxin has caused die-offs of waterfowl, too.
Harvest Mortality from Hunting
In the absence of large predators, such as wolves or mountain lions, humans play a role in keeping populations of some species of wildlife balanced.
The best example might be the use of regulated hunting to manage white-tailed deer, to help ensure a healthy age structure and balanced sex ratio in the herd. Biologists recommend seasons lengths, bag limits, and the sex of deer that can be taken during the various seasons, to manage herds on a county or regional basis.
In Kentucky there are four deer management zones — with overall management goals that include reducing herds, stabilizing herds, and promoting herd growth.
Added Mortality
There’s also added mortality, a term defined as mortality in addition to what would normally occur. An example of added mortality would be the introduction of an exotic species, such as wild hogs, that compete for food with native species, eat the eggs of ground-nesting birds, destroy wildlife habitat and introduce disease.
Natural Mortality
Biologists agree that it’s often difficult to count and gauge the impact of natural mortality.
Reports from the field and anecdotal evidence may be helpful, but the means aren’t always there to document the extent of natural mortality. An example was the 2007 outbreak of Epizootic Hemorrhagic Disease (EHD) in Kentucky’s deer herd.
The infectious, viral disease of wild ruminants occurs periodically, usually during spells of dry weather, throughout the eastern half of the United States and southern Canada.
Transmitted by biting midges, EHD poses no threat to humans or domestic animals, but can be deadly to deer.
By late September that year, hunters and land owners reported finding 2,262 dead deer, in what was characterized as the worst outbreak in Kentucky since deer herds were established in all 120 counties. The Southeastern Cooperative Wildlife Disease Group, at the University of Georgia, reported in its January 2009 newsletter that the “EHD outbreak (was) impressive, with suspected or confirmed activity reported in 812 counties in 31 states.”
For more outdoors news and information, see Art Lander’s Outdoors on KyForward.
In EHD outbreaks it’s hard to know exactly how many deer died because sick and dying animals are secretive, and go into hiding before they succumb, and scavengers, like coyotes and buzzards, are very efficient at disposing of carcasses.
Usually, natural mortality is not the major factor in determining population size.
Habitat’s Influences on Wildlife Populations
It’s well documented that wildlife numbers fluctuate with the amount and quality of habitat available, especially for nesting, and rearing young. The best example might be migratory waterfowl.
The year 1988 was the height of a severe drought on the northern U.S. and Canadian prairies. Duck nesting had been limited for several years, and the number of birds that were migrating southward in the fall flight was near record low levels.
But in the 1990s, because of the Conservation Reserve Program, grasslands were put in place, so when the water returned in 1993-94, the stage was set for a comeback of duck numbers.
High Reproductive Rates Can Offset High Mortality Rates
Wildlife find ways to overcome, or offset, high mortality rates. One way is a high reproductive rate.
In Kentucky’s (computer) deer population model it’s assumed that 20 percent of adult deer die from non-harvest mortality annually. That’s a lot of deer being killed by motor vehicles, or dying of other injuries, old age, or disease.
But while the whitetail’s reproductive success is influenced by many factors including herd density, age structure, sex ratios, and food quality and availability, deer herds are capable of increasing by as much as 40 percent a year. That’s a lot of fawns being born each spring.
Young rabbits are preyed upon heavily by hawks, foxes and coyotes, but they can make up losses by having three to five litters a year in good habitat. Rabbits can nest as early as January and as late as November, producing three to eight young each time they nest.
Quail also have a way to offset losses of young.
If their nest is disturbed, they will re-nest, and if the female is lost after the eggs have been laid, the male bird will take over nesting duties.
It’s a dangerous world out there, but wildlife finds a way to not only survive, but thrive as all renewable resources do with careful management.
Art Lander Jr. is outdoors editor for NKyTribune and KyForward. He is a native Kentuckian, a graduate of Western Kentucky University and a life-long hunter, angler, gardener and nature enthusiast. He has worked as a newspaper columnist, magazine journalist and author and is a former staff writer for Kentucky Afield Magazine, editor of the annual Kentucky Hunting & Trapping Guide and Kentucky Spring Hunting Guide, and co-writer of the Kentucky Afield Outdoors newspaper column.
