Reprinted from my Know Whitetails column, in Jan. 2005 issue of Whitetail Journal
We know that most adult does have two fawns. That could mean that for every doe you see now, in the fall there would be three deer instead of one. At that rate, the deer herd would grow at an extraordinary rate, one that just doesn’t happen in the wild. OK, so we know some fawns die, but how many and what causes their death?
Two new studies, just published in the Wildlife Society Bulletin, provide answers to fawn mortality in Pennsylvania and Minnesota. Pennsylvania researchers followed 218 fawns from birth to age 34 weeks. Since most are born around the first week of June, this means they followed their survival into February and they did so in two areas; one was mostly wooded, while the other was mixed woods and farm lands. Fawns were captured (a story in itself), then fitted with a radio collar so they could be followed and located at all times.
Here are the results of this innovative study. After 9 weeks (i. e., around the second week of August) 73 fawns were dead. Twenty-five died of natural causes (failure to nurse, enteritis, edema, heart muscle degeneration, hemorrhage, vitamin deficiency, pneumonia, dehydration, infections, gangrene, diarrhea, giardia, salmonella, and tapeworm infestation. Lots of things kill animals living in the wild), black bears got 16, coyotes got 15, other predators took 10, and 7 died from cars, farm machinery, poaching, unknowns. Though bears and coyotes took a fair number up to the 9th week, thereafter bears got none and coyotes took another 4, but none after week 12. Oh yes, legal hunting took seven fawns.
Mortality varied by habitat. By February, 47% of the 110 fawns (52) captured in the agricultural area were dead, and 62% of the 108 fawns (67) captured in the forested area were dead. They started with 218 collared fawns in June and by February we had 99 alive. Predation was much higher in the forested habitat, probably because there are more predators living there. Natural causes were twice as high in the agricultural areas. Hunting mortality was also higher in the more open farmed area.
Bottom line from this study ... predators take a bunch of fawns, especially the first 3 months of their life. Black bears, which are abundant in Pennsylvania, and coyotes, which are abundant just about everywhere, got their share of the fawns, but once fawns reach nine weeks of age, such predations drops dramatically. .
The second study was done in the open farm country of Minnesota. There researchers radio-collared 39 new-born fawns, but results were far different than those found in Pennsylvania. Only 16% of the fawns died. In fact, that low fawn mortality rate is far less than most studies (Iowa 21%, Illinois 30%, Missouri 33%). The Minnesota researchers believed that the low mortality was due to low numbers of predators in the area. In fact, another researcher conducted a coyote study in the same farm area of Minnesota and only one coyote was captured after 1,350 trap nights.
Even though coyote predation was low in Minnesota farm country, coyotes are a major predator on whitetail fawns. On an island off the coast of Maine where there is no hunting, coyotes were the major fawn predator and mortality there was 74%. In Texas where coyotes abound, a study showed a fawn loss or 72%. The fact that coyotes were the top predator in Pennsylvania is similar to results of other fawn mortality studies. In New Brunswick, coyote predation on fawns was 47%. In Iowa and Illinois, coyote predation rates of fawns was over 50%.
In another study, in the forested, northern parts of Minnesota, researchers found that of all the fawns that died, 49% were killed by coyotes and 51% were taken by wolves. And there are a number of studies that show that black bears take fawns. In addition to bears and coyotes, in Pennsylvania, bobcats also took a few fawns, but interestingly dogs or foxes did not. Other fawn mortality studies in South Carolina, Massachusetts, Texas, and New Brunswick showed that bobcats took only a few fawns.
While reviewing the literature for this article, I found another related paper. Every year thousands of fawns are picked up by people, believing them to be abandoned. Most are not abandoned, but once brought to wildlife agencies, they have no choice but to hand rear these fawns. Once raised, what do you do with such fawns? One choice is to release them back into the wild, but a recent Missouri study showed that 22 of 42 released fawns died within 30 days. By 100 days after release, 30 fawns died. Dogs, coyotes and wolves got 15, 3 died from accidents such as drowning, bobcats killed 3, 2 were poached, 1 was legally harvested, and 6 died from unknown causes.
It seems that the money and effort to raise "orphaned" fawns does not lead to long-term survival in the wild. In asnwer to the question, "what happens to orphaned fawns when released back into the wild?" Most of them die very quickly. Just leave them in the wild and they will do much better.
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Even without hunting, from a human perspective, mother nature is very, very cruel. But, the strongest survive, and the deer do well overall. Even in the area of Pennsylvania where predation rates were highest, the deer herd is still on the increase. The authors of that study concluded that since the herd is still increasing, "we believe fawn deaths from predation, hunting and poaching — causes of particular concern to hunters — are not preventing the deer population from growing."
Interesting studies, and thanks to the researchers for their hard work on behalf of deer management. Thanks also to hunters whose license and excise tax money pays for such research.
