Potential Negatives of Supplemental Feeding - Part III
Supplemental feeding has never been more popular. There are now more ranches and more acres enrolled in supplemental feeding programs than at any other time in history! In the last two articles on TrophyRoom.com I outlined whether or not a supplemental feeding program was necessary, including what benefits to the deer herd could be expected. In Part Two, I described the best ways to go about implementing a supplemental feeding program. What follows is the third of a three-part series on supplemental feeding that I hope will help you to make your feeding program more effective.
Potential Negatives of Supplemental Feeding
Although there are many positive aspects to a supplemental feeding program, there are also several potentially negative aspects. Thanks to researchers at the Caesar Kleberg Wildlife Research Institute at Texas A&M University-Kingsville, and cooperating landowners who are funding the research, we now know a lot more about these potentially negative aspects.
Drs. Charlie DeYoung, Tim Fulbright, and David Hewitt initiated a long-term, large-scale supplemental feeding study back in 2003 on two large, private ranches in the western portion of south Texas. This study is still ongoing but since the initiation, nearly a dozen different graduate students have also worked on various aspects of this project. Because this article highlights the most important findings of their research, I first need to describe their overall study design.
Each of the two landowners involved in the study constructed six 200-acre high-fenced enclosures on their ranch. Attempts were then made to stock the enclosures at three different deer densities. Two enclosures were each stocked with 10 deer to represent a “low” deer density (1 deer per 20 acres). Two additional enclosures were each stocked with 25 deer to represent a “medium” deer density (1 deer per 8 acres). Finally, the last two enclosures were each stocked with 40 deer to represent a “high” deer density (1 deer per 5 acres). Trail camera surveys were then conducted annually to monitor the deer density in each enclosure so that deer numbers could be adjusted in order to maintain the targeted densities.
Once the enclosures were built and the deer were stocked, the next step was to install two free-choice feeders near the centers of three of the six enclosures on each ranch. These feeders were placed in one of the two low density enclosures, one of the two medium density enclosures, and one of the two high density enclosures. As a result, there were six different treatments occurring per ranch: (1) low density deer herd with no feed; (2) low density deer herd with feed; (3) medium density deer herd with no feed; (4) medium density deer herd with feed; (5) high density deer herd with no feed; and (6) high density deer herd with feed. A permanent source for water was installed in all six enclosures on each ranch.
Next, permanent transect lines were established within each enclosure to allow for seasonal vegetation sampling. Parameters, such as canopy cover, biomass, and species richness were monitored along these transect lines. Three tame, hand-raised female deer were then permanently stocked within each enclosure (36 tame deer in total) to allow for graduate students to observe the deer eating so that deer diets could be intensely studied and monitored.
Potential Negative Effects on Native Habitat
One concern, first raised by Caesar Kleberg Wildlife Research Institute graduate student Mike Hehman and Dr. Tim Fulbright, was that supplementally-fed deer may be able to concentrate their browsing on the highest quality native forbs (i.e., broad-leaf weeds). If this occurred, the potential existed for these most preferred plants to be over browsed, risking the elimination of these important plant species from the habitat. The theory was that these deer, because they were supplementally fed, might be able to allocate more time to selecting the highest quality native forages available, while feeding away from the feeder sites. This was suggested because the researchers found in their scientific study, that food plot forages did not replace native forbs in deer diets.
As a result of the above concern, a host of graduate students have now looked at various vegetation responses within the six enclosures on each ranch. Dr. Tim Fulbright summarized the results of the initial studies within these enclosures and concluded that browse canopy cover, forb canopy cover, plant biomass, and forb species richness were all similar between fed and non-fed enclosures. In other words, supplemental feeding did not result in a reduction of important native browse plants or forbs.
Dr. Fulbright did report however, that there were deer density effects on the vegetation. The high deer density enclosures had lower forb species richness and lower forb canopy cover than the low deer density enclosures. Canopy cover of moderately palatable browse plants (i.e., 2nd choice plants) was also lower in the high density enclosures. He reported no differences however, in the canopy cover of highly palatable browse plants (i.e., 1st choice plants) or unpalatable browse plants (i.e., 3rd choice plants). Dr. Fulbright concluded that increasing deer density impacted the vegetation similarly regardless of whether or not supplemental feed was provided.
Graduate student Garrett Timmons and his co-workers observed tame does feeding in the enclosures each season so that their bites on vegetation could be counted. Not surprisingly, supplementally-fed deer consumed less native forage, eating around 1.3 to 1.5 ounces of native vegetation per hour. Non-fed deer on the other hand, consumed around 2.2 to 2.3 ounces per hour. He also reported that deer within the low density enclosures consumed an annual diet higher in native forbs than did deer within the high density enclosures.
Graduate student Eric Grahmann reported a lower density of preferred forbs in enclosures of non-fed deer, with a higher density of these forbs in enclosures where deer had access to supplemental feed. He concluded that supplemental feeding reduced foraging pressure on preferred forbs, the opposite of the initial concerns at the beginning of the project.
In one of the most interesting and high-tech studies to date, graduate student Ryan Darr used stable isotopes and actual bite counts of tame deer to determine that non-fed deer consumed a diet lower in digestible protein during the spring. He found no dietary differences during summer, fall, or winter for protein. He also found no seasonal differences at all for metabolizable energy. Ryan concluded that supplemental feeding did not increase selective foraging, as measured by diet quality.
No negative impacts of supplemental feeding on native habitat were found in the above-mentioned studies. This is despite the fact that the project is the largest scale, longest running supplemental feeding study ever conducted. Obviously, this is great news for all of those landowners and managers who are providing supplemental feed to their deer herds! Table One summarizes all of the above results by treatment.
The Need to Control Deer Density
Part One of this three-part series outlined all of the many positive benefits of a supplemental feeding program to a deer herd. Two of those benefits were higher reproductive rates and higher survival. Both of these benefits can quickly result in excessive deer numbers, especially if the property where feed is provided is surrounded by high fence.
Therefore, another concern with supplemental feeding is that if deer numbers are not closely monitored and tightly controlled, deer populations may get out of hand to the point that the habitat can be permanently damaged. The results of the above-mentioned studies clearly demonstrate several negative impacts of high deer densities on the native habitat. And those negative impacts resulted even when supplemental feed was provided.
As a result, a supplemental feeding program carries with it both the requirement and responsibility of removing an adequate number of deer each year. All of us like to see lots of deer when we go hunting. However, in order for both the deer herd and the habitat to be at their healthiest, deer numbers must be controlled.
The primary disease concern relates to the fact that deer are unnaturally concentrated when they congregate at permanent feeder sites. Diseases that can be spread by direct contact, such as chronic wasting disease and anthrax, are the most problematic because supplemental feeding programs increase the amount of direct contact.
Anthrax likely kills more deer in Texas than any other disease. Anthrax is caused by bacteria in the soil that result in spores that are then accidentally eaten by deer as they are grazing at ground level. Once infection is started, the bacteria can then be spread by biting flies or direct contact. Some tumors, such as fibromas and those caused by the bacteria dermatophilosis, can also be spread by direct contact.
A wide variety of parasites have negative effects on deer and all of these parasites are more easily spread from deer to deer when the chances of direct contact are increased. Ticks, liver flukes, lungworms, stomach worms, arterial worms, abdominal worms, tapeworms, lice, and mites can all be spread more easily when deer are concentrated.
Aflatoxins are another disease concern. Aflatoxins are chemical compounds produced by fungi (mold) growing on corn, peanuts, grain sorghum, or cotton. Aflatoxin can cause liver damage and alter hepatic function, especially in young fawns. A supplemental feeding program may do more harm than good if the feeders are not cleaned after each period of rainfall. Or, if aflatoxin-contaminated corn (>100 ppb) is used as the supplemental feed. Supplemental feed should be stored in dry areas away from heat, condensation, humidity, and direct sunlight.
Baits are now being developed that could be used in the future to deliver vaccines to wild deer. Graduate student Charles Coots and other researchers at the Caesar Kleberg Wildlife Research Institute are testing a variety of different-flavored baits to see which is most preferred by penned deer. This bait could then be used to house a lipid-based vaccine that could be distributed across the landscape to treat wild deer if a disease occurred that threatened people, livestock or other deer.
Effects on Non-Target Animals
Supplemental feeding not only impacts the deer herd, but it also has the potential to impact non-target animals. Raccoons and some species of birds likely benefit from supplemental feeding, as do feral hogs and javelina if they have access to the feed. However, permanent feeder sites can cause abnormally high concentrations of the above non-target animals that can increase the rate of disease and parasite transmission.
Permanent feeder sites that concentrate deer result in increased browsing of native plants in close proximity to the feeders. Raccoons can also be concentrated by permanent feeders which can result in higher rates of raccoons depredating bird nests nearby the feeder sites. Ground nesting birds such as quail may be especially susceptible.
Cost is no doubt the biggest obstacle to implementing a supplemental feeding program. Supplemental feeding is both expensive and labor intensive. The initial investment to buy feeders and fencing material is more costly than many ranch hunting operations can afford. The labor involved in initially clearing feeder sites and building exclosure fences around the feeders adds even more to the cost of the materials. However, the long-term investment of buying supplemental feed and in labor to clean, maintain, and re-fill feeders is much more than the initial expenses.
In an economics study conducted by Gary McBryde at Texas A&M University-Kingsville, it was found that food plots were cheaper than supplemental feeding in terms of the amount of feed produced and consumed by deer. However, he listed two exceptions where food plots would not be more economical. The first exception occurred when the initial investment in the machinery necessary to prepare and plant food plots could not be met by the rancher. The second exception occurred where annual rainfall was not adequate to produce at least 2,800 pounds per acre of dry matter plant material. In areas of low rainfall (most areas west of Interstate 35), expensive irrigation methods were needed to insure that food plot forage production was adequate.
Unfortunately, there really is not a cheap way to adequately provide supplemental feed. Managers cannot poor feed on the ground because cattle, hogs, javelinas, and rabbits will consume the majority of the feed, eventually costing the ranch more in wasted feed than the feeders would have cost. Managers also can’t afford not to fence out feeder sites because cattle, hogs, and javelinas will monopolize the feeders to the point that more feed is wasted than the fencing material and labor would have cost to fence out the feeders.
Zaiglin and DeYoung, in their study on supplemental feeding, found that javelinas displaced deer at feeder sites on 11 of the 12 occasions that both species were observed at the feeders at the same time. In addition, they reported that javelinas remained at the feeder sites an average of 30.1 minutes, while bucks remained only 13.4 minutes, and does remained only 11.4 minutes. They also estimated that rodents and small birds consumed a minimum of 10% of the supplemental feed, not to mention the large amounts consumed by raccoons.
Tight Lines & Straight Shots,
About the AuthorMickey has a B.S. Degree in Fisheries and Wildlife Management from Iowa State University (1988), an M.S. Degree in Range and Wildlife Management from Texas A&I University (1992), and a Ph.D. Degree in Wildlife Management from The University of Georgia (2002). He has been on the King Ranch Wildlife Department staff as the Chief Biologist since January, 1999. Mickey is an internationally recognized expert on white-tailed deer and has given seminars throughout the country on this wildlife species. He has authored or co-authored two book chapters, 18 scientific publications, and over 50 popular articles.
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