A Study of the Effectiveness of Deer Repellents on the Eating Habits of White-tailed Deer

Part of the Young Naturalist Awards Curriculum Collection.

by Chelsea, Grade: 7, Pennsylvania - 2013 YNA Winner


Figure 1
Figure 1 - Three deer in my backyard

Since our backyard abuts a nature preserve, deer come to our house almost every day to feed on our shrubs. There are always at least three (Figure 1), and there have been as many as 14 white-tailed deer. Although deer are enjoyable to watch, they can cause significant damage. The deer have eaten many of our evergreens and bushes (Figures 2 and 3).  My parents have tried spraying different products on the foliage, but have not had much success. Every spring we have to replace the bushes that the deer have destroyed.

Two photos side by side. At left: some low evergreen shrubs with some bare branches. At right: several hosta plants in brown dirt.
Figure 2 (left) - Evergreens by my house that were eaten by the deerFigure 3 (right) - Hostas by my house that were eaten by the deer

I decided to conduct a scientific study of white-tailed deer to determine the best repellent we could use on our shrubs. This project is of personal interest to my family because we can put the results into action this winter. This project will also help my community since this is an issue that most people in the local area have. We live in Allegheny County, Pennsylvania, which is known to have one of the highest deer populations in the nation (Scanlon 2012).

Background Research

Deer are herbivores that can be found foraging mainly in the early morning and late afternoon hours. A deer’s diet can change depending on what is available, their habitat and the season. For example, in the winter the deer do not have as many preferred food options, and they survive on a diet of woody plants such as trees, shrubs and vines. When herbaceous or other broadleaf plants become available, such as wildflowers or clover, the deer will switch to eating leafy plants. Deer also forage on wild grasses. In the summer, the deer are attracted to seasonal fruits like apples and seasonal crops such as wheat and corn. Deer also favor nuts, particularly acorns, in the fall. A deer herd can be from 18 to 30 deer, nationally, and from 60 to 100 deer in Pennsylvania (“Deer Overpopulation”). A typical herd range is usually less than a square mile. Add to that the fact that one deer can eat about seven pounds of food a day, and it shows the pressure deer density can place on a habitat. 

Deer are an adaptable edge species, which means that they thrive in transitional areas, which can include forests, agricultural fields, grasslands and suburban areas. A natural habitat of forests, thickets and grasslands provides cover and food for the deer, but those areas are dwindling. Suburban areas offer an abundance of high-quality food such as ornamental plantings, gardens and fertilized yards, and the suburbs also provide protection from hunters and other predators. Deer densities have increased in my home state of Pennsylvania since the early 1900s (“Deer Overpopulation”) due to urban sprawl and expanding suburban developments. Both factors have forced an increasing number of deer to include the suburbs as part of their range in order to survive. This change in habitat leads to conflicts between the deer and humans, because their foraging activities often include prize landscape plantings. Estimates of yearly damage caused by deer are more than $2 billion: $1 billion to crops, $750,000 to timber, $280,000 to house plantings and the balance to damaged cars (Furtman 2006). In fact, deer cause more damage than any other wildlife, so it is important to find a way for deer and people to coexist.

In order to combat this problem in a humane way, people have become very creative. There are more than 20 commercial deer repellents on the market. Chemical repellents are classified as predator odor products, products that burn the tongue, or foul-tasting or foul-smelling products. They are all designed to produce conditioned aversion without hurting the deer. People have devised a number of homemade repellents, too. Other ways to control deer are eight-foot-tall fences, netting, preventing reproduction, dogs, trapping and relocation, strobe lights, and pyrotechnics. The most effective method is hunting, using a gun or a bow and arrow. Deer also have a number of natural predators, such as coyotes, foxes and wolves. This background research led me to develop my experiment around finding an effective deer repellent.


The question I wanted to answer with my research was as follows: Which deterrent, when placed on a corncob, will deter the white-tailed deer from eating the corn cob? My hypothesis was that a putrescent egg product would be the most effective white-tailed deer repellent.


The following materials were used in conducting the experiment:

  • Eight matching dowel rods (3 feet high by ½ inch wide)
    Figure 4
    Figure 4 - Daily set up of my experiment
  • Eight nails (one on top of each dowel rod)
  • 128 three-inch corn cobs from the same supplier (8 per day times 16 trial days)
  • Dried blood
  • Putrescent eggs
  • Soap
  • Human hair
  • Hot sauce
  • Coyote urine
  • Ro-Pel®
Figure 5
Figure 5 - Deer eating corn early in the morning
Figure 6
Figure 6 - Deer after they finished eating the corn

For the experimental setup, I asked my father to put a nail on the top of each dowel rod and to drill a hole in the bottom of each corn cob so that the cobs could be placed on the nails (Figure 4). We did not have all of the materials, so I asked my parents to purchase them for me. I conducted two trial runs with Gala apples because my research indicated that the deer would be attracted to the apples, and they could be placed on the nails more easily (“Food Deer Eat”). However, the deer did not eat the apples and instead played with them, using their noses. I asked Meg Scanlon, a naturalist at the North Park Latodami Nature Center, about other options, and switched to corn cobs (Scanlon 2012). The two trial days with the corn cobs were successful (Figures 5 and 6). Deer like corn because corn has a high fat content, which helps them gain weight for the winter (Scanlon 2012).

Hand-drawn diagram of the essay author's house and deer areas in her backyard
Figure 7 - Drawing of my backyard

The seven deterrents I selected as independent variables were chosen to represent a sampling of the variety of deer deterrent options that are available. Each product was stored at room temperature. Four of the options were commercial products. Ro-Pel® is a bitter-taste deterrent mixture, and for putrescent eggs I used Liquid Fence®, which is primarily rotten eggs. The dried blood product is from Espoma® and the coyote urine pellets are called Shake-Away®. Two of the options were mixtures I created at home. For the soap mixture I used Ivory® dish soap at a 10% concentration mixed with water; for the hot sauce I used Tabasco® sauce at a 10% concentration mixed with water, and for the human hair I went to a local hairdresser and asked for a bag of clippings. I also used a control corn cob each day, without any repellent on it.

Methodology and Procedures

I set the experiment up in my backyard at the edge of the woods, where there is a white-tailed deer trail (Figure 7) and where the deer forage daily. I placed the rods ten feet apart s the deer could move easily between them, and to separate the odors. I set the rods at a height of three feet so woodchucks and other wildlife would not interfere with the experiment.  The procedures I used were as follows:

Figure 8
Figure 8 - My daily test recording ritual
  1. At 5 p.m. every day, for 16 days, I would collect my data chart and materials and go to the experiment plot. 
  2. I would record the daily results on the data table I created (Figure 8), noting whether the cobs were fully eaten, partially eaten, or not eaten (Figures 9-12).
  3. Then I would remove the old cobs from the rods and dispose of them.
  4. Next, I would place a fresh cob on each rod according to my diagram for that day. Every two days I randomly rotated all of the labeled rods so that the deer would not get used to the positions.
  5. Lastly, I would take one tablespoon of each deterrent and place it on one of the seven cobs according to my diagram, leaving one corn cob as a control. If it rained within the 24-hour period of a recording day, I did not count that day in the experiment because the repellent could have washed away. I would then replace the cobs at the usual time for the next day.
Figure 9 (left) - Example of a rod with no corn eaten. Figure 10 (middle) - Example of a rod with some corn eaten. Figure 11 (right) - Example of a rod with all the corn eaten.

The variable that could not be accounted for was the number of deer that came to the plot each 24-hour period. Most of the foraging activity was at night or when I was at school, so I did not have a way to record that data for each sample day. The only indicator was the amount of deer scat in the plot per day.

Figure 12
Figure 13


I assigned values of 0, 0.5 and 1 to the daily results in order to calculate an average effectiveness for each repellent (Figures 13-14). In my experiment, the putrescent egg formulation was the best white-tailed deer deterrent, which supported the hypothesis and answered the research question. Putrescent eggs scored an average effectiveness rate of 0.91, followed closely by dried blood at 0.88. The least-effective products were the soap and human hair, with rates of 0.22 each, and the control cob was eaten 84 percent of the time. Clearly, the commercial products were more effective than the homemade mixtures, and they were all more effective than not using any product at all (Figure 15). 

Figure 14
Figure 15

I concluded that putrescent eggs won because the product has a foul smell, so when the deer went near the product, the strong odor discouraged them. If they tasted it, the product also had an offensive taste. However, I did expect the coyote urine to perform better than it did (Figures 16 and 17). The naturalist said it was because the local deer have not learned to fear coyotes (Scanlon 2012). In fact, the deer seemed to be fascinated by whichever cob had the coyote urine pellets on it and would spend time sniffing it. 

If I were to repeat this experiment, it would be helpful to have a night-vision trail camera to see if there were sources of error, such as other animals impacting the experiment.

Figure 16
Figure 17

Conclusion and Importance

The efficacy of the putrescent egg formula is clearly strong. It is an easy product to apply by spraying, and is invisible when dry. The dried blood product also performed well, though it is visible when applied. The results are useful because my parents now know what deterrent to use on their shrubs. I will be sharing the information with family, friends and teachers so they will know what to use. The local naturalist has asked to see the report because she wants to know what to recommend to people when they call about having white-tailed deer issues.

Additional Research

There are many additional experiment options that would be beneficial as extensions to this research. It would be useful to run the experiment on a plant to see if the results are the same. It would be interesting to run the experiment for a longer period of time, covering more seasons and rainy days, to see if the results change. The deer tried the cobs with the egg product on them several times, so perhaps testing the egg product in combination with another product would offer a better result. However, feeding deer does more harm than good because it makes them behave unnaturally, so it would be best to limit the research (”Please Don’t Feed the Deer”).


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