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SUMMER 2005
Deer Speak
by Rory Sheats and Kathleen Cason

Karl Miller studies the language of deer: not only the sounds they make and hear, but also the sights and scents that taken together form the basis for their communication. Understanding deer behavior and how they perceive their environment may help fine-tune the ways deer populations are managed.

“What we ’re trying to do with our research is provide information - physiological, behavioral and reproductive - that is helpful in maintaining deer herds,” said Miller, a professor of wildlife ecology and management at the University of Georgia.

“In some areas of the U.S., deer overpopulation negatively impacts plants and other wildlife species and also increases the likelihood of deer-vehicle collisions, ” Miller said. “In most other places, however, where deer populations are managed through hunting, we need reliable information to help fine tune management practices. Our research can be useful in either case.”

Miller, who co-edited the deer management bible, Quality Whitetails, has been studying deer behavior formally for more than two decades and informally since he was a boy hunting in north-central Pennsylvania. His research has encompassed a broad range of topics including how deer mark their surroundings with various scents, physiology of reproduction, sexual attraction, social behavior, feeding habits and preferences, and even the meaning of the grunts, mews and other sounds that deer produce. But he may be best known for his investigations of deer communication.

“My main interest is to understand the behavior and physiology of white-tailed deer, particularly how they communicate with each other and perceive their environment,” Miller said.

For example, he studies how deer use odors produced by scent glands on their foreheads, noses, feet and legs to communicate with each other. So far, making sense of deer scents is an inexact and complicated process.

“Until someone figures out how to put a human’s mind into a deer’s brain, we will never be certain what a deer learns when it smells something ” Miller said.

The scent of a deer
Mature white-tailed bucks give off a nose-wrinkling, musky smell during breeding season. The overpowering odor is produced by a behavior called “rub-urination” where deer rub their hind legs together as they urinate onto their tarsal glands, which are located on the inner leg at the hocks. Specialized tufts of hair around the glands trap the urine, which combines with bacteria and a fatty secretion to produce the characteristic scent. In some ways, it’s similar to the way sweat and bacteria cause underarm odor in people.

“White-tailed deer actually have seven areas of glandular activity that are important in scent communication,” Miller said. “The tarsal glands are the ones that researchers understand the best and are the most important in communication among white-tailed deer.”

Miller’s team, which includes a dozen graduate students, takes various approaches in figuring out when and how deer scents are used to communicate and to determine differences associated with gender, age and season. The researchers analyze deer behavior at the university’s Whitehall Deer Research Facility in Athens, Ga., and at field sites across the country.

“For example, Dr. Miller used the captive-deer research facility to better understand how bucks use scent and visual marking of their habitat to communicate with does and other bucks,” said David Osborn, a UGA wildlife research coordinator and member of Miller’s group.

But they also use the laboratory to uncover other types of information.

“Not only have we done the basic behavioral research and looked at the morphology and function of these glands but we’ve also carried it to the next step,” Osborn said. “We’ve looked at chemicals associated with the glands and identified which bacteria interact with the urine to produce the odors.”

Tarsal-gland odor conveys socially important information to deer. It helps a doe identify her offspring, for instance. And bucks use the smell to display dominance and breeding condition to other deer, especially in breeding season, when bucks paw the ground and rub-urinate to make a “scrape” that marks territory. “It ’s the equivalent of a singles bar for deer,” Osborn said.

Rub-urination studies also may help scientists better understand biological processes such as mating. Researchers have learned that both male and female deer - during every season of the year and practically from birth - engage in rub-urination behavior. However, Miller’s studies have shown that dominant bucks urinate onto the tarsal gland much more frequently during the breeding season. Frequent rub-urination leads to chemical changes that stain the gland a dark, rusty color and give the buck its rutting odor.

“Clearly this rutting odor is important in establishing the pecking order among bucks during the breeding season,” Miller said. “However, we also have demonstrated that this odor from males can have a profound impact on the internal hormone secretions and timing of estrus among females.”

Miller’s studies of the tarsal gland may be the basis for future techniques to attract or repel deer. For instance, his findings may prove useful to hunters looking for any advantage to help bring home a prize buck. “Placing tarsal scent into a scrape may mimic a dominance challenge and perhaps cause the buck to return more often to his scrape,” he said.

Deer are particularly adept at interpreting these scents because they have a “second nose” on the roof of the mouth. This additional nose, called the vomeronasal organ or VNO, is somewhat similar to the organ snakes use to “taste” the air. In deer, the VNO appears to be used primarily to analyze urine, Miller said. When a buck sees a doe urinate, he often will take some of the urine into his mouth, introducing the scent to the VNO. Because the VNO is connected to the part of the brain that controls the deer’s reproductive condition, the scent stimulates hormones that affect the buck’s rutting condition.

What deer see and hear
Scent is not the only “language” deer use. Sights and sounds are equally important for communication.

Miller has been investigating the physiology of deer vision and hearing, in part because it may be possible to exploit those senses to minimize deer-vehicle collisions. Working with Gerald Jacobs, an expert on mammalian vision at the University of California, Santa Barbara, the researchers determined which wavelengths of light deer can see. Using sedated white-tailed and fallow deer, they measured the retina’s sensitivity to various wavelengths following a pulse of light into each deers’ eye.

They found that deer see colors much as humans do, but with red-green color blindness. “Deer might have a hard time picking a ripe tomato from a green vine, and the red taillights of a car would probably appear black to a deer,” Miller said. “On the other hand, deer may be able to see blue even better than we do.”

Doctoral student Gino D’Angelo now is mapping the rod and cone cells of the deer retina to better understand the animal’s night and color vision. He also has studies under way using trained fawns to find out how deer focus at different distances and then what shapes and patterns they can perceive.

Miller said he hopes this research may lead to more effective roadside reflectors that reduce deer-vehicle collisions.

That would be especially important in states like Georgia, where development continues to encroach on deer habitat. According to the Georgia Department of Natural Resources, about 14 percent of the state’s annual collisions are caused by deer. Nationwide, deer-vehicle collisions cost about $1 billion, according the National Highway Traffic Administration.

Miller and D’Angelo have teamed up with Bob Warren, a UGA wildlife ecologist, and George Gallagher, an animal science professor at Berry College, to evaluate wildlife warning reflectors and other devices.

Their unique approach takes the deer’s point of view, Warren said. Other researchers have tested whistles and reflectors along roadways by counting dead deer before and after placing the devices.

“Nobody has looked at how deer react to different colors, different sounds and what kind of sounds and colors they can perceive,” Warren said. “We want to see how deer react to these different mitigation techniques or devices placed along the roadway when a vehicle approaches.”

One manufacturer claims that their reflectors collect light from oncoming vehicle headlights and distribute the light along the roadway to create a visual barrier of color and light that stop deer from crossing a road. The researchers are testing amber, red, blue-green and white reflectors.

“We use infrared cameras to watch the deer at night along roadways and see how they respond to the reflectors,” D’Angelo said. The results of the study, which was sponsored by the Georgia Department of Transportation, will be released by the end of the summer.

In collaboration with UGA audiologist Al De Chicchis, D’Angelo and the deer research team also are looking at how deer hear. By exposing sedated deer to a range of sound frequencies, they can get an idea how sensitive a deer’s hearing is by measuring responses in the brainstem. Early studies show that deer detect higher frequencies than humans, although it appears that humans hear most frequencies a little better, he said.

The next step is to figure out how deer respond in the field. A sound that stimulates brainwaves may not necessarily prompt a behavioral response. “We will take this information from the lab and apply it in the field,” D’Angelo said. “We’ll see how deer respond along roadways to different sound-deterrent devices, such as deer whistles or other devices on the market and other sounds that we’ll derive.”

Managing the herd
Miller, among the nation’s most widely published experts on managing deer populations, is studying ways to reduce the impact of overpopulation on forest regeneration. For example, the standard practice for producing black cherry for furniture and veneer is to harvest the trees and allow a new crop to sprout from the stumps or seeds. Because too many deer means all the sprouts get eaten, Miller and his students are finding ways to manipulate female social groups so the forest can regenerate.

“Humans have no choice but to manage deer because we’ve eliminated natural predators,” Miller said. “Too many deer can negatively impact many other wildlife species and cause irreparable damage to the ecology of an area.”

But in some deer species, the problem is reversed. Eld’s deer, for example, is an endangered sub-tropical species that ranges from eastern India to China. Miller, in collaboration with the Smithsonian Institution’s Conservation Reserve Center, investigated the possibility that male-related odors could improve female conception rates. For one group of does, straw that had been sprayed with male urine was suspended in the stall; for another group, the straw was sprayed with water. The team found that does exposed to buck urine had higher levels of reproductive hormones and higher conception rates than does exposed to water. The findings suggest that simply the smell of a male’s urine conveys his reproductive condition and that could increase conception rates in does.

“This scent-marking mechanism of the buck could minimize the energy expended in finding and defending mates and might enable the doe to conceive early in the reproductive season when environmental conditions optimize offspring survival,” Miller said.

The tremendous complexity of deer natural history creates a huge challenge for effectively managing the species.

“Deer are highly complex,” Miller said. “But with each new discovery it becomes clearer that deer live in a world of scents, sounds and sights that is very different than how we perceive our world.”

For more information, contact Karl Miller at kmiller@smokey.forestry.uga.edu or access www.forestry.uga.edu/h/research.


Rory Sheats is a former intern in the UGA Research Communications Office.


Kathleen Cason is associate director of the Office and associate editor of UGA Research Magazine.



THE UNIVERSITY OF GEORGIA RESEARCH MAGAZINE
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www.researchmagazine.uga.edu