QUESTION: I've noticed sometimes when I spook deer they snort and run off. Other times they stare in my directions and stomp their hooves. Why do they stomp like that? - Mike J. Orangeburg, South Carolina
ANSWER: You might be surprised to learn that a fair amount of research has been done on the subject, though mostly on smaller mammals.
Scientists believe mammals stomp their feet in at least five different contexts:
1) While proclaiming or announcing territory
2) During aggressive interactions to defend territories or mates
3) As part of mating interactions
4) To indicate subordinance
5) To communicate danger from predators
I would add one more that the small mammals in my house sometimes use: To indicate anger because they didn't get what they wanted.
In the case of deer, it is believed the primary purpose of hoof stomping is to communicate the presence of danger. We can't really say whether it's intentional, or merely a nervous reaction, but it does send the message that something is amiss.
That begs the question: Why not just run away?
There is a cost-to-benefit ratio associated with every behavior. The object is to maximize that ratio, and the creatures that do so remain alive the longest.
Fleeing might be the best option in some instances, like when the threat is clearly identified and imminent.
Stomping might be a more economical option when a deer senses a threat but isn't sure what it is; or the threat is identified but not imminent.
If a coyote suddenly bursts out of the brush and charges the deer will most likely flee. If it's trotting across an open field some distance away, they might stand and stomp.
Some biologists also speculate there might be an olfactory function associated with stomping. Deer are always releasing a certain amount of scent-bearing glandular secretions from their interdigital glands as they walk. This is one way other deer can detect they've recently passed by, and how they follow them.
It is speculated that stomping might release a greater amount of secretions, and they might also contain certain chemicals released into the bloodstream when a deer is alarmed. This "danger cocktail" could act as an olfactory alarm signal to other deer that pass by.
I have, on more than one occasion, witnessed a deer stomp, then eventually run or walk off. Later, deer approaching the area where the deer stomped suddenly became alarmed or nervous. And their degree of alarm seemed to vary with time, being increasing less with time.
A third possibility is something called bone conduction hearing. Sound travels through bone, which is part of what makes hearing aids work. There is some speculation that, by stomping, then holding the front leg in a stiff, locked position, a deer can better sense vibrations that could be an approaching predator. I was unable to find any hard data on the subject, but future research will hopefully shed more light.