QUESTION: A biologist in Texas once told me that deer couldn't distinguish human urine from deer (or any other kind of animal) urine. Is there any truth to this? -- S. Peterson of Auburn, AL
ANSWER: Some say yes, others no. And I believe the truth usually lies somewhere in between.
First, here's what we can say for sure. A deer's sense of smell is much greater than our own. How much greater we really don't know, but it is acute enough that scent communication is at least as important to deer as vocal communication is to humans (probably more so).
It is believed from a single whiff of urine, a deer can detect the sex and health and possibly dominance rank and even identity of the deer that deposited it. This is due to the type and amount of individual components that occur in the urine, which vary from individual to individual, and species to species.
That strongly suggests that they can identify human urine, at least as something foreign.
But the woods are full of other creatures that also leave urine behind. Whether they can actually distinguish the creature that left it is unknown.
Some folks have suggested deer can distinguish predator urine due to higher protein levels. Maybe they can, but again, there are other predators in the woods leaving scent behind.
Diet can have a considerable effect on urine odor, as heavy coffee drinkers and asparagus fans can attest. If we humans can tell the difference, deer almost certainly can.
And odors like coffee and other human foods or medications (Vitamin B) are not commonly encountered in the woods.
The real question then becomes; does it alarm them?
Several studies have been done testing the reaction of deer to various types of urine placed in scrapes and even on decoys. Reactions to human urine varied considerably, ranging from repulsion to attraction.
Some deer were actually attracted to human urine. Furthermore, I know numerous hunters who pee from their deer stands and in deer scrapes, and though it's hardly scientific, they claim it has no adverse effects.
I suspect reactions probably vary depending on what the hunter has consumed and what kind of a mood the deer is in.
A deer that is already on edge may react more negatively to any foreign odor, be it human, four-legged predator or other.
The aroma of urine, regardless of its source, might excite a rut-crazed buck that is amped up on testosterone.
You must also bear in mind that it is difficult to impossible to deposit human urine without leaving other traces of human odor, any of which could alarm deer.