A Deer's Lip Curl Likely Supplies Its Second Smell Organ

ITwo Scent Paths

Breathing Supplies the Nose and Lip Curls Likely Supply a Second Organ

Our rule is to leave the second organ nothing to sample. Keep your urine, lures and bare hands away from scrapes, licking branches and their approach trails from the first fall scrapes through the end of the rut.

After examining 4 Hokkaido sika deer culled in January 2025, Kondoh and colleagues found paired tubes about 5 mm across forming the second organ at the base of the nasal septum. In Scandinavian moose a duct described by Vedin and colleagues may carry odor substances from both the mouth and the nasal cavity into the organ.

Researchers measured the flow into that organ in other animals. Using 5 male goats with a tube placed in the organ, Melese-d'Hospital and Hart put dye mixed with urine or plain water into their mouths. The dye concentration in the organ was markedly higher following a lip curl than when no curl occurred. After giving guinea pigs urine containing a dye that does not evaporate, Wysocki and colleagues detected dye in the organ but none on the main nose's smell lining.

According to Crump and colleagues the lip curl is a male response mainly to female urine in the breeding season. The part of female urine that triggered a curl in captive black-tailed bucks dissolved in water and barely evaporated.

IIInside the Nose

One Whitetail's Nose Held Smell Lining Only in Its Rear Fifth

Yee and colleagues cut sections from one Pennsylvania white-tailed deer nose and from a gray squirrel, a bobcat and a coyote. In all four animals the front nasal scrolls manage heat and water while the rear scrolls called ethmoturbinals hold most of the smell lining. The deer's air-warming scrolls extended far back, but only the rear 20% of the nasal cavity showed smell lining.

The deer's ethmoturbinals covered about 40% of its total nasal surface compared with more than 60% in the other three animals. The authors point to folds in the deer's ethmoturbinals that fit more smell surface into a small space. For total smell-lining area the coyote was much closer to the deer than to the bobcat. The authors say poor tissue preservation probably led them to undercount the deer's lining. Smell lining was also mainly in the rear roof of the nasal cavity in 6 Korean roe deer examined by Park and colleagues.

As Niimura and colleagues summarize, mice and rats have 1,000 to 1,200 working smell receptor genes while cattle have a similar number and people have about 400. Our search turned up no such count for any deer. The number of genes tells us nothing about range. We also found no peer-reviewed measurement supporting the popular claim that deer smell some fixed number of times better than people. FDR's scent ribbon paper also explains why wind records cannot tell us a detection distance.

IIIGland Signals

Buck Glands Have Male-Only Compounds and Black-Tailed Deer Avoided Wolf Urine

Li, Siefkes and Li note that bucks rub-urinate onto the tarsal gland and that the mix signals sex, age and maturation status at close range. From tarsal extracts of whitetails killed in the breeding season the authors identified four male-only compounds and called them cervidins A to D.

Gassett and colleagues identified 46 volatile compounds in interdigital gland secretions from 8 male whitetails. Eleven were higher in dominant bucks aged 3.5 years or older than in subordinates under a loose P ≤ 0.10 threshold. Those eleven may signal a dominant male, the authors suggest.

Chamaillé-Jammes and colleagues offered urine from wolves and black bears to black-tailed deer that had gone about 100 years without wolf predation. The deer clearly avoided wolf urine and sniffed it more but did not respond to bear urine. Which organ read those scents was not tested in any study in this section.

IVPrion Connection

Normal Prion Protein Appears in Deer Scent Glands and the Lip-Curl Organ

Ness and colleagues sampled 15 mule deer and 16 whitetails that hunters killed on Canadian Forces Base Wainwright in Alberta between 30 November and 13 December 2017. Eight tissues were checked and all eight held normal prion protein, the normal cellular form of the protein CWD prions turn into the disease form. The eight tissues came from the vomeronasal organ's front, the parotid salivary gland and six skin scent glands on the face and legs.

No sensory lining appeared in the vomeronasal sections, a gap the authors point out.

With total protein taken into account, brain tissue contained 3.7 to 23.5 times more normal prion protein than the gland samples. The authors conclude that the amount in every tissue made it a possible site for prion infection, buildup and shedding. The authors ran no tests for CWD prions in these tissues.

Ness and colleagues point to work showing that male whitetails work scrapes more than does and name saliva and urine among fluids that shed CWD prions. Our read is that the second organ samples what gathers at a scrape and its licking branch. FDR's scrape camera guide explains who touches the branch, while our urine lure guide looks at prions in urine and state lure rules.

VEvidence Gaps

Most Findings Come From Small Samples and Species Other Than Whitetails

Researchers measured the route into the second organ in 5 goats and in guinea pigs and Kondoh and colleagues caution against applying findings across species even within the deer family, so we read those tests as a likely mechanism for deer. The anatomy of the main nose comes from one poorly preserved whitetail nose and 6 roe deer, while the second organ's anatomy comes from 4 sika deer and a moose study. The prion protein survey's 31 deer all came from one Alberta base near the breeding season's end. Apart from the whitetail nose, sika deer, gene count and prion protein papers we read most sources only as abstracts. None of the sources we read measured a deer's range for smelling a hunter, and our rule has not been field-tested in any study.