There is no evidence that sound is routinely used for platypus communication, though animals occasionally produce a querulous growl (similar to the noise of complaint made by a broody hen) when they feel threatened or annoyed (Pettigrew et al. 1998).
Although aquatic mammals typically don’t rely much on their sense of smell, the platypus has an exceptionally large number of genes coding for special smell receptors located in the vomeronasal (or Jacobson’s) organ found in the roof of its mouth (Warren et al. 2008; Zhou et al. 2021). In other mammals, the vomeronasal organ is mainly used to detect odours produced by members of the same species.
Males and females both have scent glands located just under the skin in the shoulder region near the neck (Booth and Connolly 2008). The glands are much larger in males than females and become more active in both sexes in the months when breeding occurs. When males are handled at this time of year, the glands often release small drops of a pale yellow, slightly sticky fluid with a musky odour (Temple-Smith 1973). Captive males are also known to rub their shoulders and neck on grass tussocks during the breeding season (Booth and Connolly 2008), implying that the glands are used to advertise their presence, though it remains unknown if the target audience mainly comprises other mature males, mature females, or both. The odour is sufficiently strong that it may be detectable by humans at burrows that have been occupied recently by adult males (Burrell 1927).
Platypus living in Tasmania are known to urinate (as shown below) or deposit scats (as shown at right) on land close to the water. These behaviours are reasonably interpreted to be additional methods for platypus communication via scent-marking. Interestingly, animals living on the Australian mainland have never (to the best of our knowledge) been recorded to engage in such behaviours – perhaps because potential predators are more abundant on the mainland, so it’s riskier for a platypus to leave the water.
Photos courtesy of Pete Walsh (middle and bottom); APC (top)
LITERATURE CITED
Booth R and Connolly J (2008) Platypuses. Pp. 103-132 in Medicine of Australian Mammals (L Vogelnest and R Woods, eds) CSIRO Publishing: Collingwood VIC.
Burrell H (1927) The Platypus. Angus & Robertson: Sydney.
Pettigrew JD, Manger PR and Fine SLB (1998) The sensory world of the platypus. Philosophical Transactions of the Royal Society of London 353, 1199-1210.
Temple-Smith PD (1973) Seasonal breeding biology of the platypus, Ornithorhynchus anatinus (Shaw, 1799), with special reference to the male. PhD Thesis, Australian National University: Canberra.
Warren WC, Hillier LW, Graves JAM, Birney E, Ponting CP, Grützner F, Belov K, et al. (2008) Genome analysis of the platypus reveals unique signatures of evolution. Nature 453, 175-184.
Zhou Y, Shearwin-Whyatt L, Li J, Song Z, Hayakawa T, Stevens D, Fenelon JC, et al. (2021) Platypus and echidna genomes reveal mammalian biology and evolution. Nature 592, 756-762.