IN common with many mammals, olfaction (smell) is an important and acute sense for Otters. For example, in a previous Nature Notes (7th April 2022), I described the way that Otters leave Spraints (poo) in prominent places as a means of posting an enduring message. This Otter ‘Tweet’ can be ‘read’ by other otters sniffing the spraint in the following hours and days (unlike ephemeral vocal calls), and can reveal the identity of the ‘sender’, and characteristics such as health and reproductive status. In this Nature Notes I describe another Otter behaviour, that I have observed, that I find curious, and that might also be related to their sense of smell.

On at least a handful of occasions, when watching/photographing Otters, typically when the Otter first realises that I am there (perhaps because it hears the click of my camera shutter), it has opened its mouth, baring its teeth in my direction (see photograph). I have never got the impression this was an aggressive behaviour. It did not move towards me or make any aggressive vocalisations (see Nature Notes 3rd March 2022). Similarly, although the Otter may have been a little concerned, it did not seem unduly alarmed, and did not take flight.

So, what were these Otters doing? I wonder if they were exhibiting a ‘flehmen response’ as part of a process of information gathering and situation evaluation. The flehmen response can be seen in several species, e.g., cats and horses. Open mouth and baring of the teeth are accompanied by inhalation, allowing odours (airborne chemicals) to be drawn into contact with a secondary olfactory system, the vomeronasal organ (VNO – sometimes referred to as Jacobson’s organ). This is located at the base of the nasal cavity, with an opening from the roof of the mouth (in most species). Detection of pheromones (chemicals that communicate to others of the same species) is thought to be one of its primary functions. Exactly how the VNO works in Otters is uncertain, but studies of mice suggest it can also be involved in determining the need for avoidance and defensive behaviours in relation to other species. In this circumstance, the chemical substance(s) involved would be referred to as kairomones (as opposed to pheromones) – as they are of benefit to the receiving animal and transmission/reception is interspecific. Of course, this would be consistent with the dilemma facing the Otters, that I describe here. They were trying to figure out who, or what, I was.