SPRING 2003 No. 16

Page 5

A sequence of such noises, some with accompanying postural actions, registers increasing disquiet and aggression directed at other individuals, for example when contesting food or den occupancy. This begins with the ‘moan’, voiced while the eyes are fixed on the target individual, an ottery glower, as a way of issuing a threat. Next comes bouts of high pitched ‘yickering’ or ‘wickering’ – both are ‘warning off' signs, much like a dog growling, commuting the need to resort to overt aggression. Finally, if the situation escalates further these calls transpose themselves into a high wailing or caterwauling, sometimes from both animals, a noise said to resemble fox cries or a cat fight. Cubs at play imitate these same aggressive encounters, making threats and challenges, wickering and dashing around, or producing high pitched rattling sounds, often grading into shrieks and wails during a rough play fight.

So what does it all mean

Field observations have given insights into otter vocalisations, but a further dimension is revealed by scientific investigation. In one recent study of captive otters, the behaviour of a male, a female, two juveniles and two cubs was filmed and observed for 8 months, with each episode of acoustic communication analysed, based on the categories devised by Dr Rogoschik. Data was collected on uttered sounds, participating individuals and their proximity, postures and behaviour before, during and after vocalisation. Results (see below) showed that vocal interaction was indeed quite complex, often with accompanying actions and postures.

Eight types of otter vocalisations (after Rogoschnik, 1989)

1. Hiss (often with head movement) – approach to individual
2. Snort (often with head movement) – approach to individual
3. Moan (head still, eyes fixed on target individuals) – threat sound
4. Chuckle used in a variety of social situations, at short distances
5. Chuckle-chitter
6. Chitter
7. Squeal
8. Whistle – contact over long distances, especially between mother and cubs, often in long sequences

The most frequent situations involving acoustic communication were parental contacts, between female and male to the cubs (and to the human researchers) and cubs towards the female (but interestingly, not so much to the male or juvenile otters), and during play activity. It emerged that vocalisations occurred preferentially on land and along the riverbanks and rarely while fishing, travelling, feeding or sprainting. Furthermore it was discovered that use of various calls were unevenly distributed across the different senders and recipients.

This prompts all sorts of questions and theories. Could some otters be more extrovert and vociferous than others, or have certain idiosyncrasies? Or might it be that captive otters behave differently than wild ones? It seems that vocal communication is particularly important in two aspects of the otter’s life: firstly as a cub and for the rearing of cubs, to maintain contact and during play, and secondly, as an adult, to serve as a spacing mechanism, establishing and preserving personal distances and thereby precluding direct conflict and aggression.

Comparative studies with other otter species, the South American Giant Otter (Ptenonura), suggest this would be consistent with the European otter’s more solitary lifestyle. The Giant Otter lives gregariously and uses a much more elaborate system of screams, wails, barks and explosive snorts as well as many intermediate types of calls.

We may never be able to work out how an otter is thinking. But at least now when walking along the riverbank, we might have some idea of the things they are talking about.

Reference: Acoustic communication and related behaviour of captive otters (Lutra lutra) by Claudio Gnoli, Claudio Prigioni & Paola Polotti (from the internet)

Teach yourself Otter
Part 1: In the restaurant

Stephen Carroll

Otter spotting in Dublin

One of Ireland's national treasures is the book of Kells, a manuscript copy of the Gospels produced sometime around the eighth or ninth century and now housed in the library of Trinity College, Dublin. It is famous throughout the world for the beauty and intricate designs if its decorated pages. On one page of the book, which has been described as 'the finest expression of Celtic illumination', the artist has included a small vignette of an otter with salmon in its mouth. It is probable the earliest surviving image of an otter in Europe and is just one of a number of pictures of animals and birds which appear throughout the book.

Aidan Meehan has made a detailed study of the illustrations in the Book of Kells and he has emphasised the deeper meaning which lies in the religious symbolism of the images of wildlife which appear in its pages. "The person who painted this perfect cameo of an otter was not an observer of nature in an artistic or scientific sense, but more as one who looks for clues as to the meaning in life itself, in which natural events are approached as metaphors for hidden meanings". Meehan suggests one possible interpretation of the picture as the human soul, being caught and lifted up out of its own element and transformed by Christ, depicted as the otter.