3.5 Senses: smell
Smell is rightly emphasised in LoM as important to carnivores. It offers advantages over visual and sound signals, which may be difficult to detect, for example at night or in dense vegetation. Furthermore, scent marks 'hang around' longer. The most familiar examples are the urine and faeces deposited regularly at special places.
Who is not familiar with the male dog that leaves token amounts of urine to re-anoint the same lamp post each day? By cocking their legs they raise the level of the scent mark to the nose level of other individuals of the same species (i.e. conspecifics). Wolves also scent mark by urinating; dominant animals are said to do so as often as once every three minutes or so - and indeed more frequently near to the borders of their territory, where they are likely to encounter the scent from strangers.
Watch the TV programme from 13.03-16.03 on prey capture and scent marking in the brown hyena. Write down a brief summary of the ways in which scent is used when marking grass.
There are two components to the deposits they leave on grass. The one that is longer-lived (and positioned lower) is rich in fat and milky white when first deposited and lasts several weeks. It is thought to signal to other clans of hyenas to 'keep out' - the area is already occupied. The black paste above it is shorter-lived and is thought to convey information important to the other hyenas in the group.
It may well be that the black paste marks an unproductive hunting area, its fading reflecting time elapsed since recent bouts of futile hunting. Each individual brown hyena is estimated to deposit close to 3000 scent marks a year from their anal pouch, in conspicuous and usually elevated sites. Stoats too leave scent marks, here to claim territory, and their sense of smell develops at a very early age. As you read in LoM [p. 125], young female pups are already able to smell and identify a mature male, inviting him to copulate - even though they are too young to have opened their eyes or to reproduce.
The African civet marks its territory with powerfully scented dung heaps. It marks its food using the secretion of glands on its neck and chin; but its most famous scent, produced by another gland, is valued by the makers of the most expensive perfumes. This perineal gland is a small pouch between the anus and the tail and produces several grams each week of a powerful-smelling oily secretion.
The European badger displays 'squat-marking' - pressing the rear end to the ground, to leave a scent mark of gland secretions and faeces. The boundaries of a badger's territory are marked in such a way. Both sexes squat-mark but males do so more often than females, and dominant females more frequently than subdominant ones. They also squat-mark bedding before taking it into the set.
As well as marking objects, it is common for canids, felids, mustelids and viverrids (see Table 1) to mark other members of the species - so-called social marking. A badger squat-marks on the flank of another badger; the frequency of marking in a social group is related to the position occupied in the hierarchy. A dominant boar in a group of six adult badgers has been shown to be responsible for nearly 70% of all social marking. On the darkest night, badgers will sniff each other's flanks, implying recognition by smell. Similarly, domestic dogs sniff each other's anal region; hyenas do so with even greater enthusiasm during their encounters, broadening their attention to the genital areas.
On the basis of what you've read in this section, how important do you consider the sense of smell to be in the life of carnivores? Now speculate on how it could influence group behaviour. (There will be some answers in the section that follows.)
You may have noticed a mention of David Macdonald's The New Encyclopedia of Mammals in this section. If you feel that you would like to follow up in more detail some of the issues that have been raised in this series of units, then I recommend this book.