Introduction

Compared with communication in other sensory domains and with scents that are released into the air, scent marking is unusual because the signal remains long after the signalling behaviour; for example, the flank gland marks of male golden hamsters Mesocricetus auratus deposited on glass in the laboratory are detected by other hamsters 40 days later and vaginal secretion marks are detected at least 100 days after deposition (Johnston & Schmidt, 1979). In the field, the paste scent marks deposited by brown hyaenas Crocuta crocuta can be detected by humans for at least 30 days (Gorman, 1990) and klipspringers Oreotragus oreotragus respond to preorbital gland marks that have been exposed to direct sun for at least seven days by an increase in scent marking (Roberts, 1998). In many species, especially those that live solitarily, there is often no receiver present when the marks are deposited. Consequently, scent marks are necessarily general broadcast signals that usually have several functions, depending on the age, sex, reproductive status, social status and individual identities of both senders and receivers.

One type of marking, scent counter-marking, is directed at the scent marks of other individuals, but again these individuals are often not present to observe the signalling behaviour. I consider the term scent counter-marking to include two different types of behaviour: (a) over-marking, in which the second individual's scent at least partially overlaps that of the first individual; and (b) adjacent marking, in which the second individual's scent is close to that of the first individual but does not overlap it.