Crane dances as play behaviour

All species of crane (Gruidae) engage in a spectacular behaviour known as dancing (Ellis et al. 1998). Crane dances have inspired humans since the Stone Age (Russell & McGowan 2003), and imitation dances are known in numerous human cultures worldwide (Armstrong 1943). However, the function of this behaviour is poorly understood, and explanations for it are sometimes contradictory. Lorenz (1963) considered crane dance to be an appeasement ceremony. However, this explanation cannot be true in many situations in which dances are performed. Cranes dance most often when relaxed, and often while not involved in any obvious social interaction; they also sometimes dance while alone (Potapov et al. 1987; V. Dinets pers. obs.). It is known that dances are particularly common in unpaired sub-adults; a common explanation is that dancing facilitates socialization and pair formation (Archibald & Meine 1996). However, sub-adults in well-established flocks dance more often than in those in recently formed flocks, where the need for socialization would presumably be higher (Potapov et al. 1987). Also, birds begin dancing very early in life, sometimes when just 2 days old, long before they are old enough to form pairs (Archibald & Meine 1996). In the reintroduced flock of Whooping Crane Grus americanus in Louisiana, year-old birds in flocks dance frequently (V. Dinets pers. obs.), even though cranes of this species do not start breeding until they are at least 2, and more commonly 3 years old (Allen 1952). Interestingly, yearlings that are not in flocks dance less often (V. Dinets pers. obs.); adults in established pairs seldom dance (Archibald & Meine 1996). So while it seems likely that dancing is a form of social behaviour, it seems unlikely that its primary function in subadults is socialization and pair formation. Dancing can also serve as displacement activity when cranes are nervous, but in most cases it is not performed in response to readily apparent stimuli (Archibald & Meine 1996). It usually occurs when the birds are relaxed and at ease (Potapov et al. 1987) and is often contagious (Archibald & Meine 1996). At the autumn staging grounds of Demoiselle Crane Antropoides virgo in Mongolia, thousands of individuals can sometimes be seen dancing at the same time (V. Dinets pers. obs.). Finally, it is important to note that courtship rituals of cranes involve prolonged bouts of dancing. In this case, the function of dancing seems to be obvious. But this is unlikely to apply to dances by immature birds, unpaired adults and migratory/ wintering flocks. Cranes are known to be playful birds. Although no study of play behaviour in cranes has been published, people working with captive cranes report that play behaviour is common, particularly in juveniles and sub-adults. Such observations exist for Whooping and Sandhill Grus canadensis Cranes (J. Chandler pers. comm.), for Redcrowned Grus japonensis, White-naped Grus vipio, Common Grus grus, Siberian Grus leucogeranus, Hooded Grus monachus and Demoiselle Cranes (V.E. Flint pers. comm.), and for Grey Crownedcrane Balearica regulorum (B. Machedra pers. comm.). Re-introduced Whooping Cranes (yearlings) in Louisiana have been reported to play with Styrofoam duck and geese decoys, sometimes breaking them apart in the process (P. Lamartiniere pers. comm.). On some occasions, dancing is combined with object play (T.L. Perkins pers. comm.). It is reasonable to suggest that dancing is also a form of play behaviour, at least when performed outside a pair-forming context. This has been suggested before (Archibald & Meine 1996), but only in passing. Burghardt (2005) developed a set of five criteria for determining whether a certain behaviour can be classified as play. These criteria are now widely *Email: dinets@gmail.com