Signal behavior in cranes (the Siberian Crane Sarcogeranus leucogeranus, the White-naped Crane Grus vipio, and the Red-crowned Crane Grus japonensis) in the context of the ritualization hypothesis

Abstract

Signal behavior of three crane species was chosen to test the logic of the ritualization hypothesis. Its claims to explain the origin and functioning of the “highly ritualized” communication signals in birds are discussed. It is shown that such signals are observed in a wide range of situations, including those in the absence of a social partner for communication (perceiver). In its presence a signal may be performed in a way that it cannot be perceived by the partner. The same actions (“ritualized preening”) vary in length and intensity, and such variability is present in nearly all situations. In each situation, it is difficult to discriminate between the ritualized preening and actual comfort behavior. It may take place even when a social partner is present. Short preening that may be readily considered as ritualized signals are more common in the all situations, including those with an absent partner. The endogenous cyclicity in unison calling by mates indicates that communication cannot be regarded as a simple exchange of signals in accordance to the ‘stimulus-reaction’ principle. Similar actions by the more ancestral Siberian Crane may appear to be more ritualized than in the evolutionary advanced Red-crowned Crane. All these findings contradict the concept of emancipation and ritualization of behavioral actions during evolution and selection for increasing communication efficiency. According to that hypothesis, during this process such actions, due to selection for more efficient communication, evolve into discrete meaningful communication signals (displays). They stand out against the background of the monotonous, unexpressive (non-signal) everyday behavior and thus appear as the main carriers of information serving principal communication functions. A more realistic approach seems to be the understanding of communication as a process of a continuous mutual fine-tuning of the social partners’ behavioral attitudes towards each other. In either participant, its behavior is an integral structure, inseparable into categories of more or less important signals (flow of behavior). Even minor changes in performance by one individual reflect alteration in its motivational state which, in its turn, changes that of the other participant and the subsequent lines of its behavior.