Neighbour–stranger call discrimination in a nocturnal rail species, the Corncrake Crex crex

Abstract

The acoustic signals of birds are commonly used for individual recognition. Calls or songs allow discrimination between parent and offspring, between mates and between territorial neighbours and strangers. In this study, we investigated vocal neighbour-stranger discrimination in a nocturnally calling rail species, the Corncrake, Crex crex. We conducted interactive playback experiments with 43 males. All males were tested twice on the same night, and their responses to the calls of a familiar neighbour and the calls of an unfamiliar stranger were measured. The Corncrake males responded more aggressively to the playback of a stranger's calls. They approached the speaker more rapidly, spent more time close to the speaker and physically attacked the speaker more frequently. We found no significant differences between the vocal responses to the playback of neighbours' and strangers' calls. Thus, although calling plays an important role in Corncrake territorial interactions, it is only a first line of defence in which males signal aggression towards intruders by calling, similar to singing in passerines. The lack of differences in vocal responses and the presence of clear differences in other behavioural responses demonstrate that the absence of a differential vocal response does not imply the absence of discrimination. Although the individual nature of the Corncrake call has been mentioned in a few previous studies, this study provides the first experimental evidence that Corncrake males indeed use calls for neighbour-stranger discrimination.Notably, because of the Corncrake's dense wet meadow habitat and its tendency to signal at night, it is probable that acoustic individual discrimination in the Corncrake is crucial for making correct decisions during aggressive encounters with rivals.

Individually Specific Call Feature Is Not Used to Neighbour-Stranger Discrimination: The Corncrake Case

“…Similar proportions of males approached or attacked the speaker in this study and in our previous study of corncrake neighbour-stranger discrimination, a study in which we used natural calls produced by neighbours and strangers (Fig. 3) [9]. In the present study, however, male corncrakes did not appear to respond differently to artificial calls containing the PPDs of neighbours versus strangers: they were equally aggressive in both cases.…”

The evolution of vocal learning

“…Nottebohm further doubted that vocal learning does anything to enhance vocal recognition, as logically the increases in vocal repertoire size allowed by vocal learning should make recognition harder, not easier. Additional examples of individual recognition of unlearned vocalizations have come to light since Nottebohm's criticism [53,54 ], making the case for an 'individual recognition' advantage even more dubious. Explicit tests of the effects of vocal production learning on individual recognition would help to clarify further the position of this individual recognition hypothesis.…”

Individual Signature in a Lekking Species: Visual and Acoustic Courtship Parameters May Help Discriminating Conspecifics in the Houbara Bustard

“…Songbirds acquire vocalizations by learning and might consequently produce a large range of acoustic variations in their songs, facilitating conspecific individual recognition and discrimination (Beecher 1982;Pytte & Suthers 1999). Individual signature has also been demonstrated in species producing vocalizations which are not culturally transmitted and are syntactically simple, but nevertheless support complex information, for example, in Pelecaniformes (McGregor & Byle 1992), in Gruiformes (Budka & Osiejuk 2013) and in Sphenisciformes (Jouventin & Aubin 2002).…”