Function of vocalization length and warble repertoire size in orange-fronted conures

Bird vocalizations consist of songs and calls. The calls tend either to be given singly or to consist of multiple elements given in a rapid string. The multi-element bird calls of some nonpasserines resemble passerine song and can contain many diverse elements. Multi-element vocalizations can change the signal message by varying the number of elements and/or the diversity and selection of element types. The use of multi-element variation has been extensively studied in passerine songs, but only rarely in nonpasserines. Here we examined two multi-element vocalization types in a wild parrot, the orange-fronted conure, Eupsittula canicularis: 'warbles' consist of diverse elements (heterotypic) whereas 'peaches' consist of repetitions of the same element (homotypic). Both call types are used in aggressive interactions between pairs or flocks. We used playbacks to wild conure flocks in Costa Rica to determine whether the number of elements (both types) and/or the diversity of elements (warble repertoire size) produced differentiable responses. Both short and long peach call series usually elicited retreat, but longer series led to reduced warbling and increased soft contact calls (zip calls) when responses were compared with those of short series. The warble stimuli mainly affected the approach behaviour leaving most call rates unaffected: more flocks left the area in response to long warbles with large repertoires, whereas short, small repertoire stimuli resulted in a closer approach. Both experiments showed that the length of both types of multi-element call and element diversity in warbles are salient to the wild conures. The results suggest that longer series of both call types and higher diversity warbles may be perceived by the birds as more aggressive, leading to the observed patterns of approach, retreat and interaction. The results suggest that vocal complexity in parrots has a signal value similar to that found in passerines.