Species limits in the Elegant Pitta (Pitta elegans) complex from Wallacea based on bioacoustic and morphometric analysis

Abstract

Background The Elegant Pitta (Pitta elegans) complex displays a remarkable diversity of morphological and bioacoustic traits across five taxa currently recognized as subspecies. They differ in plumage characteristics (such as red versus black belly patches; supercilium color and extent; and white versus black throats), in lifestyle (resident versus migratory) and in vocalizations. We investigated the morphological, bioacoustic and ecological differences across all taxa after recent studies demostrated the importance of these traits in recognizing biological species limits across pittas. Methods Morphometric analysis was carried out by measuring tarsus, wing, tail and bill lengths of 15 specimens at the Natural History Museum, UK, and plumages were inspected across 106 unique individuals from four different repositories. Bioacoustic analysis was based on 134 range-wide sound recordings. Two types of calls, territorial calls and alarm calls, were analyzed using different sets of parameters. Principal component analysis and the Isler Criterion were applied to the measurements. Playback trials were conducted to explore the levels of response of each taxon to the call types of the other taxa. Results The territorial call of concinna exhibits a distinct two-element motif, while elegans, maria and virginalis utter a three-element motif in which the first two elements are given in quick succession. On the other hand, vigorsii, produces both two-element and three-element motifs with longer breaks in between elements. As further corroborated by the playback trials, the three taxa elegans, virginalis and maria form a tight vocal cluster, whereas each concinna and vigorsii are distinct. The alarm call turned out to be less diagnostic even though most taxa did roughly separate into different vocal clusters. Morphometric analysis failed to produce strong differences, but plumage distinctions among multiple taxa are pronounced. Conclusions We suggest splitting the Elegant Pitta into three biological species based on bioacoustic and—less so—plumage evidence: (1) Temminck’s Elegant Pitta P. elegans (including subspecies elegans, virginalis and maria), (2) Wallace’s Elegant Pitta P. concinna (monotypic), and (3) Banda Elegant Pitta P. vigorsii (monotypic).