An extralimital Ixobrychus record from the Solomon Islands

Ixobrychus is a widespread genus, with 10 species recognised globally. Two Ixobrychus species have been recorded on islands of the Solomon Archipelago (Billerman et al. 2022). Yellow Bittern (Ixobrychus sinensis) has historically occurred on Bougainville as a highly localised breeding resident and Black Bittern (Ixobrychus flavicollis) is a widespread breeding resident throughout (Dutson 2011).

Tetepare Island (8°45′S, 157°32′E) in the Western Province of the Solomon Islands, remains the largest uninhabited island in the South Pacific. Over 80 avian species have been recorded on the island, including I. flavicollis via an incidental record prior to 2006 (Read and Moseby 2006). Here we present an unidentified Ixobrychus species that was photographed on Tetepare on 1 September 2023 (Fig. 1). The bird was incidentally detected by sight by the authors and was recorded <5 m above sea-level in secondary rainforest, close to beach-forest interface. Prominent black chevrons across wing coverts and scapulars, black crown feathers with light margins and buff tertial tips may suggest an immature bird. The combination of black chevrons, black primaries, and lack of white spotting on upperparts rule out morphologically similar species including Ixobrychus cinnamomeus, Ixobrychus dubius and Ixobrychus eurhythmus (see Supplementary material Fig S1 and File S1). Feathers were not worn, suggesting this bird was not in a moult phase (Jenni and Winkler 2020). Hybridisation between Ixobrychus species has been considered unlikely. Bittern hybrids are rarely reported, with the subject bird not representative of either I. flavicollis or I. sinensis; the only two locally occurring bitterns. The subject bird is noticeably smaller than I. flavicollis. Lack of geographic overlap of other morphologically similar species and the immature status of the subject further suggest that this bird is unlikely a hybrid and is of local origin (I. McAllan and D. James 2023, pers. comm., R. Hutchinson 2024, pers. comm.).

Fig. 1.

An unidentified Ixobrychus bittern recorded on Tetepare Island, Solomon Islands. Image depicting distinct chevrons across the scapulars and wing coverts, a unique field mark of this bird. Photo credit: Maxwell de Beer.

Biodiversity, including avifauna, in the Solomon Islands remains understudied. While few ornithological surveys have taken place on Tetepare in recent times, new island records continue to be documented (McCullough et al. 2023). The documentation of new geographic records and potential identification of an undescribed species is of immense significance for the conservation of remaining habitat in the Solomon Islands. Tetepare is of critical importance for biodiversity conservation in the region and remains an outstanding model for conservation led by Traditional Owners. Future research is essential to further document this species where we recommend non-lethal sample collection for genetic-based analysis.

Supplementary material

Supplementary material is available online.