Species delimitation within the Glaucidium brodiei owlet complex using bioacoustic tools

Abstract

Background: The taxonomy of the Collared Owlet (Glaucidium brodiei) species complex is confused owing to great individual variation in plumage colouration seemingly unrelated to their distribution. Although generally recognised as a single species, vocal differences among the subspecies have been noted by field recordists. However, there is no study assessing the vocal differences among these four subspecies. Methods:We obtained 76 sound recordings of the G. brodiei species complex comprising all four subspecies. We conducted bioacoustic examinations using principal component analysis and the Isler criterion to quantitatively test species boundaries within the G. brodiei complex. In addition, we compared plumage colouration among 13 specimens of the G. brodiei complex deposited at the Natural History Museum at Tring, UK and the Lee Kong Chian Natural History Museum, Singapore to ascertain the presence of plumage differences across taxa. Results:We found the Bornean and Sumatran populations vocally similar to each other, but distinctly different from the mainland and Taiwan populations. The vocal pattern seems to corroborate plumage distinctions in the colouration of neck collars: the Bornean and Sumatran taxa share a white neck collar, whereas the continental and Taiwan taxa share a rufous neck collar. Conclusions:We propose the taxonomic elevation of the Sumatran and Bornean populations to species level as Sunda Owlet G. sylvaticum, with one subspecies on Sumatra (G. s. sylvaticum) and Borneo (G. s. borneense) each. Our study corroborates the importance of bioacoustics in ascertaining species boundaries in non-passerines, and emphasises the significance of incorporating multiple species delimitation approaches when making taxonomic decisions.

The interplay of colour and bioacoustic traits in the differentiation of a Southeast Asian songbird complex

“…The Isler criterion is based on two conditions: (i) the ranges of measurements between two populations must not overlap, and (ii) the means () and standard deviations ( SD ) of the population with lower measurements ( a ) and the population with higher measurements ( b ) have to fulfil the following equation: , where t i refers to the t‐ score at the 95th percentile of the distribution for n − 1 degrees of freedom. The Isler criterion was initially devised for New World antbirds (Isler et al., 1998), but has since been applied across various songbirds (Cros & Rheindt, 2017; Gwee et al., 2019a; Prawiradilaga et al., 2018) and nonoscines (Gwee et al., 2017, 2019b; Ng et al., 2016; Ng & Rheindt, 2016; Rheindt et al., 2011; Sangster & Rozendaal, 2004).…”

“…refers to the t-score at the 95th percentile of the distribution for n − 1 degrees of freedom. The Isler criterion was initially devised for New World antbirds (Isler et al, 1998), but has since been applied across various songbirds (Cros & Rheindt, 2017;Gwee et al, 2019a;Prawiradilaga et al, 2018) and nonoscines (Gwee et al, 2017(Gwee et al, , 2019bSangster & Rozendaal, 2004).…”

The interplay of color and bioacoustic traits in the speciation of a Southeast Asian songbird complex

“…where t i refers to the t-score at the 95 th percentile of the distribution for n -1 degrees of freedom. The Isler criterion was initially devised for New World antbirds (Isler et al, 1998), but has been applied across various songbirds (Cros & Rheindt, 2017;Prawiradilaga et al, 2018;Gwee et al, 2019b) and non-oscines (Sangster & Rozendaal, 2004;Gwee et al, 2017;Gwee et al, 2019a).…”

Taxonomic revision of the Savanna Nightjar (Caprimulgus affinis) complex based on vocalizations reveals three species

“…Most species of nightjars and owls have a cryptic plumage which has long hampered taxonomic study of their species limits. During the last two decades, quantitative comparisons of songs have helped clarify species limits in several groups, including pygmy owls [Glaucidium [Howell and Robbins 1995;Gwee et al 2019)], scops owls [Otus (Rasmussen et al 2000;Sangster et al 2013)], screech owls [Megascops (Krabbe 2017;Dantas et al 2021)], hawk owls (Ninox [Rasmussen et al 2012;Gwee et al 2017]) and nightjars [Caprimulgus ( [Sangster and Rozendaal 2004)]. Three aspects make songs in these groups useful for taxonomic purposes.…”