Príncipe Island (1°31.80'N–1°43.20'N, 7°19.80'E–7°28.20'E) is located in the Gulf of Guinea, ca. 220 km offshore Gabon (Fig. 1). Part of the Cameroon Line of Volcanoes, its oldest sub-aerial rocks date to the origin of the line at ca. 30 Ma (Burke 2001). With a surface area of 139 km² (ca. 17 km long and 8 km wide), it has a relatively flat low-lying area in the north, contrasting with the rugged central and southern region characterised by high ridges that rise up to 948 m a.s.l. at Pico do Príncipe (Jones and Tye 2006). It has an oceanic equatorial climate, with an annual precipitation that can reach 5,000 mm. Most of the accessible regions of the island were cleared and converted to plantations (Jones and Tye 2006). Some of those areas were abandoned and regenerated into secondary forest (Atkinson et al. 1991; Castanheira-Diniz and Cardoso-de-Matos 2002; Jones and Tye 2006). The remaining area is covered with two types of native forest stratified by altitude: lowland and montane rainforest, the latter being restricted to Pico do Príncipe and the surrounding summits (Exell 1944).

Figure 1. 

Altitudinal A and land use maps B of Príncipe Island, with the limits of the Príncipe Obô Natural Park (PONP) and its buffer zone, and the two localities where the four individuals of the candidate species of Otus from Príncipe were captured; inset: location of Príncipe in Africa.

Fieldwork for specimen and tissue sample collection, measurements, and additional bioacoustics recordings took place in May 2017, July 2018, and January 2019. All samples and vocalisation recordings were collected within Príncipe Obô Natural Park, in the south of Príncipe (Fig. 1). Locality information was recorded using a GPS receiver (Garmin GPS Map 62s; Garmin International Inc., Olathe, Kansas, United States).

On May 29, 2017, in the Ribeira Porco area (1°33.03'N, 7°22.29'E, Fig. 1), one individual was captured using mist-nets (Fig. 2A), measured and a blood sample collected. This individual was euthanised by inhaling an Isoflurane 1 mL/5 L solution, dissected, fixed with absolute EtOH, and preserved in 80% EtOH. Afterwards, the specimen was prepared as a study skin and spread wing, and the partial skeleton was prepared following a modified procedure (Cataldo 2017) from that described by Davis and Payne (1992) and Baker et al. (2003). Previously to being captured, recordings of its vocalisations and of those of a second bird were obtained using a recorder (Edirol R-09HR, Roland, Japan) and a microphone (MKE 400, Sennheiser, Germany); these were elicited by playing back previously recorded vocalisations of this taxon to attract it into the nets. The voucher specimen was photographed to document life colouration and appearance (Fig. 2A). The voucher was deposited in the ornithological collection of the Natural History and Science Museum of the University of Porto (Table 1).

Figure 2. 

The candidate species of Otus from Príncipe A female specimen MHNC-UP-AVE7000, showing colouration in life (available also in the Macaulay library (ML): ML470442301; grey-brown morph) B female (left, sample P9-037) and male (right, sample P9-038) grey-brown morphs captured at Boca do Inferno on January 28, 2019 (ML470438621) C rufous morph individual photographed at Ribeira Porco area on July 04, 2016 D daytime sighting of a grey-brown morph individual between Rio São Tomé and Ribeira Porco on January 19, 2019 (ML470443361, only the rufous upperparts are clearly seen) E grey-brown morph individual photographed in the Ribeira Porco area on January 21, 2019 F fully developed brood patch of a female rufous morph (sample P8-001) captured in the Ribeira Porco area on January 20, 2019 (ML470440211). ML – Macaulay Library. Photographs: A – HP B, D, F – MM and BF C – PV E – Paul van Giersbergen.

In this study, species diagnosis was based upon four lines of evidence: morphometrics, plumage colouration and pattern, song, and DNA sequence data.

Species and subspecies limits of scops-owls are challenging to ascertain, leading to numerous taxonomic arrangements. This study follows the taxonomic arrangement and nomenclature of The Clements Checklist of Birds of the World (Clements et al. 2021). Terminology and description scheme follow Sangster et al. (2013), and the features used for the description are depicted in the Suppl. material 3. Description of colour in life is based on the holotype, with some reference to variation as observed in specimens photographed in the field (Fig. 2).

Four scops-owl individuals from Príncipe (including the vouchered specimen) were captured in the field. These were measured together with representatives of four of the five species of the Afro-Palearctic clade (sensu Pons et al. 2013) and O. brucei obsoletus (Cabanis, 1875). The latter was included due to the potential affinities of O. brucei (Hume, 1872) with African species (Pons et al. 2013). The Arabian Scops-Owl O. pamelae Bates, 1937 was not included, but we measured individuals of O. senegalensis feae (Salvadori, 1903) from Annobón Island, considered by some authors as a distinct species (Collar and Boesman 2020; Gill et al. 2021). The morphometric dataset includes measurements collected from museum specimens and living individuals measured in the field (Table 1).

Measurements were taken as follows: bill length from the bill tip to where the culmen enter the feathers (Bilen); bill length from the anterior end of the nares to the tip (Binares); bill width (Biwid) and bill depth (Bidepth) at the anterior end of nares; head+bill (Hebi), from the tip of the bill to the opposite point on the back of the skull; middle toe length (Midt); tarsus length (Tarlen), from the tibiotarsus joint to the distal end of the tarsometatarsus, when the foot is held to the leg; tail length (Tailen), from where the ruler stops at the root of the central pair of rectrices and to the tip of this same pair (by sliding the ruler between the rectrices and the undertail coverts); body length (Bolen) from the top of the head to the tip of the central pair of rectrices; wing length (Wilen), flattened, from the carpal joint to the tip of the longest primary; wing formula, sequence of primary feathers ordered by size; and length of primary feathers (P4–P10, in which P1 is the closest to the body), which were transformed in shortfall of P4–P10 to tip of longest primary. Body, wing, and tail length were measured with standard wing and tail rulers to the nearest 1.0 mm. The length of the primary feathers was measured to the nearest 1.0 mm with a ruler with a pin at the origin; the pin is inserted between two primary feathers until it touches the skin (Jenni and Winkler 1989). All other measurements were made using a digital calliper (Mitutoyo CD-P15K, Mitutoyo Corporation, Kawasaki, Japan) to the nearest 0.1 mm. All measurements were collected by MM, BF, and RL (Table 1). A constant of one was added to each number to make all shortfalls non-zero. All mea­surements were log-transformed (base-10) to normalise distributions (McDonald 2014).

The four individuals from Príncipe were sexed with a molecular protocol (Griffiths et al. 1998), and comprised three females and one male (Table 1). For the statistical analyses males and females were treated together due to the low sampling size, and the fact that most museum specimens were not sexed.

Morphometric differences were explored using a Principal Component Analysis (PCA), performed using the FactoMineR package (Lê et al. 2008) and carried out using R v. 3.6 (R Core Team 2017) in RStudio v. 1.1.447 (RStudio Team 2015). Measurements were size-standardised to prevent the dominance of variables invol­ving larger measurement units, thus allowing comparisons between variables. The wing formula was not used in the analyses. Since several individuals had missing data, to maxi­mise the number of analysed specimens of each species only the following variables were used in the PCA: Bilen, Binares, Biwid, Tarlen, Wilen, and Tailen. This dataset included 44 specimens from seven taxa, including three individuals from Príncipe. Welch’s ANOVA (recommended for unbalanced designs, different samples sizes, and different standard deviations; McDonald 2014), was used together with Games-Howell post-hoc comparisons to test whether the groups differed from each other.

We used colour standards (Köhler 2012) to describe the plumage of the species of the Afro-Palearctic clade, except for O. pamelae, but including O. senegalensis feae (see Suppl. material 6). The topographic terms of the scops-owl body are detailed in the Suppl. material 3.

We compared the calls of the candidate species with the calls of scops-owls from the Afro-Palearctic clade, O. brucei, and the Sokoke Scops-Owl O. ireneae Ripley, 1966 (Tables 2, 3). Otus ireneae is not part of the Afro-Palearctic clade but was included because it has the most similar calls to the ones of the candidate species. Recordings were collected from Xeno-canto (XC; www.xeno-canto.org), Avian Vocalizations Center (AVoCet; https://avocet.integrativebiology.natsci.msu.edu), The Internet Bird Collection (www.hbw.com/ibc), the private collection of PV and the collection of vocalisations obtained during fieldwork on Príncipe by co-authors. Newly collected calls were deposited in Xeno-canto (Suppl. material 7). From each independent source, only one recording was used (unless there were only very limited recordings available). In total, 43 recordings from ten taxa were analysed (Suppl. material 7). In most owls, both sexes produce similar calls for territorial defence, mate attraction, and pair-bonding (Marks et al. 1999; König et al. 2008), therefore our analyses included both male and female recordings. Vocalisations of scops-owls are generally made up of a simple primary call composed by the repetition of the same note (Marks et al. 1999). The call of the Cyprus Scops-Owl O. cyprius (von Madarász, 1901) is composed by the coupling of one long and one short note (Flint et al. 2015), and both note types were included in the analysis. The candidate species primary call is characterised by a repeated note (Suppl. material 4: Fig. S2A, B), but its repertoire also includes a cat-like “kee-a-u” note (Suppl. material 4: Fig. S2C, D). The latter was not included in the analysis.

Recordings were sampled using a 16-bit accuracy and a sampling rate converted to 12 kHz in Avisoft-SASLab pro v. 4.3 (Avisoft Bioacoustics). The following 16 variables were collected for each note: F1, frequency at start (peak frequency at 0s, Hz); F2, frequency at end (peak frequency at last of four call intervals, Hz); F3, frequency at 25% of total duration (peak frequency at the first interval, Hz); F4, frequency at midpoint (peak frequency at the second interval, Hz); F5, frequency at 75% of total duration (peak frequency at the third interval, Hz); F6, frequency at maximum amplitude (frequency at maximum amplitude of note, Hz); F7, maximum frequency (maximum frequency through the note, Hz); F8, minimum frequency (minimum frequency through the note, Hz); DT1, total duration (duration, s); DT2, time to maximum amplitude (time to maximum amplitude of note, s); DT3, time to maximum frequency (time to maximum frequency of note, s); DT4, internote interval (start time – end time of previous note, s); DF1, frequency drop from start to end (F2-F1, Hz); DF2, frequency range (F7-F8, Hz); DFT1, slope from 25% to 75% of total duration ([F5-F3]/∆t, Hz/s); DFT2, slope from midpoint to end ([F2-F4]/∆t, Hz/s). The 16 variables were extracted from the analysis of the spectrograms. We used a Fast Fourier Transformation size of 512 points, a 100% frame size and a temporal resolution overlap of 87.5% (flat top window type), resulting in a frequency resolution of 86 Hz and a temporal resolution of 4.5 ms. Frequencies were analysed between 0.5 Hz (highpass) and 2.25 Hz (lowpass), except for O. brucei with the highpass set at 0.0 Hz; the greyscale was set to 30%. When background noise hampered the measurement of the variables, frequencies were filtered and adjusted by shortening the interval between the highpass and the lowpass.

For each recording, variables were measured on six notes and their means (Suppl. material 8) were used as sample points to calculate the ranges, means and standard deviations for each taxon. A constant of 3000 was added to each computed value to ensure that the dataset only included positive numbers. All measurements were log-transformed (base-10) to normalise distributions (McDonald 2014).

PCA was performed using the FactoMineR package (Lê et al. 2008) using R v. 3.6 (R Core Team 2017) in RStudio v. 1.1.447 (R Studio Team 2015). Measurements were size-standardised to make the variables comparable. Welch’s ANOVA and Games-Howell post-hoc comparisons were used to test whether the groups differed from each other (McDonald 2014).

Blood samples were collected non-destructively from the brachial vein of mist-netted individuals and were stored in 96% ethanol for genetic analysis (see molecular dataset: Table 4). Blood samples of the scops-owl from Príncipe were collected at Boca do Inferno (1°36.16'N, 7°24.06'E, ca. 300 m a.s.l.) (n = 2) and close to Ribeira Porco (1°33.03'N, 7°22.29'E, ca. 100 m a.s.l.) (n = 2), both localities within Príncipe Obô Natural Park (Fig. 1; Suppl. material 9). We obtained four blood samples of O. hartlaubi (Giebel, 1872) from São Tomé (Suppl. material 9), and were lent one blood sample of O. senegalensis feae (Annobón), and one blood sample of Moheli Scops-Owl O. moheliensis Lafontaine & Moulaert 1998. We were lent additional samples from museum specimens, including toe-pad samples for one of each of the two subspecies of the Sandy Scops-Owl, O. icterorhynchus icterorhynchus (Shelley, 1873) and O. i. holerythrus (Sharpe, 1901), from the American Museum of Natural History, New York (AMNH) (Table 4).

Total genomic DNA was extracted from blood and tissue samples using an overnight Proteinase K digestion (10 mg/ml concentration) followed by a standard high-salt extraction method (Bruford et al. 1992). Before the extraction, blood was removed from the ethanol and left to dry in the incubator. Genomic extractions of toe-pads samples were performed using a specific protocol for museum samples (Dabney et al. 2013).

Mitochondrial and nuclear markers (mtDNA and nuDNA, respectively) were amplified and sequenced for the samples that were available to us. For mtDNA we amplified a fragment of the 12s and 16s ribosomal RNA genes (12S and 16S), ATPase subunit 6 (ATP6), cytochrome oxidase subunit I (COI), cytochrome b (CYTB), nicotinamide adenine dinucleotide dehydrogenase subunits 2 and 3 (ND2 and ND3). The nuDNA markers were: leucine-rich repeat and WD repeat-containing protein (KIAA1239), myoglobin intron-2 (MYO2), Recombination Activating Gene 1 (RAG1), sacsin (SACS), TGFb2 intron-5 (TGFB2), and titin (TTN).

Standard polymerase chain reactions (PCR) were performed in a final volume of 25 µl using 1 µl of each primer (10 pmol), 0.4 µl of total dNTPs (10 mM; Promega), 0.1 µl of 5 U/ml GoTaq Flexi DNA Polymerase (Promega), 5 µl of 5X Green GoTaq Flexi Buffer (Promega), 4 µl of MgCl₂ (25 mM; Promega). The first PCR of the fragments amplified using a nested PCR approach (KIAA1239, SACS, TTN) were performed in half total reaction volume (12,5 µl). Primers and PCR conditions are provided as Suppl. material 10. For the amplification of the toe pads, we amplified shorter fragments of the MYO2, ND2, and ND3 genes. Successfully amplified products were purified and sequenced using dye-labelled dideoxy terminator cycle sequencing on an ABI 3730XL automated sequencer at Macrogen Inc.

PCR amplification of CYTB and ND2 sequences of O. cyprius, O. i. icterorhynchus, Wallace’s Scops-Owl O. silvicola (Wallace, 1864), and four subspecies of the Mountain Scops-Owl (Blyth, 1846) [O. spilocephalus vandewateri (Robinson & Kloss, 1916), O. s. vulpes (Ogilvie-Grant, 1906), O. s. luciae (Sharpe, 1888), and O. s. hambroecki (Swinhoe, 1870)] was performed in seven fragments of ca. 180–200 bp using custom-made primers (see Suppl. material 10). PCR products were cycle-sequenced in both directions using the Big Dye Terminator v. 3.1. Sequences were read on an ABI 3100 capillary sequencer (Applied Biosystems, Foster City, CA, USA). Samples amplified and sequenced at Muséum national d'Histoire naturelle, Paris (MNHN) (Table 4) followed Pons et al. (2013).

Chromatograms of newly generated sequences were checked by eye, edited and aligned using BioEdit v. 7.0.5.3 (Hall 1999). All newly determined sequences were submitted to GenBank (accession numbers provided in Table 4).

Six different datasets were compiled for different purposes, detailed below.

This published work and the nomenclatural acts it contains have been registered in ZooBank, the online registration system for the ICZN. The LSID (Life Science Identifier) for this publication is: urn:lsid:zoobank.org:pub:0731A37D-B363-43C9-A1AC-69F5E10F6810. The electronic edition of this work was published in a journal with an ISSN, and has been archived and is available from the following digital repositories: https://zookeys.pensoft.net/.

Following the integration by congruence approach (Padial et al. 2010), we consider independent evolutionary lineages as separate species if two or more independent lines of evidence support their distinctiveness. The candidate species: i) differs in morphology from other Otus species (Fig. 3); ii) has a very distinct call (Tables 2, 3; Figs 4, 5); iii) forms a distinct monophyletic group (Fig. 6) that iv) differs from the nearest taxa by a mitochondrial uncorrected pairwise sequence divergence (p-distance) similar or larger than the divergence observed between other currently accepted sister species pairs of the genus Otus (Table 5); v) has no haplotype sharing at some of the analysed nuclear markers (Fig. 7). We interpret the concordance between these independent lines of evidence as strong support for its distinctiveness and species status (Avise and Ball 1990; Padial et al. 2010; Sangster 2018). Therefore, we conclude that the candidate species from Príncipe is a distinct species that we describe herein as Otus bikegila sp. nov., and for convenience we will use this name throughout the manuscript, anticipating its formal description below.

Figure 3. 

A Principal Component Analysis scatterplot of morphological measurements of Otus species and B the correlation circle in which ‘contrib’ corresponds to the contribution of the variables in accounting for the variability in the Principal components. Morphological measurement abbreviations – Bilen: bill length from bill tip to where culmen enters feathers; Binares: bill length from the anterior end of the nares to the tip; Biwid: bill width; Tarlen: tarsus length; Tailen: tail length; Wilen: wing length.

Figure 4. 

Oscillograms and spectrograms of 2-s sections of the song of O. bikegila sp. nov. (XC619448), O. hartlaubi (XC673669), O. senegalensis senegalensis (XC45502), O. senegalensis feae (XC340505), O. pembaensis (XC253581), O. pamelae (XC371431), O. scops (XC383983), O. cyprius (XC256102), O. brucei (XC158086), and O. ireneae (XC147630). Each section refers to an individual owl. For more information about the recordings used see Suppl. material 7. Codes from Xeno-canto.org database.

Figure 5. 

A Principal Component Analysis scatterplot of bioacoustics variables of Otus species and B the correlation circle in which ‘contrib’ corresponds to the contribution of the variables in accounting for the variability in the Principal components. Bioacoustic parameters – F1: frequency at start; F2: frequency at end; F3: frequency at 25% of total duration; F4: frequency at midpoint; F5: frequency at 75% of total duration; F6: frequency at maximum amplitude; F7: maximum frequency; F8: minimum frequency; DT1: total duration; DT2: time to maximum amplitude; DT3: time to maximum frequency; DT4: internote interval; DF1: frequency drop from start to end; DF2: frequency range; DFT1: slope from 25% to 75% of total duration; DFT2: slope from midpoint to end.

Figure 6. 

Multi-locus phylogeny of scops-owls (Strigidae: Otus). Phylogram (50% majority rule consensus tree) from a Bayesian Inference analysis of the dataset 2, including 12S, 16S, ATP6, COI, CYTB, ND2, ND3, KIAA, MYO2, RAG1, TGFB2, and TTN gene fragments. Asterisks denote posterior probabilities values: (*) 0.85–0.94, * 0.95–0.98, ** 0.99–1. Scale bar corresponds to 0.02 substitutions per site. Strix aluco was set as outgroups (not shown on the figure).

Figure 7. 

Haplotype network reconstruction for the nuclear KIAA, MYO2, TGFB2, and TTN gene fragments in Otus bikegila sp. nov., O. hartlaubi, O. senegalensis senegalensis, O. senegalensis feae, O. pembaensis, O. pamelae, O. scops, and O. brucei (when available). Area of circles is proportional to the number of individuals with that haplotype. The smallest circles (white) represent unsampled or extinct haplotypes.

In the PCA, the first two components presented eigenvalues higher than one (Suppl. material 11), representing 81.7% of the variation. PC1 (60.9% of the variance) was negatively correlated with all variables related with bill, tarsus length and tail length, whereas PC2 (20.8% of the variance) was positively correlated with wing length (Suppl. material 11). Otus bikegila sp. nov. is within the variation of O. pembaensis and separated from the other species (Fig. 3). All other taxa are separated from each other, except O. senegalensis feae that is within the variation of O. senegalensis senegalensis (Swainson, 1837).

For the Welch’s ANOVAs, O. brucei obsoletus was not included due to the small sample size. All variables differed significantly between species (P < 0.05), except Bidepth (Suppl. material 12). Games-Howell post-hoc test provided significant values for all the species only for Bilen and Biwid because of missing data from some specimens. This test was used to identify the morphological diagnostic characters detailed in the Diagnosis section.

In the PCA, four components presented eigenvalues higher than one (Suppl. material 13), representing 87.6% of the variation. PC1 (56.8% of the variance) mostly represented frequency characteristics of the note, being positively correlated with the frequency variables F1-F8, but also with DT1. PC2 (14.1% of the variance) mostly represented temporal characteristics of the note, being negatively correlated with DT2, DT3, DT4, and DF1. PC3 (9.1% of the variance) was negatively correlated with DFT1 and DFT2, and PC4 (7.6% of the variance) was positively correlated with DF2. Plotting individuals on PC1 versus PC2 (Fig. 5) confirmed our hearing-based assessment that the calls of O. bikegila sp. nov. are unique but closest to the ones from O. ireneae, both characterised by short notes repeated at a fast rate (Fig. 4). One sample of O. senegalensis senegalensis, also came close to those of O. bikegila sp. nov. but, otherwise, the calls of the new species are clearly separated from the other species of the Afro-Palearctic clade. Samples of O. brucei, O. pembaensis and the short note of O. cyprius are clearly distinct from all other species. Samples of the long note of O. cyprius overlap with samples of O. scops. Samples of O. pamelae and O. hartlaubi are contained in the variation of O. senegalensis senegalensis and samples of O. senegalensis feae and O. scops overlap with it.

Means of all bioacoustic variables differed significantly (P < 0.05) between species (Suppl. material 14). Low sample size prevented performing the Games-Howell post-hoc test between all taxa pairs. This test identified the bioacoustic diagnostic characters detailed in the Diagnosis section.

The ND2 sequences (Dataset 1; 1037 pb) of the four samples of Otus bikegila sp. nov. were identical (Table 5). Otus bikegila sp. nov. is a distinct mitochondrial lineage (Dataset 2; Fig. 6), belonging to the Afro-Palearctic clade. The genetic distance between this species and the other taxa included in Dataset 1 ranged between 4.1% (O. bikegila sp. nov. vs. O. hartlaubi and O. scops) and 9.1% (O. bikegila sp. nov. vs. O. brucei obsoletus). The smallest genetic distances were observed between O. senegalensis senegalensis and O. senegalensis feae (0.7%), followed by O. senegalensis feae and O. pamelae (3.0%); the highest value was recorded between O. bikegila sp. nov and O. brucei/O. hartlaubi (9.1%).

The concatenated sequences of the phylogenetic dataset (Dataset 2; 12,925 bp; Suppl. material 2) were optimally partitioned in seven partitions (Suppl. material 15).

The topology of the majority rule consensus tree (Dataset 2; Fig. 6) is largely in agreement with previously published phylogenies of the genus Otus (Fuchs et al. 2008; Pons et al. 2013), and increased the resolution of these by resolving some po­lytomies. An important improvement relatively to Fuchs et al. (2008) and Pons et al. (2013) was the inclusion of 13 additional taxa besides O. bikegila sp. nov. Otus icterorhynchus was found to represent a relatively basal lineage, sister to the clades containing the Afro-Palearctic and the Indo-Malayan/Indian Ocean species (PP = 1), rather than being sister to O. ireneae, as often hypothesised. The two subspecies of O. icterorhynchus were recovered as sister taxa, albeit with a very high genetic divergence (only one sample per taxon). Otus brucei (from the Arabian Peninsula to Asia) was the sister lineage to the Afro-Palearctic clade (PP = 1). Other novel insights are detailed in the discussion.

Otus bikegila sp. nov. samples were recovered as monophyletic, and formed a clearly distinct lineage belonging to the Afro-Palearctic clade. It was recovered as the sister lineage (PP = 1) of the clade formed by O. senegalensis senegalensis, O. senegalensis feae, O. hartlaubi, and O. pembaensis (Fig. 6).

The best model of sequence evolution for each marker used for the divergence times analyses are listed in the Suppl. material 16. The genus Otus started to diversify ca. 7.8 mya (95% high posterior density [HPD]: 6.2–9.6). The two primary cla­des diverged at ca. 6.3 mya (95% HPD: 5.1–7.7), and went on to diversify at similar times: i) O. icterorhynchus/O. moheliensis: 4.3 mya (95% HPD: 3.3–5.3), and ii) O. spilocephalus/O. bakkamoena marathae clade 4.6 mya (95% HPD: 3.7–5.6). Otus bikegila sp. nov. diverged from the O. hartlaubi/O. pembaensis/O. senegalensis clade ca. 0.9 mya ago (95% HPD: 0.7–1.1), an estimate similar (e.g., O. mirus/O. longicornis: 1 mya 95% HPD: 0.7–1.3) or greater (O. socotranus/O. insularis/O. sunia: 0.8 mya 95% HDP: 0.6–1.1) than the divergence estimated between closely related and well accepted species.

Nuclear markers independently supported the evolutionary independence of the taxa of the Afro-Palearctic clade. The taxa included in the analysis shared no haplotypes for markers KIAA1239 and TGFB2; the latter was the most variable of the analysed nuclear markers with a total of 19 haplotypes (Fig. 7). For MYO2, O. hartlaubi and O. brucei had no shared haplotypes, whereas O. bikegila sp. nov., O. scops and O. senegalensis had some unique haplotypes but shared the most common one (Fig. 7). Otus hartlaubi and O. scops did not share any TTN haplotype, with O. bikegila sp. nov. having both one unique haplotype and one shared with O. senegalensis feae (Fig. 7).

 Otus bikegila sp. nov.

https://zoobank.org/0731A37D-B363-43C9-A1AC-69F5E10F6810

Figs 2A, 8

Material

Holotype. MHNC-UP-AVE7000: São Tomé and Príncipe • ♀, adult, moulting; Príncipe Island, South Príncipe, ca. 500 m NW of Ribeira Porco river mouth (Fig. 1); 1°33.03'N, 7°22.29'E; ca. 100 m a.s.l.; 29 May 2017; HP and Ceciliano do Bom Jesus leg.; skin prepared by Vanya Rohwer, skeleton prepared by Vanya Rohwer and Daniele Cataldo; left wing removed for wing mounting, all bones with the exception of the left tarso-metatarsus (tarsus) removed for skeleton preparation; Audio-recorded by HP (Xeno-canto audio: XC619445, XC619447; GenBank: 12S OM978880, 16S OM978895, ATP6 OM913485, COI, OM937282; CYTB, OM937307; ND2, OM937351; ND3, ON016156; KIAA1239, OM937319; MYO2, OM937336; RAG1, ON016107; SACS, ON016118; TGFB2, ON016136 and TTN, ON016141; Gulf of Guinea database of MM: P7-04.

Diagnosis

The new species (Figs 2, 9) is assigned to the genus Otus based on genetic and morphological similarities to other known species of this genus. Phylogenetic analyses place it within the Afro-Palearctic clade, making generic placement unambiguous. Placement of the new species in Otus is further supported by its morphological characters: small size, distinctive ear-tufts, facial disc, short rounded wings, and short tail. The new species differs from the other described taxa of the Afro-Palearctic Otus clade (O. hartlaubi, O. senegalensis, including O. s. feae sometimes treated as a distinct species, O. pembaensis, O. pamelae, O. scops, O. brucei) by high genetic differentiation (pairwise ND2 distance ranging from 4.1% to 9.1%), by the lack of haplotype sha­ring at the KIAA1239 and TGFB2 nuclear markers, as well as from a combination of morphological, genetic and natural history (bioacoustics) traits.

Figure 8. 

Otus bikegila sp. nov., female holotype (MHNC-UP-AVE7000). Views A dorsal B ventral C lateral D left wing top and E left wing under. Millimetric paper on the background and colour reference plate (Colorchecker, X-Rite Inc.) for size and colour assessment.

Figure 9. 

Principe Scops-Owl Otus bikegila sp. nov. from Príncipe Island, Africa. Left: Adult rufous morph in the typical posture. Right: Adult grey-brown morph in a stress posture, when it raises the ear tufts to increase the efficiency of camouflage. Original artwork by MNC.

We provide here a diagnosis relatively to the closely related species belonging to the Afro-Palearctic clade and also to O. ireneae due to the similarity in their calls. The diagnosis is based on the following analysed morphological characters: 1) Biwid; 2) Binares; 3) Tarlen; 4) Wilen; 5) Tailen); 6) SP10; 7) SP9; 8) SP4; on the following analysed bioacoustics characters: 9) F1; 10) F2; 11) F3; 12) F4; 13) F5; 14) F6; 15) F7; 16) F8; 17) DT1; 18) DT2; 19) DT4; 20) DF1; 21) DF2; 22) DFT1; 23) DFT2; and on the 24) list of diagnostic substitutions identified at the analysed nuclear mar­kers (Tables 1–4; Suppl. materials 12, 14).

In overall appearance, O. bikegila sp. nov. is most similar to O. hartlaubi from which it differs in one morphological and 10 bioacoustic characters: longer Wilen (145 to 151 mm vs. 130 to 139 mm), lower F1 (781.7 to 961.7 Hz vs. 1078.3 to 1360.0 Hz), lower F2 (933.3 to 1020.0 Hz vs. 1155.0 to 1285.0 Hz), lower F3 (980.0 to 1090.0 Hz vs. 1330.0 to 1478.3 Hz), lower F4 (950.0 to 1050.0 Hz vs. 1295.0 to 1483.3 Hz), lower F5 (931.7 to 1020.0 Hz vs. 1250.0 to 1418.3 Hz), lower F6 (976.7 to 1090.0 Hz vs. 1331.7 to 1480.0 Hz), lower F7 (1035.0 to 1106.7 Hz vs. 1407.5 to 1526.7 Hz), lower F8 (868.3 to 973.3 Hz vs. 1066.7 to 1267.5 Hz), shorter DT1 (0.231 to 0.248 s vs. 0.267 to 0.315 s), shorter DT4 (0.992 to 1.121 s vs. 9.181 to 15.998 s). Otus bikegila sp. nov. differs from O. hartlaubi also by the following molecular characters: KIAA (T vs. C in site 347); TTN (G vs. C in site 91); MYO2 (G vs. A in site 2); TGFB2 (C vs. A in site 28, G vs. A in site 33, G vs. T in site 47, T vs. C in site 99, A vs. G in site 178, G vs. T in site 305, C vs. G in site 369).

Otus bikegila sp. nov. differs from O. senegalensis senegalensis in seven morphological and one bioacoustic characters: higher Biwid (9.0 to 11.8 mm vs. 4.8 to 8.0 mm), larger Binares (11.3 to 12.6 mm vs. 8.0 to 12.5 mm), longer Tarlen (30.5 to 35.1 mm vs. 20.0 to 24.2 mm), longer Wilen (145 to 151 mm vs. 103 to 145 mm), longer Tailen (75 to 85 mm vs. 40 to 65 mm), longer SP10 (37 to 40 mm vs. 10 to 32 mm), longer SP9 (13 to 18 mm vs. 1 to 16 mm), lower F4 (950.0 to 1050.0 Hz vs. 1095.0 to 1236.7 Hz); and in the following molecular characters: TGFB2 (A vs. G in site 178, T vs. G in site 344).

Otus bikegila sp. nov. differs from O. senegalensis feae in one morphological and four bioacoustic characters: larger Biwid (9.0 to 11.8 mm vs. 6.4 to 6.8 mm), lower F2 (933.3 to 1020.0 Hz vs. 1132.5 to 1230.0 Hz), lower F7 (1035.0 to 1106.7 Hz vs. 1250.0 to 1357.5 Hz), shorter DT1 (0.231 to 0.248 s vs. 0.402 to 0.441 s), shorter DT4 (0.992 to 1.121 s vs. 7.127 to 7.479 s); and in the following molecular characters: KIAA (T vs. C in site 347, T vs. C in site 503); TGFB2 (A vs. G in site 178, T vs. C in site 285, G vs. C in site 392).

Otus bikegila sp. nov. differs from O. pembaensis in one morphological and nine bioacoustic characters: shorter SP4 (6 to 9.5 mm vs. 11 to 21 mm), higher F1 (781.7 to 961.7 Hz vs. 506.7 to 636.7 Hz), higher F2 (933.3 to 1020.0 Hz vs. 613.3 to 773.3 Hz), higher F3 (980.0 to 1090.0 Hz vs. 621.7 to 770.0 Hz), higher F4 (950.0 to 1050.0 Hz vs. 633.3 to 780.0 Hz), higher F5 (931.7 to 1020.0 Hz vs. 651.7 to 783.3 Hz), higher F6 (976.7 to 1090.0 Hz vs. 638.3 to 776.7 Hz), higher F7 (1035.0 to 1106.7 Hz vs. 660.0 to 790.0 Hz), higher F8 (868.3 to 973.3 Hz vs. 530.0 to 660.0 Hz), shorter DT4 (0.992 to 1.121 s vs. 5.043 to 7.570 s); and in the following molecular characters: TGFB2 (A vs. G in site 178, T vs. C in site 285, C vs. T in site 345).

Otus bikegila sp. nov. differs from O. pamelae in seven bioacoustic characters (morphology not analysed): lower F1 (781.7 to 961.7 Hz vs. 1031.7 to 1213.3 Hz), lower F2 (933.3 to 1020.0 Hz vs. 1111.7 to 1268.3 Hz), lower F4 (950.0 to 1050.0 Hz vs. 1096.7 to 1366.7 Hz), lower F5 (931.7 to 1020.0 Hz vs. 1083.3 to 1291.7 Hz), lower F6 (976.7 to 1090.0 Hz vs. 1160.0 to 1403.3 Hz), lower F7 (1035.0 to 1106.7 Hz vs. 1220.0 to 1516.7 Hz), lower F8 (868.3 to 973.3 Hz vs. 1020.0 to 1123.3 Hz).

Otus bikegila sp. nov. differs from O. scops in seven morphological and 11 bioacoustic characters: higher Biwid (9.0 to 11.8 mm vs. 5.5 to 7.8 mm), larger Binares (11.3 to 12.6 mm vs. 9.0 to 11.5 mm), longer Tarlen (30.5 to 35.1 mm vs. 22.0 to 28.0 mm), shorter Wilen (145 to 151 mm vs. 147 to 165 mm), longer SP10 (37 to 40 mm vs. 12 to 24 mm), longer SP9 (13 to 18 mm vs. 0 to 7 mm), shorter SP4 (6 to 9.5 mm vs. 10 to 29 mm), lower F1 (781.7 to 961.7 Hz vs. 1335.0 to 1695.0 Hz), lower F2 (933.3 to 1020.0 Hz vs. 1152.5 to 1275.0 Hz), lower F3 (980.0 to 1090.0 Hz vs. 1155.0 to 1260.0 Hz), lower F4 (950.0 to 1050.0 Hz vs. 1200.0 to 1285.0 Hz), lower F5 (931.7 to 1020.0 Hz vs. 1193.3 to 1318.3 Hz), lower F6 (976.7 to 1090.0 Hz vs. 1210.0 to 1326.7 Hz), lower F7 (1035.0 to 1106.7 Hz vs. 1336.3 to 1628.3 Hz), lower F8 (868.3 to 973.3 Hz vs. 1140.0 to 1253.3 Hz), shorter DT4 (0.992 to 1.121 s vs. 2.423 to 2.789 s), higher DF1 (6.7 to 178.3 Hz vs. -420.0 to -182.5 Hz), lower DFT1 (-581.5 to 45.2 Hz/s vs. 181.5 to 662.3 Hz/s); and in the following molecular characters: KIAA (T vs. C in site 347, A vs. G in site 632); TTN (T vs. C in site 535, G vs. A in site 536, G vs. T in site 634); TGFB2 (G vs. A in site 33, G vs. T in site 47, A vs. G in site 178, T vs. C in site 285).

Otus bikegila sp. nov. differs from O. cyprius in four bioacoustics characters (morphology and nuclear markers not analysed): presence of a monosyllabic primary song (O. cyprius has a distinctive di-syllabic primary song), lower F1 (781.7 to 961.7 Hz vs. 1236.7 to 1400.0 Hz [long note] and 1058.9 to 1223.3 Hz [short note]), shorter DT4 (0.992 to 1.121 s vs. 3.035 to 3.643 s [long note] and 3.116 to 3.714 [short note]), and having a higher DF1 (6.7 to 178.3 Hz vs. -283.3 to -165.0 Hz [long note] and -113.3 to -58.1 [short note]).

Otus bikegila sp. nov. differs from O. brucei in 11 bioacoustic characters (morphology not analysed): higher F1 (781.7 to 961.7 Hz vs. 285.0 to 388.3 Hz), higher F2 (933.3 to 1020.0 Hz vs. 891.7 to 946.7 Hz), higher F3 (980.0 to 1090.0 Hz vs. 356.7 to 530.0 Hz), higher F4 (950.0 to 1050.0 Hz vs. 356.7 to 493.3 Hz), higher F5 (931.7 to 1020.0 Hz vs. 335.0 to 450.0 Hz), higher F6 (976.7 to 1090.0 Hz vs. 370.0 to 510.0 Hz), higher F7 (1035.0 to 1106.7 Hz vs. 370.0 to 530.0 Hz), higher F8 (868.3 to 973.3 Hz vs. 270.0 to 373.3 Hz), longer DT1 (0.231 to 0.248 s vs. 0.090 to 0.133 s), longer DT2 (0.078 to 0.112 s vs. 0.032 to 0.053 s), higher DFT2 (-250.3 to 21.7 Hz/s vs. -1653.0 to -1387.3 Hz/s); and in the following molecular characters: MYO2 (T vs. C in site 22; C vs. T in site 118; C vs. T in site 129).

Otus bikegila sp. nov. differs from O. ireneae in one bioacoustic character (morpho­logy and nuclear markers not analysed): longer DT4 (0.992 to 1.121 s vs. 0.409 to 0.447 s).

Description of the holotype

Morphological measurements available in Table 1. The topographic terms of the scops-owl body are detailed in the Suppl. material 3.

General colouration : Back, Burnt Amber 48 with Robin Rufous 29 shades; front, Pale Buff 1 feathers with Cinnamon 21 and Dusky Brown 285 markings (forming stripes defined by Dusky Brown 285 lines) with Robin Rufous 29 shades.

Head : Chin feathers Pale Buff 1 with Sayal Brown 41 shading along shaft, ending with a bristle-like barb Sepia 286. Throat feathers Pale Buff 1 with Pale Pinkish Buff 3 and Sepia 286 dots and markings sometimes forming bands; Pale Buff 1 shaft proximally becoming Pale Pinkish Buff 3 and Sepia 286 distally. Feathers of forehead Sepia 286 and few Pale Buff 1 shading. Tip of the head triangle Prout’s Brown 47. Triangle outside facial disk with an overall appearance Prout’s Brown 47, triangle with feather with Sepia 286 middle stripe along shaft, Prout’s Brown 47 and Sepia 286 in their internal portion and Sepia 286 and Pale Buff 1 in the outer portion but always ending with Prout’s Brown 47 or Robin Rufous 29 in the distal portion. Triangle delineated by Pale Buff 1/Smoke Grey 266 stripes (the eyebrows). Eyebrows Pale Buff 1/Smoke Grey 266 down to the bill: Pale Buff 1 feathers ending with a thin Cinnamon 21 line followed by a broader Jet Black 300 band; Pale Buff 1 feathers with middle Sepia 286 stripe along shaft and densely vermiculated with Sepia 286 and Cinnamon 21 shades; eyebrows feathers in distal portion are Pale Buff 1 densely vermiculated with Sepia 286 and Cinnamon 21 shades, ending in Prout’s Brown 47. Crown feathers Prout’s Brown 47 with Sepia 286 middle stripe along shaft, Pale Buff 1 in proximal section and Prout’s Brown 47 with Sepia 286 vermiculation along mid and distal portion. Ear tuft not visible in the mounted specimen, but with feathers Pale buff 1 in proximal section becoming Cinnamon 21 with densely Sepia 286 vermiculation and ending with Prout’s Brown 47; ear feathers pull up some of the eyebrow feather with Sepia 286 and Cinnamon 21 dense vermiculation. Nape feathers Pale Pinkish Buff 3 with well-defined Sepia 286 irregular stripes, ending with middle Sepia 286 stripe along shaft and Burnt Amber 48. Neck feathers with longer underfeathers (then in nape) with middle Sepia 286 stripe along shaft with Pale Pinkish Buff 3, Pale Buff 1, Pale Pinkish Buff 3 and becoming Pale Buff 1 and Burnt Amber 48 all with Sepia 286 irregular markings. Overall appearance of rictal bristles: Jet Black 300 patches with Cinnamon 21 and Pale Buff 1 shades next to the bill (following with Pale Buff 1/Smoke Grey 266 eyebrows); bristles with terminal Jet Black 300 colour; bristles closer to the bill Pale Buff 1 in proximal position, changing into Cinnamon 21 and ending in Jet Black 300 or Pale Buff 1 in the proximal section and Jet Black 300 in distal section; bristles closer to the eye Jet Black 300 in proximal position, changing into Cinnamon 21 and ending in Jet Black 300 or only Jet Black 300 (the shortest one). Rim with two narrow Raw Umber 23 bands, one on each side, not extending to the centre; Pale Buff 1 feathers with Sepia 286 irregular markings, becoming Cinnamon 21 (with no Sepia 286 markings), ending with Raw Umber 23. Facial disk feathers Pale Buff 1 with multiple bands of Sepia 286 (generally 3), the terminal Sepia 286 bands is preceded by a thin Robin Rufous 29 band; feather ending with 2 to 5 bristle-like barbs.

Upperparts : Overall colour of mantle (i.e., upper back) and rump: Burnt Amber 48 with Robin Rufous 29 shades. Feathers Sayal Brown 41 with middle Sepia 286 line along shaft, and with irregular Sepia 286 markings in the proximal section. Feathers turning Cinnamon-Rufous 31 with Sepia 286 markings in the distal portion of the feather. Mantle is delimited distally (neck) by a Cinnamon-Rufous 31 band and late­rally by a series of 8 feathers that are lighter in colour (Cinnamon-Rufous 31): outer vane Light Buff 2 with Cinnamon-Rufous 31 shades and with a Sepia 286 curve line that defines a Raw Sienna 32 colour close to shaft, one or more Sepia 286 spots on distal outer vane; outer vane ending distally with Raw Sienna 32 with Sepia 286 mar­kings; inner vane is Raw Sienna 32 with Sepia 286 irregular markings. These feathers appear to make a line that delineates the outside of the mantle. Similarly, the feathers of the mantle at the base of the neck form a lighter Cinnamon Rufous 31 line that follows the external side of the folded wings, making a triangle. Scapulars as upperparts. Proximal shaft Pale Buff 1, Vandyke Brown 282 in distal portion; Vandyke Brown 282 middle stripe along shaft. Outer vane is Cinnamon 21 with Sepia 279 markings and inner vane is Sepia 279 with Cinnamon 21 markings.

Underparts : Breast overall Pale Buff 1 with Sepia 286 irregular markings and Robin Rufous 29 shading. Breast feathers Pale Pinkish Buff 3 with Sepia 286 dots and markings proximally and Pale Pinkish Buff 3 shaft, distally Sepia 286 with Pale Pinkish Buff 3 dots and markings forming irregular bands, middle Sepia 286 stripes along shaft. Belly overall similar to breast but with colours more defined and with Light Buff 2 shadings. Belly feathers Pale Pinkish Buff 3 in proximal section followed by a Sepia 286 V stripe. This is followed by a Pale Buff 1 broad band delimitated distally with a thin Pale Pinkish Buff 3 line followed by a Sepia 286 line. Distally, these feathers are Pale Buff 1 with irregular spots Sepia 286 and Pale Pinkish Buff 3. Some feathers on the belly and the vent have a marked middle and broad Sepia 286 line along shaft. Vent is similar to breast and belly but with feathers Cinnamon 21 in proximal section followed by a Sepia 286 stripe. This is followed by a Pale Buff 1 broad band delimitated distally with a thin Cinnamon 21 followed by a Sepia 286 line. The feather then becomes Pale Buff 1 with a Cinnamon 21 thin band followed by a Sepia 286 line, ending with a Pale Buff 1 colouration with Sepia 286 irregular dots and markings. Flank feathers Pale Buff 1 with Cinnamon 21 shading followed by a broad Cinnamon 21 V stripe followed by a Sepia 286 line, ending with a broad Pale Buff 1 section with Sepia 286 markings only in the very distal portion. Undertail coverts are similar to flanks but with more defined bands. Feathers are Pale Buff 1 followed by a broad Cinnamon 21 band defined distally by a thinner warm Sepia 40 line. This colouration is repeated twice. Feathers end with a broad Pale Buff 1 band followed by a Cinnamon 21 band with irregular Warn Sepia 40 markings. Tarsus covered with feathers to base of toes. Feathers overall similar to flank but with less Pale Buff 1 and more Cinnamon 21 shading and one or two Sepia 286 dots in distal section. Tarsus fea­thers have a larger proportion of Pale Buff 1 close to toes. Tarsus feathers are Pale Buff 1 proximally, followed by Cinnamon 21 shading and Sepia 286 markings distally (approximately 1/4 of the feather distally), no middle stripe along shaft. Toes feathers are Pale Buff 1 with Cinnamon 21 shadings and Sepia 286 markings only in the distal section.

Wing : Overall Prout’s Brown 47 with Dark Greyish Brown 284 leopard blotches. Primaries shaft Vandyke Brown 282. Outer vane of primaries with six or seven ‘leopard’ Dark Greyish Brown 284 spots in Cinnamon 21 background becoming Pale Buff 1 in some instances. Spots interior with a gradient of Cinnamon 21 to Dark Greyish Brown 284 with lighter spots on outer primaries. Spots circumference with Dark Greyish Brown 284 to Jet Black 300. ‘Leopard spots’ start faint (P1-P2-P3) and become stronger moving outwards. Inner vane of primaries with Dark Greyish Brown 284 with Cinnamon 21 shadings towards the distal section of the feather. Exterior edge makes a Pale Buff 1 line. Under-primaries have a Pale Buff 1 shaft proximally becoming Cinnamon 21 towards the distal portion. Outer vane of under-primaries is proximally Hair Brown 277 with Pale Pinkish Buff 3 irregular triangles, becoming Cinnamon 21 in distal section with Sepia 279 lines delimiting the leopard spots that are fading towards the distal portion of the feather. Inner vane of under-primaries is Hair Brown 277 with Light Buff 2 markings in proximal section and Cinnamon 21 markings in distal section. Secondaries shaft Vandyke Brown 282. Outer vane of secondaries is similar but much less marked pattern than primaries: spots on outer vanes less marked, fading into the background towards S10. Inner vane of seconda­ries with Sepia 279 with Cinnamon 21 shadings and markings especially towards the distal section of the feather. Under-secondaries have a Pale Buff 1 shaft proximally becoming Cinnamon 21 and later Sepia 279 towards the distal portion. Outer vane of under-secondaries with Hair Brown 277 with Cinnamon 21 markings. Inner vane of under-secondaries with Hair Brown 277 with six to seven Light Buff 2 triangles only on the outer part of the inner vane, which become irregular markings (Cinnamon 21 in colour) towards the distal portion of the feather. Tertiaries shaft like primaries (Vandyke Brown 282). Outer and inner vane of tertiaries similar in colour and similar to the outer vane of the secondaries. Under-tertiaries have Pale Buff 1 shaft proximally becoming Cinnamon 21 and later Sepia 279 towards the distal portion. Outer and inner vanes of under-tertiaries are similar: Cinnamon 21 with irregular Sepia 279 lines in the proximal portion, becoming irregular dots towards the distal section; terminal 1/5 with a Sepia 279 middle stripe along shaft. Primary coverts with Vandyke Brown 282 shafts. Outer vane of primary coverts with Sepia 279 with Cinnamon 21 markings becoming more packed towards the distal portion of the feather. Inner vane of primary coverts is similar to outer but with less packed Cinnamon 21 markings. Secondary coverts are overall Sepia 279 with Cinnamon 21 markings. Shaft is Vandyke Brown 282. Outer vane of secondary coverts with a Pale Buff 1 blotch delimited proximally by a Sepia 279 thin and sharp line. This blotch can have in its inner parts a Cinnamon 21 blotch delimited by a Sepia 279 thin and sharp line. Additional Sepia 279 lines distributed heterogeneously can be found on the outer vane. Inner vane of secondary coverts Sepia 279 with Light Buff 2 markings in proximal section and Cinnamon 21 markings in the distal portion of the feather. Lesser coverts with shafts Pale Buff 1 proximally and Vandyke Brown 282 in distal portion. Vandyke Brown 282 middle stripe along shaft. Outer vane of lesser co­verts Cinnamon 21 with Sepia 279 markings and Pale Pinkish Buff 3 markings delimited irregularly by Sepia 279 dashed lines. Inner vane of lesser coverts Sepia 279 with Cinnamon 21 markings. Coverts in the under-wings with Pale Buff 1 shaft. Outer vane on the coverts from the under-wings is Pale Buff 1 and Light Buff 2 with one Sepia 279 leopard spot and some additional (but rare) Sepia 279 markings. Inner vane of the coverts from the under-wings Pale Buff 1 and Light Buff 2 with Light Neutral Grey 297 colouration that become Sepia 279 distally. Alula shaft is Vandyke Brown 282. Outer vane of alula with five Verona Brown 37 ‘leopard’ spots delimited by Sepia 279 lines which is sharper in distal portion. Leopard spots separated by Pale Pinkish Buff 3 with Cinnamon 21 shadings. Inner vane of alula Sepia 279 with four Light Buff 2 partial bands.

Tail : Verona Brown 37 with Sepia 286 markings that fades towards the distal portion of the feather. Shaft Sepia 286. Outer feathers of the tail have an outer vane Verona Brown 37 with broad Sepia 286 bands, and an inner vane with broad poorly defined Sepia 286 bands intercalated by Light Buff 2, Pale Pinkish Buff 3 and more distally Verona Brown 37 bands.

Bill : Dusky Brown 285 and lower bill Light Buff 2.

Iris : Yellow.

Vocalisations : Call recordings collected at the moment of specimen collection included the call of the holotype and a second individual (XC audios: XC619445, XC619447): one emitted the main call type (the single repetitive note used in the bioacoustic analyses), and the other the cat-like call. We believe that the holotype individual was the one giving the main call, but this was uncertain. Thus, it is not possible to provide bioacoustics parameters specific to the holotype.

Variation : Morphometric variation in O. bikegila sp. nov. is based on the analysis of three additional individuals, of which one is a male (Table 1; Fig. 2). The male (P9–038) had shorter tarsus and wing length than the female holotype and the other two females. This result is consistent with the reversed sexual dimorphism in size described for all species of scops-owls (Marks et al. 1999; König et al. 2008). Two colour morphs (rufous and grey-brown) have been documented in the field (Figs 2, 9). Molecular sexing of the four captured individuals has shown that colour morph is not associated with sex. Examples of the grey-brown morph include the holotype (Figs 2A, 8), individuals P9-037 and P9-038 (Fig. 2B), and individuals photographed in the field (Fig. 2D, E); examples of the rufous morph include the first photographed individual of this species (Fig. 2C) and individual P8-001 (Fig. 2F). Plumage pattern and colour of the latter is similar to the holotype, although in the rufous morph the eyebrows are less marked, the underparts are more similar in colour to the upperparts and have more prominent sepia marks and stripes along the feather shafts. In the field, we observed no differences in the rate of occurrence of the two morphs.

Vocalisations were recorded at the type locality by MM in 2002, 2007, 2011, 2018 and 2019 and at Boca do Inferno in 2019, and by PV at the type locality in 2016. The call of O. bikegila was described in Melo and Dallimer (2009). Among vocalisations of Otus species, the primary call of O. bikegila sp. nov. is unique in consisting in a short, undulated note emitted at a fast repetition rate, reminiscent of insect calls, of ca. one note per second (Tables 2, 3; Fig. 4; Suppl. material 4: Fig. S2A). Vocalisations were often performed in duet (Suppl. material 4: Fig. S2B), with intercalated or overlapping notes. Otus bikegila sp. nov. is able to produce a cat-like “kee-a-u” note, which is emitted both in duets (Suppl. material 4: Fig. S2D) and by single birds (Suppl. material 4: Fig. S2C). We confirmed in the field that the same individual can produce both calls. Bioacoustic parameters (mean ± standard deviation) of the primary and of the cat-like notes are available in Tables 2, 3.

Etymology

The species name is a patronym honouring Ceciliano do Bom Jesus, known as ‘Bikegila’ (Suppl. material 5). The species epithet name is intentionally defined as an invariable noun in apposition (not a noun in the genitive case) for better pronunciation; no confusion with the species authority is possible because the noun is an oral nickname.

Bikegila, a native of Príncipe Island, began the ‘Príncipe Scops-Owl saga’ in 1998, when he shared with MM reports of two sightings of birds that looked like owls in parrot nests. Since then, Bikegila took part in every field effort that led to the bird’s discovery for science; he also led the capture of all sampled individuals, including the holotype, which required ingenious ways to erect canopy nets. For almost 25 years, Bikegila has put all his resources, including bottomless fieldwork skills and a vast knowledge of Príncipe, towards the successful completion of innumerable research projects in a terrain that the collector José Correia considered to be the “bad among the bad or the worse among the worse” [sic] (Diary, 2 September 1928, Archives AMNH, New York). Besides his skills, Bikegila’s “cheerful temperament, possibly the first requirement for an undertaking in inhospitable regions” (von Humboldt 1841), coupled with an unbeatable gift for story-telling and an underlying quiet wisdom, contributes as much to making the expeditions he leads memorable and successful. A former parrot harvester, Bikegila became a warden of Prín­cipe Obô Natural Park soon after its creation; he is now a much sought-after nature guide.

We believe that most field researchers are grateful to the ‘Bikegilas’ with whom they are/were honoured to work with. As such, the name is also in recognition of all the people, around the world, who through their deep relationship with and knowledge of the regions they inhabit, play key roles in the description of new species and of new sites to science.

Common name

We propose the English common name Principe Scops-Owl, the name for São Tomé and Príncipe as Kitóli-do-príncipe, and the name for the Portuguese list of the birds of the world as Mocho-do-príncipe. All common names refer to Príncipe Island, from where it is endemic.

Distribution and natural history

All records from O. bikegila sp. nov. come from old-growth native lowland rainforest with mid-height (14–20 m) trees (Fig. 10), with the species apparently preferring lower elevations (Melo and Dallimer 2009; Freitas et al. 2022). Its area of occurrence is fully within the limits of Príncipe Obô Natural Park. Detailed surveys have been carried out to determine the area of occupancy of this species, to estimate its population size, ecological requirements, and to propose an IUCN Red List category (Freitas et al. 2022).

Figure 10. 

A aerial view of the south of Príncipe Island home of Otus bikegila sp. nov., and B habitat of the type locality at ca. 150 m a.s.l. Photographs: A Alexandre Vaz B MM.

The holotype (Figs 2A, 8; female MHNC-UP-AVE7000), collected on 29 May 2017, was undergoing a well-advanced moult, a process that takes place after the breeding season. The female captured close to Ribeira Porco, in January 2019 (P8-001) had a fully developed brood patch (Fig. 2F), whereas the female captured at Boca do Inferno on the same month (Fig. 2B, left) was growing back the belly feathers, suggesting that she had a recent brood patch. This indicates that breeding takes place in December-January, as with most bird species of the islands of São Tomé and Príncipe (Jones and Tye 2006; Madeira 2018).

Otus bikegila sp. nov. starts calling at dusk and continues throughout the night. Contrarily to the Sao Tome Scops-Owl O. hartlaubi that regularly vocalises during the day, O. bikegila sp. nov. seems to require darkness to sing, although on a single occasion one individual was heard during the day (Melo and Dallimer 2009). Response to the playback of its call was fast and intense at all times of the year we were able to test it, with birds of either sex approaching the speaker. This indicates that O. bikegila sp. nov. is territorial all-year round as it is known from most sedentary cavity-nesting owls (Marks et al. 1999; König et al. 2008). During the day it may roost outside of tree cavities, as suggested when we accidentally flushed one bird when taking habitat measurements. In this situation the bird raised its ear tufts, which are otherwise seldom observed (Fig. 2D).

Multiple lines of evidence were brought together to demonstrate, unambiguously, that the recently discovered population of scops-owls on Príncipe Island makes a well-differentiated species, Otus bikegila. Genetic distances, and associated divergence times, to its closest relatives were in the range of those separating currently accepted species (Table 5). Morphological differences, although present, did not stand out (for the human eye at least), whereas vocalisations were unique and clearly distinctive (even for the human ear) and, in fact, it was bioacoustics that led to the discovery of the population of the Principe Scops-Owl. Its unique vocalisations were closest to those of O. ireneae, an Otus species from which it is distantly related, underscoring the value of song in scops-owls to assess taxonomic status but not for inferring taxonomic affinities (Fuchs et al. 2007). Phylogenetic data placed O. bikegila as the sister lineage of the clade containing all African scops-owl species of the Afro-Palearctic clade (sensu Pons et al. 2013 and Fig. 6), rather than as the sister species of O. hartlaubi endemic to the neighbouring island of São Tomé. This leads to the curious conclusion that Príncipe was likely the first island in the Gulf of Guinea to be colonised by a species of scops-owl, albeit the last species to be discovered and described for science. It also begs the question if an undescribed scops-owl waits to be discovered in the extensive rainforests of Bioko Island, the only island of the Gulf of Guinea without records of a scops-owl. This apparent absence is puzzling as Bioko is a land-bridge island, which has been connected to the mainland in multiple instances in the past (Rohling et al. 1998; Lambert and Chappel 2001), and currently lying at ca. 30 km from Cameroon where O. icterorhynchus, a rainforest specialist, is present.

Although it may seem odd for a bird species to remain undiscovered for science for so long on such a small island, this is by no means an isolated case when it comes to owls. For example, the recently described Rinjani Scops-Owl O. jolandae Sangster, King, Verbelen & Trainor, 2013 was found to be a previously undescribed species from Lombok Island, Indonesia (Sangster et al. 2013). Similarly, the Anjouan Scops-Owl O. capnodes (Gurney, JH, 1889) was rediscovered in 1992 (Safford 1993), 106 years after its last observation, in an area of primary forest that is smaller and more regularly visited than that of Príncipe, and the Flores Scops-Owl O. alfredi (Hartert, E, 1897), rediscovered in 1994, 98 years after the previous report (Widodo et al. 1999).

Our phylogenetic analyses confirmed the supported nodes from previous phylogenies (Fuchs et al. 2008; Pons et al. 2013), resolved previously unsupported nodes, and provided novel insights in the affinities of species not previously included.

In relation to African taxa, the most interesting result came from the inclusion of samples from the two subspecies of the only African Otus species never sequenced before: the Sandy Scops-Owl O. icterorhynchus. Together with O. ireneae, this is the only species on the African continent that is a lowland forest specialist (albeit each species occupies very distinct forest types), and the two species were widely hypothesised as being closely related (Marks et al. 1999; König et al. 2008; Holt et al. 2020). Perhaps more surprisingly, O. icterorhynchus has been considered to form a superspecies (‘yellow-billed scops-owls’) with two Asian taxa, the Andaman Scops-Owl O. balli (Hume, 1873) and the Sumatran Otus spilocephalus stresemanni (Robinson, 1927) (Marshall 1978), although ‘stresemanni’ could be an anomalous form of another species and/or a hybrid (Pamela Rasmussen in Holt et al. 2020). Our phylogenetic analyses clarify the affinities of O. icterorhynchus, which was found to be sister to the clade containing the Afro-Palearctic and the Indo-Malayan/Indian Ocean clades. Each of its subspecies was available to us by a single individual, but their genetic divergence levels overlap with the levels found between many currently accepted scops-owls sister species pairs.

This study better resolved the branching sequence within the Afro-Palearctic clade, except for the position of O. pamelae that could not be determined, contra Pons et al. (2013) who recovered it as the sister lineage of this clade. Instead, O. brucei, with populations extending from the Arabian Peninsula into Asia, was recovered as the sister lineage of the clade which then branches into African and Eurasian subclades (assu­ming that O. pamelae is sister to O. scops).

The internodes separating O. senegalensis (mainland and Annobón Island), O. hartlaubi (São Tomé Island), and O. pembaensis (Pemba Island) are very short, indicating that the divergence between these three species (i.e., the colonisation of both islands from their mainland ancestor) occurred almost simultaneously, creating a hard polytomy. Our analyses failed to identify solid lines of evidence for the distinctiveness of O. senegalensis feae from O. senegalensis senegalensis, although we did identify a diagnostic morphological character (bill length from tip to nares, Suppl. material 12) and three molecular diagnostic characters at the TGFB2 gene (C vs. T in site 285, T vs. G in site 344, C vs. G in site 392). In a dataset with a wider taxonomic sampling of O. senegalensis but fewer sequencing data, the Annobón sample nested within the mainland samples (unpublished data). A better sampling of O. senegalensis senegalensis from across its range will help to resolve this taxonomic issue.

Our sampling increased considerably the taxon coverage for the centre of the diversity of the Otus genus, the Indo-Malayan region (Marks et al. 1999), but has failed to solve most of the many taxonomic pending issues. The Ryukyu Scops-Owl O. elegans (Cassin, 1852), a species restricted to small oceanic islands from the northern Philippines to Japan, and included for the first time in a phylogenetic study, was recovered as the fourth Asian representative of the Indo-Malayan/Indian Ocean clade (Fig. 6; sensu Pons et al. 2013), albeit with no statistical support. At this stage, our results mainly highlight the need for using a phylogeographic-level sampling scheme across the region (i.e., multiple samples per site covering all areas of occurrence) to enable a thorough systematic revision of the Indo-Malayan taxa, a crucial step towards reconstructing the diversification history of the genus Otus.

Our molecular dataset confirmed the low levels of divergence (well within intraspecific variation) of three taxa pairs that are currently treated either as separate species or subspecies. These pairs are: i) O. senegalensis senegalensis (mainland Africa) and O. s. feae (Annobón Island), treated as separate species by del Hoyo (2020) and Gill et al. (2021) based on Collar and Boesman (2020); ii) O. scops and O. cyprius, treated as a distinct species by Gill et al. (2021) and Clements et al. 2021, based on Flint et al. (2015); and iii) the two species from Madagascar, the Malagasy Scops-Owl O. rutilus (Pucheran, 1849) and the Torotoroka Scops-Owl O. madagascariensis Grandidier, A, 1867, whose specific status was proposed by Rasmussen et al. (2000) and adopted by most authorities (e.g., Clements et al. 2021, del Hoyo 2020, Gill et al. 2021), but contested by Fuchs et al. (2007) using a representative geographic sampling.