Calyptorhynchus, Desmarest, 1826

Smith, Brian Tilston, Thom, Gregory & Joseph, Leo, 2024, Revised Evolutionary And Taxonomic Synthesis For Parrots (Order: Psittaciformes) Guided By Phylogenomic Analysis, Bulletin of the American Museum of Natural History 2024 (468), pp. 1-87 : 18-19

Calyptorhynchus and Zanda

Calyptorhynchus and Zanda are large predominantly black cockatoos with distinctively colored, broad subterminal tail panels, predominantly red or orange-yellow in Calyptorhynchus and yellow to creamy white in Zanda . Bill color is often sexually dimorphic (less prominently so in C. lathami ) and Zanda also have sexually dimorphic ear-covert patches broadly concolorous with the subterminal tail band. Vocalizations are distinctive, typically being an oddly “funereal” cry in Zanda and higher pitched somewhat wheezy cries in Calyptorhynchus .

In the Calyptorhynchinae, relationships among the five conventionally recognized species are stable and well supported across phylogenomic trees and a previously inferred species tree ( White et al., 2011). We support the generic placement of the species funerea , baudinii , and latirostris in Zanda Mathews, 1913 . Zanda was in synonymy with Calyptorhynchus for most of the 20th century, but its reinstatement began with Schodde’s (1997) recognition of it at subgeneric rank within Calyptorhynchus . Following White et al.’s (2011) molecular study, its elevation to genus level has become conventional ( Gill et al., 2023; Dickinson and Remsen, 2013). Saunders and Pickup (2023a) have revisited and reinforced support for the recognition of Zanda based on morphological and vocalization data. Divergence between Zanda and Calyptorhynchus dates to 19.2 Mya and divergences within each genus date to 0.6–2 Mya and 8.4 Mya, respectively (fig. 2).

Turning to species-level systematics, we note that an analysis of genome-wide single nucleotide polymorphisms (SNPs) ( Ewart et al., 2020) found that the Red-tailed Black Cockatoo ( Calyptorhynchus banksii ) comprises five evolutionarily significant units, the corresponding species-group epithets of which are banskii, graptogyne, naso, escondidus, and samueli. Unsurprisingly, some uncertainties remain in relationships among these five taxa, given their shallow divergence times. Ewart et al. (2020), however, made two taxonomic recommendations: (1) synonymy of banksii and macrorhynchus in nominotypical banksii and (2) that samueli, the three isolated populations of which did not form a single monophyletic group, should be broken into eastern and central populations, samueli, which did form a single monophyletic group, and western population, escondidus, which was sister to naso and which they newly described at subspecies rank.

Saunders and Pickup (2023a) elevated the five subspecies to species rank. Key elements of their decision were morphometric analyses, the time of divergence (latter half of the Pleistocene; Ewart et al., 2020), and their allopatry. Presentday geographic interactions and gene flow between banksii and samueli in eastern Australia seem highly probable, however, and warrant further study regardless of their taxonomic status (see maps in Saunders and Pickup, 2023a). Similarly, but perhaps with a lower probability, escondidus and banksii may be in geographic and genetic contact in northwestern Australia. One species with five subspecies or five monotypic species are among equally plausible arrangements in light of the data available: five geographical units appear monophyletic, but their divergences are shallow relative to many other species and there is no extensive sympatry to affirm species status by that criterion.

The shallow divergence between Z. latirostris and Z. baudinii warrants discussion. This pair is among the most notable examples in ornithology of cryptically differentiated sibling species ( White et al., 2014). Saunders (1974, 1979) elegantly showed on morphological grounds that the two taxa are distinct, primarily in bill morphology. This work led to the removal of latirostris from synonymy of baudinii and recognition of the two taxa at species rank. Next, White et al. (2011) presented a multilocus phylogenetic analysis arguing that radiation within Zanda into three species happened relatively recently, within the last 1.3 million years. White et al. (2014) pursued genetic differentiation between Z. latirostris and Z. baudinii with microsatellite data. They suggested that the differentiation between the two taxa started during anthropogenic land clearing in the 20th century. They also remarked that some gene flow is still occurring between the two but estimated that fewer than 10 individuals per generation are moving between regions separated by an anthropogenically generated barrier of unsuitable habitat.

Saunders and Pickup (2023a) presented an updated synthesis of all data concerning this pair. They disputed White et al.’s (2014) claim of differentiation within the past ~100 years, a finding that was corroborated with our phylogenomic data that dates the split at 0.6 Mya (0.2–1) (fig. 2). Further, they found no morphological indication of hybridization and stressed the overlapping breeding ranges of the two taxa, surely here a gold standard for species-level recognition. On adding our data to these syntheses, we conclude that while population-level sampling of Z. latirostris and Z. baudinii with genomic methods now available is likely to be highly rewarding, the optimal taxonomic conclusion at this point is that they indeed represent two species.

Taxonomic subdivision of Z. funerea , in contrast, has become far more contentious since Saunders and Pickup (2023a, 2003b) proposed that the three taxa at best tentatively recognized as subspecies within it by earlier treatments ( Schodde and Mason, 1997; Forshaw and Cooper, 2002) should be elevated to species rank. Our sampling has not addressed variation within Z. funerea . We are highly skeptical of Saunders and Pickup’s (2023 a, 2023b) proposal to elevate three questionably recognizable subspecies within Z. funerea to species rank but will address this in more detail elsewhere.