Rodrigues Starling

Rodrigues Starling
The holotype bones
Conservation status
Extinct  (mid-18th century)  (IUCN 3.1)[1]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Order:	Passeriformes
Suborder:	Passeri
Infraorder:	Passerida
Superfamily:	Muscicapoidea
Family:	Sturnidae
Genus:	Necropsar Günther & Newton, 1879
Species:	N. rodericanus
Binomial name
Necropsar rodericanus Günther & Newton, 1879
Location of Rodrigues
Synonyms
Necrospa rodericanus Shelley, 1900 Necrospar rodericanus (lapsus) Testudophaga bicolor Hachisuka, 1937

The Rodrigues Starling (Necropsar rodericanus), alternatively spelled Rodriguez Starling, is an extinct and quite enigmatic songbird species. It is the only valid species in genus Necropsar, and provisionally assigned to the starling family (Sturnidae). This bird used to inhabit Rodrigues in the Mascarenes and at least one of its offshore islets. The record of its erstwhile existence is limited to an old travel report and a few handfuls of subfossil bones.^[1]

Taxonomy

Restoration by John Gerrard Keulemans which was partially based on a specimen that turned out to be an albinistic Grey Trembler (right)

In 1726, the marooned Frenchman JulienTafforet described his encounters with the bird on an offshore islet in his report Relation d'île Rodrigue, which documented his 9-month stay in 1725. In 1874, Reverend Henry Horrocks Slater, a naturalist of the British Transit of Venus expedition, found subfossil bones of a starling-like songbird on Rodrigues proper, as had magistrate George Jenner shortly before. These are generally assumed to belong to the bird Tafforet wrote about. Some additional bones were found in 1974. Together, they represent most of the skeleton, except for the spine, pelvis and the small bones, and are mainly in the Cambridge Museum. The IUCN regards the Rodrigues Starling as a valid species, because Tafforet's report and the bones provide compelling evidence that it existed.^[1][2][3][4]

The bones found by Slater's team were the basis of the first scientific discussion by Albert Günther and Alfred Newton in 1879.^[2] According to Günther and Newton, the Rodrigues bird was closely related to the Bourbon Crested Starling (Fregilupus varius). Several authors have intimated that they would rather have placed the species in Fregilupus, but none seem to have actually done so. Even though James Greenway listed N. rodericanus as a junior synonym of F. varius, his description indicates that this was an inadvertent error. The 1974 bones allowed for a more thorough assessment, verifying that the Rodrigues bird is appropriately placed in the monotypic genus Necropsar, established by Slater in 1879. In 1900, believing Necropsar to be a misspelling, G. E. Shelley "corrected" it to Necrospa and attributed it – erroneously – to Philip Sclater. He also gave the authors of the species name as Günther and Newton, but their original text assigns authorship to Slater.^[2][5][6][7] Masauyi Hachisuka, believing the carnivorous habits described by Julien Tafforet to be unlikely for a starling and the lack of a crest suggesting against a close relationship with Fregilupus. He was reminded of corvids by the black-and-white plumage, and assumed the bird seen in 1725 was some sort of "chough". These at his time were often still held to include the White-winged Chough (Corcorax melanorhamphos) – which is actually not a corvid – and the "ground choughs" (Podoces). Still, Hachisuka believed Günther's and Newton's assessment regarding the bones to be accurate, only that according to him Tafforet's record could not have pertained to that bird. Thus, in 1937 he described the hypothetical "chough" as Testudophaga bicolor ("Bi-coloured Chough"). Hachisuka's assumptions are generally disregarded today for a number of reasons (see below).^[3][8][9]

N. rodericanus was frequently confused with a supposedly related but smaller species "N. leguati", described with specimen D.1792, a skin in the World Museum Liverpool, as holotype. This was also called "White Mascarene Starling" and variously considered a distinct parapatric or allopatric species, an immature, a colour morph or a female. It led some to believe that the Rodrigues Starling became extinct only about 1830, when the Liverpool specimen was collected. D.1792, however, was eventually identified as an albinistic individual of the Martinique Trembler (Cinclocerthia gutturalis).^{[5][8][10][11][12]}

Systematics

The Bourbon Crested Starling, a possible relative

Molecular phylogenetic analysis confirms Fregilupus varius to be a starling.^[13][14][15] The affiliations of N. rodericanus, presumably but not certainly closely related to it, have been open to more dispute. Mid-20th century studies found some similarities between the Bourbon Crested Starling and the Prionopidae (helmetshrikes and woodshrikes). The Necropsar bones, while indeed reminiscent of Fregilupus (and the Prionopidae), remind much more of a starling's.^[3][16][17] In recent times, several songbirds of the Madagascar region, whose relationships were believed to have been resolved, were instead found to be part of the vangas (Vangidae) or the as of 2009 unnamed "Malagasy warblers". These have both undergone spectacular adaptive radiations and might conceivably have evolved an insular starling-like form. Phylogenetically, an affiliation between the "Mascarene starlings" and either of the two Malagasy radiations – or the Prionopidae, for that matter – cannot be discounted as yet, in particular as no detailed comparisons seem to have ever been made.^{[15][18][19][20]}

That Tafforet compared his birds to a thrush and not to some other similarly sized bird – a quail or a grosbeak for example – at least suggests that they were rather thrush-like in habitus, and thus probably belonged to the basal Passeri or the Muscicapoidea, and not to the Sylvioidea, let alone the often colourful and sexually dimorphic and/or "finch"-like Passeroidea. Even the latter have, however, evolved an island taxon with highly unusual feeding habits (the Vampire Finch Geospiza difficilis septentrionalis). On account of the vocalisations, a placement with the Sturnidae seems indeed more likely than with more basal Passeri: the latter generally have harsh voices, while starlings' songs are indeed composed of a lively, diverse and usually quite musical chatter. It is interesting to note, though, that Tafforet did not compare the vocalizations more explicitly to those of e.g. the European Starling, a very widespread and common bird he almost certainly knew.^[21][22]

Description

According to Tafforet, the bird was slightly larger than the Common Blackbird (Turdus merula) he knew from France. This would imply a total length of about 25–30 cm, and a weight of perhaps 90–130 g. Judging from the bones, the bird was about 10% smaller than the Hoopoe Starling (Fregilupus varius), its presumed closest relative. Consequently, its length would have been about 25–28 cm and its weight perhaps 100–120 g when adult.^[2][23][24]

Skull of N. rodericanus (detail: articular facet of the mandible)

Its skeleton largely agreed with F. varius in proportions, but differed in some details. The skull was shaped somewhat differently, being longer (about 29 mm long from the occipital condyle), narrower (21–22 mm), with the eyes set slightly lower, the upper rims of the eye sockets being some 8 mm apart. The interorbital septum was more delicate, with a larger hole in its center. The bill was about 36–39 mm long, less curved than in F. varius and proportionally a bit deeper, and seems to have had larger nostrils, with the nostril openings in the bone 12–13 mm in length. The mandible was about 52–60 mm long and 4–5 mm deep proximally. Its ulna was somewhat shorter by comparison – measuring 37–40 mm versus 32–35 mm for the humerus – and the keel on its sternum was a bit lower, but its power of flight was not reduced. It had strong quill knobs on the ulna, indicating the secondary remiges were well-developed. One coracoid measured 27.5 mm in length, and one carpometacarpus was 22.5 mm long. The leg and feet had the same proportions in both; in N. rodericanus the femur measured around 33 mm, the tibiotarsus 52–59 mm, and the tarsometatarsus 36–41 mm.^[2]

The head and body plumage was white; tail and wings were partially black. It is not known whether the non-black (presumably white) part of the wings was a patch or wing-stripe, or simply the wing coverts or fringes or one vane, as is commonly seen in birds in general. Reconstructions tend to show the tail with black tips and lighter feather bases. But while this is more likely than white-ended black rectrices, these too are seen in some birds and thus the tail pattern is essentially conjectural; it might just as well have had white fringes or vanes for example. The beak, as well as the feet, were reported as yellow by Tafforet.^[2]

Tafforet makes no mention of marked sexual dimorphism, or of a pronouncedly different juvenile plumage. His 9-month visit is likely to have encompassed at least part of the breeding season, and if so almost certainly a time where postbreeding moult took place and when immature birds were around. Thus it may very well be that outward sexual and age differences were subdued or absent in N. rodericanus. The Bourbon Crested Starling had no pronounced sexual dichromatism either, but immature birds had a buffy tinge. The beak of its adult females was about one-tenth shorter than in males; it may be that this was due to niche partitioning to better utilize the limited resources of its island home. Too few skull remains of N. rodericanus have been found to date to assess whether it was similarly dimorphic. Among its limb bones – of which a larger number is known – the smallest do in fact measure 10% less than the largest.^[2][5][23]

Hypothetical restoration, based on subfossils and descriptions

Tafforet's complete 1726 description of the bird reads as follows, in Alfred Newton's 1875 translation:

A little bird is found which is not common, for it is not found on the mainland. One sees it on the islet au Mât [Ile Gombrani], which is to the south of the main island, and I believe it keeps to that islet on account of the birds of prey which are on the mainland, as also to feed with more facility on the eggs of the fishing birds which feed there, for they feed on nothing else but eggs or turtles dead of hunger, which they well know how to tear out of their shells. These birds are a little larger than a blackbird [Reunion Merle], and have white plumage, part of the wings and tail black, the beak yellow as well as the feet, and make a wonderful warbling. I say a warbling, since they have many and altogether different notes. We brought up some with cooked meat, cut up very small, which they eat in preference to seed."^[25]

Behaviour and ecology

Though there is no direct evidence that the bones are from the same species as Tafforet's birds, the absence of another suitable extinct or extant candidate and the severe competitive exclusion on such a resource-poor island like Rodrigues make it rather likely. No similar bird is known from elsewhere in the Mascarenes, excluding the possibility that the Rodrigues records refer to an ephemeral population of vagrants.^[26][27]

In his report, Tafforet asserted however that he did not encounter his Île Gombrani bird on mainland Rodrigues. He mentions some that were kept by his party, perhaps indicating that the breeding season so coincided with his 9-month visit for easily caught fledglings to be present. No mention is made of nesting sites on Gombrani, but even 30 years earlier few small birds were found to nest on mainland Rodrigues on account of the rats. While N. rodericanus might have been a ground-nester, this is not so likely; its presumed relatives are generally tree-nesting birds and starlings in particular are often cavity-nesters. There is, however, some woodland on Île Gombrani even today, and the abundant shrubs would have provided ample nesting sites. It is sometimes asserted as certain that the birds kept by Tafforet's party were not adult, but that is conjecture; the original text is ambiguous in that respect. With no report of nesting whatsoever, all that can be said is that Tafforet's encounter probably coincided with the end of the breeding season, after the young had fledged – if N. rodericanus was not easily caught even as adults, which is well possible and was noted in many Mascarene birds (including Fregilupus varius).^[21][28]

The Hurricane Palm (Dictyosperma album), one of the few palm species native to Rodrigues, is largely confined to the eastern mainland

Tafforet was not sure why the birds were absent from Rodrigues proper, though he was inclined to attribute it to birds of prey scaring off N. rodericanus. This might refer to migrant falcons (Falco), vagrant Réunion Harriers (Circus maillardi) which were more widespread in the Mascarenes in former times, and to the resident Rodrigues Owl (Mascarenotus murivorus). The former two, with their presence only temporary, are unlikely to have exerted a marked evolutionarly pressure on such a sizable endemic resident landbird. The owl on the other hand was not much larger than N. rodericanus and though probably able to subdue them would – in particular its smaller (Morepork-sized) males – have preferred less hefty victims. It is unlikely that the large passerine observed by Tafforet was originally confined to the islet, though seasonally it may have well been so. Overall, the absence of the bird from Rodrigues proper in 1725 is somewhat puzzling, but it may indicate an already-precarious state of the mainland fauna of Rodrigues (see also below).^[17][29]

The birds found by Tafforet's party lived on the Île au Mât (today Île Gombrani – sometimes transcribed "Combrani", "Gombranis" or "Mombrani"), an offshore islet of Rodrigues. The bones were found in caves on the Plaine Corail, the island's southwestern calcarenite limestone plateau east of today's Sir Gaëtan Duval Airport. Île Gombrani is due southeast offshore the Plaine Corail; consequently, the bird must have been fairly numerous at least on the island's southwestern end in former times. The close geographical and ecological association of Tafforet's record and the bones further supports the assumption that all records refer to a single species.^{[3][30][31][32]}

Many other species endemic to Rodrigues became extinct after humans arrived, and the island's ecosystem is heavily damaged. Before humans arrived, forests covered the island entirely, but very little remains today. The Rodrigues Starling lived alongside other recently extinct birds, such as the Rodrigues Solitaire, the Rodrigues Parrot, Newton's Parakeet, the Rodrigues Rail, the Rodrigues Owl, the Rodrigues Night Heron, and the Rodrigues Pigeon. Extinct reptiles include the Domed Rodrigues giant tortoise, the Saddle-backed Rodrigues giant tortoise, and the Rodrigues day gecko.^[33]

Diet

Tafforet also recorded some details on the birds' feeding habits. The food of the adults is described as "nothing else but [seabird] eggs or some turtles dead of hunger", and they apparently made effective use of the stout beak in foraging, tearing turtle flesh from the shells and presumably breaking open eggs. The (possibly young) birds kept by his party were given seeds of some tree and chopped-up cooked meat – possibly salt pork, beef or mutton which were the standard fare for ocean voyages at that time, but perhaps more likely turtle and tortoise meat procured on the island, as his group was effectively stranded on Rodrigues. Tafforet notes that the birds preferred the meat. Since it is unclear what vegetable food precisely Tafforet's party offered the birds, nothing can be said for certain on this. However, it is clear that the birds were at least not exclusively vegetarian. The skull shows an attachment scar above the temporal fossa which indicates it was used for "gaping" and forceful probing as in starlings. The supraoccipital ridge on the skull is quite strongly developed and a biventer muscle attachment in the parietal region below it is conspicuous. This indicates strong neck and jaw muscles, agreeing well with how Tafforet describes the birds' procuring meat from dead turtles. The presumably related Bourbon Crested Starling (Fregilupus varius) had also notably robust neck and jaw muscles and a good "gaping" ability.^[2][16][34]

Domed Rodrigues giant tortoise

These "turtles dead of hunger" may have been the giant tortoises then found on Rodrigues, Domed Rodrigues Giant Tortoise (Cylindraspis peltastes) and Saddle-backed Rodrigues Giant Tortoise (C. vosmaeri), both extinct by about 1800, but perhaps more likely Green Turtles (Chelonia mydas) and Hawksbill Turtles (Eretmochelys imbricata). The abundant vegetation on Île Gombrani is unlikely to have allowed land tortoises to starve even if they were able to reach the islet (which is not certain). Seabirds whose eggs would have been technically available as food to N. rodericanus were the Brown Noddy (Anous stolidus), Lesser Noddy (A. tenuirostris), White Tern (Gygis alba) and Roseate Tern (Sterna dougallii) which still are found on and around Rodrigues, as well as the Indopacific/Indian Ocean Sooty Tern (Onychoprion fuscatus nubilosus), Abbot's Booby (Papasula abbotti) and the Red-footed Booby (Sula sula) which are now extirpated or uncertain breeders on Rodrigues but were recorded by Tafforet and others. The Great Frigatebird (Fregata minor) and perhaps also the Lesser Frigatebird (F. ariel) were formerly recorded on Île Gombrani, but only to prey on other birds' eggs; though they bred on nearby Île Frégate, these aggressive birds are unlikely to have their eggs attacked successfully by a passerine. Bourne's Petrel (? Pterodroma sp.) which is entirely extinct, as well as the extirpated Barau's Petrel (P. baraui) and Mascarene Petrel (Pseudobulweria aterrima), seem to have nested near the top of Rodrigues' mountains in burrows, and their eggs were thus inaccessible to avian predators. Whether the eggs of the Wedge-tailed Shearwater (Puffinus pacificus), White-tailed Tropicbird (Phaeton lepturus) and Red-tailed Tropicbird (P. rubricauda) – cavity-nesters still breeding on offshore islets of Rodrigues – would have been readily available prey for N. rodericanus is doubtful. With Île Gombrani formerly noted for its abundance of Sooty Terns, it seems that this species yielded most of the "eggs of the fishing birds" Tafforet mentions as staple food of his songbird. Particularly the noddies, noted for their extremely docile behaviour, make notable secondary candidates.^[35][36]

Extinction

The cause for this bird's extinction and its date are not known, but can be deduced with fair certainty. With the dating of Tafforet's observation – and the identification of him as the author, which had long eluded researchers^[7] –, a terminus post quem for the extinction is established. Rodrigues is a small island, and was often visited throughout the 18th century to capture tortoises and sea turtles (until Cylindraspis peltastes and C. vosmaeri went extinct about 1800, too). By 1740, a major trade in these had developed, as their relatives on the other Mascarene islands were already gone or nearly so. The island must thus have been surveyed to a considerable degree by the mid-18th century. When A. G. Pingré during the French 1761 Transit of Venus expedition observed the seabird colonies of Île Gombrani in 1761, he found them still healthy; no trace of Tafforet's bird was noted, however, while the burgeoning Testudines-based economy of the island offered little other food than tortoise dishes in the nearly 15 weeks he stayed. Neither did Philibert Marragon see the birds some decades later; he already remarked upon the tortoises' impending extinction though. Quite likely, N. rodericanus became extinct within one decade of 1740.^{[37][38][39][40]}

Plaine Corail was probably more wooded in Leguat's time, but already had numerous hard-to-miss karst features (from where the bones of N. rodericanus were recovered)

That Tafforet did not encounter it on the main island, with a population essentially confined to one or a few islets and vulnerable to any stochastic catastrophe such as a tsunami or Mauritius cyclone, is suggestive of an extinction shortly thereafter. It is uncertain, however, whether his survey of the inhospitable^{[Note 1]} Plaine Corail region was thorough enough to find any birds remaining there. François Leguat, who was marooned with his companions in 1691–1693 on the north coast where now is Port Mathurin, does not explicitly mention the birds either in his extensive writings. Though his party visited most accessible parts of the island, he does not mention the striking karst-like landscape.^[41][42]

In general, the cause of the birds' disappearance was almost certainly some introduced species, rather than habitat destruction or overhunting, as the reports of the first long-term inhabitants contain no mention of the bird any more. Feral goats and other likely candidates were only present after Leguat's visit, but he noted the large numbers of rats, for which he had no satisfying explanation^{[Note 2]} (but see below). The initial rat population has been identified from old bones as Black Rats (Rattus rattus), though starting in the late 18th century these were probably replaced by the Brown Rat (R. norvegicus) which predominates today. As a tree-climbing predator of nestlings and eggs, the Black Rat would certainly represent a major threat to any insular endemic songbird. Species likely to have carried avian diseases to Rodrigues were not introduced until after the disappearance of N. rodericanus, and thus it seems as good as certain that Tafforet's bird was killed off by the Black Rat, succumbing when these finally reached the offshore islets. At Leguat's time, he noted that the islands he visited seemed rat-free,^{[Note 3]} and he reasoned that the Rodrigues Grey Pigeon ("Alectroenas" rodericana) nested only there because on the mainland rats were already too numerous.^{[Note 4][8][43][44]}

It is not clear when rats arrived on the island. Leguat's report is the first comprehensive one, and he mentions the main island overrun with them – and he does not mention the bulbul and presumed Old World babbler that once lived there. While Arabic, Swahili and maybe Pandyan sailors knew Rodrigues as (probably) Diva Harab ("Desert Island")^{[Note 5]} before the 16th century, the Late Medieval voyages of the Indian Ocean trade seem quite long ago even for the extreme overpopulation of rats observed by Leguat to develop. The island was relocated by Portugal in 1507 and visited (mainly by Dutch ships) occasionally from 1601 on; Leguat mentions inscriptions cut by Dutch sailors in the bark of several trees.^{[Note 6]}

With N. rodericanus as rare as to be overlooked for two years in 1693, still extant in 1725,^{[Note 7]} but extinct shortly thereafter, and some mainland birds apparently already extinct by 1691, it was probably roughly between 1550 and 1650 that the Black Rat settled Rodrigues.^{[31][45][46][47]}

Notes

References

Sources