Great Maui crake

Great Maui crake
Conservation status
Extinct (early-mid 2nd millennium)  (IUCN 3.1)
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Order:	Gruiformes
Family:	Rallidae
Genus:	Porzana
Species:	†P. severnsi
Binomial name
†Porzana severnsi Olson & Helen F. James, 1991
Island of Maui (Landsat pseudocolor image) Great Maui crakes inhabited at least the southern third of the bigger eastern part of the island

The great Maui crake or great Maui rail ("Porzana" severnsi) is an extinct bird species from Maui, Hawaiian Islands, known only from subfossil bones. The holotype (USNM collection numbers 378344 to 378363) are the bones of one almost-complete skeleton, found in Auwahi Cave on the lower southern slope of Haleakalā at 1,145 m AMSL. Its first remains, however, were recovered in 1972 and/or 1974 from lower Waihoi Valley further east and less than half as far uphill.

It was known as the larger Maui rail until its formal description, to distinguish it from the other flightless rail species which lived on Maui until after the arrival of humans. Traditionally placed in the "wastebin genus" Porzana, it almost certainly does not belong there, but while its placement in subfamily Himanthornithinae is generally agreed upon, its precise affiliations are disputed. Its scientific name refers R. Michael Severns, in honour of his pioneering discoveries of lava caves with remains of extinct animals on Maui.

Description and systematics

The great Maui crake was similar to this Ash-throated crake in size and shape, but with much shorter wings and possibly darker and/or duller plumage

The great Maui crake was the larger of two species of rail found on the island of Maui. It was roughly the size of a Ash-throated crake or half again as large as the Hawaiian rail, about 20-25 cm (8-10 in) altogether, with a fairly thin and almost straight beak some 2 cm (slightly less than 1 inch) long, and weighing roughly 100 grams (3.5 oz). It was flightless due to its small wings – the entire arm, from fingertips to shoulder joint, was only about 5.5 cm (some 2 in) long, and the humerus was about 10% smaller in all dimensions than in the Great Oʻahu crake which was similarly-sized and also flightless. In the holotype, the sternum was even partially unossified despite the bird being fully grown, and had 6 large holes which would have prevented the development of anything but vestigial flight muscles. The legs, on the other hand, were at least as well-developed as in the Oʻahu species, with the tarsometatarsus measuring 36 mm on average.

The species' plumage is unattested, but most likely it had a brownish-greyish cryptic coloration – possibly almost blackish, or with some dark or pale spotting on the upperside – and perhaps with white-and-black vertical barring on the body between legs and tail like its probable relatives.

At the time of its description, the great Maui crake was placed in genus Porzana, which at that time was already suspected to be a polyphyletic assemblage of rails which consisted of at least 2 different lineages. Cladistic analyses were conducted for the species, but the results are not consistent: In 1998 it was analyzed in a combined group together with the other extinct Hawaiian rails in a morphology-based analysis. This analysis could only place it with certainty within a group which roughly corresponds to subfamily Himanthornithinae as it is circumscribed today; as later analyses revealed that the Hawaiian rails are almost certainly not a monophyletic group, it is unsurprising that the chimeric combined pseudo-"taxon" could not be placed more certainly. The morphological data were included in a 2021 study which also utilized DNA sequence data to create a well-supported framework aiding placement of prehistoric species for which no molecular data was available. Here, the great Maui crake was resolved as sister species to the small Maui crake ("P." keplerorum), and these two in turn as sisters to the Laysan rail (Zapornia palmeri), suggesting the Maui crakes are both also members of the revalidated genus Zapornia, which was long included in Porzana.

However, ancient DNA had successfully been isolated from both Maui crakes, and used in a molecular phylogenetic analysis; here, the Maui crakes did not turn up as sister species, but while the smaller species was indeed clearly part of the Zapornia clade, the relationships of "P." severnsi could not be determined with any amount of certainty. What seems clear is that it was not part of the lineage of the Spotless crake (Zapornia tabuensis) and its closest relatives; however, as of 2023 neither the raw DNA sequence data, nor details and results of the analytical methods beyond a brief summary in 2003 had been published. As the sister genus of Zapornia, Rallina, was at that time still believed to be a very distantly related lineage of rails, it is unlikely to have been included in the analysis, which also probably used only a few short snippets of DNA. Consequently, with limited data and probably lacking the proper outgroup to Zapornia, all that can be concluded from the molecular analysis is that "P." severnsi might have belonged to a different branch of Zapornia than the Spotless crake – in line with the 2021 study –, or it might have been a distinct lineage in tribe Zapornini, or – less likely – belonged to another tribe of Himanthornithinae. If this is true, the morphological similarities between the Maui crakes found in the 2021 analysis would represent convergent evolution, e.g. due to the limited ecosystem diversity on Maui enforcing similar adaptations in both species. In any case, placement in genus Porzana is almost certainly wrong, as this has turned out to be a lineage of Himatornithidae that is entirely unrelated to Zapornia.

Ecology and extinction

The drier western part of the great Maui crake's known range. The visible coastline is almost exactly adjacent to that in the from image below.
Many localities where remains of the species were found are in the upper left quarter of the photo.

Its ecology is mostly conjectural, but not likely to have differed much from the still-extant, slightly smaller, and probably fairly closely related Henderson crake. It was almost certainly omnivorous, feeding mostly on invertebrates, seeds, and perhaps occasionally fruit, bird eggs, and carrion. The shape of the fossil premaxilla and mandible suggests that its bill was moderately robust, of modest height, with only a slight curve at the very tip, and notably compressed laterally; while the premaxillary symphysis is quite short, the mandibular symphysis is a remarkably long and troughlike fusion of the mandibular rami – compared to the similar-sized Great Oʻahu crake which presumably ate similar-sized items, the Maui species was better able to extract food from small and narrow crevices, with the stiff and narrow mandible especially suited for open-mouthed probing. The great Maui crake's remains have so far been found only on the drier parts of Haleakalā, but below the almost desert-like upper slopes, in a region which even before human settlement and associated deforestation was mostly covered in shrubland and open koa/ʻōhiʻa lehua forest and at least seasonally arid.

The Hawaiian crow or ʻalalā once inhabited Maui, and probably preyed on great Maui crakes occasionally. Today, it is extinct in the wild.

The more humid eastern part of the species' known range. Note rain clouds barely extending to the leeward side of Haleakalā.
Lava tubes near the center of the photo have yielded additional remains of this rail.

Its flightlessness indicates that predation pressure was not overly strong; at any rate, mammalian predators were absent on Maui before humans arrived. Of the animals that might have preyed on "P." severnsi, the pueo owl still inhabits the island today, while Great and Lesser frigatebirds roam the offshore waters and occasionally venture overland to forage for small land animals; all these species would have posed a threat to an unwary great Maui crake. More dangerous would have been the Hawaiian hawk and – especially during nesting – the ʻalalā crow, which are not found on Maui today. The latter persisted at least to the initial stages of humans settlement, and is attested for this island by subfossil remains however, while the former is not, so either the Hawaiian hawk's breeding population on Maui was small, or it only ever occurred there as a vagrant – prehistoric hawk remains are rare on all islands which formerly made up Maui Nui, while on Oʻahu to the northwest and the Big Island to the southeast they are much more numerous. In addition, Maui probably was visited by vagrant individuals, or even held a resident population, of the mime harrier, which resembled a sparrowhawk in wing anatomy and probably hunted small birds in the shrubbery; while it was specialized for feeding on songbirds like Hawaiian honeycreepers, it was perfectly capable of preying at least on juvenile great Maui rails too. Finally, the Maui stilt-owl, which could hunt equally well on the wing and on foot, was the smallest member of its genus Grallistrix, roughly the size of a Desert owl. Technically, it could tackle a half-grown great Maui crake, or an adult it surprised while asleep – but it probably was only barely capable of subdueing a full-grown and alert adult "P." severnsi: similar-sized owls generally eat prey weighing less than 50 g (about 2 oz), and rarely ever attack animals the presumed weight of an adult great Maui crake. In this regard, the different abundances of the two Maui crakes among the remains of Maui's prehistoric birds are notable – usually, of two coexisting and closely related species with similar habits, the smaller species is expected to be more numerous, but among Maui crakes it seems to have been the other way around. Possibly, the stilt-owl preyed extensively on the smaller rail and largely avoided the larger one, and/or the larger rail was more fecund, with a clutch size of around 6 eggs as is typical for volant Zapornia and Rallina, and unlike the 2-3 eggs attested for the flightless and island-dwelling Laysan rail and Henderson crake. What is clear is that the stilt-owl was found in the very same deposits that yielded material of the great Maui crake, and that some ecological factor or parameter must have differed strongly between the two rail species.

Other than in Auwahi Cave, remains of this species have also been found in several other lava caves on the southern slope of Haleakalā, as well as in the Lower Waihoi Valley Cave about halfway between Hana and Kīpahulu near the eastern tip of the island, i.e. basically all across the southern part of today's Hana district. It ranged from sea level at least halfway up Haleakalā, and possibly as high as 1,860 m above sea level. Whether it inhabited other parts of Maui – such as the tropical rainforest on the northeastern slope of Haleakalā –, or whether it was restricted to the semi-arid woodland habitat where its remains were found, is not yet known; as of 2023 no deposits elsewhere on Maui have been studied. Before human settlement, and to some extent even today, similar habitat to where the great Maui crake's remains were found extended to the western side of Haleakalā, and all the way to Puʻu Kukui volcano which forms Maui's western end.

Before humans arrived, at least on eastern Maui the great Maui crake was apparently far more plentiful than its smaller relative; it is attested by abundant remains whereas considerably less "P." keplerorum material was recovered. While no "P." severnsi were found in a cultural context such as a village hearth or midden yet, it is very likely that the great Maui crake was eaten by Polynesian settlers, especially after the giant flightless moa-nalo ducks had been hunted to extinction. It may have also have been predated by Polynesian rats that were introduced by those settlers. In addition, the region where its remains were discovered is one of the most long-standing areas of dryland taro cultivation on Maui, and was extensively deforested starting about 1400 CE, which possibly decreased the carrying capacity for any remaining rails and certainly increased opportunities for people to hunt them. By November 26 1778, when Maui was discovered by Europeans, the species was apparently entirely extinct already.

References

• Boyer, Alison G. (2008): Extinction patterns in the avifauna of the Hawaiian islands. Divers. Distrib. 14(3): 509-517. doi:10.1111/j.1472-4642.2007.00459.x PDF fulltext
• Garcia-R, Juan C. & Matzke, Nicholas J. (2021): Trait-dependent dispersal in rails (Aves: Rallidae): Historical biogeography of a cosmopolitan bird clade. Mol. Phylogenet. Evol. 159: 107106. doi:10.1016/j.ympev.2021.107106 PDF preprint
• James, Helen F.; Stafford, Thomas W. Jr.; Steadman, David W.; Olson, Storrs L.; Martin, Paul S.; Jull, A.J.T. & McCoy, Patrick C. (1987): Radiocarbon dates on bones of extinct birds from Hawaii. Proc. Natl. Acad. Sci. USA 84(8): 2350-2354. doi:10.1073/pnas.84.8.2350 PDF fulltext
• Kirch, Patrick V.; Coil, J.; Hartshorn, A.S.; Jeraj, M.; Vitousek, Peter M. & Chadwick, O.A. (2005): Intensive Dryland Farming on the Leeward Slopes of Haleakala, Maui, Hawaiian Islands: Archaeological, Archaeobotanical, and Geochemical Perspectives. World Archaeol. 37(2: Garden Agriculture): 240-258. doi:10.1080/00438240500095074 PDF fulltext
• Kirchman, Jeremy J.; McInerney, Nancy Rotzel; Giarla, Thomas C.; Olson, Storrs L.; Slikas, Elizabeth & Fleischer, Robert C. (2021): Phylogeny based on ultra-conserved elements clarifies the evolution of rails and allies (Ralloidea) and is the basis for a revised classification. Ornithology 138(4): .1–21. doi:10.1093/ornithology/ukab042 PDF fulltext
• König, Claus & Weick, Friedhelm (2009): Owls of the World (2nd ed.) (Helm Identification Guides). A&C Black. ISBN 978-0713665482
• Livezey, Bradley C. (1998): A phylogenetic analysis of the Gruiformes (Aves) based on morphological characters, with an emphasis on the rails (Rallidae). Phil. Trans. Roy. Soc. B 353(1378), 2077-2151. doi:10.1098/rstb.1998.0353 PDF fulltext
• Olson, Storrs L. (1973): A Classification of the Rallidae. Wilson Bull. 85(4): 381-416. PDF fulltext
• Olson, Storrs L. & James, Helen F. (1982): Prodromus of the fossil avifauna of the Hawaiian Islands. Smiths. Contrib. Zool. 365: 1-59. doi:10.5479/si.00810282.365 PDF fulltext
• Olson, Storrs L. & James, Helen F. (1991): Descriptions of Thirty-Two New Species of Birds from the Hawaiian Islands (Part I. Non-Passeriformes). Ornithol. Monogr. 45: 1-88. PDF fulltext</ref>
• Olson, Storrs L. & James, Helen F. (1997): Prehistoric status and distribution of the Hawaiian hawk (Buteo solitarius), with the first fossil record from Kauai. Bishop Mus. Occas. Pap. 49(Records of the Hawaii Biological Survey for 1996 – Part 2: Notes): 65–69. PDF fulltext
• Slikas, Beth (2003): Hawaiian birds: lessons from a rediscovered avifauna. Auk 120(4): 953-960. doi:10.1093/auk/120.4.953
• Slikas, Beth; Olson, Storrs L. & Fleischer, Robert C. (2002): Rapid, independent evolution of flightlessness in four species of Pacific Island rails (Rallidae): an analysis based on mitochondrial sequence data. J. Avian Biol. 33(1): 5-14. doi:10.1034/j.1600-048X.2002.330103.x PDF fulltext
• Taylor, P. Barry & van Perlo, Ber (1998): Rails: a guide to the rails, crakes, gallinules, and coots of the world (Helm Identification Guides). Yale University Press, New Haven. ISBN 0-300-07758-0