The Rodrigues night heron (Nycticorax megacephalus) is an extinct species of heron that was endemic to the Mascarene island of Rodrigues in the Indian Ocean. The species was first mentioned as "bitterns" in two accounts from 1691–1693 and 1725–1726, and these were correlated with subfossil remains found and described in the latter part of the 19th century. The bones showed that the bird was a heron, first named Ardea megacephala in 1873, but moved to the night heron genus Nycticorax in 1879 after more remains were described. The specific name megacephala is Greek for "great-headed". Two related extinct species from the other Mascarene islands have also been identified from accounts and remains: the Mauritius night heron and the Réunion night heron.
The Rodrigues night heron was robust, its bill was comparatively large, stout and straight, and its legs were short and strong. It is estimated to have been long, and its appearance in life is uncertain. There was marked sexual dimorphism, males being larger. Little is known about the bird's behaviour, but the contemporary accounts indicate that it ate lizards (probably the Rodrigues day gecko), was adapted to running, and although able to fly, rarely did so. Examinations of the known remains have confirmed its terrestrial adaptations; one researcher thought the species flightless but this idea has not been accepted by others. The species could not be found by 1763, and it is thought to have been driven to extinction by human-related factors such as the introduction of cats.
Taxonomy The French traveler Francois Leguat mentioned "bitterns" in his 1708 memoir A New Voyage to the East Indies about his stay on the Mascarene island of Rodrigues from 1691–93. Leguat was the leader of a group of nine French Huguenot refugees who settled on Rodrigues after they were marooned there. Leguat's observations on the local fauna are considered some of the first cohesive accounts of animal behaviour in the wild. In 1873, the French zoologist Alphonse Milne-Edwards described subfossil bird bones from Rodrigues he had received via the British ornithologist Alfred Newton. These had been excavated in 1865 under the supervision of his brother, Colonial Secretary Edward Newton, by the police magistrate George Jenner, who found the specimens in a cave on the Plaine Corail, near Rodrigues solitaire remains.
Milne-Edwards correlated the bones with the "bitterns" of Leguat's account, but found that they were instead consistent with belonging to a species of heron, whose large head and short legs made it understandable that it was compared to a bittern. He considered the skull different from all other herons in size and shape, but found the tarsometatarsal foot bone similar to that of the extant heron genus Ardea, and therefore named the new species Ardea megacephala. The specific name megacephala is Greek for "great-headed", and references the large head and jaws of this species. The bones examined by Milne-Edwards included the skull, tarsometatarsus, tibiotarsus (lower leg bone), femur (thigh-bone), sternum (breast-bone), coracoids (part of the shoulder-girdle), humerus (upper arm bone), and metacarpals ("hand" bones). The holotype specimen (the specimen the specific name and original scientific description is attached to) is an incomplete but probably specimen catalogued as UMZC 572 at the Cambridge University Museum of Zoology. This specimen since appears to have lost a humerus, a dorsal rib, both femora, a tibiotarsus, and both tarsometatarsi.
In 1875, A. Newton correlated references to "bitterns" with the heron in the then recently rediscovered 1725–26 account of the French sailor Julien Tafforet, Relation de l'Ile Rodrigue, which he thought confirmed Milne-Edwards's conclusions. More fossils were obtained from caves by the palaeontologist Henry H. Slater in 1874, and these were described by the German zoologist Albert Günther and E. Newton in 1879, with the benefit of bones not known at the time of Milne-Edwards's original description. They included the two last cervical vertebrae (of the neck), fifth dorsal vertebra (of the back), pelvis, scapula (shoulder blade), ulna (lower arm bone), radius (lower arm bone), second phalanx of the inner toe, and first of the hind toe. These bones are now part of the collection of the Natural History Museum, London. Günther and Newton did not find it necessary to describe these bones, as they were the same form as in other herons, particularly the night heron genus Nycticorax, and they therefore transferred the Rodrigues species there, as Nycticorax megacephalus.
In 1893, E. Newton and the German ornithologist Hans Gadow referred to the bird as Ardea (Nycticorax) megacephala, and the British zoologist Walter Rothschild used the original name Ardea megacephala in 1907, while noting that he was inclined to believe the three extinct Mascarene herons (which had previously been assigned to either Ardea or Butorides) all belonged in Nycticorax. The Japanese ornithologist Masauji Hachisuka concluded in 1937 that this species was little related to any other heron, and moved it to a new genus as Megaphoyx megacephala. He also used the common name "Rodriguez flightless heron", due to his conviction that it had lost the ability to fly. In 1953, Hachisuka used the name "flightless heron" and added that this species was "quite remarkable" among herons, and not closely related to any other heron, extant or extinct. The American ornithologist Pierce Brodkorb kept the species in Nycticorax in 1963.
The British ecologist Anthony S. Cheke referred to the bird as Nycticorax ('Megaphoyx') megacephalus in 1987; in the same book, the British ornithologist Graham S. Cowles stated that a then recently rediscovered skull in the NHM confirmed that the species was a Nycticorax night heron. He also considered the two extinct herons of the other Mascarene islands, the Mauritius night heron (N. mauritianus) and the Réunion night heron (N. duboisi), to belong to that genus. In 1999, the French palaeontologist Cécile Mourer-Chauviré and colleagues considered the tarsometatarsi of the Mascarene night herons closer in proportion to the black-crowned night heron (N. nycticorax) than to other members of the genus, particularly the nankeen night heron (N. caledonicus).
An associated but incomplete skeleton preserving the skull and jaws was discovered in Caverne Poule Rouge in 2006. Cheke and the British paleontologist Julian P. Hume stated in 2007 that although the Mascarene night herons may have originated in Madagascar, the black-crowned night heron that they probably descended from is so widespread that they could also have colonised from Asia. Due to the diminished flight capabilities of the Rodrigues and Mauritius night herons, they suggested that the Mascarenes must have been colonised twice in any case, as these birds could not have been the ancestors of the longer-winged Réunion night heron.
Hume explained in 2023 that night herons have successfully colonised oceanic islands and archipelagos, the island endemic species becoming increasingly adapted to a terrestrial lifestyle due to a lack of terrestrial mammals. This led to increased size and robustness in their legs, with a corresponding shortening of the wings, which led to lesser flight capabilities compared to their ancestral populations, as well as more robust jaws. Hume stated that while there had been no molecular analysis to examine the interrelationships of the Mascarene herons, the Rodrigues and Mauritius species appear to have been closely related. Hume added that a complete Rodrigues night heron sternum he had found in Caverne Dora in Plaine Corail near other subfossil bird bones was the only known specimen of this species photographed in the location it was found, and that radiocarbon dating of a nearby Rodrigues scops owl humerus gave a range of 3060–2870 years before present.
Description
The Rodrigues night heron was robust, its bill was comparatively large, stout and straight, and its legs were short and strong, and more robust than those of the related Mauritius night heron. There was marked sexual dimorphism in the Rodrigues night heron, which is also present in the black-crowned night heron, and the male was the largest. There is a 17.5% length difference in the tibiotarsus between male and female specimens, 9.3% difference in the tarsometatarsus, and a 9.1% difference in the available mandibles. The difference was almost the same in the Mauritius night heron, and there was little dimorphism in the Réunion night heron.
The Rodrigues night heron is estimated to have been long. Measurements of the bones available by the late 19th century show that the skull was long, the upper mandible was long and wide at the base, and the lower mandible was long. The sternum was long, the scapula , the coracoid , the humerus , the ulna , the radius , and the metacarpal . The pelvis was long, the femur , the tibiotarsus , the tarsometatarsus , and the second phalanx bone .
The Réunion night heron was the largest of the three Mascarene night heron species in most features, except for in the tarsometatarsus, which was almost the same size as in the Rodrigues night heron, and the femur, which was smaller than in the Rodrigues species. In the Rodrigues night heron, the supratendinal bridge ("bridge" over a tendon) of the tibiotarsus was entirely ossified (turned to bone), whereas it was incompletely ossified in the Réunion species, and unknown in that of Mauritius. The wing-bones of the Rodrigues and Mauritius species, including the humeri, ulnae, and carpometacarpi, were quite reduced, and the legs, the femora in particular, were longer than in extant species. The short and thick proportions of the tarsometatarsi in the Mascarene species were closest to the black-crowned night heron within their genus, this robustness probably being accentuated by the reduced flight abilities of the Rodrigues and Mauritius species.
The life appearance of the Rodrigues night heron is uncertain. Hachisuka speculated that Leguat referred to these birds as "bitterns" because their colouration may have reminded him of the plumage of the bitterns native to France, whose feathers are buffish, mottled with black. On the other hand, Tafforet likened them to egrets, which are white, so Hachisuka thought this a contradiction of Leguat, if it also referred to colouration. One 1674 account stated that the related Réunion night heron had "grey plumage, each feather tipped with white, the neck and beak like a heron and the feet green", which is similar to juveniles of extant Nycticorax herons. Hume stated in 2023 that this probably means that the Mascarene herons retained their juvenile (paedomorphic) plumage into adulthood, as is the case for some other island birds.
Behaviour and ecology
Little is known about the behaviour of the Rodrigues night heron apart from the two contemporary descriptions, but it was better documented that its Mauritius relative. Leguat's 1708 description reads as follows, referring to these birds as "bitterns":
The "lizards" mentioned were probably geckos of the genus Phelsuma (there were six gecko species on Mauritius), such as the now extinct Rodrigues day gecko, which reached in length. Leguat and his companions were fond of these quite tame lizards, letting them feed from their tables, and therefore tried to protect them from the aggressive herons. In 2023, Hume interpreted Leguat's account as indicating that the bird was very tame and confiding, and not afraid of humans, as is common in many island birds.