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Discovery of the First Mascarene Giant Tortoise Nesting Site on Rodrigues Island, Indian Ocean (Testudinidae: Cylindraspis)

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Discovery of the First Mascarene Giant Tortoise Nesting Site on Rodrigues Island, Indian Ocean (Testudinidae: Cylindraspis) Herpetology Notes, volume 14: 103-116 (2021) (published online on 10 January 2021) Discovery of the first Mascarene giant tortoise nesting site on Rodrigues Island, Indian Ocean (Testudinidae: Cylindraspis) Julian P. Hume1,*, Owen Griffiths2, Aurèle Anquetil Andre3, Arnaud Meunier3, and Roger Bour4,† † We dedicate this paper to our friend, colleague, and co-author Roger Bour, a world expert on Mascarene tortoises and a life-long steam train fanatic, whose passing came much too soon. Abstract. Five species of giant tortoise (genus Cylindraspis) once occurred in huge abundance on the Mascarene Islands of Mauritius, Réunion, and Rodrigues. They disappeared after colonisation of the island by humans in the 17th and 18th centuries, primarily due to over-hunting and predation of eggs and young by introduced pigs and cats. So rapid was their extinction that virtually nothing is known about their life history, especially nesting and egg-laying behaviour. Here we report the discovery on Rodrigues of the first Mascarene tortoise-nesting site, which contained intact nesting chambers, complete egg clutches and fossil remains of a known native predator of tortoise eggs. We further compare the nesting behaviour with the giant tortoises of Aldabra Atoll in the Seychelles and the Galapagos Archipelago in Ecuador and provide details of the decline and extinction of Mascarene tortoises, most notably those of Rodrigues, for which good historical records exist. Keywords. Mauritius, Réunion, Aldabrachelys gigantea, Chelonoidis, egg chamber, clutches, extinction “There are such plenty of land-turtles in this Isle [Rodrigues], that sometimes you see two or three thousand of them in a flock; so that one may go above a hundred paces on their backs; or, to speak more properly on their carapaces, without setting foot to the ground.” [François Leguat 1708: 65] Introduction due to direct human impacts and the introduction of invasive species, epitomised by the loss of the iconic The isolated, volcanic Mascarene Islands of dodo, Raphus cucullatus (Linnaeus, 1758), of Mauritius Mauritius (20.3°S, 57.6°E), Réunion (21.1°S, 55.5°E), (Cheke and Hume, 2008). A diversity of endemic giant and Rodrigues (19.7°S, 63.4°E) are situated in the tortoises once inhabited these islands, with Cylindraspis southwestern Indian Ocean, with Madagascar, the indica (Schneider, 1783) on Réunion featuring highly nearest large landmass, some 665 km to the east of variable shell shapes, the dome-shelled C. inepta Réunion. Rodrigues (Fig. 1A) is the smallest of the Günther, 1873 and the saddleback-shelled C. triserrata Mascarene Islands, only 17.7 km long and 8.5 km wide, Günther, 1873 on Mauritius, and the dome-shelled C. with a surface area of 104 km². The Mascarenes have peltastes (Dumeril & Bibron, 1835) and the saddleback- been subject to extremely high biota extinction rates shelled C. vosmaeri (Suckow, 1798) on Rodrigues (Arnold, 1979; Bour, 1980, 1981; Bour et al., 2014a). Although giant tortoises were abundant on all of the Mascarenes, Rodrigues harboured one of the densest 1 Bird Group, Department of Zoology, Natural History Museum, populations of giant tortoises on Earth, estimated at Akeman Street, Tring, Herts HP23 6AP, United Kingdom. 150,000–200,000 individuals (North-Coombes, 1971). 2 La Vanille Réserve des Mascareignes, Senneville, Rivière des The importance of giant tortoises as fresh meat and Anguilles, Mauritius. 3 Francois Leguat Giant Tortoise and Cave Reserve, Anse to obtain oil for mariners on long sea voyages resulted Quitor, Rodrigues Island, Mauritius. in their over-exploitation, and as soon as settlement 4 Muséum National d’Histoire Naturelle, 57 rue Cuvier, 75005 began on the Mascarenes, thousands were killed Paris, France. indiscriminately (Mondini, 1990; Cheke and Bour, * Corresponding author. E-mail: [email protected] 2014). The Mauritius mainland populations disappeared © 2021 by Herpetology Notes. Open Access by CC BY-NC-ND 4.0. by 1721, with only small numbers of tortoises surviving 104 Julian P. Hume et al. Figure 1. (A) Map of Rodrigues Island with place names mentioned in the text. A globe with Rodrigues marked as a point (inset) shows the position of the island in the southwestern Indian Ocean. Based on remains and historical observations, giant tortoises were found in all of these localities, including the islets, but would have formerly occurred all over the island. The white rectangle identifies Petit Butte and the tortoise nesting area. (B) Precise location and excavation pits of the tortoise nesting area at Petit Butte. The white outline designates the approximate maximum extent of the tortoise nesting area. Discovery of the First Cylindraspis Giant Tortoise Nesting Site on Rodrigues Island 105 on surrounding islets until the 1730s, or possibly until Freycinet (1825) reported the discovery of the first as late as the 1870s on Round Island (Cheke and Hume, fossil bones and eggs of Cylindraspis tortoises on 2008; Cheke and Bour, 2014). Réunion tortoises were Mauritius (the present whereabouts of this material extirpated by the 1730s in the lowlands (Bory de Saint- is unknown), which had been buried in volcanic tuff Vincent, 1804; Bour, 1979, 1981; Cheke and Bour, and could be dated to the Middle Pleistocene, since 2014) but, remarkably, a small population survived in the last eruption on the island occurred around 31,000 the remote montane refuge of Cilaos until at least 1840 YBP (Moore et al., 2011; Cheke et al., 2016). The only (Hermann, 1903; Bour et al., 2014a; Cheke and Bour, other discovery of Cylindraspis eggs in the Mascarenes 2014). Tortoises on Rodrigues remained comparatively was made by Bour et al. (2014a), who described four unmolested until the early 18th century, but after the incomplete eggs of C. indica buried in soft sediment and extinction of the populations on Mauritius and Réunion, excavated by Jean-Pierre Esmiol and Roger Bour near attention turned to the more off-the-beaten-path Boucan-Canot, northwestern Réunion. Unusually for Rodrigues (North-Coombes, 1994). extant giant tortoises, the eggs were ellipsoidal and not The Huguenot refugee François Leguat had reported spherical (but see below). the abundance of tortoises during his stay in 1691–93 During an excavation on the right side of their (Leguat, 1708), and in 1725 a reconnaissance party garden to insert a septic tank at Petit Butte, Plaine was sent from Réunion to ascertain the importance Corail, southwestern Rodrigues, in 2017, the Milazar of then uninhabited Rodrigues to French colonial family noticed a continuous layer of broken eggshells strategy, which included ships’ mate Julien Tafforet at approximately 400 mm depth (identified hereafter (North-Coombes, 1971; Dupon, 1974). Tafforet as PB1). Destruction of the site during excavation became marooned on Rodrigues for eight months and prompted Denis Claude Milazar to start a second small subsequently wrote a detailed report on the island and excavation on the left side of the garden (PB2). Careful confirmed the abundance of giant tortoises (Tafforet, removal of sediment revealed almost complete tortoise 1725–26). As a direct result, a tortoise hunting station eggs and a possible nesting chamber, but the discovery was set up on Rodrigues in 1735 to provide meat and oil lacked contextual data. AAA and AM returned to the to the burgeoning colonies on Mauritius and Réunion site for further analysis and examined the eggs and (Herbert and Nichelson, 1780; Cheke and Hume, the locality. Once the importance of the discovery was 2008; Hume, 2019). A holding pound was installed on realised, a scientific team led by JPH and OG excavated Rodrigues to prepare tortoises for shipment, with an the site in 2018 in a community effort that included equivalent facility at Port Louis, the capital of Mauritius, participation of local landowners, staff of the François to receive them (Cheke and Hume, 2008; Cheke and Leguat Cave and Giant Tortoise Reserve (FLR), Bour, 2014). North-Coombes (1994) estimated that Mauritius Wildlife Foundation (MWF), and members of over 280,000 tortoises were butchered on Rodrigues or the Rodrigues Regional Assembly (RRA). This process exported alive between ca. 1732 and 1771, with around proved extremely productive, with fossil remains found 10,000 taken annually for the first two decades. It was over a substantial area adjacent to the coast (Fig. 1B). only due to the collapse of the giant tortoise populations Here we report on the excavation of the first recorded in the 1770s that the slaughter ended, as it was then no nesting site of the endemic Mascarene giant tortoises, longer viable to collect them (North-Coombes, 1971). which includes the description of eggs and egg A single live tortoise was collected in 1786 on the chambers, and the discovery of unhatched young and Plaine Corail, southwestern Rodrigues (Hume et al., an associated natural predator. We further compare 2015), with the last record of two seen around 1795 the nesting behaviour of Rodrigues Cylindraspis giant in inaccessible gorges by the Civil Administrator of tortoises with those of other giant tortoises and discuss Rodrigues, Philibert Marragon (Bour et al., 2014b). the reasons for their decline and extinction, most notably Such was the speed of their extinction that virtually for those on Rodrigues, for which historical data exists. nothing was recorded about the life history of the Mascarene giant tortoises, especially nesting and egg- Materials and Methods laying behaviours. Reports that the tortoises sought out dry coastal areas for laying, with the eggs incubated by Only part of the left side of the Milazar family garden the sun, were the only exceptions (Leguat, 1708; Mundy remained pristine, so excavation of two further sites in Temple, 1914; Lougnon, 2006). (PB3 and PB4) began to the west (PB3) and to the south 106 Julian P. Hume et al. (PB4) of PB2 (Fig. 1B). PB3 and PB4 measured 3 x 2.5 a 1-m, twice-daily sea level rise and fall.
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