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Ornithol. Sci. 18(2): 169-175

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Ornithol. Sci. 18(2): 169-175 Ornithol Sci 18: 169 – 175 (2019) REVIEW ARTICLE Preventing the extinction of the Lord Howe Woodhen (Hypotaenidia sylvestris) through predator eradication and population augmentation Dean PORTELLI1 and Nicholas CARLILE2,# 1 Department of Environment and Natural Resources, P.O. Box 1120, Alice Springs, NT, 0871 Australia 2 Office of Environment and Heritage, P.O. Box 1967, Hurstville, NSW, 2220 Australia ORNITHOLOGICAL Abstract The Lord Howe Woodhen (Hypotaenidia sylvestris) is endemic to Lord Howe Island off the mid-east coast of Australia and came perilously close to extinc- SCIENCE tion as a result of hunting pressure and introduced predators. A recovery program was © The Ornithological Society implemented in the 1970s to reverse the decline of the species through eradicating of Japan 2019 introduced predators (pigs, cats and goats) and augmenting the population through an in situ captive-breeding program. In 1980, three wild breeding pairs were taken into captivity from Mount Gower. Over the four years of the captive-breeding program, 76 chicks were produced from the original founders and their progeny and an additional four chicks were artificially reared from eggs collected from a wild pair. Almost all woodhens were liberated across four release sites, but only 13% of released birds were resighted and numbers increased at only one of these sites and then declined. A captive-bred female that was released into the lowlands paired with a wild male (which had been temporarily held in captivity) and bred prolifically, leading to rapid population growth in the lowlands. The subpopulation on Mount Gower increased fivefold in the decade following the captive-breeding program, despite the removal of the three breeding pairs (which were released elsewhere) and receiving no aug- mentation from the captive-breeding program. The woodhen population continues to expand and it is likely the eradication of invasive rodents from Lord Howe Island during 2019 will facilitate further population growth. Key words Rallidae, rail, Gallirallus, recovery program LORD HOWE ISLAND main island and its surrounding islets support 239 species of indigenous plants, with 113 endemic spe- Lord Howe Island is a crescent-shaped volcanic cies (DEC 2006). Endemism is similarly high among remnant located in subtropical waters 580 km off the the 1,608 invertebrate species identified from the mid-east coast of Australia. It has extensive shallow island group (Cassis et al. 2003). The island group’s coral reefs enclosed in a lagoon on the western side, native mammalian fauna comprises one extant and and is surrounded by several offshore islets, includ- one extinct microbat species (Duncan et al. 1999). ing Balls Pyramid (551 m) situated 23 km to the Like many islands worldwide, Lord Howe Island has south. Lord Howe Island is 11 km long, covers 1,455 experienced numerous bird extinctions since people ha and comprises two eroded volcanic peaks reaching first visited the island: three endemic species and 875 m (Mount Gower) and 771 m (Mount Lidgbird) five endemic subspecies have become extinct (Hutton in the south; a series of flats and lower hills in the 1991). Eighteen resident terrestrial bird species and middle (the lowlands); and a range of hills rising 14 migratory seabirds currently breed within the to 209 m in the north, which are the remains of a island group (Hutton 1991). This includes the Lord caldera shield (McDougall et al. 1981; Fig. 1.). The Howe Woodhen (Hypotaenidia sylvestris; hereafter woodhen), which is an endemic species that came perilously close to extinction and is currently clas- (Received 25 May 2017; Accepted 10 April 2019) # Corresponding author, E-mail: Nicholas.Carlile@environment. sified as Endangered by the IUCN (Birdlife Interna- nsw.gov.au tional 2016). 169 D. PORTELLI and N. CARLILE (see Olson 1973), but later revisions to the taxonomy of the Rallidae confirmed the woodhen belonged to the widespread genus Gallirallus (Kirchman 2012, García-R et al. 2016). The taxonomy of Gallirallus was revised by del Hoyo and Collar (2014), who placed the woodhen in a new genus, Hypotaenidia, along with nine other species. The male woodhen can be readily distinguished from the female by its larger size and more upright stance (Miller & Mullette 1985). They are monogamous and territo- rial, breed mostly during late spring to early summer, lay clutches of 1–4 eggs, and are capable of rearing more than one brood per year (Miller & Kingston 1980, Miller & Mullette 1985). POPULATION DECLINE AND ITS CAUSES From the discovery of the island in 1788 until it was first settled in the early 1830s, the woodhen was reportedly abundant (Table 1) and readily har- vested in large numbers by passing sailors (Miller & Kingston 1980; Frith 2013). Although historical accounts of the size of the woodhen population are anecdotal, it had declined substantially by the mid- 19th century, and as early as the 1880s its extinction was considered imminent (Miller & Kingston 1980; Frith 2013). Collectors failed to obtain woodhen Fig. 1. Distribution of Lord Howe Woodhen. Shaded areas specimens in 1853 despite an extensive stay on the indicate where woodhens were recorded during annual sur- island (MacDonald in Hindwood 1940). Moreover, veys between 2008 and 2015 (Lord Howe Island Board scientists and an eminent ornithologist struggled, or unpublished). Black circles indicate localities where woodhen failed, to locate the species in the late 1880s and occur outside the area surveyed each year. Stars indicate the early 1900s (Frith 2013). By 1936, the species was approximate location of the four main release sites (white confined largely to the rugged upper slopes and pla- stars) and the site where a captive-bred female was released teaus of the two southern mountains (Hindwood and paired with a wild male (black star). Contour intervals are 1940). From 1971, surveys estimated the surviv- spaced 20 metres apart. The lowlands are located either side of the airstrip. ing population of woodhen on Mount Gower num- bered 22 individuals, including only eight breeding pairs (Disney 1972; Fullagar & Disney 1975), with DISCOVERY AND DESCRIPTION OF THE a further 3–5 pairs estimated from the summit of LORD HOWE WOODHEN Mount Lidgbird (Fullagar & Disney 1975). By the late 1970s, only ten pairs were found on the summit The woodhen is a medium-sized (mean adult body and slopes of Mount Gower, two birds (both male) mass: 536 g male, 456 g female), dull olive brown, on Mount Lidgbird and a single bird in the lowlands flightless rail, with a long recurved bill, short tail, (Miller & Mullette 1985). The dire state of the popu- and chestnut flight feathers that are finely barred lation was well-established, but the efforts required black (Marchant & Higgins 1993). The first men- to reverse the decline were unclear due to unknown tion of the species was in 1788 (Miller & Kingston risks and costs (Recher & Clarke 1974). 1980), but it wasn’t formerly described until 1869 The dramatic decline of the woodhen was attrib- when Sclater named it Ocydromus sylvestris (Sclater uted to several factors; however, the relative impor- 1869). The woodhen was traditionally placed in the tance of each in driving the species towards extinc- genus Tricholimnas with the New Caledonian Rail tion is unclear. Anthropogenic impacts began with 170 Preventing the extinction of the Lord Howe Woodhen Table 1. Chronology of events for the Lord Howe Woodhen 1788 to 2018. Date and event Impact on woodhens and population status 1788 humans first visit Lord Howe Island Harvested for food. Woodhen common across island Early to mid-1800s feral pig and goat populations estab- Presumed predation by pigs. Habitat degraded by pigs and goats lished 1830s to 1850s human settlement and arrival of domestic Harvested for food. Predation by dogs and cats within settled dogs and cats areas. Woodhen remain common outside of settlement 1918 black rats colonise island from beached trading ship Impact of rats unclear 1936 visit to island by ornithologist Woodhens restricted to southern mountains Early 1970s first woodhen surveys 11–13 woodhen pairs remaining 1976 eradication of feral cats commenced 1979 eradication of pigs commenced Late 1970s woodhen resurveyed 10 woodhen pairs remaining 1980 woodhen captive-breeding program commenced Three woodhen pairs removed from Mount Gower to captive- breeding centre Early 1982 woodhen pair commence breeding at Salmon Woodhens increase in number and spread from Salmon Beach Beach into adjoining settlement 1982 cat eradication ceased, and ownership regulated Feral cat population eradicated and importation and breeding of domestic cats banned 1984 woodhen captive-breeding program ceased 81 woodhens released over 4 seasons across the lowlands and mountain slopes (no woodhens released on mountains) 1985 pig eradication program ceased Pig population effectively eradicated (one boar remaining) 1985 annual woodhen surveys commenced 11 woodhens counted on Mount Gower plateau 1988 woodhen survey 92 woodhens counted in settlement 1995 woodhen survey 55 woodhens counted on Mount Gower plateau 1999 eradication of goats commenced Goat population effectively eradicated (only three females present by 2012) 2002 woodhen survey 127 woodhens counted across accessible areas 2018 woodhen survey 221 woodhens counted across accessible areas hunting of woodhens for food by sailors and early indicates they were not the sole cause of the decline. settlers (Miller & Kingston 1980; Frith 2013). The Cats (Felis catus) were first brought onto the island introduction of several mammals to the island exacer- in the early to mid-1800s and subsequently estab- bated the decline. Pigs (Sus scrofa) were released on lished a feral population (Miller & Mullette 1985). the main island in ~1800 to provide a source of meat The impact of cat predation is poorly documented, for passing sailors and became widespread over the but it was probably partly responsible for the wood- southern half of the island (Miller & Mullette 1985). hen decline in the northern half of the island (NSW Pigs disturbed the forest floor where woodhens for- NPWS 2002).
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