Important Areas Henderson Michael Brooke

Abstract Subtropical Henderson Island is one of the Pitcairn in the central South Pacific. Although over 600 years of Polynesian occupation have left an ecological mark, not least the continuing presence of Polynesian Rattus exulans, the 37-km2 island is the Pacific’s best example of an ecologically intact raised coral island. For this reason it was designated a World Heritage Site in 1988. Four landbirds occur, all endemic to the island, of which the most distinctive is the flightless Henderson Crake Porzana atra. The others are a lorikeet, a fruit dove and a warbler. abound. These comprise a mix of widespread tropical such as boobies and noddies, and species with more restricted Pacific distributions, notably Pterodroma petrels. For one of these, the P. atrata, Henderson is the only known nesting station. However, fieldwork has established that the rats are devastating predators of petrel chicks. To benefit petrels and to achieve wider ecosystem restoration, eradication is now being actively planned. If successful, it would be easily the largest rat eradication achieved on British territory.

enderson Island is a name that is Remote does not imply unwelcoming. perversely uninformative. It neither Mean monthly temperatures vary from Hgenerates an instant association with around 23°C (February) to 16°C (June), one of the giants of exploration, like the Ross while annual rainfall, about 1,600mm, is Sea, nor smacks of fire and brimstone, like plentiful but not excessive (Spencer 1995). Tierra del Fuego, nor smells of frangipani Trade winds from an easterly or southeasterly wafting across the South Seas, like Tahiti. But direction predominate. Benign indeed, espe- prosaically named Henderson, one of the cially in the absence of mosquitoes and other UK’s two World Heritage Sites designated for invertebrate irritants. its natural history, as opposed to cultural, From afar, Henderson appears as a low interest, is in fact a South Pacific conserva- slab barely showing above the horizon. But tion jewel. increasing numbers of gadfly petrels hint to Lying just south of the Tropic of Capri- the approaching seafarer that land is not far corn at 24°20’S 128°20’W, Henderson is one off. Most of that land is a pan-flat plateau, of the . The other islands of about 30 m above sea level. Two-thirds of the this UK Overseas Territory are Pitcairn itself, perimeter is surrounded by vertical cliffs the only inhabited island and famously the dropping into blue waters that are supremely hideaway of the Bounty mutineers, and the clear because ocean productivity in the low atolls of Oeno and Ducie (all three of region is low. The remaining third of the them also Important Bird Areas). To a first island is girt with coral reefs, a narrow lagoon approximation, the islands are halfway and white beaches. On one of those beaches, between New Zealand’s North Island and the East Beach, Green Turtles Chelonia mydas Ecuador. Some 4,500 km from the nearest nest. Behind the beaches are pockets of continental land, 37-km2 Henderson is one of woodland which give way to fern-clad slopes the world’s remotest islands (fig. 1). rising towards the plateau woodland.

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The plateau woodland rises to about 6 m and is thick, so thick in fact that it is difficult and sometimes impossible to walk except where a path has been cut by machete. Also impeding progress are the rough condi- tions underfoot: brittle slabs of dead coral, giant clam shells, limestone dissected by 2-m ‘crevasses’. These provide the clue to Henderson’s origin and ultimately its biological interest. The volcanic base of Henderson, emerging from the abyssal plain 2 km below, is about 13 million years old (Spencer 1995). When this emerged from the sea, an island surrounded by reefs

was presumably formed and, Art © Fluke in time, this developed into a Fig. 1. Henderson Island and the Pitcairn group. low atoll. Then, around one million years ago, 170 km to the southwest, History Pitcairn erupted. As a result, the earth’s crust In 1988, Henderson’s natural history was not under Pitcairn was depressed while, by a well known, since visits had been few and far process of lithospheric flexure, the crust between. European discovery is attributed to under Henderson started to rise. So too did the Portuguese sailor Pedro Fernandez de the overlying Henderson Island, and it con- Quiros, who passed without landing in 1606 tinues to rise at about 1 mm per decade. The (but named it San João Baptista). The island result is that the coral of the plateau has now received its current name when visited in been high and dry and very dead for about 1819 by the British East India Company ship 380,000 years (Blake 1995). Hercules under the command of Captain Most of the Pacific’s raised coral or Henderson. The following year witnessed one makatea islands of any size have been sub- of the most remarkable episodes in Hen- stantially damaged by human settlement. Not derson’s recorded history. Three small whale- so Henderson, which currently has no boats arrived carrying the surviving crew of permanent human inhabitants. What makes the whaler Essex, wrecked 2,700 km to the this particularly significant is that the island’s north by an irate Sperm Whale Physeter gradual continuing uplift has enhanced catodon, the inspiration for Herman Henderson’s biological interest. No longer do Melville’s Moby Dick. After a hungry, week- tropical storms wash over the island, setting long sojourn on Henderson, the 17 seamen the evolutionary clock back to zero. Instead, set forth in their boats for Chile. The voyage terrestrial plants and reaching the saw intense hardship, the disappearance of island have the opportunity to evolve and one boat, and cannibalism. Only five men ultimately speciate into endemic taxa. It was survived. Meanwhile, the three sailors who this combination of high endemism and an elected to remain on Henderson were rescued intact, distinctive ecosystem relatively unbur- after a stay of four months (Philbrick 2000). dened with introduced species that led to Not surprisingly, this episode added little to Henderson’s designation as a World Heritage the stock of scientific knowledge. This stock Site in 1988. was, however, increased a century or so later

British Birds 103 • August 2010 • 428–444 429 Brooke Michael Brooke 242. While apparently pristine and used by nesting Green Turtles Chelonia mydas, Henderson’s East Beach is depressingly cluttered with such jetsam as fishing buoys and plastic bottles. Michael Brooke 243. Climb a tree in the centre of Henderson and the view across the canopy cloaking the flat plateau is the same in every direction. A compass is essential! All photographs in this article were taken during a visit to Henderson in August/September 2009.

430 British Birds 103 • August 2010 • 428–444 Henderson Island by a phosphate-prospecting party which evidence of this occupation, which is obvious spent about five months on Henderson in even to a non-specialist, for example human 1912 under D. R. Tait, without finding com- bones and crafted clam shells. A large mercially useful deposits. midden crammed with fish and bird bones Specifically scientific visits followed from extends over some 300 m by 30 m under the the Whitney South Seas Expedition (1922), woodland behind the North Beach, in the the Mangarevan Expedition (1934) and the very spot opposite the reef passage used as a Westward Expedition (1971). In the early campsite by modern expeditions. The ebb 1980s, an American strip-mining millionaire, and flow of the Polynesian occupation was A. M. ‘Smiley’ Ratliff, proposed building a unravelled by Marshall Weisler of the holiday home and airstrip. This proposal 1991/92 Expedition and brought to wider drew howls of anguish from the conservation notice by Jared Diamond (2005) in his book community, indirectly contributed to the Collapse. World Heritage designation, and prompted a In the early centuries of the occupation, realisation that Henderson was inadequately those few tens of people dwelling on Hen- documented. A small Smithsonian Exped - derson maintained contact with Pitcairn, 170 ition in 1987 might have been the precursor km to the southwest, and Mangareva in the to a larger venture. However, this did not Gambier group of southeast French Poly- eventuate and the Sir Peter Scott Commem - nesia, a further 450 km to the northwest. The orative Expedition to the Pitcairn Islands of evidence of contact with those two islands 1991/92 filled the gap. The expedition comes from archaeological items such as vol- involved 34 people from seven countries, canic glass tools and oyster-shell fish-hooks with expertise in most branches of natural respectively, derived from materials not avail- history. Their efforts, spread over 15 months, able on Henderson itself. While the bones of documented Henderson’s biota, geology and children suggest that the Henderson popula- archaeology. Since then, there have been tion was resident, it was very possibly supple- several shorter follow-up visits, but the sheer mented by visitors from Pitcairn at key times difficulty of reaching isolated Henderson and of year, for example during the turtle nesting the inaccessibility of most parts of the island season, which runs from January to March. still curtail scientific progress. However, around 1450, inter-island contact It was this isolation that shaped the period ceased. Instead of Pitcairn’s volcanic stone, of Polynesian occupation, which began the inhabitants turned to locally sourced around AD 900 (Weisler 1995). To this day, giant clam shells for their stone tools, Hen- nearly all of Henderson’s larger caves show derson’s limestone being wholly unsuitable.

The Pitcairners’ use of Henderson When the Bounty mutineers reached Pitcairn in 1790, they did not know of Henderson. The first visit by Pitcairners to Henderson was in 1843, and two further visits were made in 1851. These were little more than reconnaissance visits, and were only possible because of the chance availability of a vessel for the journey. In the past 80 years, journeys made to Henderson have had the primary aim of harvesting the ‘tou’ Cordia subcordata and ‘miro’ populnea woods favoured for carving the curios now so important to the Pitcairn economy. Tou is probably a Polynesian introduction: it is found only behind the North and East Beaches on Henderson. Rosewood or ‘miro’ is also a Polynesian introduction, restricted to the North Beach and North West Beach woodlands. From the late 1930s occasional trips were made to cut wood. Often the wooden Pitcairn long-boats would literally hitch a ride to Henderson on a Panama-bound ship, and then sail home with the trade winds following. Only since the arrival of the tough, aluminium-hulled long-boats (Tin, the first, was delivered in 1983) have regular trips to Henderson been possible. Pitcairners usually visit Henderson once a year, but occasionally pay up to three visits in a year when weather conditions are particularly favourable. These visits, normally accompanied by the Pitcairn Conservation Officer, potentially allow management activity.

British Birds 103 • August 2010 • 428–444 431 Brooke Michael Brooke 244. Sheltered from the prevailing easterly trade winds, Henderson’s North West Beach is usually calm enough to allow landing, but the vegetation behind the beach is particularly thick. Richard Richard Cuthbert 245. Any protracted visit to Henderson entails bringing ashore all foodstuffs and enough drinking water to last until rainwater can be caught on specially adapted tarpaulins.

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Two centuries later, occupation ceased. before the cataclysmic impact of the Polyne- Whether the final inhabitants breathed their sians (Steadman 1995). The Henderson last on Henderson or decided to cobble species, probably derived from the Spotless together a raft and escape what had become a Crake P. tabuensis (Ripley 1977), is small (c. prison will never be known. 70 g) and all-black in plumage, with red- Although the Polynesian occupation did orange legs and an olive-and-black bill. The not destroy Henderson’s ecology, it left an breeding period is extensive, with eggs laid indelible mark. At least six snail species dis- from mid July to mid February. Sometimes appeared (Preece 1995). Whether their disap- older chicks help to rear their younger sib- pearance was due to predation by the lings. Population estimates have varied Polynesian Rats Rattus exulans, introduced between 3,240 and 6,200 individuals (Graves by the Polynesians, or because of other eco- 1992; Jones et al. 1995). Either way, it is not logical perturbations is unknown. And there scarce. Its pugnacity at the nest seems to were during this period profound impacts on provide adequate protection against rat pre- bird populations. These were first publicised dation, although it may be that rats depress by David Steadman and Storrs Olson (1985), the rails’ food supply and hence their who documented bones collected in 1971 numbers. and whose paper’s title provocatively men- The Henderson Fruit Dove Ptilinopus tioned ‘man-caused extinctions on an “unin- insularis, a small, handsome, red-capped rep- habited” island’. The full extent of these avian resentative of a widespread across the extinctions was documented by Graham Pacific, has a population numbering about Wragg (1995) during the 1991/92 Expedi- 3,000 individuals (Brooke & Jones 1995). tion. The plant community was also changed While the raspberry-like fruits of Procris forever. For example, Cordyline fruticosa pedunculata are especially important in the (called ‘ti’), introduced because its broad dove’s diet, perhaps because they are a source leaves could provide thatching or food wrap- of water as well as nutrition, the diet includes ping, remains common in clifftop communi- most fruit species available on the island. ties fringing the plateau. This is slightly surprising because another Just as the Polynesians arrived from the three pigeon species – of which more below – west, so generally did the flora and fauna, were resident until rendered extinct after the presumably because of the far greater density Polynesians’ arrival. How did the four species of stepping-stone islands to the west of Hen- partition the available but limited food derson as compared with the east. The resources? Furthermore, the routine occur- western origin is well exemplified by the rence of frugivorous pigeons on remote flora, comprising 71 vascular plants recorded Pacific islands prompts classic chicken-and- (Kingston & Waldren 2003), nine of which egg questions. How could the pigeons estab- are endemic to Henderson and one endemic lish before fruits were available year-round, to the Pitcairn group (occurring on Hen- but how could fruiting trees establish before derson and Pitcairn only). Since the next there were pigeons to provide seed-dispersal substantial island eastward, , is services? 1,300 km away, it is not surprising that a Scarcest of the landbirds is the Henderson number of plant genera (e.g. Alyxia) reach Lorikeet Vini stepheni, also known as their eastern limit on Henderson, adding to Stephen’s Lory, of which there are about the island’s biogeographical interest (Flo- 1,200 individuals. As is true of the other rence et al. 1995). endemic landbirds, it is clearly derived from congeners found farther west in the Pacific, Landbirds but today the Henderson Vini species is the Of pre-eminent interest among the landbirds only member of the genus still to be living in is the flightless Henderson Crake Porzana habitats little altered by humanity. It feeds on atra, one of possibly seven species of flight- nectar, pollen (using its brush tongue), fruit less rails extant on Pacific Islands. This total and arthropods (Trevelyan 1995). No nest is a sorry remnant of an estimated 800 has ever been found. species that formerly dwelt across the Pacific The Henderson Reed Warbler Acrocephalus

British Birds 103 • August 2010 • 428–444 433 Brooke Michael Brooke 246. The endemic nectar-feeding Henderson Lorikeet Vini stepheni is a poorly known endemic: the nest has never been found. taiti is a fairly robust ‘utility’ Acrocephalus about 2,500 km west of Henderson. One dis- warbler in the mould that seems to routinely tinctive feature of the three species is the ten- evolve on remote islands. There are compa- dency towards albinism, which Holyoak rable species on, for example, the Cape (1978) suggested might aid individual recog- Verdes, the Seychelles, the Hawaiian Islands nition in the absence of a warbling song. The and (Pacific) Christmas Island. The Hen- warbler is the commonest of the landbirds, derson species is closely related to the Pitcairn with a population around 10,000 individuals Reed Warbler A. vaughani and the Rimitara (Graves 1992; Brooke & Hartley 1995). Egg- Reed Warbler A. rimitarae, the latter found laying takes place from September to December, when around one-third of territories are occupied not by pairs but by trios. Such trios, either of one male and two females or two males and one female, are of birds unrelated to one another. Possibly, if territories are hard to obtain in the stable conditions of Henderson, coali- tions of three birds Michael Brooke 247. Allied to the Spotless Crake Porzana tabuensis, the Henderson Crake aid territory acqui- P. atra is one of the few species of flightless rail to have survived the Polynesian sition (Brooke & impact in the South Pacific. (The individual shown here is in temporary captivity). Hartley 1995).

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Shorebirds and other migrants wintering in Polynesia, had been seen previ- Henderson is so remote and so manifestly ously on Oeno and Pitcairn (Brooke 1995a), not en route from somewhere to somewhere so its occurrence on Henderson might have else that passage migrants are effectively been anticipated. unknown. That said, shorebirds visit regu- larly, with numbers greatest during the Extinct landbirds northern winter. The commonest is the While Henderson today is home to just four Bristle-thighed Curlew Numenius tahitiensis, landbird species, there were formerly more reaching a maximum of about 50 (Brooke (Wragg 1995). An extinct ground dove Galli- 1995a). Food includes small Ocypode ghost columba leonpascoi had relatively enlarged leg crabs and the berries of a shrub . and reduced wing bones, suggesting that it Since the world population of this Vulnerable was nearly, if not actually flightless (Worthy species is about 7,000 individuals, the Hen- & Wragg 2003). This pattern of reduced derson population, nearing 1% of the global wings and enlarged legs is repeated in total, is one of the reasons why the island is another extinct columbid, the imperial recognised as an Important Bird Area. pigeon Ducula harrisoni (Wragg & Worthy Next in abundance is the Wandering 2006). The third pigeon to vanish after the Tattler Heteroscelus incanus, of which up to Polynesian arrival, Bountyphaps obsoleta, was 30 have been recorded. Other species (e.g. the largest and most distinct of the three, Grey Plover Pluvialis squatarola, Pacific belonging to a newly described genus Golden Plover P. fulva and Sanderling (Worthy & Wragg 2008). Calidris alba) occur in tiny numbers. The final known extinction was of a sand- Remarkably, Henderson is visited, possibly piper in the genus Prosobonia, to which the routinely, by a landbird migrant. This is the extant but now extremely rare (and Endan- Long-tailed Koel Urodynamis taitensis, which gered) Tuamotu Sandpiper P. cancellata was recorded for the first time in August 2009 belongs (though the latter is sometimes (R. Cuthbert pers. comm.) The species, an placed in Aechmorhynchus). While the Hen- austral migrant breeding in New Zealand and derson form was apparently a distinct species Michael Brooke 248. The Henderson Fruit Dove Ptilinopus insularis is a member of a genus represented by about 15 similar species across Polynesia and further species in Australasia and southeast Asia.

British Birds 103 • August 2010 • 428–444 435 Brooke Michael Brooke 249. Henderson’s most numerous and visible migrant is the Bristle-thighed Curlew Numenius tahitiensis, which breeds in Alaska. Up to 50 are present during the northern winter. Michael Brooke 250. Although Great Frigatebirds Fregeta minor and Masked Boobies Sula dactylatra are not the best of friends, especially when the Booby, as here, is forced to regurgitate its catch, it seems that frigatebirds obtain only a small proportion of their food by such kleptoparasitism.

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(Wragg 1995), it is difficult to conceive that pairs seems likely. That scourge of boobies, about 3 km of beach and a few hundred the Great Frigatebird Fregeta minor, has a hectares of open terrain at the south end of similar nesting season to the Red-footed Henderson could have sustained the world Booby, and there are probably around 100 population of an endemic wader species. Did pairs. Red-tailed Tropicbirds Phaethon rubri- the extinct sandpiper’s range perhaps extend cauda nest throughout the year, mostly in to Oeno and Ducie, and farther afield to the rocky niches either around the clifftops or in ? the open terrain of the south end. A guess of In contrast to these extinct endemics, the 250 pairs is the best available. other known landbird extinction on Hen- Four tern species occur on Henderson. derson was of the still-widespread Pacific Both Brown Anous stolidus and Black Swallow Hirundo tahitica. The bones of this Noddies A. minutus lay in September and species were found mostly in cave sites and October and their populations number included a significant proportion of imma- around 100 pairs. The small and entrancing tures, and it seems highly probable that it Blue-grey Ternlet Procelsterna cerulea is seen once bred on the island (Wragg 1995). so regularly around Henderson’s cliffs that it seems inconceivable that it does not breed; Seabirds but nests have not actually been found. The The assemblage on Henderson con- fourth breeding tern species, the Fairy Tern tains a mix of widespread tropical or sub- Gygis alba, is certainly the most numerous, tropical species and regional specialities. nesting through the year and in woodland Before considering the latter intriguing across the island. There could be 10,000 group, mostly petrels, I shall mention the pairs. Finally, while the remains of Sooty former. Terns Sterna fuscata have been discovered Around 50 pairs of Masked Booby Sula among Polynesian material and the species is dactylatra nest on the North and East seen overhead today, there is no evidence of Beaches of Henderson. Egg-laying is year- breeding, past or present. round whereas that of the Red-footed Booby S. sula is concentrated in the months Petrels and the impact of rats June–August (Brooke 1995a). Because Red- Henderson is, without question, one of the footed Boobies are tree-nesters and their petrel capitals of the world, and this is nests are scattered across the plateau, no ade- reflected in the archaeological studies. Petrel quate census has been possible, but 100–200 bones outnumbered those of any other group

EBA, IBA and AZE status Henderson is an Endemic Bird Area because all four landbirds, the crake, dove, lorikeet and warbler, are confined to the island and are therefore recognised as restricted-range species (i.e. have global distributions of less than 50,000 km2). All four are classified as Vulnerable (www.birdlife.org). Henderson qualifies as an Important Bird Area on several criteria (Brooke 2006): (i) It holds significant populations of six Globally Threatened Species – Henderson Petrel, Henderson Crake, Bristle-thighed Curlew, Henderson Fruit Dove, Henderson Lorikeet and Henderson Reed Warbler. (ii) It holds the entire world population of four restricted-range species, i.e. the four landbird species. (iii) It holds at least 1% of the world population of Henderson, Herald and Kermadec Petrels and of Fairy Terns. (iv) More than 10,000 pairs of seabird regularly breed on the island. Henderson is an Alliance for Zero Extinction site (AZE: a global initiative among biodiversity conservation organisations which aims to prevent extinctions by identifying and safeguarding key sites where species are in imminent danger of disappearing – see www.zeroextinction.org) since it is the only known nesting station of the Endangered Henderson Petrel.

British Birds 103 • August 2010 • 428–444 437 Brooke Michael Brooke 251. Allied to the noddies, the diminutive Blue-grey Ternlet Procelsterna cerulea has a distribution that stretches across the tropical and subtropical Pacific. Michael Brooke 252. Nearly all the world’s Murphy’s Petrels Pterodroma ultima nest in the Pitcairn Islands, on Henderson, Ducie and Oeno. The latter two are now rat-free; Henderson may become so.

438 British Birds 103 • August 2010 • 428–444 Henderson Island in the first analysis, that of the 1971 finds by island area. On that basis, the populations reported by Steadman & Olson (1985). The of Herald Pterodroma heraldica and Hen- same was true in Graham Wragg’s (1995) derson Petrels P. atrata are 11,000 and 16,000 report. A little over half (6,894 out of 12,976) pairs respectively, with Kermadec Petrels of the bones unearthed belonged to the P. neglecta totalling perhaps 10,000 pairs. medium-sized gadfly petrels now living on Until the 1991/92 Expedition, Herald and the island. This abundance suggests both that Henderson Petrels had been viewed as pale surface-nesting petrels were immensely and dark morphs of the one species, Herald important in the diet of the Polynesian Petrel. In the course of that expedition, colonists and that they were formerly very Brooke & Rowe (1996) assembled behav- abundant. The latter is entirely possible. If ioural and molecular evidence to make the the nesting density had been one pair for case that the two forms, which paired strictly every six square metres, only half the density assortatively, were two species. While pale currently prevailing on Ducie (Brooke Herald Petrels are widespread in the Pacific, 1995b), then Henderson might have accom- Henderson is the only proven nesting station modated about 6 million pairs when the of the dark Henderson Petrel, which had first Polynesians first settled. been collected in 1769 by Daniel Solander on If these speculative calculations are even Cook’s first voyage, about 100 km southwest roughly correct, then today’s populations are of Henderson. but pale shadows of the past. Because of the The final, reasonably common species difficulty of moving over the Henderson known to nest on Henderson is Murphy’s plateau, and because the three more Petrel P. ultima. While the other three species numerous species breed throughout the year, nest on the plateau, Murphy’s Petrel nests the census figures reported (Brooke 1995b) either in the woodland behind the beaches or are rough-and-ready. They are derived by in low fern scrub close to the island’s cliffs. It assuming that all nesting attempts within 3 m is also the only species that is firmly seasonal, of the machete-cut paths of known length are with laying occurring between late May and detected over the year, and then multiplying early July. Although the population is not Michael Brooke 253. A rare sight on Henderson Island, a well-grown Murphy’s Petrel Pterodroma ultima chick. Over 95% of chicks are eaten, within a week of hatching, by Polynesian Rats Rattus exulans. This suggests that the Murphy’s Petrel colony on Henderson is sustained by immigration, presumably from the far larger colony on Ducie.

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large, around 2,500 pairs, the accessibility of eggs and then rather promptly lost their breeding pairs allowed me to gather fairly chicks. Candidate predators were either the detailed incubation data. Remarkably, the 50- large Coenobita hermit crabs or the rats day incubation is completed in about three introduced by the Polynesians some 700 stints. After the female has laid, the male years ago (Weisler 1994). After a number of takes the first turn, averaging 19.3 days. long and uncomfortable vigils, the culprits There follows a stint of similar duration by were spotted: rats. While the newly hatched the female and then the male for a second chick remains under its parent, it is safe. But, time. The egg normally hatches towards the after a day or two, when it moves to one side, end of the male’s second stint. it becomes vulnerable. With the parent pro- It is intriguing to speculate where viding only desultory and, it must be said, Murphy’s Petrels might travel during their incompetent protection, the rats are able to off-duty periods. A conservative flying speed approach and snatch the chick, pulling it of 40 kph and 12 hours of straight-line flying away from the nest. It is then eaten, some- per day would give a bird, off-duty for 19 times while still alive. Often only the hatched days, a potential foraging radius of 4,600 km. shell and a bloody morsel of flesh a metre This would certainly bring the highly pro- from the nest remain. An estimated 25,000 ductive Antarctic Polar Front, 3,260 km to chicks a year meet this grisly fate. the south, within range. Even the rich waters Because of this heavy rat predation, off California, 6,500 km to the north, could breeding success was extremely low, under be reached if the birds flew for more than 12 20% for Herald and Henderson Petrels, hours a day, and Murphy’s Petrels are seen under 5% for Murphy’s Petrel (Brooke most often in those waters during the incu- 1995b). While in theory the Henderson pop- bation months of June and July. ulations of Herald, Kermadec and Murphy’s During the 1991/92 Expedition, it quickly Petrels could be sustained by immigration became evident that these four petrel species, from other colonies, such as that on Ducie, nesting under cover of vegetation but essen- there is no substantive evidence that this is tially on the ground, typically hatched their the case. On the other hand, in the absence of Alve Henricson 254. Population modelling suggests that the Henderson Petrel Pterodroma atrata, not certainly known to breed other than on Henderson Island, is progressing steadily towards extinction because of rat predation on chicks.

440 British Birds 103 • August 2010 • 428–444 Henderson Island Michael Brooke 255. The Kermadec Petrel Pterodroma neglecta is a species that varies from white-bellied, white- headed individuals to those that are entirely dark. However, all morphs have the characteristic white primary shafts. known colonies elsewhere, there is no source 2003, with RSPB support, was it possible to of immigrants to sustain the Henderson return for a period of fieldwork timed to Petrel population. I return below to the ques- coincide with the Murphy’s Petrel hatching tion of how this population may persist. period. Predation on their chicks was just as Following these field observations, severe as that 12 years earlier and so it Wildlife Management International, a New seemed fair to assume that predation on Zealand consultancy, proposed a rat eradica- Henderson Petrel chicks was also equally tion programme in the Pitcairn Islands. severe. Furthermore, stable-isotope analysis While rat predation on the small atolls of (Brooke et al. 2010a) suggested that petrels Oeno and Ducie appeared less severe than on were a fairly minor component of rat diet. Henderson itself, at least the creation of two This implied that, if petrel numbers dwin- rat-free havens in the Pitcairn Islands could dled, there was no reason to hope that rat only benefit petrels and other wildlife. In the numbers would also decline and allow petrel event, the 1997 rat operations on Oeno and recovery via reduced predation. Throw in the Ducie, funded by the British Government results of mathematical modelling and a clear and World Wide Fund for Nature, were com- conclusion emerged: the Henderson Petrel pleted successfully, while two rat eradication would become extinct without conservation attempts on the larger, more rugged and intervention (Brooke et al. 2010a). more logistically complex Pitcairn were Before considering the practicalities of rat unsuccessful. eradication on Henderson Island, I should At this stage, rat eradication on Hen- mention other procellariiform species associ- derson itself was reckoned impractical. ated with the island. The specific identity of However, the issue of whether the Henderson Phoenix Petrels Pterodroma alba, identified Petrel was on a steady downward trajectory either in the fossil record (e.g. Steadman & towards extinction loomed. Pertinent to the Olson 1985) or recorded by the Whitney answer was whether the rat predation Expedition in 1922 (Murphy & Pennoyer observed in 1991 was the norm. Only in 1952) is open to question. In fact, the single

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Whitney specimen shows features interme- rats from Henderson. With support from the diate between P. alba and P. heraldica (Brooke UK Foreign Office’s Overseas Territories 1995b). But, given that Hadoram Shirihai Environment Programme (OTEP), a feasi- (pers. comm.) saw birds with such interme- bility study was commissioned (Brooke & diate characters in flight over Henderson in Towns 2008). This concluded that rat eradi- 2006, this is a puzzle still awaiting conclusive cation on Henderson, using helicopters to resolution. Shirihai also saw Collared Petrels broadcast cereal bait containing the anticoag- P. brevipes offshore. It is certainly possible ulant poison brodifacoum, was feasible but that this species also breeds. challenging. But there were still unanswered The Polynesian occupation coincided with questions to be resolved before it would be the local extirpation of Wedge-tailed Puffinus prudent to give the green light to the project. pacificus and Christmas Shearwaters P. nativ- The first question concerned the hermit itatis, Black-winged Petrels Pterodroma crabs, which exist at high densities in the nigripennis and Polynesian Storm-petrels beach-back woodland and eat bait pellets Nesofregetta fuliginosa (Wragg 1995). While without being harmed. If pellets are removed rats probably played a critical role in the dis- by crabs, they are of course unavailable to the appearance of the smaller species, other rats. Therefore, could a modest increase in factors may have contributed to the loss of the baiting density, above that used on other Wedge-tailed Shearwaters. That said, islands, achieve the aims of feeding the crabs recolonisation by all four species could be first and leaving enough for the rats? hoped for if rats were eliminated. The next question concerned the rails, which, from experience on New Zealand Planning for rat eradication on islands, might suffer a temporary reduction Henderson in population from bait pellets. While there is In the past 20 years, the ability of conserva- no expectation of more than a short-lived tionists to rid islands of rats has increased by setback to the wild population, no risk of col- leaps and bounds, to the extent that the lateral accidental extinction is acceptable. results of the 2003 visit prompted the RSPB Therefore, a captive population, safe from to think ever harder about the eradication of poison, must be established during the Michael Brooke 256. Although the rats Rattus exulans introduced to Henderson by the Polynesians are principally vegetarian, they are also important predators of petrel chicks.

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Visiting Henderson Not to beat about the bush, visiting Henderson is very difficult. Smaller cruise ships with around 100 passengers do visit the island for a few hours as part of a Tahiti–Easter Island journey that also includes landings at Pitcairn and Ducie. See, for example, Hapag-Lloyd Cruises (www.hl-cruises.com) or Zegrahm Expeditions (www.zeco.com). These are luxury operators and correspondingly expensive. Sometimes people passing the island on yachts step ashore but, in the absence of a safe anchorage, a landing cannot be guaranteed. Those contemplating bona fide scientific work, involving a longer stay, should contact [email protected] to obtain the necessary permissions. Once that is done, it will still be necessary to charter a boat for the journey from Mangareva, which can be reached by Air Tahiti flights, to Henderson at a cost likely to run into tens of thousands of pounds. Finally, it is planned that MV Claymore (www.visitpitcairn.pn) will provide a more regular link for passengers and supplies between Mangareva and Pitcairn than has been the case in the past. It could be that this link will occasionally provide opportunities for passengers to extend their journey to include a short visit to Henderson. baiting operation. Could it be shown that proceed in August/September of either 2011 rails can be caught ‘on demand’ and kept or 2012. healthy in captivity for a month or more? Once the bait had been distributed, the Finally, there is a paucity of information ship would sail away. Two years later, the stan- about the impact, if any, of brodifacoum on dard interval, a return visit to Henderson snails. Are Henderson’s endemic snails at risk would confirm, all being well, the absence of during a baiting operation? rats. This would be easily the largest rat eradi- Further fieldwork in August and Sep- cation achieved on British territory, and a tember 2009, supported by OTEP and the convincing signal that the British Govern- Packard Foundation, addressed these ques- ment was taking its conservation responsibili- tions (Brooke et al. 2010b). This fieldwork ties in the UK’s Overseas Territories seriously. confirmed that: with increases in bait density With the patter of rats’ feet no longer that did not involve unacceptably high input heard among the leaf litter, Henderson would of poison to the environment, crab hunger slowly be transformed. Landbirds, no longer could be assuaged, leaving sufficient bait for competing for food with rats, would prob- rats; rails could be caught and held in small ably increase. Some insect species, possibly wire cages, where they thrived on an insecti- currently kept at very low population levels vore rearing mix; and snails showed no by rat predation and therefore undetected, interest in poison bait pellets, let alone sus- might emerge. And petrel populations would ceptibility to them. recover. Since there is no reason to suppose that their squid prey is any less abundant The future than it was in pre-Polynesian times, the petrel With a green light given to a major restora- populations could recover to numbers last tion project on Henderson, the RSPB is now seen 1,000 years ago. This recovery would putting its considerable expertise behind the take some 100 years to complete, and not be search for funds1. It is hoped that the target, witnessed by either the author or any BB in excess of £1.5 million, will be achieved by a readers alive today, but it would surely be a combination of contributions from major major conservation victory. charitable foundations, private donors and Acknowledgments the British Government. The operation, The work described had its genesis in the Sir Peter using a ship to transport helicopters and bait Scott Commemorative Expedition. Subsequent direct from New Zealand, would then fieldwork was supported by the RSPB, the UK’s

1 To support this vital work, visit www.rspb.org.uk/hendersonisland or contact David Agombar at the RSPB on 01767 693360, e-mail [email protected]

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Overseas Territories Environment Programme and the Wilson Bull. 104: 32–43. David & Lucile Packard Foundation. Without transport Holyoak, D. T. 1978. Variable albinism of the flight to and from Henderson, nothing would have been feathers as an adaptation for recognition of achieved: thanks to the skippers and crews of the individual birds in some Polynesian populations of vessels, Te Manu, Searcher, Braveheart and Claymore. Acrocephalus warblers. Ardea 66: 112–117. Thanks too to the Pitcairn Islanders, who were always Jones, P. J., Schubel, S., Jolly, J. N., Brooke, M. de L., & welcoming when we passed through their island. Vickery, J. A. 1995. Behaviour, natural history, and the Claire Spottiswoode and Rosie Trevelyan commented annual cycle of the Henderson Island Rail (Porzana helpfully on a draft. atra). Biol. J. Linn. Soc. 56: 167–183. Kingston, N., & Waldren, S. 2003. The References phytogeographical affinities of the Pitcairn Islands – a model for South-eastern Polynesia? Blake, S. G. 1995. Late Quaternary history of J. Biog. 30: 1311–1328. Henderson Island, Pitcairn Group. Biol. J. Linn. Soc. Murphy, R. C., & Pennoyer, J. M. 1952. Larger petrels of 56: 43–62. the genus Pterodroma. Am. Mus. Novit. 1580: 1–43. Brooke, M. de L. 1995a. The modern avifauna of the Philbrick, N. 2000. In the Heart of the Sea. Harper Pitcairn Islands. Biol. J. Linn. Soc. 56: 199–212. Collins, London. — 1995b. The breeding biology of the gadfly petrels Preece, R. C. 1995. Systematic review of the land snails Pterodroma spp. of the Pitcairn Islands: of the Pitcairn Islands. Biol. J. Linn. Soc. 56: 273–307. characteristics, population sizes and controls. Ripley, S. D. 1977. Rails of the World: a monograph of the Biol. J. Linn. Soc. 56: 213–231. family Rallidae. Boston, Godine. — 2006. Pitcairn Islands. In: Sanders, S. M. (ed.), Spencer, T. 1995. The Pitcairn Islands, South Pacific Important Bird Areas in the UK Overseas Territories, Ocean: plate tectonic and climatic contexts. pp. 185–199. RSPB, Sandy. Biol. J. Linn. Soc. 56: 13–42. — & Hartley, I. R. 1995. Nesting Henderson Reed- Steadman, D. W. 1995. Prehistoric extinctions of Pacific warblers Acrocephalus vaughani taiti studied by island birds: biodiversity meets zooarchaeology. DNA fingerprinting: unrelated coalitions in a stable Science 267: 1123–1131. habitat? Auk 112: 77–86. — & Olson, S. L. 1985. Bird remains from an — & Jones, P. J. 1995. The diet of the Henderson fruit archaeological site on Henderson Island, South dove Ptilinopus insularis. I. Field observations of fruit Pacific: man-caused extinctions on an “uninhabited” choice. Biol. J. Linn. Soc. 56: 149–165. island. Proc. Natl. Acad. Sci, USA 82: 6191–6195. — & Rowe, G. 1996. Behavioural and molecular Trevelyan, R. 1995. The feeding ecology of Stephen’s evidence for specific status of dark and light Lory and nectar availability in its food plants. morphs of the Pterodroma heraldica. Biol. J. Linn. Soc. 56: 185–197. Ibis 138: 420–432. Weisler, M. I. 1994. The settlement of marginal — & Towns, D. R. 2008. A Feasibility Study for the Polynesia: new evidence from Henderson Island. Eradication of Kiore Rattus exulans from Henderson J. Field Archaeol. 24: 83–102. Island. RSPB, Sandy. — 1995. Henderson Island prehistory: colonization —, O’Connell, T. C., Wingate, D., Madeiros, D., Hilton, and extinction on a remote Polynesian island. G. M., & Ratcliffe, N. 2010a. The potential for rat Biol. J. Linn. Soc. 56: 377–404. predation to cause decline of the globally Worthy, T. H., & Wragg, G. M. 2003. A new species of threatened Henderson Petrel Pterodroma atrata: Gallicolumba: Columbidae from Henderson Island, evidence from population modelling, the field and Pitcairn Group. J. Roy. Soc. NZ 33: 769–793. stable isotopes. Endangered Species Research — & — 2008. A new genus and species of pigeon 11: 47–59. (Aves: Columbidae) from Henderson Island, Pitcairn —, Cuthbert, R. J., Henricson, A., Torr, N., Warren, P., & Group. In: Clark, G., Leach, F., & O’Connor, S. (eds.), O’Keefe, S. 2010b. Towards Rat Eradication on Terra Australis 2. Islands of Inquiry: colonisation, Henderson Island: fieldwork report August–September seafaring and the archaeology of maritime landscapes, 2009. RSPB, Sandy. pp. 499–510. ANU E Press, the Australian National Diamond, J. 2005. Collapse: how societies choose to fail University, Canberra. or succeed. Penguin Books, London. Wragg, G. M. 1995. The fossil birds of Henderson Florence, J., Waldren, S., & Chepstow-Lusty, A. J. 1995. Island, Pitcairn Group: natural turnover and human The flora of the Pitcairn Islands: a review. impact, a synopsis. Biol. J. Linn. Soc. 56: 405–414. Biol. J. Linn. Soc. 56: 70–119. — & Worthy, T. H. 2006. A new species of extinct Graves, G. R. 1992. The endemic landbirds of imperial pigeon (Ducula: Columbidae) from Henderson Island, Southeast Polynesia: notes on Henderson Island, Pitcairn Group. natural history and conservation. Hist. Biol. 18: 127–140.

Michael Brooke, Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ

Since completing a DPhil on the Manx Shearwaters of Skokholm Island, Michael Brooke has studied seabirds around the world. He led the 1991/92 Sir Peter Scott Commemorative Expedition to the Pitcairn Islands, and has subsequently worked to promote conservation there in conjunction with the UK Overseas Territories Conservation Forum and the RSPB.

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