The Stephens Island Wren (Xenicus (Traversia) lyalli) is famous for being (erroneously) considered the only known species to be entirely wiped out by a single living being. This bird was a flightless, nocturnal native of Stephens Island, New Zealand, which fed on insects.
According to the common lore, the entire population was killed by the lighthouse keeper's cat named Tibbles in 1894, but this is not what actually happened (see below). The scientific name commemorates the assistant lighthouse keeper, David Lyall, who brought the bird to the attention of science. Originally, it was described as a distinct genus, Traversia, in honor of naturalist and curio dealer Henry H. Travers who procured many specimens from Lyall, but usually it is considered to be part of the Xenicus "wrens", which are not wrens at all, but a similar-looking New Zealand lineage of primitive passerines, better referred to as acanthisittids.
Archeological work has revealed that Xenicus lyalli was widespread on the main islands of New Zealand in earlier times. Its disappearance from there was probably due to predation by the kiore (Polynesian Rat, Rattus exulans), which may have been introduced by the M?ori. How the flightless bird crossed the 3.2 km of ocean to Stephens Island is not clear, although the presence of Hamilton's frog (which is killed by exposure to salt water) suggests that rafts of vegetable matter would cross the sea often enough. Thus, it is a matter of sheer luck that the Stephens Island Wren was found alive by scientists (at least for some months), because anything that could bring them to the island would just as well allow kiore to cross over.
It is the best known of the extremely few (five or so) flightless passerines known to science (Millener, 1989), all of which were inhabitants of islands and are now extinct. The others were relatives of Xenicus and the Long-legged Bunting from Tenerife, all of which were only discovered recently and became extinct in prehistoric times. In addition, the Bush Wren (another acanthisittid recently extinct) and the Chatham Islands Fernbird (an "Old World warbler") were almost flightless and capable of a hopping flutter at best.
Much of what is commonly assumed to be established knowledge about this species' extinction is wrong or misinterpreted, starting with the account by Rothschild (1905) who claimed that a single cat had killed all the birds. The research of Galbreath & Brown (2004) and Medway (2004) has uncovered much of the actual history of the bird during the short time it was known to researchers.
Early June?: A track to the site of the proposed lighthouse site is cleared, starting the period of human activity on the island.
February 22: Marine Engineer John R. Blackett surveys the site for the proposed lighthouse.
April: Preparations for the construction of the lighthouse are begun by starting to build a tramway and a landing site for boats.
April: Clearance of land for the lighthouse and the associated farm begins (3 lighthouse keepers and their families, 17 people in total, would eventually be living on the island). The first report of the species was a note on the island's birdlife made by the construction worker F. W. Ingram, which mentions "two kinds of wren" (the other was probably the rifleman).
January 29: The lighthouse commences working.
February 17-20?: This is a likely date for introduction of cats to Stephens Island. What can be said with any certainty is that at some time in early 1894, a pregnant cat brought to the island escaped.
June?: A cat - probably one of the young animals taken in as a pet; the name "Tibbles" is apparently conjectural and it does not seem to have belonged to Lyall - starts to bring carcasses of a species of small bird to the lighthouse keepers' housings. Lyall, who was interested in natural history, has one taken to Walter Buller by A. W. Bethune, second engineer on the government steamboat NZGSS Hinemoa.
Stephens Island Wrens (bottom right) by John Gerrard Keulemans
Before July 25?: The specimen reaches Buller, who at once recognizes it as distinct species and prepares a scientific description, to be published in the journal Ibis. Bethune lends Buller the specimen so it can be sent to London for the famed artist John Gerrard Keulemans to make a lithograph plate to accompany the description.
Winter - early spring (Southern Hemisphere): Lyall finds several more specimens. He tells Buller about 2 more (but does not send them to him), and sells 9 to Travers.
October 9: Travers, who recognizes the commercial value of the birds, sidelines Buller and offers the birds to Walter Rothschild, who was wealthier and thus more likely to pay a high price, further piqueing Rothschild's interest by writing, "in a short time there will be [no "wrens"] left". Rothschild acquires his 9 specimens.
October 11/12: Edward Lukins makes a list of birds on Stephens Island; he apparently confuses the species with the South Island Wren.
December 19: Rothschild has quickly prepared a description of the bird, as Traversia lyalli, which is read by Ernst Hartert at the British Ornithologists' Club meeting. Philip Sclater, the Club's president and editor of the Ibis who knows of Buller's article in preparation, brings up the matter to Hartert, who says he cannot withdraw Rothschild's description without consent.
December 29: Rothschild's description appears in the Bulletin of the British Ornithologists' Club.
January 24: Travers offers Rothschild a specimen preserved in alcohol (with viscera intact) for £5 (about £415 in 2002's money: UK House of Commons Library, 2003). Rothschild apparently agrees, but never receives the bird.
February 4-9: Travers and three assistants searched the island for the bird, but found none.
Before February 11?: Lyall writes to Buller: "...the cats have become wild and are making sad havoc among all the birds."
March 7: Travers supplies Rothschild with some details of the bird's habits. To his knowledge, the species had only been seen alive twice until then. He has only been able to procure one additional specimen, brought in by the cat as the bird was dying, which also had been preserved in alcohol.
March 16: The Christchurch newspaper The Press writes in an editorial,
April: Buller's description of Xenicus insularis appears in the Ibis. The name is immediately reduced to a junior synonym. In the same issue, Rothschild's description is reprinted, with some additional remarks on the bird's apparent flightlessness. The race to describe the bird sparks much animosity between the two men, and Buller never forgives Rothschild beating him; for details and quotes, see Fuller (2000).
August: In a paper for the Wellington Philosophical Society, Buller speaks of a female bird he recently had examined. He later purchases this specimen.
November 28: Travers informs Hartert that Lyall was not able to find more specimens during the winter, and believes the bird to be extinct. He offers 2 alcohol specimens for sale, for the price of £50 apiece (nearly £4200 in 2002's money - to compare, the average lighthouse keeper's wage in 1895 was £140 a year).
December: Travers tries another search for the bird, again without success.
"there is very good reason to believe that the bird is no longer to be found on the island, and, as it is not known to exist anywhere else, it has apparently become quite extinct. This is probably a record performance in the way of extermination."
May 13: Travers, unable to sell the birds at such a high price, now wants to sell his specimens for £12 each, about £1000 in 2002's money.
June: Lyall gets assigned to another lighthouse and leaves Stephens Island.
December 31-January 7 or longer: Hugo H. Schauinsland collects birds on Stephens Island, but cannot find many and no "wrens" at all. On January 7, he collects the only specimen of the local South Island Piopio acquired during his stay. It is the last record of these birds.
July 31: The principal lighthouse keeper Patrick Henaghan requests shotguns and ammunition from the Marine Department to destroy the "large number of cats running wild on the island."
September 5: Travers writes James Hector that he has one more specimen available. At some time before this date, he had sold Buller one specimen for Henry Baker Tristram and claimed he had two additional ones.
December 27: Travers writes to Hector, saying that Stephens Island "is now swarming with cats".
August 1: The new principal lighthouse keeper, Robert Cathcart, has shot over 100 feral cats since his arrival on November 24, 1898.
Travers offers "his specimen of the Stephen's Island Wren" to the government for £35 (c. £2700 in 2002); apparently, the bird is bought and deposited at the Colonial Museum with other skins. The collection is not reviewed until 1904, by which time a fifth has to be discarded due to insect damage. No record is made of the specimen since the offer, but the eventual sale's price suggests it was among the collection deposited at the Colonial Museum.
Travers sells one specimen to the Otago Museum.
Buller publishes his Supplement, in which he keeps using his name, Xenicus insularis. He furthermore quotes an anonymous correspondent to The Press,
"And we certainly think that it would be as well if the Marine Department, in sending lighthouse keepers to isolated islands where interesting specimens of native birds are known or believed to exist, were to see that they are not allowed to take any cats with them, even if mouse-traps have to be furnished at the cost of the state."
Rothschild publishes his book Extinct Birds. In a remarkable breach of nil nisi bonum (especially considering both men's social standing), it contains several acrimonious attacks on Buller, who had died the previous year.
In conclusion and considering Buller's August 1895 note, it is probable that the species was exterminated by feral cats during the winter of 1895. Assuming the date of February, 1894, for cat introduction was correct (there were certainly cats around in the winter months of that year), the winter months of 1895 would see the second generation of cats born on the island reaching an age where the Stephens Island wren would have made ideal prey. Habitat destruction, sometimes given as an additional reason for the birds' disappearance, was apparently not significant: in 1898, the island was described as heavily forested, and there was little interference with habitat beyond the lighthouse and its associated buildings. Large-scale destruction of habitat started in late 1903, by which time X. lyalli was certainly extinct.
Cats were eradicated on Stephens Island between 1916 and 1925.
15 specimens (excluding prehistoric bones) are known nowadays. Additionally, there are some uncertainties suggesting that some additional ones might have existed, but this is not very likely.
- Rothschild's specimens, all of which were collected between July and October, 1894:
- Natural History Museum, London: three (NHM 18184.108.40.206; 19220.127.116.11; 1918.104.22.168).
- American Museum of Natural History, New York City: four (AMNH AM 554502; AM 554503; AM 554504; AM 554505).
- Academy of Natural Sciences, Philadelphia: one (ANSP 108,631).
- Harvard Museum of Comparative Zoology, Cambridge, Massachusetts: one (MCZ 249,400).
- Buller's specimens, collected at unknown dates between 1894 and 1899:
- Carnegie Museum, Pittsburgh: one (CMNH 24639), labelled as fermale and dated 1894 in Buller's handwriting. Apart from the date discrepancy, it could be the bird Buller spoke of in August, 1895; possibly the specimen was collected months before Buller had examined it. Alternatively, it could be the Bethune bird in case Buller kept it (he initially seems to believe it to be a female), as Rothschild (1907) believed. DNA analysis could at least clarify the bird's sex.
- Canterbury Museum, Christchurch: AV917 and AV918, a pair from the collection of Buller's son, dated 1899. They were acquired between late 1896 and 1899, but may have been collected before that date.
- World Museum Liverpool: one (B 22.214.171.124). Purchased by Buller from Travers for Tristram, probably after late 1896 (but may have been collected earlier). Sold to the museum in October, 1898.
- Te Papa, Wellington: one (5098) mounted specimen without data; may be Travers' specimen sold in 1901 or another one. This photograph by Dr Paddy Ryan shows the Te Papa specimen and another one - possibly the Otago Museum bird, but the matter is not clear.
- Otago Museum, Dunedin: one, but two catalog numbers (AV739 and AV7577) exist. It is not clear whether they represent re-cataloguing of the one specimen sold by Travers in 1905, or whether a specimen was lost.
- Unaccounted for (all collected in 1894 or very early in 1895):
- Bethune's specimen: lent to Buller for the description, apparently later given back. If so, it was probably deposited at the Colonial Museum (now part of Te Papa) for safekeeping between 1895 and 1897, or
- Buller's female mentioned in August, 1895, or even both (if neither is CMNH 24639).
- 2 of Lyall's first 3 specimens (one was given to Bethune) remain unaccounted for. They may be part of Rothschild's 9, or Buller's 3. They were not in Buller's possession as of early February, 1895.
- Travers' "lost" specimen referred to in January, 1895. It is not certain that this specimen was indeed lost; it may have been one of the alcohol specimens mentioned in November, 1895, and Travers may simply have withheld it so he could fetch a higher price as the bird became extinct.