Tibble and the wren

One of the most frequently told stories about invasive species on islands or on the effect of cats on biodiversity is the tale of Tibble and Stephens Island Wren.

Extinct bird Xenicus lyalli (Xenicidae), male (lower) & female (upper).
From Buller, Walter Lawry, A History of the Birds of New Zealand.
Supplementary Notes to the 'Birds of New Zealand'. Vol. II.. 1905.

In a few words and following a common version, Tibble was the cat and only companion of the light-house keeper on Stephens Island and it's supposed to be the sole responsible of the extinction of the one flightless passerine, the local endemic Xenicus (Traversia) lyalli in 1894.
The story is easy to tell and remember: a villain, a victim and a moral (no hero, this time), but, in fact, as usual, reality is a bit more complex.

First, this is not the only known flightless passerine, but they were few of them, maybe just four (all of them extinct and all except one were New Zealand's wrens). This is the only that was still extant when known for science.

Second, the species was not endemic from Stephens Island, as the English name suggests, but relict to the island where it survives in recent times, although it is common in fossil deposits from both of the main islands before the arrival of maoris with kiores  (Worthy and Holdaway 1994).

Third, Lyall was not the light only human inhabitant of the island, neither the lighthouse keeper. He was the assistant and there were other people living there.

Fourth, and most important: how many "tibbles" where there? The first record of a single cat being responsible of the extinction is due, apparently, to Rothschild (1905). 

Image from
http://www.terranature.org/wren.htm

After Galbreath and Brown (2004), the Stephens Island wren Xenicus (Traversia) lyalli is widely quoted as having been discovered and promptly exterminated from its only locality, Stephens Island, New Zealand, by a single lighthouse keeper’s cat. Examination of archival and museum records indicates that this account is oversimplified, and throws more light on the roles of the lighthouse keeper David Lyall, the dealer Henry Travers, and the ornithologists Sir Walter Buller and Walter Rothschild. Cat predation probably was the main factor in the wren’s extinction, but not necessarily by a single cat: cats became established on Stephens Island in 1894, increased rapidly and exterminated several other species before they were eliminated. We are not sure if  "Tibble" was the name of any of them.

Fifth, the species didn't disappeared in 1884. following the same authors, extinction of the wren was more extended than generally stated: 10 specimens were evidently brought in by a cat in 1894, but another two-four were obtained in 1895, and two-three more after that and possibly as late as 1899. Fifteen of these specimens are still held in museums. 

Last, but not least, the simplified story forgets some other victims because cats were responsible for several more extinctions on Stephens island. Medway (2004) explains how Stephens Island provides the classic example in the New Zealand region of the effect that predation by feral cats (Felis catus) can have on an island land bird fauna. Twenty-five species of native New Zealand land birds were recorded on the island in the early 1890s when it was still forested and free of mammalian predators. It is probable that Stephens Island still had its original land bird fauna at that time. The land bird species included large populations of the extinct Stephens Island piopio (Turnagra capensis minor), and the endangered South Island saddleback (Philesturnus c. carunculatus).
Cats were introduced to Stephens Island probably in 1894. They soon became feral and multiplied rapidly. The evidence indicates that cats were responsible for the rapid demise of the native land bird fauna of the island.

References

• Galbreath, R. & Brown, D. (2004): The tale of the lighthouse-keeper's cat: Discovery and extinction of the Stephens Island wren (Traversia lyalli). Notornis 51(4): 193–200.
• Medway, D.G. (2004): The land bird fauna of Stephens Island, New Zealand in the early 1890s, and the cause of its demise. Notornis 51(4): 201–211.
• Rothschild, W. (1905): On extinct and vanishing birds. Proceedings of the 4th International Ornithological Congress, London: 191-217.

Introduced predators selectively culls medium-sized species from island mammal faunas

Hanna, E., & Cardillo, M. (2014). Predation selectively culls medium-sized species from island mammal faunas. Biology letters, 10(4), 20131066.

Globally, elevated extinction risk in mammals is strongly associated with large body size. However, in regions where introduced predators exert strong top-down pressure on mammal populations, the selectivity of extinctions may be skewed towards species of intermediate body size, leading to a hump-shaped relationship between size and extinction risk. The existence of this kind of extinction pattern, and its link to predation, has been contentious and difficult to demonstrate. Here, we test the hypothesis of a hump-shaped body size–extinction relationship, using a database of 927 island mammal populations. We show that the size-selectivity of extinctions on many islands has exceeded that expected under null models. On islands with introduced predators, extinctions are biased towards intermediate body sizes, but this bias does not occur on islands without predators. Hence, on islands with a large-bodied mammal fauna, predators are selectively culling species from the lower end of the size distribution, and on islands with a small-bodied fauna they are culling species from the upper end. These findings suggest that it will be difficult to use predictable generalizations about extinction patterns, such as a positive body size–extinction risk association, to anticipate future species declines and plan conservation strategies accordingly.

Cat responsible of extinctions on Mangere Is.

Tennyson, A. J. D., & Millener, P. R. (1994). Bird extinctions and fossil bones from Mangere Island, Chatham Islands. Notornis, 41(supplement), 165-178.

Fossil bones and earlier observations indicate that up to 22 species of bird have become extinct on Mangere Island. The extinctions appear to have been primarily a result of predation by cats, but human hunting and bush clearance are likely to account for the disappearance of some species. A crested penguin Eudyptes ?n.sp., two species of Pterodroma petrel, a shelduck Tadorna ?n.sp., Dieffenbach's Rail Gallirallus dieffenbachii, and a kaka Nestor ?n.sp. are present in fossil deposits on Mangere Island, but have not been reported from the island before. The relative proportion of remains in the deposits suggest that Blue Penguins Eudyptula minur, Broad-billed Prions Pachyptila vinata and Sooty Shearwaters Puffinus griseus have become more common on the island. Any such increases on Mangere Island, could have been a response of a few species to the large decrease in numbers and diversity that has affected seabirds as a whole at the Chatharns. Some seabird species mav have been able to increase because of reduced competition for-food.

How the Macquarie Island parakeet became extinct

Taylor, R. H. (1979). How the Macquarie Island parakeet became extinct. New Zealand Journal of Ecology, 2, 42-45.

For 70 years following the discovery of Macquarie Island in 1810 the endemic parakeet Cyanoramphus novaezelandiae erythrotis remained plentiful, despite the introduction of cats (Felis catus) and other predators. The crucial factor in the bird's rapid disappearance between 1881 and 1890 appears to have been the successful liberation of rabbits (Oryctolagus cuniculus) in 1879. This led to great increases of feral cats and introduced wekas (Gallirallus australis) and presumably to greatly intensified predation on parakeets.

Changes in numbers of parakeets, rats,mice, feral rabbits, feral dogs, feral cats and wekas on Macquarie Island 1810-1920. Diagrammatic reconstructionfrom early accounts (Cumpston, 1968). Not to scale.

More on Macquarie island cats

Mammal extinctions on Australian islands due mainly to cats

Burbidge, A. A., & Manly, B. F. (2002). Mammal extinctions on Australian islands: causes and conservation implications. Journal of Biogeography, 29(4), 465-473.

Aim

Data on Australian landbridge islands were analysed to seek relationships between the extinction of mammals on islands and a number of variables related to the islands, the native mammal species that occur on them and the presence or absence of exotic mammalian predators. The data base included attributes of the mammals (mean adult body weight, diet and shelter habitat) and of the islands [area, rainfall, presence/absence of significant areas of rockpile habitat, presence/absence of European red fox Vulpes vulpes Linnaeus, 1758, feral cat Felis catus Linnaeus, 1758, and rats Rattus rattus (Linnaeus, 1758) and R. exulans (Peale, 1848)].

Methods

Statistical analysis of the 388 cases where a Critical Weight Range (CWR) mammal is extant and the forty-one cases where a CWR mammal is extinct was conducted using logistic regression to model the probability of extinction as a function of the island and mammal variables.

Results

Foxes and cats are correlated with CWR mammal extinctions, but cats are associated with extinctions particularly on more arid islands. Extinctions are more likely on islands with an absence of significant areas of rockpile habitat and where the native mammal is restricted to the ground's surface, and is relatively large.

Conclusions

An association between the presence of cats and native mammal extinctions has not previously been demonstrated for Australian islands. The introduction of exotic predators to Australian islands with native mammal species should be avoided and should any of these predators establish all means should be employed to eradicate them. For Australian continental islands the introduction of exotic predators, not habitat clearance, has been the major factor in extinctions.

The iguana tragedy

Kutschera, U., & Kleinhans, S. 2013. Alfred Russel Wallace and the destruction of island life: the Iguana tragedy. Theory in Biosciences, 1-7.

The Galápagos Islands (Ecuador) are usually associated with the explorations and theoretical deductions of Charles Robert Darwin (1809–1882), but Alfred Russel Wallace (1823–1913) also investigated these islands and published several reports on the living world of this unique archipelago. In contrast to Darwin, Wallace described the destruction of natural ecosystems by humans and foresaw the resulting extinction of species. Here, we outline two case studies pertinent to Wallace’s prediction. First, we summarize the behavior of the predator-naive marine iguanas (Amblyrhynchus cristatus) on the Galápagos Islands, which are threatened by feral dogs and cats imported by humans. We also describe the unique life cycle of the spiny-tailed iguana (Ctenosaura bakeri) from the island of Utila (Honduras), a rare species whose populations are declining because of habitat destructions. In contrast to these threatened, endemic island species, the Green iguana (Iguana iguana) is still widely distributed, although, as a result of de-forestation, in some areas of South America local populations have disappeared. We conclude that Wallace was correct in his prediction that, because of human activities, numerous species of animals and plants will be driven to extinction, notably on islands.

Feral Dog with iguana Photo Galapagos Conservation Society

Lessons to be learnt from loss of the pipistrelle

A recent paper in the journal Conservation Letters alleges that failure to act quickly on evidence of rapid population decline has led to the first mammal extinction in Australia in the last 50 years, the Christmas Island pipistrelle bat (Pipistrellus murrayi).

Since 26 August 2009, there have been no recordings of the echolocation call of the tiny bat, which is native to Christmas Island. It is now presumed extinct.

In a recently published paper in Conservation Letters, scientists analysed the conservation decision making process associated with the decline of this species and concluded that it illustrated the need for strong leadership on extinction issues.

Among the chain of events analysed was a February 2009 report by Dr Lindy Lumsden – Principal Research Scientist with the Arthur Rylah Institute for Environmental Research, and foremost authority on this species – warning that only 20 bats remained on Christmas Island. Government funding was then allocated to establish a captive breeding program, but that proved too little, too late.

The Christmas Island pipistrelle fed on insects and roosted in tree hollows and decaying vegetation. Just a few decades ago, the bat was widespread on Christmas Island and roosted in groups of 50 or so animals.

‘It is estimated that a single pipistrelle consumes its body weight in insects per night,’ lead author Tara Martin, of CSIRO’s Ecosystem Services, told the conservation website Mongabay.

‘While the loss of the pipistrelle is likely to lead to more insects, it is too early to tell what the long term ecological impact of this will be on the island.’

Scientists are unsure as to what pushed the bat to extinction. It is possible that a combination of stressors was responsible, including invasive animals such as feral cats, the common wolf snake, and a recent invasion of yellow crazy ants. Disease is another possibility, though researchers could find no sign of the bats suffering from illness...

http://www.ecosmagazine.com/paper/EC12309.htm

Martin, T. G., S. Nally, A.A. Burbidge, S. Arnall, S.T. Garnett, M.W. Hayward, L.F. Lumsden, P. Menkhorst, E. McDonald-Madden & H.P. Possingham. 2012. Acting fast helps avoid extinction.Conservation Letters, 5(4), 274-280.

Failure to act quickly on evidence of rapid population decline has led to the first mammal extinction in Australia in the last 50 years, the Christmas Island Pipistrelle (Pipistrellus murrayi). The fate of another iconic species, the migratory Orange-bellied Parrot (Neophema chrysogaster), monitored intensively for over 20 years, hangs in the balance. To inform future conservation management and decision making, we investigate the decision process that has led to the plight of both species. Our analysis suggests three globally relevant recommendations for minimizing species extinction worldwide: (1) informed, empowered, and responsive governance and leadership is essential; (2) processes that ensure institutional accountability must be in place, and; (3) decisions must be made whilst there is an opportunity to act. The bottom line is that, unless responsive and accountable institutional processes are in place, decisions will be delayed and extinction will occur.