Confirmation that the last Australian shrew has disappeared forever

Australia’s only shrew, the Christmas Island shrew, Crocidura trichura, has now been classified as extinct, closing the book on a native lineage that once scurried through the island’s rainforest at night. 

An analysis places this loss within a sobering national tally of 40 terrestrial mammal species gone since 1788.

On October 10, 2025, the IUCN Red List, the global inventory that evaluates extinction risk categories, posted an update that moved the shrew to Extinct.

Christmas Island lies about 930 miles west of mainland Australia, yet the decision’s weight is felt continent wide.

Crocidura trichura now extinct

This case is not just an island story. It signals how small, specialized mammals can slip past our attention until they are gone.

To connect the story with current field evidence, the assessment draws on research from Australian conservation scientists.

They analyzed decades of survey data and historical records to test whether any Crocidura trichura individuals might still survive undetected on the island.

Their work combined archival reports with modern field techniques to estimate the likelihood of persistence after more than a century of sparse sightings.

Australia’s mammal losses are not abstract numbers. They reflect eroded ecological jobs, from seed dispersal to insect control, that once ran quietly in the background.

Each confirmed extinction also sharpens the need for earlier detection and faster action. Waiting for certainty can be a costly luxury when sample sizes are measured in single digits.

Brief history of Crocidura trichura

The shrew was once widespread on the island’s plateau and coastal terraces. Early accounts described it as abundant in dense rainforest.

In 1900, early naturalists described Crocidura trichura as widespread across the island’s rainforest, noting that its sharp, bat-like calls could be heard from every direction at night. 

This population was endemic, found only in one place, and likely arose after natural colonization from nearby islands. Isolation brought uniqueness, but it also meant limited defenses against new threats.

Mining, settlement, and introduced species altered the island’s ecology through the twentieth century. Each change added pressure on small insectivores living close to the forest floor.

What we actually know and what we do not

Only four confirmed records exist after 1900, with captures in 1958, 1984, and 1985. The record since then is a striking absence, despite many surveys.

Using a structured protocol that compared how easily Crocidura trichura could be detected with the scale of past searches, one study estimated a 96.3 percent chance that the shrew no longer survives.

The figure reflects both the thoroughness of survey efforts and the animal’s naturally secretive behavior.

Shrews can be hard to find, even when present. Yet decades of fieldwork with varied methods, from pitfall traps to targeted searches, did not produce a single verified individual.

Uncertainty should be recognized, but it cannot become an excuse for inaction. When a population may already be gone, the difference between careful assessment and fatal delay can be only a matter of time.

Disease and invaders

A rapid collapse in the island’s native mammals followed the arrival of black rats around 1900. There is molecular evidence that a rat borne trypanosome likely drove two endemic rats to extinction within a decade.

A trypanosome, a single celled parasite that infects blood, can move swiftly through naive hosts. In small island populations, such infections can leave no room to recover.

Predation and competition amplified the risks. Invasive species including feral cats and pest ants, reshaped the island’s food webs in ways hostile to small mammals.

Expert assessments also link the 1980s introduction of the Asian wolf snake, Lycodon capucinus, to severe reptile decline across the island. That invasion underscores how one new predator can topple multiple native lineages in sequence.

What this loss should change

Three lessons stand out. First, disease surveillance must be part of island biosecurity, not an afterthought when mortalities begin.

Second, rapid response capability matters. When a tiny remnant is found, the default should be to test captive assurance options quickly and transparently.

Third, monitoring must fit the target species. Acoustic tools, refined environmental DNA methods, and detector dogs can extend our reach when bodies are few and eyes miss what is rare.

Learning from Crocidura trichura

Guard the front door by tightening quarantine for ships, aircraft, and cargo. Pathogens and predators are far easier to keep out than to remove once established.

Invest in earlier, species specific detection. The right trap, lure, or sensor matters more than broad but mismatched effort.

Integrate predator control with habitat management in protected areas. Small mammals recover best when multiple pressures are reduced together rather than one at a time.

Finally, measure success by trends in populations, not inputs. If the numbers do not move, change the plan before time runs out.

The study is published in Australian Mammalogy.

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