By Matt Walker
Editor, Earth News
An artist's impression of the rarely seen and now extinct Alaotra grebe
The Alaotra grebe is extinct, according to the latest assessment of the world's rarest birds.
The last known sighting of the bird was in 1985 and experts have now confirmed its demise, killed off by a combination of poaching and predatory fish.
The Malagasy species, which lived in Lake Alaotra, is the first confirmed bird extinction since 2008.
However, fortunes have improved for rare birds such as the Azores bullfinch and Colombian yellow-eared parrot.
The Alaotra grebe (Tachybaptus rufolavatus) was a medium-sized bird with small wings that inhabited Lake Alaotra and surrounding areas in Madagascar.
Due to its tiny wings, the bird was thought incapable of flying long distances, living a mainly sedentary lifestyle on the lake and in surrounding ponds and highland lakes.
The only known photo of an Alaotra grebe
Twelve Alaotran grebes were sighted at Lake Alaotra in December 1982, and two near Andreba on Lake Alaotra in September 1985.
Some birds with characteristics of the grebe were seen in 1985, 1986 and 1988, but these are thought to be hybrids with another grebe species.
Surveys in 1999 and a visit by experts in 2000 found no individuals, or any grebes belong to the same genus Tachybaptus.
No direct observations of the species have been made since and hopes that the bird might survive were dashed after a recent expedition to nearby Lake Amparihinandriamabavy failed to find any grebes.
Officials have now declared the bird extinct in the latest update to the IUCN Red List of endangered and threatened birds.
The Red List, regarded as the most authoritative assessment of the state of the planet's species, draws on the work of scientists around the globe.
"No hope now remains for this species. It is another example of how human actions can have unforeseen consequences," says Dr Leon Bennun of Birdlife International, which evaluates the status of rare birds for the IUCN Red List.
The grebe is thought to have been driven to extinction by a combination of factors.
The bird, usually found in pairs, fed almost exclusively on fish in Lake Alaotra, a large brackish lake which had shores once covered in dense papyrus and reeds.
But in recent years, fishermen have covered much of the lake with monofilament nylon gill-nets which can kill diving waterbirds.
These nets were introduced after the grebe had already significantly declined, though they may have killed remaining birds.
Carnivorous fish (Micropterus and Ophiocephalus) introduced into the lake are also thought to have significantly contributed to the grebe's extinction, while the introduction of other invasive mammals, fish and plants likely depleted the grebe's food sources.
Azores bullfinches are faring better
Poaching also reduced its numbers.
Knowing exactly when a species has gone extinct is extremely difficult, as records of sightings can be patchy or unsubstantiated.
Also, comprehensive surveys must be completed to ensure a species does not survive in previously unexplored habitats.
For those reasons, species are often declared extinct many years after they have last been seen.
The last bird species to be confirmed extinct is the Liverpool pigeon (Caloenas maculata), declared extinct in 2008.
However, this Pacific species is known from just two specimens, one of which has been lost. It likely went extinct before Europeans colonised the Pacific.
In 2005, the Thick-billed Ground-dove (Gallicolumba salamonis) was declared extinct, it too known from two specimens, the last caught in 1927.
Other birds declared extinct in the 21st Century include the Hawkins's Rail (Diaphorapteryx hawkinsi), Reunion Shelduck (Alopochen kervazoi) and Kamao (Myadestes myadestinus) among others.
Modern species thought to be extinct, but not yet confirmed, include the Po'ouli (Melamprosops phaeosoma).
The last known survivor of this honeycreeper species died in captivity in 2004, despite huge efforts to rescue it.
Surveys have yet to be done to confirm it no longer survives on the remote highland slopes of Hawaii.
Another species suffering from the impacts of invasive species is the Zapata Rail (Cyanolimnas cerverai) from Cuba.
Yellow-eared parrots have been downgraded
It has been updated to "Critically Endangered" on the latest Red List, under threat from introduced mongooses and exotic catfish.
Only one nest has ever been found of this species.
However the new Red List does highlight some conservation success stories.
The Azores bullfinch (Pyrrhula murina) has been downlisted from "Critically Endangered" to "Endangered" after efforts to restore its habitat.
In Colombia, the Yellow-eared parrot (Ognorrhynchus icterotis) has also benefited from protection of its nest sites and education programmes, leading to its status being downgraded to "Endangered".
Around 190 bird species out of more than 10,000 known are thought to have gone extinct since modern records began.