3 May 2018

Solving the world’s great bird mysteries

Keen-eyed readers will note that we ‘lost’ a species in the 2017 Red List update – the Liberian Greenbul is no longer recognised as a valid species by BirdLife. But mourn not its loss: this is simply the latest in a long line of taxonomic avian mysteries to have been solved...

In 2017, the Liberian Greenbul was reclassified as an invalid species © HBW
In 2017, the Liberian Greenbul was reclassified as an invalid species © HBW
By James Lowen

They make a wacky bunch. A squashed Ethiopian nightjar from which only a single wing could be retrieved. An Andean hummingbird known solely from a single skin bought in a Bogota market. An African shrike kept captive in Germany to prove its existence and spare its demise. A Madagascar ‘vanga’ that actually belonged to a separate bird family altogether. A Brazilian seedeater that ‘existed’ for two centuries before its true identity was fathomed. And a greenbul from Liberia revealed by the 2017 Red List to be a species that never was.

At one time or another, this sextet has featured on a shortlist of the world’s greatest bird-taxonomy mysteries. Several of the conundrums represented by these creatures have now been solved. Others remain avian enigmas, frustrating our understanding and confusing decisions on whether, how and where to conserve them. Given that species are the fundamental unit of conservation, this matters.

Accurately determining what constitutes a true species is the key to astute allocation of conservation resources. If an apparently valid species transpires to be a morph or hybrid, conservationists risk having invested inadvisably. Conversely, if a valid species is overlooked or dismissed, we may have squandered opportunities to safeguard it.


Two specimens of a disputed species, Blue-wattled Bulbul © Nigel Collar


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The 2017 Red List update clears up one notorious mystery. Formerly considered Data Deficient, Liberian Greenbul Phyllastrephus leucolepishas been reclassified as ‘Not Recognised’ (or, in other words, an invalid species). Discovered in 1981 in Liberia’s Cavalla Forest, greenbuls were observed occasionally by their finder over the course of three years... but never seen again.

This intrigued Lincoln Fishpool, formerly BirdLife’s Global Important Bird Area Co-ordinator. He and others noted that Liberian Greenbul differed from the widespread Icterine Greenbul Phyllastrephus icterinus only in exhibiting whitish spots on its wings. Might these, Fishpool mused, simply relate to an aberrant plumage? “The lack of subsequent sightings anywhere made one wonder”, he recalls. A determined Fishpool joined an expedition to Cavalla Forest – but failed to find any greenbuls with spotted wings. If it were a true species, it appeared to be extinct.

If it were a true species... It was time to engage in a different brand of detective work: DNA analysis. This provided overwhelming support for Fishpool’s suspicion that Liberian Greenbul was actually, after all, Icterine Greenbul.

Fishpool confesses to feeling slightly sad that Liberian Greenbul was never a valid species. “Had it been so, there would have been stronger grounds for pursuing the protection of Cavalla Forest – an Important Bird & Biodiversity Area that is home to 20 globally threatened birds and mammals,“ says Fishpool. Nevertheless, he is philosophical about the greenbul’s demise: “We have more than enough valid conservation targets to worry about.”

The greenbul saga recalls the case of an even more controversial African landbird. Discovered in Somalia in 1989, Bulo Burti Boubou Laniarius liberatus disconcerted some museum ornithologists by being described from a live bird rather than the dead specimen traditionally demanded as evidence. This individual – the only one known – was then transferred to a German aviary before being returned to Somalia. Seventeen years later, molecular biologists showed Bulo Burti Boubou to be a previously unrecorded colour morph of Manda Boubou Laniarius nigerrimus rather than a distinct species. This particular bush-shrike was as much boo-boo as boubou.

The Nechisar Nightjar was described as a new species on the basis of a single wing

Roger Safford, BirdLife International’s Senior Programme Manager for Preventing Extinctions, was involved in another particularly eye-opening discovery. Surveying an isolated Ethiopian grassland in the 1990s, he and his colleagues picked up a roadkill nightjar. They later described it as a new species, Nechisar Nightjar Caprimulgus solala, on the basis of the single wing salvaged.

“Although palaeontologists do it all the time, this was the first bird species in modern times described from such an incomplete specimen”, says Safford.


This is all the world has ever seen of the mysterious Nechisar Nightjar © Roger Safford


The nightjar’s subsequent history is no less obscure than its bizarre discovery. There has never been a confirmed sighting. Although a book recounts the tale of a purported rediscovery in 2009, no evidence has been presented to verify this: there is no photograph, unequivocal video or sound-recording. This particular enigma has dissipated back into the African night.

Even experts sometimes get it plain wrong – spectacularly in the case of Bluntschli’s Vanga Hypositta perdita. Ferreting among specimens collected by a Swiss anatomist 60 years earlier in south-east Madagascar, a German museum curator discovered two unidentified nestlings. In 1996, he described them as a new species, Bluntschli’s Vanga. “Many ornithologists were unconvinced, thinking it was actually the unknown juvenile of Nuthatch Vanga Hypositta corallirostris,” says Safford. “But the feet were wrong for a tree-climbing vanga.”

It took DNA analysis to reveal that Bluntschli’s Vanga “was not even a vanga but a juvenile White-throated Oxylabes Oxylabes madagascariensis” – a species in an entirely different family. “The critical error was assuming that the bird was a vanga”, says Safford. “This case teaches us to be open-minded when determining whether a species is new.”

Even when evidence is available that should help resolve a conundrum, sleuths do not always see eye-to-eye. Bogotá Sunangel Heliangelus zusii is known only from a skin purchased by a priest in a Colombian market in 1909 – without hint of where it was caught. The hummingbird was part of the massive, early-20th century feather trade that serviced the sartorial desires of European and North American fashionistas. It has never been seen in the flesh.


Are we close to solving the puzzle of the Bogotá Sunangel? © HBW


The sunangel’s centenary was celebrated by DNA analysis supporting its identity as a valid species. But this is undermined, says Stuart Butchart (BirdLife International’s Chief Scientist), by “tantalising new molecular evidence in the pipeline” arguing that the hummingbird is indeed a hybrid, its mother probably a Long-tailed Sylph Aglaiocercus kingii. If it is confirmed that ‘Bogotá Sunangel’ is not a valid taxon, it is likely that BirdLife International will no longer recognise it as a species.

In relation to ornithologists involved in previously suggesting it was a valid species, Butchart argues: “If this new evidence survives the test of peer-review, it illustrates the need for adequate sampling of potential relatives when carrying out genetic analyses.”

From a conservation perspective, this may be a relief. “With no clue as to where in the Andes this hummingbird came from, it was impossible to know what threats it faced and what actions were needed”, says Butchart. The same is true for Hooded Seedeater, or “one of the great enigmas of South American ornithology”, as described by Argentine ornithologist Nacho Areta. He and colleagues devoted months trying (and failing) to rediscover the bird known only from an 1823 specimen, before determining that it was not a valid species. Accordingly, conservationists can cease fretting about how to conserve it.

Even happier endings transpire when long-lost species are properly rediscovered. Roger Safford re-found Anjouan Scops-owl Otus capnodes in the Comoros Islands, a full century after it was last seen by an ornithologist. Subsequent research suggests it is less rare than feared; the 2017 Red List update downlists it to Endangered. Meanwhile, in montane Venezuela, Táchira Antpitta Grallaria chthonia eluded everyone for 60 years. Was it extinct? Was it even real?

The antpitta’s eventual rediscovery in 2016 delights Stuart Butchart. Unravelling this particular conundrum, says Butchart, “means we can move to the next phase of understanding the species’ status, threats and conservation solutions”.

Arguably, rediscovering a lost bird is even more valuable than discovering a new species

Butchart wants such success stories to galvanise birdwatchers into exploring off the beaten track. Arguably, rediscovering a lost bird is even more valuable than discovering a new species. Among a long list of ‘missing’ or mysterious birds that form priorities for such expeditions, Butchart fingers Semper’s Warbler Leucopeza semperifrom St Lucia (“surely it still exists!”), Jerdon’s Courser Rhinoptilus bitorquatus from India (“lost for a century, re-found then lost again”) and Blue-wattled Bulbul Pycnonotus nieuwenhuisiifrom Kalimantan (“perplexing... might DNA analysis show it to be an invalid taxon?”).

Safford agrees, believing that “we shouldn’t ever give up” on bird mysteries. From a man brave enough to describe a species of nightjar from a single wing and to rediscover an owl lost for a century, that is advice worth heeding.