For the first time, mainland extinctions eclipsed island extinctions, primarily due to rampant deforestation in South America, especially in Brazil, to make way for large-scale agriculture and industrial activities
In some circumstances it can be safely assumed that if a certain event had occurred, evidence of it could be discovered by qualified investigators. In such circumstances, it is perfectly reasonable to take the absence of proof of its occurrence as positive proof of its non-occurrence.”
— Irving M. Copi, Introduction to Logic (1953), p. 95
Absence of evidence is not evidence of absence.”
Absence of evidence
Thanks to our best efforts to completely remake the world according to our standards, eight more species of birds are probably extinct, including three species of parrots, according to a new study by Birdlife International.
This new study, led by BirdLife International’s Chief Scientist, Stuart Butchart, and his collaborators tested six statistical methods to analyse 51 Critically Endangered birds, using a range of thresholds to assign species to the IUCN Red List Categories, and compared their results with the species’ current categories (ref). The methods simultaneously quantified three factors: intensity of threats, timing and reliability of records, and the timing and quantity of search efforts for the species. Based on their analysis, Dr. Butchart and his collaborators recommend that if both the probability that a species remains extant based on threats and the probability based on records and surveys falls below 0.5, it should qualify as Critically Endangered (Possibly Extinct), whereas if both probabilities fall below 0.1 it should qualify as Extinct. Their novel approach resulted in an 80% match with the current IUCN Red List classification of species.
Based on their analysis, Dr. Butchart and his collaborators recommend that eight birds be reclassified on the IUCN Red List, with three being reclassified as Extinct.
Historically, most avian extinctions resulted from the impacts of invasive alien species (46%) and hunting/trapping (26%) on islands. But surprisingly, Dr. Butchart and his collaborators found that five of the eight confirmed or suspected extinctions took place on the South American mainland, with four of them occurring in Brazil, a disturbing finding that reflects the devastating effects of habitat loss due to rampant deforestation in this part of the world.
“Ninety per cent of bird extinctions in recent centuries have been of species on islands,” Dr. Butchart said in email. “However, our results confirm that there is a growing wave of extinctions sweeping across the continents, driven mainly by habitat loss and degradation from unsustainable agriculture and logging.”
The extinct parrots include the elusive New Caledonian lorikeet, Charmosyna diadema (last spotted in 1987), an island species that nested in arboreal termite nests or epiphytic ferns in the forests of New Caledonia. Although it is not clear, this mysterious little parrot could have been driven extinct by one or more of a variety of threats: introduced rats, cats, or habitat fragmentation and destruction.
Two of the four South American blue macaw species are also recommended to be classified as Extinct: the glaucous macaw, Anodorhynchus glaucus (last seen in 1998), and Spix’s (little blue) macaw, Cyanopsitta spixii, which Dr. Butchart and his collaborators recommended be treated as Extinct in the Wild, since there is a captive population estimated to number somewhere between 60-80 individuals. The disappearance of the glaucous macaw from its range in Argentina, Uruguay and Brazil is linked to trapping for the wild bird trade (as is true for all the blue macaws), and to large-scale agriculture, which prompted uncontrolled clearing of the yatay palm, Butia yatay, whose nuts were its primary food.
The public first became aware of the plight of the Spix’s macaw after watching the 2011 animated film Rio, which tells the story of Blu, a captive-raised Spix’s macaw who travels to Brazil to mate with Jewel, the last-known wild member of the species. Later in 2016, the conservation and parrot worlds were briefly set aflame with hope when an individual was spotted and filmed flying over the small town of Curaçá, which is in this species’s historic range (more here). Sadly, that individual, which has never been seen again, is believed to have been an escaped cage-bird.
In addition to the two extinct macaws, two endemic Brazilian songbirds are also listed as Extinct — the cinnamon-colored cryptic treehunter, Cichlocolaptes mazarbarnetti (last seen in 2007), and its doppelgänger, the Alagoas foliage-gleaner, Philydor novaesi. Both birds disappeared after the last remnants of their forest habitat were replaced with sugar cane plantations and pasture. The Alagoas foliage-gleaner actually managed to hang on until 2011, when it was last sighted and filmed. Recordings of both species’ songs and calls exist (for example, here and here), and serve as a haunting reminder of these lost species.
The Pernambuco pygmy owl, Glaucidium mooreorum, is a small insect-eating owl endemic to the state of Pernambuco in Brazil. Although it was last seen in 2001, it was only formally described as a species that was new to science in December 2002 after two study skins were examined (ref). Due to the almost complete destruction of its habitat by illegal logging, this owl species was recommended to be treated as Critically Endangered (Possibly Extinct).
Another island species, the po’o-uli, or black-faced honeycreeper, Melamprosops phaeosoma, was also recommended to be treated as Extinct. The po’o-uli was a snail-eating Hawaiian songbird that has not been seen in the wild since 2004, which is the same year that the last captive individual of the species died (you can read more in my review of the book detailing the heartrending conservation effort devoted to this species).
The Java lapwing, Vanellus macropterus, is another island species that was recommended to be listed as Critically Endangered (Possibly Extinct). Large with extremely long legs and distinctive plumage markings, this wading bird was really difficult to miss, and it was last spotted in 1994. It inhabited marshes and river deltas of Java, and possibly Sumatra and Timor as well. This species succumbed to extensive habitat degradation and destruction of its marshy home, combined with relentless hunting.
Evidence of absence?
As I read this study, I was concerned that the models predict higher than expected probabilities of survival based upon unsubstantiated observations. One such example is the ivory-billed woodpecker, Campephilus principalis, which is certainly extinct and likely has been since the early-to-mid 20th Century, despite the presumption by Dr. Butchart that it may have been alive in 2006, but may now have gone extinct (ref).
“The issue is, where do these ‘expectations’ come from?” said ecologist Mark Burgman, a professor at The University of Melbourne, who specializes in applying model-based risk assessment to problems in conservation biology, and who was not part of this study.
“All records are uncertain to some extent, even museum and herbarium records that ‘seem’ concrete,” Professor Burgman explained in email. “Scientists form opinions about the likelihood that a species is extinct from all kinds of sources. These papers are trying to assemble all the evidence, give each element appropriate weight, and then combine them rationally into an overall judgement.”
“The methods themselves are sound, but the contributing data may not be,” Professor Burgman added. “Thus, if we discover in hindsight, that the outputs of these analyses are consistently too optimistic, then the fault will lie in the fact that we have given too much credibility to some observations rather than others. But it’s very difficult to know a priori which the culprits might be. This is an empirical question, and only careful observation will resolve it. Hopefully, in time, we’ll learn enough to be able to assign weights to evidence correctly.”
Rare species are often elusive, and may live in terrain that makes it difficult to see them even under the best of conditions.
“Determining whether a species has gone extinct is challenging as it is often difficult to tell if the last few individuals have died, especially for poorly known species in remote locations,” Dr. Butchart explained in email. “While we need an accurate measure of extinction rates, giving up on a species prematurely risks committing the so-called ‘Romeo Error’, where conservation efforts are abandoned prematurely on the presumption that the species has disappeared.”
On the other hand, it’s important to remember that essential resources for conservation efforts are often in short supply.
“We’ve got limited conservation resources so we need to spend these wisely and effectively. If some of these species have gone we need to redirect these resources to those that remain,” Dr. Butchart said in email.
Recognizing that accurate assessments of the moment of extinction are difficult to make with many elusive species, the paper’s authors point out that the “possibly extinct” classification is an extremely cautious judgment which almost certainly means that the species has vanished.
This method could be applied to other taxa, such as mammals, amphibians, or even plants, according to Dr. Butchart, who said their methodology would increase the robustness of extinction rate estimates and species classifications on the IUCN Red List. There are plenty of “test candidates” available: currently, more than 26,000 species worldwide are now threatened with extinction according to the most recent Red List. Because humans are driving this, the Sixth Great Extinction Event, plenty more species are being added to the list.
Dr. Butchart and his colleagues’ statistical model estimates a revised total of 187 avian extinctions have occurred since 1500.
“The results show that the state of the world’s birds is significantly worse than previously estimated,” Dr. Butchart said in email. Yet, there is still hope. This analysis provides conservation biologists with vital information on where to focus their efforts.
This brings us back to Spix’s macaw, which is Extinct in the Wild, but still exists in captivity. Has this species been saved? Considering that many species lose their wild culture after being taken into captivity, at least some people think a species hasn’t been “saved” at all if it only exists in a cage. Certainly, it would be a grave injustice to suggest that captive breeding alone is conservation: on one hand, aviculture is a wonderful tool for helping to preserve a species, but on the other hand, it does not and cannot solve ecological problems.
“While the results suggest that it is too late to help some iconic species, birds are better known than any other taxonomic class, so we know which species are at greatest risk and what actions and which locations are needed to save them,” Dr. Butchart said. “Our study should inspire a redoubling of efforts to prevent further human-induced extinctions in the coming years.”
Stuart H.M. Butchart, Stephen Lowe, Rob W. Martin, Andy Symes, James R.S. Westrip, and Hannah Wheatley (2018). Which bird species have gone extinct? A novel quantitative classification approach, Biological Conservation, 227(4):9–18 | doi:10.1016/j.biocon.2018.08.014