Nevermore

Leaving Not One Black Plume as a Token to Remember Them

Sometimes, species do not survive the threats that they face as described in the stories this season. This can occur because the declines are too severe to counteract, but also because the environment increases the vulnerability of certain species when conditions shift. One of the major environmental factors that can lead to extinction is isolation. If a species is unable to relocate, it will be more likely to die off if it is unable to adapt quickly.

This isolation is frequently seen on islands, especially those of low size and high distance from the mainland. In fact, a significant fraction of the species that have gone extinct within the historical time-frame (i.e. after the existence of written records) were found only on a single island or small group of them. We’ve already looked briefly at the vulnerabilities of island populations in the story on the Critically Endangered black stilt of New Zealand.

For this week, we’ll be looking at an archipelago in the Indian Ocean near Madagascar called the Mascarene Islands. This trio of islands is the site of one of the most famous and iconic recent extinctions. The dodo, Raphus cucullatus, was a flightless bird native to the island of Mauritius and closely related to pigeons and doves. It went extinct less than 100 years after its first formal sighting in 1598, though many people believed for some time that it was a myth and had never existed.

While the common wisdom was that the dodo was hunted to extinction by people, more recent evidence indicates that introduced predators (such as feral pigs, cats, and dogs) and habitat destruction were of greater influence in their decline and eventual disappearance. The dodo is a well known example of extinction and has entered the modern lexicon as shorthand for a person or group that is old-fashioned or unwilling to change with shifting conditions. However, in the century following the dodo’s disappearance, three other species of birds in the area also went extinct that are little known today.

These birds were night herons, all of them members of the genus Nycticorax. Currently, only two living species exist in that genus, one of which is the relatively common and Least Concern black-crowned night heron, Nycticorax nycticorax, seen above and below. Each species was found on one of the three islands: the Rodrigues night heron, Nycticorax megacephalus, the Réunion night heron, Nycticorax duboisi, and the Mauritius night heron, Nycticorax mauritianus.

‘Nycticorax’ means ‘night raven’ in Greek (hence the Edgar Allen Poe reference in the title), though they are not closely related to ravens or other corvids like crows and jays but belong instead to the family of herons, egrets, and bitterns. There are seven living species of night herons (so called because they tend to feed at night, though they can still be seen during the day), which had all at one point been grouped in Nycticorax, but now are placed in three separate genera.

Little is known about the trio of Mascarene night herons because the islands were not regularly inhabited until the 17th century, being away from typical shipping lanes of the time and of little strategic or economic interest. The small size of the islands contributed to the vulnerability of these birds and many other species when human colonization began in earnest. Rodrigues is only 108 sq. km, Mauritius is 1,860 sq. km, and Réunion is 2,512 sq. km. To put this in perspective, all three islands combined are only slightly larger than the state of Rhode Island.

Similar to the dodo, the three night herons were not wary of humans and would only flee if chased. Two of the species, Nycticorax megacephalus and Nycticorax mauritianus, preferred to flee on foot and showed evidence of evolving toward flightlessness. Also similar to the dodo, there is little hard evidence of widespread hunting by humans, but habitat destruction and introduced species would have devastated both. The reasons for the extinction of the species on Réunion, Nycticorax duboisi, are still unclear, since it was actually a strong flyer and less vulnerable to the changes brought to the island by human inhabitants. All three species went extinct sometime between the late 17th and mid 18th centuries, about 40 to 100 years after the extinction of the dodo.

Species go extinct. It is part of the natural progression of life. On average, throughout geologic time, two to five marine taxonomic families go extinct every million years. However, since the ‘Cambrian explosion’, there have been five recognized major mass extinction events (and many more minor ones) where extinctions have exceeded this background average. The most recent was 65 million years ago at the end of the Cretaceous Period, best known for wiping out the (non-avian) dinosaurs.

Because of this natural progression, it could be easy to argue that fighting extinction in the present day is ‘interfering’ with natural processes. However, extinction rates since the year 1900 are 1,000 times the background rate. This means that what we are seeing now is not just species dying out normally, but an accelerated die off due to numerous factors, many of them influenced by human actions as detailed throughout this season of stories. This idea is an excuse to do nothing dressed up as an appeal to nature.

It would also be easy to feel overwhelmed and hopeless, to throw up our arms in defeat and believe that averting extinction is impossible after the changes we have made to the world. My final two weeks for Season 3 will be dedicated to helping combat this helpless feeling. When we caused the extinctions of the dodo and the three Mascarene night herons, we did not fully understand the consequences our actions would have. We have a much better understanding now, which means we also have a chance at reversing some of the damage.