Tag: psittaculidae

Strange Symmetries #23: Convergent Earvolution

Although it’s not visible externally, owls have one of the most striking modern examples of asymmetry. The ears of many species are uneven, with the right ear opening positioned higher up than the left, giving them the ability to pinpoint the sounds of their prey much more accurately.

But surprisingly this isn’t a unique anatomical trait that only ever evolved once in their common ancestor.

Instead, multiple different lineages of owls have actually convergently evolved wonky ears somewhere between four and seven separate times.

The boreal owl (Aegolius funereus), also known as Tengmalm’s owl, is a small 25cm long (~10″) true owl found across much of the northern parts of both Eurasia and North America. While most other owls’ asymmetrical ear openings are formed just by soft tissue, the boreal owl’s lopsided ears are actually visible in the bones of its skull.

But despite how many times owls have convergently evolved asymmetrical ears, and how successful this adaptation has been for them, for a long time it seemed to be something that no other animals have ever mimicked.

In the early 2000s asymmetric ears were reported in the skulls of some troodontid dinosaurs, which seem to have been nocturnal hearing-based hunters similar to owls, but proper details on this feature still haven’t been formally published.

Then, just a couple of weeks ago, another example was finally announced.

The night parrot (Pezoporus occidentalis) is a small ground-dwelling parrot found in Australia, close to the same size as the boreal owl at around 22cm long (~9″). Critically endangered and very elusive, it’s rarely seen and little is known about it – and it was presumed extinct for much of the 20th century, until more recent sightings of living individuals confirmed that the species is still hanging on.

Recent studies of preserved museum specimens have revealed that it seems to have poor night vision but excellent hearing, and that its right ear opening is noticeably asymmetrical, bulging out sideways from its skull. Much like owls the night parrot relies on acute directional hearing to navigate in darkness, but since its diet consists mainly of seeds it’s probably not using this ability to locate food sources. Instead it may be listening out to keep track of the precise locations of other parrots, and for the approach of predators – so its sharp sense of hearing may be the reason this unique bird has so far just barely managed to survive the presence of invasive cats and foxes.

Island Weirdness #25 – The Broad-Billed Parrot

The dodo wasn’t the only unique bird to evolve on Mauritius. While about eight other endemic bird species still survive today, there were at least twice that many before the arrival of humans in the late 1500s – including the broad-billed parrot Lophopsittacus mauritianus.

Also referred to as the “Indian raven” in historical accounts, it was a fairly large bird measuring between 45 and 65cm in length (1′6″-2′1″). Unusually for a parrot it had a high degree of sexual dimorphism, with males being significantly bigger than females.

Many images depict it as entirely black or blue-grey, but this seems to be based on a misinterpretation. More recent translations of old Dutch descriptions suggest it was actually much more colorful, with a red beak, blue head, and reddish body.

It had a proportionally big head and a flattened skull, and seems to have had a highly specialized diet, using its its large strong beak to crack open hard seeds and nuts like modern hyacinth macaws.

It was near-flightless, capable of taking to the air only with difficulty, and was said to be “bad-tempered”. Attempts to keep individuals in captivity failed, the birds refusing to eat, and while the wild population had apparently learned to be wary of humans by the late 1660s by that point it was already too late. Much like the dodos they lived alongside, a combination of deforestation, hunting, and predation by invasive mammal species sent them into extinction by the 1680s.