Tag: strigiformes

São Miguel Scops Owl

When owls find their way onto isolated islands lacking any terrestrial predators, they have a tendency to take up that role for themselves – evolving longer legs and shorter wings, and specializing more towards hunting on foot. From New Zealand to Hawaii to the Caribbean to the Mediterranean to Macaronesia, leggy island ground-owls have independently happened over and over again in the last few million years—

—And, unfortunately, they’ve all also become victims of the Holocene extinction, their fragile island ecosystems too easily disrupted by human activity and the arrival of invasive species.

The São Miguel scops owl (Otus frutuosoi) was found only in the Azores on São Miguel Island. About 18cm tall (~7″), it was slightly smaller than its relative the Eurasian scops owl, with longer legs, a wider body, and much shorter wings.

Its wing proportions indicate it would have been a poor flyer, instead primarily hunting on foot in the dense laurisilva forests. Since there were no terrestrial mammals or reptiles on São Miguel at the time, its diet probably mainly consisted of insects and other invertebrates – and it would have in turn been the potential prey of larger predatory birds like buzzards and long-eared owls.

All currently known subfossil remains of the São Miguel scops owl date only from the Holocene, between about 50 BCE and 125 CE. It’s likely that it was extinct by the 1400s, following the settlement of humans in the Azores, destruction of its forest habitat, and the introduction of rodents, cats, and weasels.

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 #59 — Terrestrial Otters & Owls

The Mediterranean island of Crete had very few predators during the Pleistocene, with most being birds of prey. And with the terrestrial carnivore niches in the ecosystem left vacant, it was a semi-aquatic mammal and an owl that ended up taking advantage of that opportunity.

Neither were large enough to threaten the dwarf elephants and hippos, and don’t even seem to have habitually eaten even the smallest of the miniature giant deer. Instead these Cretan predators focused much more on the smaller land vertebrates on the island, preying on birds, shrews, rodents, amphibians, and reptiles.

A stylized illustration of an extinct otter. It has a blunt snout and chunky legs.
Lutrogale cretensis

Lutrogale cretensis (previously known as Isolalutra cretensis) was a close relative of the modern smooth-coated otter. It was about the same size as its living cousin, around 1m long (3’3″), but had stronger jaws and chunkier limbs.

Its skeleton shows features associated with walking and running more than swimming, and it seems that this was something of a “land otter” — still able to swim, but spending most of its time on land similar to the modern small-clawed otter.

Shellfish were likely still the main part of its diet, indicated by its crushing teeth. But it probably also regularly ate whatever small terrestrial vertebrates it could catch, since more aquatic otters are already known to prey on those types on animals when they can.

A stylized illustration of an extinct giant little owl. It has longer legs than its modern relatives, almost resembling a large burrowing owl.
Athene cretensis

Athene cretensis was yet another weird island owl, but this time not a descendant of a Strix or Tyto species. Instead this owl was descended from the Eurasian little owl — except it had become much much larger.

It stood around 60cm tall (2′), over three times bigger than its living relative. Its legs weren’t quite as long as those of the modern burrowing owl, but they were still proportionally much longer than those of little owls and show adaptations for terrestrial movement. Little owls already sometimes chase down prey on foot, and Athene cretensis was probably even more of a ground-based hunter, convergently similar to the Hawaiian stilt-owls and the Cuban terror owls.

Preserved pellets show that it ate small mammals and birds, mainly large mice.

Its wings were still quite large, and it was probably also a good flier — and may even have spread over to some of the Dodecanese islands to the east of Crete, since a wing bone closely resembling that of Athene cretensis has been found on Armathia.

Both of these predators seem to have disappeared around the end of the Pleistocene, at the same time as many of the other native Cretan species about 21,500 years ago. Much like the situation with Candiacervus, this may have been a result of a combination of a rapidly shifting climate and the presence of humans disrupting the already fragile island ecosystem.

Island Weirdness #48 — Chunky Cranes & Terror Owls

Like many other isolated islands ancient Cuba lacked any large land predators, allowing some birds to exploit more terrestrial lifestyles.

A stylized illustration of an extinct flightless sandhill crane. It has a somewhat chunkier beak than its modern relatives, along with smaller wings and thicker legs.
Grus cubensis

The Cuban flightless crane (Grus cubensis, or possibly Antigone cubensis) lived during the Late Pleistocene and Holocene. It was probably a descendant of the sandhill crane — and although an endemic variety of sandhill crane still exists in Cuba today, the two aren’t directly related to each other and instead are the result of two different colonization events.

It was about the same size as modern sandhill cranes, around 60cm tall at the back (2′) with a full height of about 1m (3’3″), but it was much more heavily built. It had stockier legs and a thicker beak, suggesting it may have been specialized for a different ecological niche than its ancestors, and its wings were reduced enough that it was probably completely flightless.

A stylized illustration of an extinct giant owl. It has proportionally short wings and long stilt-like legs.
Ornimegalonyx oteroi

And, once again, there was also a weird owl on this island.

Ornimegalonyx oteroi was closely related to true owls in the genus Strix, and in a great example of convergent evolution did the exact same thing as the Grallistrix stilt-owls — it evolved into a long-legged short-winged ground-based apex predator.

But it was almost twice the size of its Hawaiian cousins, measuring about 1.1m tall (3’7″) and potentially being the largest owl to ever exist. Its remains were so big, in fact, that they were initially mistaken for those of a terror bird.

It was powerfully built and was probably a good runner, mainly preying on giant rodents and dwarf ground sloths. While its wings and flight muscles were reduced it might not have been entirely flightless, and it may have been still been capable of turkey-like short bursts of flight.

Three other species of Ornimegalonyx also stalked ancient Cuba at the same time, varying slightly in size from each other and probably each specializing in a different size class of prey.

Remains of both of these birds have been found in natural petroleum seeps on the northern coast of Cuba that date to as recently as about 6000 years ago, around the same time that humans first arrived. After that point they probably both went extinct very quickly — the flightless cranes were probably actively hunted and eaten into extinction, and the terror owls would have disappeared as their prey species dwindled away due to the same hunting pressures.

Island Weirdness #46 — Tyto pollens

The islands of the Caribbean looked very different during the Pleistocene ice ages, when changing sea levels meant larger areas of land were exposed — and one of the most extreme examples of this was the Bahamas, much larger than they are today, with most of the Bahaman Banks exposed and over 10 times more land area.

Tyto pollens was an enormous barn owl, around 1m tall (3’3″), the size of a large eagle and one of the biggest owls to ever exist. It lived in old-growth pine forests on what is now the Andros Island archipelago and preyed mostly on Bahamian hutias, which were originally the only terrestrial mammals in the Bahamas.

It probably evolved in Cuba, and colonized the Bahamas shortly after the hutias did, sometime in the last 400,000 years during a glacial period when a particularly low seal level meant the islands were only about 30km apart.

It was the main nocturnal predator in the Bahamas, and much like its older Italian relative Tyto gigantea it also had a giant hawk counterpart in the daytime: the huge Titanohierax.

Although many popular online sources refer to Tyto pollens as being flightless, it actually had large robust wings and could probably fly quite well. This might be due to some confusion between it and a completely different giant Caribbean owl, Ornimegalonyx.

The Lucayan people probably reached Andros Island sometime around 1000 CE, and coexisted with the giant owls for several centuries. It was only after European arrival in the 1500s and the felling of their forest habitat that they seem to have vanished.

Local legends of an owl-like creature called the chickcharney may have been inspired by historical encounters with Tyto pollens, and suggest that they were aggressively territorial.

Island Weirdness #42 — Tall Owls & Short Ibises

The complete lack of land mammals on the Hawaiian islands left the terrestrial predator niches available to birds — and it was owls who ended up taking advantage of that role in the ecosystem.

The Grallistrix owls were found on Kauaʻi, Oʻahu, Molokaʻi, and Maui, with each island having its own endemic species. They were a type of true owl, probably descended from a species of Strix, and developed especially long legs that led to their nickname of “stilt-owls”.

A stylized illustration of an extinct owl. It has short wings and very long stilt-like legs.
Grallistrix geleches

The Molokaʻi stilt-owl (Grallistrix geleches) was the largest of the four known species, about 60cm tall (2′). Although it had proportionally short wings it was still capable of flying, and probably specialized in stalking and ambushing smaller birds like Hawaiian honeycreepers in the dense forests.

(These owls were also the inspiration for the pokémon Decidueye!)

A stylized illustration of an extinct flightless ibis. It has a downward-curving beak, small wings, and relatively short thick legs compared to other ibises.
Apteribis glenos

Meanwhile the forest floor insectivore niche was occupied by Talpanas on Kauaʻi, but on the other main islands a different type of bird took up the same role.

Apteribis was an ibis closely related to the modern white ibis and scarlet ibis, with three different species found on the islands of Maui, Molokaʻi, and Lānaʻi.

The Moloka’i flightless ibis (Apteribis glenos) was a typical example of the genus, about 50cm long (1’8″). It was flightless, with reduced wings, and had unusually short stocky legs that gave it proportions much more like a kiwi than an ibis. And it probably lived very much like a kiwi, too, probing around in the forest litter with its beak searching for snails and other invertebrates.

We even have an idea of the coloration of these birds, thanks to subfossil remains with preserved feathers. They seem to have been brown and beige, similar to the juvenile plumage of their close relatives.

The arrival of humans at least 1000 years ago would have unfortunately been devastating to both the stilt-owls and the flightless ibises. The combination of hunting, habitat destruction, and invasive dogs, pigs, and rats attacking them and their ground-based nests probably drove them all into extinction very quickly.

Island Weirdness #17 – Tyto gigantea

The largest terrestrial predators on the Late Miocene Gargano-Scontrone island(s) were unusually big hedgehog-relatives, and likewise the local aerial predators also increased in size compared to most of their cousins on the mainland.

Tyto gigantea was a massive barn owl, estimated to have been at least as large as the modern eagle-owl – probably measuring somewhere around 80cm in length (2′7″). It likely grew so big thanks to the lack of competition and in order to keep up with the larger sizes of its prey, since the rodents and pikas of Gargano-Scontrone were also comparative giants.

Alongside the slightly smaller species Tyto robusta it would have been the dominant nocturnal predator on the island(s), while during the daytime the golden-eagle-sized buzzard Garganoaetus occupied the same large-carnivorous-bird niche.