The evolution of falcons is rather poorly understood. Thanks to genetic evidence we know that they’re closely related to seriemas, parrots, and passerines, but their fossil record is patchy and little is known about the early members of their lineage.
But a group knows as masillaraptorids are giving us a rare glimpse at what some early falconiforms were up to. Known from the Eocene of Europe, these long-legged predatory birds seem to have been caracara-like terrestrial hunters specializing in chasing down prey on foot – although their wings and tails indicate they were also still strong fliers.
Danielsraptor phorusrhacoides lived during the early Eocene, about 55 million years ago, in what is now eastern England. Although only known from partial remains, it was probably around 45-60cm long (~1’6″-2′), and it had a large hooked beak with a surprising amount of convergent similarity to those of the flightless South American terror birds.
Its mixture of falcon-like and seriema-like features may indicate that the common ancestor of both of these bird groups was a similar sort of leggy ground-hunting predator.
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.
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.
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.
About 60-65cm long (2′-2’2″), it was similar in body size to larger individuals of its living relatives but was heftier built and had slightly longer legs, and its wings were reduced enough that it was either a very weak flier or entirely flightless.
It lived only in the dry scrubland around the southern coast of the island, and probably mainly preyed on reptiles, small rodents, and crabs using its strong legs — a lifestyle very similar to the modern secretarybird. Like other caracaras it would have also opportunistically scavenged on carrion, which there would have been little competition for.
The known remains of Caracara tellustris date to as recently as 100 CE, showing that it existed well into the Holocene and survived through the initial arrival of humans on its island home (about 4000 BCE). This is likely due to its inhospitable hot, arid, and thorny habitat, where it would have been left relatively undisturbed, and it may even have persisted until the time of European colonization in the 1500s.
Unfortunately the scrubland was also very limited in size and the Jamaican caracara would have always been quite a rare species. If it was still around by then it would have faced a combination of introduced predatory mammals and habitat destruction by agriculture, which would have driven it into extinction so quickly its existence was never even noticed by naturalists at the time.
Like many other isolated islands ancient Cuba lacked any large land predators, allowing some birds to exploit more terrestrial lifestyles.
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.
And, once again, there was also a weird owl on this island.
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.
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.
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”.
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!)
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.
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.
With the slightly larger females reaching lengths of around 1.4m (4’7″) and hefty body weights of 15kg (33lbs), it was the largest eagle known to have ever lived, and one of the largest of all birds of prey. Yet its wings were actually proportionally short for its size, spanning about 2.5m (8’2″), giving it less ability to soar but much better maneuverability when flying in the thick vegetation of scrubland and forests.
At its size and weight when striking it would have hit its prey with a force equivalent to a falling cinder block, and with no major competitors it could have fed from a single large kill for many days.
As apex predators Haast’s eagles would also have never been particularly numerous, and their population was very sensitive to the availability of their prey species.
Unfortunately the early Māori people also found the large flightless birds like the moa to be delicious easy meals, and by the early 1400s the eagle had disappeared alongside its main food sources. Legends about a giant human-eating bird called the pouakai are thought to be based on folk memory of Haast’s eagle, and it may well have occasionally preyed on the settlers during the short time it coexisted with them.
Living between about 2.5 million and 13,000 years ago, it would have stood around 80cm tall (2′7″), with a wingspan of almost 2m (6′6″) and a fairly hefty body weight of 3kg (6.6lbs). Its feet had less grasping ability than other eagles but it also had particularly strong leg muscles, suggesting it was much better adapted for walking around on the ground.
With its large size, long legs, and terrestrial habits it seems to have convergently evolved to fill the same ecological niche as the modern secretarybird – a grassland-dwelling walking predator that hunted on foot, kicking and stomping small prey animals like snakes, lizards, and rodents.
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.