Owls (Strigiformes)
The largest owl of all time was the Cuban Ornimegalonyx at 43.3 inches tall probably exceeding 9 kg (20 lb).

Arredondo estimated the height of Ornimegalonyx to have been 1.1 metres (3 ft 7 in) tall and it probably easily exceeded 9 kilograms (20 lb). It had very long legs for its size, but was bulky overall and probably short-tailed. The modern owl that most resembles the Cuban giant owl in proportions is probably the dainty burrowing owl, the only surviving owl closely tied to the ground. This implies similar adaptations to the terrestrial lifestyle, but not a close phylogenetic relationship.
One of the largest living owl, the Eurasian eagle owl (Bubo bubo), reaches 4 kg in weight, and Peters (page 188) has reported them taking roe deer fawns that weigh 17 kg as prey This suggests that Ornimegalonyx could have killed prey of 35 kg or more. Modern owls are known to use a pouncing strategy - where they drop from elevated perches onto prey, spreading their wings only just before hitting their target.The modern kakapo (Strigops habroptila) is a flightless island parrot and is convergent, in some ways, with owls. Like Ornimegalonyx, it is the largest and heaviest member of its order, it has reduced wings, and a reduced keel of the sternum, but it can parachute by leaping from trees with its wings outspread, potentially covering several meters at an angle of descent less than 45 degrees.
The legs and feet of the Cuban giant owl appear to be very large and powerfully built. This supports the theory that they were strong runners, hence the alternate name, cursorial. The keel of the sternum was reduced and the owl may have been capable of short burst of flight. It is probable that, like a modern wild turkey, the owl only took flight when extremely pressed, more often choosing to run.
The Cuban giant owl is believed to have preyed principally on large rodents including Heteropsomys, Capromys, Geocapromys, and Macrocapromys (the size of modern nutria or capybara) and the ground sloths Cubanocnus, Miocnus, Mesocnus, and Megalocnus. It was probably an ambush predator that would pounce on unsuspecting prey with its crushing talons.

Pigeons (Columbiformes)
The largest pigeon ever was the dodo (Raphus cucullatus), weighing 23 kg (51 lb) and standing 1 m (3.3 ft) tall.

Rodrigues solitaire (Pezophaps solitaria), a brown, long-necked birds that were superficially ratite-like. All three species may have exceeded 1 m (3.3 ft) in height. All were carelessly hunted it into extinction by humans and introduced animals. The dodo is the most frequently crowned as the largest ever pigeon, as it could have weighed as much as 28 kg (62 lb), although recent estimates have indicated that an average wild dodo would have weighed around 10.2 kg (22 lb), scarcely larger than a male turkey.If dodos were this light, the Rodrigues solitaire may have been larger. Some estimates claim tha solitaire was merely swan-sized but others estimate weights of up to 27.8 kg (61 lb)

Gamebirds (Galliformes)
The largest in this group was a giant flightless Sylviornis, a bird 1.70 m (5.6 ft) long and weighing up to about 30 kg (66 lb).

Sylviornis is an extinct genus of galliform bird containing a single species, S. neocaledoniae, or erroneously, "New Caledonian Giant Megapode". Technically, the latter is incorrect because it has recently been found not to be a megapode, but the sole known member of its own family, the Sylviornithidae; at the time of its description, it was believed to be a ratite. Sylviornis was never encountered alive by scientists, but it is known from many thousands of subfossil bones found in deposits, some of them from the Holocene, on New Caledonia and the adjacent Оle des Pins.
Sylviornis was a huge, flightless bird, 1.7 m (5.6 ft) long altogether, and weighing around 30 kg (66 lb) on average. It is the most massive galliform known to have ever existed. It had a large skull with a high and laterally compressed beak surmounted by a bony knob. Its legs were rather short, but had strong toes with long nails. The skeleton has a number of peculiarities and differences that make Sylviornis stand apart from all other known birds: the clavicles were not fused to a furcula, the number of caudal vertebrae was very high, and the ribcage and pelvis were almost dinosaurian in appearance. The wings were reduced to small stubs.
A large proportion—up to 50% in some deposits—of the remains found were from juvenile animals. Thus, it has been theorized that Sylviornis had a clutch of at least two, more probably closer to 10 eggs, and that the average lifespan was not much more than 5–7 years, which would be extremely low for such a large bird. Apparently, the bird did not incubate its eggs but built a mound similar to the megapodes. Tumuli on the Оle des Pins which were initially believed to be graves were found to contain no human remains or grave goods, and it has been hypothesized that they were in reality the incubation mounds of Sylviornis. As these mounds are up to 5 m high and 50 m wide even after nearly four millennia, they seem too large to have been made by the giant scrubfowl, an extinct New Caledonian species of megapode.
Little can be said about the lifestyle of Sylviornis. It was probably a slow-moving browser, and the structure of the bill and feet suggest that roots and tubers it dug up formed a major part of its diet.
The bird was hunted to extinction by the Lapita ancestors of the Kanak people, who settled New Caledonia around 1500 BC. Predation by feral dogs and pigs probably also played a part. The legacy of Sylviornis persists in Kanak oral history in the form of stories giving a rough description of the bird and some of its habits. The native name was du.


Giant Swan - Cygnus falconeri

Cygnus falconeri, the Giant Swan, was a very large Siculo-Maltese swan known from the Middle Pleistocene. Its dimensions are described as exceeding those of the living Mute Swan by one-third, which would give a bill-to-tail length of about 190–210 cm (6.2 to 6.9 feet). A weight estimation has it at 26 kg (65 pounds). It would have been taller, though not heavier, than the region"s dwarf elephants. Due to its size, it may have been flightless, or semi-flightless despite a 3 meter (9.8 foot) wing span. It was well adapted for walking, and apparently a land feeder. It became extinct before the increase in human activity in the region, so its disappearance is thought to have resulted from extreme climate fluctuations. Related to the climate fluctuations would have been a temporary land-bridge to Italy that allowed European competitors on to the Island.
Like the dwarf elephant and other Mediterranean island endemics, it likely became isolated when the Mediterranean re-flooded about 5.3 million years ago.
Islands can do strange things to animals: large ones shrink (insular dwarfism) while little ones suddenly grow (insular gigantism). There are numerous examples of both phenomena, but I came across a case that interests me more because it relates to my study subject: waterfowl.
On Sicily and Malta there lived a giant swan, known as Cygnus falconeri, with a total length (bill to tail) of more than two meters and a wing span over three meters. The nice thing is that is lived next to dwarf elephants. Imagine that, a giant swan accompanied by a dwarf elephant. How things have changed...

Songbirds (Passeriformes)
The largest songbird is the extinct giant grosbeak (Chloridops regiskongi) at 11 inches (28 cm) long.

The King Kong grosbeak or giant grosbeak (Chloridops regiskongi) is a prehistoric species of Hawaiian honeycreeper, that was endemic to Hawaiʻi. It had the largest beak of the three Chloridops species known to have existed. The King Kong grosbeak was described from fossils found at Barber"s Point and Ulupau Head on the island of Oʻahu.t was 11 inches (28 cm) long, making it one of the largest Hawaiian honeycreepers. It was probably just a larger form of the Kona grosbeak.
The unusual name given to the species came from a reporter’s misquoting of ornithologist Storrs L. Olson’s discovery of the then-unnamed species as being "a giant, gargantuan, King Kong finch."

Cormorants and allies (Pelecaniformes)
The largest cormorant was the spectacled cormorant of the North Pacific (Phalacrocorax perspicillatus), which went extinct around 1850, was larger still, averaging around 6.4 kg (14 lb) and 1.15 m (3.8 ft).



The species was first identified by Georg Steller in 1741 on Vitus Bering"s disastrous second Kamchatka expedition. He described the bird as large, clumsy and almost flightless – though it was probably reluctant to fly rather than physically unable – and wrote "they weighed 12–14 pounds, so that one single bird was sufficient for three starving men." Though cormorants are normally notoriously bad-tasting, Steller says that this bird tasted delicious, particularly when it was cooked in the way of the native Kamtchadals, who encased the whole bird in clay and buried it and baked it in a heated pit.
Apart from the fact that it fed on fish, almost nothing else is known about this bird. The population declined quickly after further visitors to the area started collecting the birds for food and feathers, and their reports of profitable whaling grounds and large populations of Arctic foxes and other animals with valuable pelts led to a massive influx of whalers and fur traders into the region; the last birds were reported to have lived around 1850 on Ariy Rock (Russian: Арий Камень) islet, off the northwestern tip of Bering Island.
A presumed prehistoric record from Amchitka Island, Alaska, is based on misidentification of double-crested cormorant remains.

Parrots (Psittaciformes)
The largest parrot is the extinct Norfolk Island kaka (Nestor productus), about 38 cm long.