Keeping promises isn’t always easy, but – following what is hopefully a forgiveable hiatus – here we get back to that short series on obscure island-dwelling, recently extinct animals. It started with a map of the Caribbean. Then we got through (some of the) island otters and canids, and then more of the canids… the good news is that here we have that long-awaited, much-asked-for ‘titan-hawks and monster pigeons’ article. The bad news: I got carried away on the titan-hawks and other raptors, and the pigeons will have to wait, sorry…
It now seems that big raptors were important predators on islands worldwide until very recently. As usual, the extinction of these birds can probably (although not certainly) be blamed on anthropogenic causes: hunting, persecution, habitat disruption and/or ecological disturbance. Species that are still with us, like the widespread Golden eagle Aquila chrysaetos and the Imperial eagle A. heliaca were found on Mallorca and Corsica during the Pleistocene*, and a particularly large form of Golden eagle – named as the subspecies A. c. szimurgh – inhabited Pleistocene Crete. Alcover & McMinn (1994) noted that these big eagles would have preyed on the endemic Mediterranean artiodactyls, like the dwarf megacerine deer Megaloceros cazioti, the weird Balearic goat Myotragus balearicus and the Cretan deer Candiacervus, though I don’t know whether there’s any direct evidence for these inferred predatory relationships.
* What used to be called the Imperial eagle is now two species: the Eastern imperial eagle of eastern Europe and Asia, and the Spanish imperial eagle A. adalberti of the Iberian Peninsula. I don’t know which of the two the extinct Mediterranean birds belonged to.
The biggest eagle part II
Sea eagles (Haliaeetus) formerly inhabited Mediterranean islands and the Hawaiian islands during the Pleistocene and/or Holocene. Madagascar had the large, lemur-hunting Stephanoaetus mahery and New Zealand had the biggest eagle we know of, the awesome Haast’s eagle Harpagornis moorei (though read on). I previously wrote about Haast’s eagle on Tet Zoo ver 1 here but never got round to finishing things and publishing part II, so I may as well get that over and done with here. It’s old news now, but back in 2005 the big deal was that Haast’s eagle – traditionally given its own genus (Harpagornis) and thought to be close to or part of the big-bodied Aquila eagle clade (Holdaway 1992) – turns out to be part of a clade of small-bodied eagles. This discovery means that we have to revise our ideas on the affinities of the giant eagle, but also shows that a totally unexpected and incredible thing happened during the evolutionary history of this bird [adjacent image shows John Megahan's much-reproduced reconstruction of Haast's eagle vs moa pair].
As demonstrated by Bunce et al. (2005), DNA from Haast’s eagle indicates that the species is actually nested within Hieraaetus – the hawk-eagles – and hence should be renamed Hieraaetus moorei. All other Hieraaetus species are quite small (they weigh about 1 kg and have wingspans of c. 1.2 m: Haast’s eagle weighed up to 13 kg and had a wingspan of c. 2.6 m), so the ancestor of Haast’s eagle must have been small too. It’s inferred that – on arriving on a landmass lacking competitors and with an abundance of large, terrestrial prey – a small Hieraaetus species rapidly evolved into a powerful giant. We know from well documented taphonomic evidence that Haast’s eagle could and did kill even the very biggest of the contemporary moa, and unlike big eagles in continental environments it could probably get away with gorging itself at a carcass without having to worry about flying off in a hurry [adjacent image shows Booted eagle H. pennatus].
Giant buteonines from Gargano
During the late Miocene or early Pliocene (this age depends on which source you consult), what is now the Gargano Peninsula on the Adriatic coast of southern Italy formed an island archipelago inhabited by numerous island-endemic tetrapods. Among these were exceptionally large dormice, hamsters and mice, the giant long-skulled Deinogalerix hedgehogs (there are five species, not just one as you might think from the popular literature), an otter, European pikas, and the multi-horned artiodactyl Hoplitomeryx.
Rarely mentioned, however, are the buteonine hawks Garganoaetus freudenthali and G. murivorus (Ballman 1973, 1976). G. freudenthali was about the size of a Golden eagle while G. murivorus was probably hawk-eagle sized. What might be two additional, buzzard-sized Garganoaetus species are also known. Several features distinguish Garganoaetus from other hawks and eagles, most notably its peculiar tarsometatarsus where the trochlea for digit 4 extended as far distally as the other trochleae. On the basis of various (other) tarsometatarsal characters, Garganoaetus was argued by Ballmann (1973) to be a buteonine: that is, a member of the accipitrid group that includes true buzzards (Buteo) and their close relatives (buzzard-eagles, crab-eater hawks, solitary eagles, Harris hawk Parabuteo unicinctus, Lizard buzzard Leucopternis schistacea and others). Buteonines are mostly New World raptors; they are good at soaring, have long, broad wings and tend to have short tails. A recent study supported their monophyly (Lerner & Mindell 2005).
Large barn owls were also present on Gargano: Tyto robusta was described by Ballman (1973) as similar in size to a Snowy owl Bubo scandiacus while T. gigantea was even larger than a Eurasian eagle owl B. bubo, making it the largest known barn owl of all time. Some internet sources say that T. gigantea was twice as big as B. bubo: so far as I can tell from Ballman (1973) – it’s in German – he only said that it was larger than B. bubo. There were also smaller barn owls (T. santicalbani), some additional owls which remain poorly known, a species of Palaeortyx (a pheasant also known from Miocene France), a pigeon, swift, and warbler (Ballmann 1973, 1976). The Gargano avian assemblage has more recently been studied by Pavia and Göhlich (2004). In addition to the taxa described by Ballmann, they also reported an ibis, a duck, a small raptor, rails, a new bustard, and shorebirds.
West Indian giant crab-eater hawks
Garganoaetus freudenthali is interesting in being the size of a big eagle, even though it was apparently more closely allied to buzzards and other buteonines. Similar in some respects are the so-called titan-hawks and other large raptors of the West Indies. The most oft-mentioned of these extinct raptors is the species originally described as Aquila borrasi Arredondo, 1970. It comes from the Pleistocene of Cuba and was even noted by Arredondo (1976) as being similar in size and morphology (in tarsometatarsal anatomy anyway) to Garganoaetus; Arredondo also noted that A. borrasi was longer in the tarsometatasus than any living eagle, with a longer and more robust femur than any living eagle, and with ungual phalanges about twice as large as those of a Golden eagle! Despite these proportions, the tarsometatarsi of A. borrasi are more gracile than those of Aquila eagles, so it probably wasn’t able to tackle large-bodied mammalian prey as Golden eagles and other large Aquila species can [adjacent image shows Savanna hawk Buteogallus meridionalis: read on for relevance].
During my most formative years I always assumed that A. borrasi was a relatively well known species, all because of a Cuban stamp – shown at the top of the article – which depicts a nice life restoration of this species. Alas, that life restoration is but a fiction, and nothing more than a souped-up version of Arthur Singer’s painting from the 1960s of an Ornate hawk-eagle Spizaetus ornatus swooping in to catch an iguana. In fact, A. borrasi has always been poorly known and mysterious. Arredondo’s original classification of A. borrasi as part of Aquila reflects the common usage of the latter generic name as a ‘waste-basket’ for various raptors that are not really close relatives, and it’s been suggested several times that Arredondo’s Cuban raptor is actually more similar to Buteogallus, the four (or five) Central and South American buteonine hawks sometimes called the crab-eaters, or mangrove hawks, or black hawks. Olson & Hilgartner (1982) then suggested that A. borrasi might belong to Titanohierax, a genus named by Alexander Wetmore in 1937 for the species Titanohierax gloveralleni (more on that one in a minute). A. borrasi has therefore been referred to as Titanohierax borrasi in the more recent literature (e.g., Olson & Hilgartner 1982, Milberg & Tyrberg 1993, Alcover & McMinn 1994).
However, the big news is that a new paper on this taxon has just appeared (Suárez & Olson 2007), and it argues that…. A. borrasi isn’t just similar to Buteogallus, it is a Buteogallus, albeit a gigantic species about one-third larger than the largest living species, the Great black hawk B. urubitinga [shown in adjacent image]. Buteogallus is an interesting raptor for various reasons (Lerner & Mindell 2005, do Amaral et al. 2006); I’ll come back to it later. If Buteogallus borrasi, as it’s now known, was essentially a giant version of the Great black hawk, it presumably lived in a similar way: a sluggish, soaring hawk of mangroves and heavily wooded riverine habitats that preyed on crustaceans, lizards and large insects.
The Bahaman titan-hawk
Titanohierax gloveralleni, the type species of Titanohierax (sometimes called the Bahaman titan-hawk), was first named by Alexander Wetmore in 1937 for fragmentary specimens from Pleistocene deposits on Little Exuma in the Bahamas (Little Exuma and Great Exuma are north-east of central Cuba, west of Andros Island, and south of New Providence and Eleuthera). Additional material was later reported from New Providence by Olson & Hilgartner (1982). Burness et al. (2001) estimated the mass of the Bahaman titan-hawk as 7.3 kg, which would make it similar in size to the biggest living eagles, the Philippine eagle Pithecophaga jefferyi and Harpy eagle Harpia harpyja, according to some measurements anyway (upper weights of 8 or 9 kg are given for females of these two species, but data is poor and these figures may be exceptional).
Bits and pieces referred to the genus Titanohierax (but not to the species T. gloveralleni) have been reported from Hispaniola and Grand Cayman, with the implication being that these large raptors were apparently widespread throughout the West Indies. However, now that some material previously thought to belong to Titanohierax is now thought referable to Buteogallus, some of these specimens might require reidentification. What sort of raptor was T. gloveralleni? Olson & Hilgartner (1982) noted that it might be particularly closely related to Geranoaetus melanoleucos, the Black-chested buzzard eagle [shown in image above]. If this is correct then T. gloveralleni would be another buteonine in close phylogenetic proximity to Buteogallus and other buzzard-like raptors (Lerner & Mindell 2005).
Even more mysterious than T. gloveralleni is the Cuban giant-hawk Gigantohierax suarezi Arredondo & Arredondo, 2002 (the paper that first named this species is dated 1999, but wasn’t published until 2002). Apart from the fact that it was big and endemic to Cuba, not much is known about it. The type specimen is a particularly big, strongly pneumatized left femur (Arredondo & Arredondo 2002), though material referable to this species has now been reported from three cave sites. Uncertainty remains as to the affinities of Gigantohierax, though it may well have been another buteonine.
The Woodward ‘eagle’
The most recently identified West Indian large raptor is Amplibuteo woodwardi (sometimes called the Woodward eagle), but it’s not a newly named species. Amplibuteo was originally described for the species A. hibbardi from the Pleistocene Talara Tar Seep of Peru, and in the same paper it was also argued that Morphnus woodwardi from Rancho La Brea, originally described in 1911, should also be identified as a species of Amplibuteo. More recently, Amplibuteo has been reported from the Pliocene of Florida and Arizona, and it was still living in Florida during the Pleistocene. The members of this genus therefore appear to have been widespread across North America. Indeed the recognition of A. woodwardi on Cuba (Suárez 2004) indicates that it crossed from the North American mainland to the Greater Antilles, and that it may await discovery on islands other than Cuba [adjacent pic is taken from here and labelled as that of a Woodward eagle, hence my use of it here. However, it's mislabelled and is in face a Merriam's teratorn Teratornis merriami. Thanks to Bill Unzen for bringing this to my attention].
A. woodwardi was probably similar in size to Buteogallus borrasi and Titanohierax gloveralleni (i.e., big), but it apparently differed from B. borrasi at least in being a bird of semi-arid grassland habitats, where it presumably preyed mostly on reptiles and smaller mammals. Given that complete skeletons are known, there should be accurate data on its size and inferred wingspan, but if such data exists I haven’t seen it. What would Amplibuteo have looked like when alive? In their description of the new Pliocene species A. concordatus (from Florida and Arizona), Emslie & Czaplewski (1999) suggested that Amplibuteo might be congeneric with Harpyhaliaetus, the extant Neotropical solitary eagles. The two solitary eagle species are broad-winged, very short-tailed, dark grey or blackish eagles with occipital crests. They are noisy, often eat snakes, and the Crowned solitary eagle (H. coronatus) is said in some accounts to be partially crepuscular and to hunt skunks, which makes it interesting to say the least. It would be very neat if A. woodwardi was at all like this. If Emslie & Czaplewski (1999) were right about Amplibuteo being close to Harpyhaliaetus, then – yet again – these raptors were buteonines [image below shows Crowned solitary eagle H. coronatus].
So, what with all these big buteonines, the West Indian avifauna has proved really interesting. But remember that the prehistoric Caribbean raptor fauna was considerably more diverse than this: the big West Indian buteonines lived alongside small buteonines (including true buzzards), accipiters, ospreys, true falcons, caracaras, barn owls, burrowing owls, various other extinct owls (some of which were very large and either poorly flighted or flightless), New World vultures, and teratorns (although members of these groups did not necessarily all live on the same island at the same time). Where are they now? Exactly why so many of them became extinct remains relatively unstudied, but it is likely that the loss of presumed prey species – the various terrestrial rodents and other mammals, for example – was a major factor in their decline. Other factors were involved too, but I’m not about to discuss them now.
Finally – that’s another ‘to do’ ticked off the list. Just pandas, phytosaurs, astrapotheres, rhynchosaurs, pyrotheres, giraffids, Piltdown, amphisbaenians, beluwhals, palaeophiids, meiolaniids, de-hominization, knuckle-walking, tortoises, kinglets, Eotyrannus and… monster pigeons to go. Watch this space, I’ll do them all tomorrow. Yeah.
Refs – –
Alcover, J. A. & McMinn, M. 1994. Predators of vertebrates on islands. BioScience 44, 12-18.
Arredondo, O. 1976. The great predatory birds of the Pleistocene of Cuba. Smithsonian Contributions to Paleobiology 27, 169-187.
– . & Arredondo, C. 2002. Nuevos género y especie de ave fósil (Falconiformes: Accipitridae) del Cuaternario de Cuba. Poeyana 470-475, 9-14.
Ballman, P. 1973. Fossile Vögel aus dem Neogen der Halbinsel Gargano (Italien). Scripta Geologica 17, 1-75.
– . 1976. Fossile Vögel aus dem Neogen der Halbinsel Gargano (Italien), zweiter Teil. Scripta Geologica 38, 1-59.
Bunce, M., Szulkin, M., Lerner, H. R. L., Barnes, I., Shapiro, B., Cooper, A. & Holdaway, R. N. 2005. Ancient DNA provides new insights into the evolutionary history of New Zealand’s extinct giant eagle. PLoS Biology 3 (1), e9.
Burness, G. P., Diamond, J. & Flannery, T. 2001. Dinosaurs, dragons, and dwarfs: the evolution of maximal body size. Proceedings of the National Academy of Sciences 98, 14518-14523.
do Amaral, F., Miller, M., Silveira, L., Bermingham, E. & Wajntal, A. 2006. Polyphyly of the hawk genera Leucopternis and Buteogallus (Aves, Accipitridae): multiple habitat shifts during the Neotropical buteonine diversification. BMC Evolutionary Biology 6, 10 doi:10.1186/1471-2148-6-10
Emslie, S. D. & Czaplewski, N. J. 1999. Two new fossil eagles from the Late Pliocene (late Blancan) of Florida and Arizona and their biogeographic implictations. Smithsonian Contributions to Paleobiology 89, 185-198.
Holdaway, R. N. 1994. An exploratory phylogenetic analysis of the genera of the Accipitridae, with notes on the biogeography of the family. In Meyburg, B.-U. & Chancellor, R. D. (eds) Raptor Conservation Today. WWGBP/The Pica Press, pp. 601-649.
Lerner, H. R. L. & Mindell, D. P. 2005. Phylogeny of eagles, Old World vultures, and other Accipitridae based on nuclear and mitochondrial DNA. Molecular Phylogenetics and Evolution 37, 327-346.
Milberg, P. & Tyrberg, T. 1993. Naïve birds and noble savages – a review of man-caused prehistoric extinctions of island birds. Ecography 16, 229-250.
Olson, S. L. & Hilgartner, W. B. 1982. Fossil and subfossil birds from the Bahamas. Smithsonian Contributions to Paleobiology 48, 22-60.
Pavia, M. & Göhlich, U. B. 2004. Revision of the fossil bird association of the neogene of the Gargano (Apulia, SE Italy). In Buffetaut, E. & Le Loeuff, J. (eds) Sixth International Meeting of the Society of Avian Paleontology and Evolution, Abstracts. Quillan, France. 28th September – 3rd October, 2004, pp. 52-53.
Suárez, W. 2004. The identity of the fossil raptor of the genus Amplibuteo (Aves: Accipitridae) from the Quaternary of Cuba. Caribbean Journal of Science 40, 120-125.
– . & Olson, S. L. 2007. The Cuban fossil eagle Aquila borrasi Arredondo: a scaled-up version of the Great black-hawk Buteogallus urubitinga (Gmelin). Journal of Raptor Research 41, 288-298.