Saturday, May 27, 2006

More 'beautifully interesting' birds (part II)

In a desperate effort to complete the list of my ten most ‘beautifully interesting’ bird species, part of the 10 bird meme (see previous blog), here are some more. I’ll reach the full ten eventually.

5. Ground tit Pseudopodoces humilis

If convergence is one of the most interesting evolutionary phenomena, then the Ground tit should become a text-book example of it, on par with thylacines vs wolves and ichthyosaurs vs dolphins. Described in 1871 by A. Hume, the Ground tit is a weak-flying brown passerine of the Tibetan plateau, often superficially likened to a wheatear. But for most of the time that we’ve known of it, it has not gone by the name Ground tit at all: rather, it has been termed Hume’s ground-jay (or Little ground-jay or Tibetan ground-jay or Hume’s ground-pecker). This is because, you see, it was always regarded as a ground-jay, that is, as a terrestrial corvid. While superficially similar to true ground-jays (the four Podoces species), it was always regarded as a highly aberrant member of Corvidae, and as the smallest member of the group. Hume in fact initially described P. humilis as a member of Podoces. Like Podoces, P. humilis possesses a slender, decurved bill, pale brown plumage and a dry, open-country habitat. However, they’re also highly different. While ground-jays run, P. humilis hops, and while ground-jays use stick nests, P. humilis nests in tunnels or burrows. Ground-jays are also much larger than P. humilis and exhibit white wing patches and dark, iridescent plumage patches. In recognition of these differences, P. humilis was given its own subgenus within Podoces in 1902, and in 1928 this was elevated to generic status.

But the allocation of P. humilis to Corvidae wasn’t really doubted until prominent osteological differences between P. humilis and ground-jays were noted by Borecky (1978). Borecky doubted the classification of P. humilis as a corvid and hinted at an affinity with starlings. In her 1989 phd study on corvid phylogeny, Sylvia Hope agreed that P. humilis was utterly unlike corvids, and most like nuthatches and tits. Despite these objections, P. humilis has remained classified as a corvid in most standard works on Corvidae (Goodwin 1986, Madge & Burn 1999) and indeed in most general works on birds. To resolve the issue once and for all, Helen James and colleagues performed a detailed analysis of the morphology and genetics of P. humilis, comparing it widely with other passerines (James et al. 2003). All the data showed, pretty conclusively, that P. humilis is not a corvid, but in fact a parid. A tit. A unique, highly novel tit to be sure, but a tit nonetheless, hence the new vernacular name. Incidentally, the paintings in James et al. (2003) were produced by my good friend Julian Hume. His office is next door to mine.

6. Blakiston’s fish owl Bubo blakistoni

If you think evolutionary convergences are cool, then you’ll love reversals. Morphological features or aspects of behaviour that have been modified during the evolution of a lineage don’t have to ‘stay’ changed – as Louis Dollo thought they did (this is where so-called Dollo’s Law come from) – they can change back to the ancestral state if this is what works. Of the four fish owl species, Blakiston’s is the biggest and most formidable, with a wingspan approaching 2 m and a total length of c. 60 cm (could it beat a Eurasian eagle owl in a fight? Perhaps). Endemic to Siberia, eastern China, Japan, Sakhalin Island and other eastern Asian islands, it inhabits cool, remote forests and can cope with harsh winters. Some have suggested that during its history it may have suffered from competition with sea eagles (Hume 1991), which are similar in size and ecological requirements. Sadly, this remarkable bird is highly endangered.

As is well known, owls in general have soft plumage and unusual fringes of tiny barbs along the leading margins of their flight feathers. These features - both specializations that permit silent flight in a group of birds that rely on sensitive hearing - are derived relative to the condition that owls inherited from their ancestors. But fish owls don’t need to be silent given that they’ve specialized to prey on animals that live under water, and they’ve consequently reversed back to the primitive condition. Fish owls also have longer legs than those of other owls, and their feet sport rough spiny scales that resemble those of fish-eating raptors like ospreys. B. blakistoni is unique among fish owls in having feathered legs. Interestingly, fish owls walk down to the water’s edge and will even wade into the shallows. They then sit motionless, waiting for prey to come within range. They don’t just eat aquatic prey, but also terrestrial birds and mammals. Fish owls are also remarkable among owls in reportedly feeding on carrion.

How does B. blakistoni fit into owl phylogeny? Until recently, the fish owls were considered to represent a distinct genus, Ketupa, and Ketupa was considered closely related to, but distinct from, the eagle owls Bubo. Recent genetic studies have found instead that the Ketupa species are nested within Bubo (as is Nyctea, the Snowy owl), and consequently both Ketupa and Nyctea have been sunk into synonomy with Bubo (Wink & Heidrich 1999). These results are supported by osteological characters, but unfortunately this data has yet to be published (it’s included in Ford’s 1967 phd thesis, and I’ve heard that a version of this is due to be published soon). I don’t have a copy of König et al. to hand, so I don’t know exactly how the fish owl species fit into Bubo. The feathered legs and other characters of B. blakistoni, however, suggest that, among fish owls, this species is the most basal. Overall, it seems like the one fish owl that is most like ‘normal’ eagle owls.

7. Shoebill Balaeniceps rex

Also called the Shoe-billed stork, She-billed stork [not a typo], Whale-bill or Whale-headed stork, B. rex is a long-legged big-billed waterbird of central Africa, and a specialist denizen of papyrus swamps. Though known to the ancient Egyptians, it wasn’t described by science until John Gould named it in 1851. Before that time it was a cryptid, as an 1840 sighting of this as-of-then-unidentified bird had been published by Ferdinand Werne in 1849 (Shuker 1991).

Standing 1.4 m tall, the Shoebill can exceed 2.6 m in wingspan and is best known for its remarkable wide bill. This can be up to 25 cm long, is larger in males than females and, like that of pelicans, cormorants and gannets, lacks external nostril openings. The birds use the bill to grab at large aquatic prey like lungfishes, catfish, tilapia, snakes, turtles and frogs. They’re reputed to eat antelope calves, but this is highly unlikely to say the least (Renson 1998), and apparently carrion. Little known is that the Shoebill is one of a handful of birds that occasionally practices quadrupedality: when Shoebills lunge forward while grabbing prey, they sometimes use their wings to help push themselves upright.

The affinities of the Shoebill have been controversial. Gould regarded it as a pelican and data from egg-shell microstructure and ear morphology was used by later authors to support this view. Unlike pelicans however, the long toes of the Shoebill are unwebbed and it is stork-like in some aspects of behaviour, practicing bill clattering and also dribbling water onto its eggs and young during the heat of the day. Based on stapedial morphology, Feduccia (1977) argued that the Shoebill really is a stork. It is also heron like in its possession of powder-down and some other features, and some workers have argued that it is really an aberrant heron. As recently shown by Gerald Mayr (2003) however, the morphological evidence best supports a position for the Shoebill close to Steganopodes, the clade that includes frigate birds, pelicans, gannets, cormorants and anhingas (traditional Pelecaniformes is not monophyletic as tropicbirds are apparently closer to procellariiforms than they are to members of Steganopodes).

More to come. For the latest news on Tetrapod Zoology do go here.

The shoebill image, taken by Doug Janson, is from here.

Refs - -

Borecky, S. R. 1978. Evidence for the removal of Pseupodoces humilis from the Corvidae. Bulletin of the British Ornithologists’s Club 98, 36-37.

Feduccia, A. 1977. The whalebill is a stork. Nature 266, 719-720.

Goodwin, D. 1986. Crows of the World. Trustees of the British Museum (Natural History) (London).

Hume, R. 1991. Owls of the World. Parkgate Books (London).

James, H. F., Ericson, P. G. P., Slikas, B., Lei, F.-M., Gill, F. B. & Olson, S. L. 2003. Pseudopodoces humilis, a misclassified terrestrial tit (Paridae) of the Tibetan Plateau: evolutionary consequences of shifting adaptive zones. Ibis 145, 185-202.

Wink, M. & Heidrich, P. 1999. Molecular evolution and systematics of the owls (Strigiformes). In König, C., Weick, F. & Becking, J.-H. Owls: a Guide to the Owls of the World. Pica Press (London), pp. 39-57.

Madge, S. & Burn, H. 1999. Crows & Jays. Christopher Helm (London).

Mayr, G. 2003. The phylogenetic affinities of the Shoebill (Balaeniceps rex). Journal of Ornithology 144, 157-175.

Renson, G. 1998. The bill. BBC Wildlife 16 (10), 10-18.

Shuker, K. P. N. 1991. Extraordinary Animals Worldwide. Robert Hale (London).


Blogger Mike Taylor said...

Huh? Thylacines are nothing like ichthyosaurs.

11:40 PM  
Anonymous Anonymous said...

Would you really call it "Dollo's so-called Law"? I mean, there are morphological adaptations that don't seem to be reversible. Whales and Seals aren't going to develop fingers, and ostriches can't regrow the ancestral theropod's hands.

An owl that's turned itself into an osprey is pretty damn cool, anyway. I wonder if it's retained the acute hearing? You wouldn't think a fishing bird would need that. From the image, it looks like it has reduced eye size compared to other owls -- is it diurnal?

Doug M.

5:31 AM  
Blogger Matt Mullenix said...

Any zoologist who ponders whether a fish owl could beat an eagle owl in a fight has my vote! Great site!

2:08 PM  
Blogger Darren Naish said...

Thanks to everyone for comments. It was inevitable that some joker would say 'Huh? Thylacines are nothing like ichthyosaurs' at some point, so the text has been altered accordingly :)

Response to Doug M: it's true that some evolutionary modifications might be irreversible, but to be honest I'm hard pressed to think of any. Whales, seals and ostriches may in fact be able to re-develop free fingers, and in fact we know that they still have the genetics that would theoretically allow this. There's a lot more that could be said about this subject, so I'll stop there.

On Blakiston's fish owl: good question about the hearing. So far as I know fish owls have hearing (and visual abilities) as acute as that of other eagle owls. But I've never spoken to anyone with first-hand knowledge of this species. All fish owls, I think, are primarily nocturnal.

Finally, thanks Matt for your comment. You'll see from the eagle owl blog that a lot of people seem to have an unhealthy interest in the intraspecific combat skills of birds of prey. We'll have to run some sort of computer-generated 'raptor death match' one day.

8:32 PM  
Blogger Matt Mullenix said...

That death-match idea sounds like quality entertainment. :-)

Falconry experience takes some of the fun out of this particular question, though, as most of the raptors seem aligned in such a way that one simply eats the other with little contest. You almost have to compare across continents to find different birds within similar niches to get a good show----maybe Harpy vs. Crowned Eagle, or Pygmy owl vs. Pygmy falcon!

Food for thought. :-)

However, we do have a neat and surprisingly rare contest to be seen here: Mississippi kite vs. Swallowtailed kite. A STK researcher I know recently watched a fantastic dogfight between these two ordinarily compatible species over some small contested tidbit. Both those birds can really fly....

7:17 PM  

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