By popular request, in this and in a few later articles I’ll be reposting the rest of the Ten Bird Meme text originally posted at Tet Zoo ver 1 in 2006 (where appropriate, I’ve added corrections and updates). The ‘Ten Bird’ birds I’ve covered so far are Ifrita, Shoebill, Tibetan ground-pecker, and Flying steamer duck. And here we continue with… Blakiston’s fish owl Bubo blakistoni [images from here].
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’ comes from) – they can change back to the ancestral state if this is what works (of course, they’re not really ‘changing back'; rather, they’re becoming modified further, such that they only resemble the ancestral state). Of the four Asian 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 (Fogden 1984). 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. Frogs are important in the diet of B. blakistoni but crayfish – said by some authors to be a major food item – are apparently not (Slaght & Surmach 2008). 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. 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, Olsen et al. 2002). These results are supported by osteological characters, but unfortunately this data has yet to be published (it’s included in N. Ford’s 1967 phd thesis, and I’ve heard that a version of this is due to be published soon [UPDATE: still no news on this in 2008/9]). The feathered legs and other characters of B. blakistoni suggest that this is the most basal of the fish owls… but I could be wrong.
PS: an important new paper on B. blakistoni appeared last year: Slaght & Surmach (2008). It’s available free here. See also the Blakiston’s Fish Owl Project [screen-capture shown here]: download a Blakiston’s fish owl ringtone and buy fish owl merchandise – seriously!
Refs – –
Fogden, M. 1984. Fishing owls, eagle owls and the snowy owl. In Burton, J. A. (ed) Owls of the World. Eurobook (Oxford), pp. 53-85.
Hume, R. 1991. Owls of the World. Parkgate Books (London).
Olsen, J., Wink, M., Sauer-Gürth, H. & Trost, S. 2002. A new Ninox owl from Sumba, Indonesia. Emu 102, 223-231.
Slaght, J. C. & Surmach, S. G. 2008. Biology and conservation of Blakiston’s fish owls in Russia: a review of the primary literature and assessment of the secondary literature. Journal of Raptor Research 42, 29-37.
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.