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Monday 22nd December, 2014

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How Many Owls Are There?

  • Female Snowy owl Nyceta (Bubo) scandiaca by Terry Evison
  • Copyright © Terry Evison

This is the most frequently asked question the Trust receives – and the answer is “how long is a piece of string”? It all depends on who you ask and which authority you prefer! The fact is, with the advent of DNA analysis techniques, the list of owl species and subspecies changes with amazing speed these days. Some species come and some species go – and to be honest, some of these changes result in many a ‘lively’ argument within the owl world.

Many people have their own views on exactly what constitutes a species, a subspecies (i.e. a population of a species in which certain sub-populations can be distinguished physically by differences such as in plumage and size, and now, increasingly – especially with owls – by voice differences), a cline (an unofficial term also used to describe a constant geographical gradation in character, e.g. changes in plumage colour), or morph (where somewhat indiscriminately different forms, e.g. grey, brown and red tawny owls or North American screech owls, occur within populations of a full species). Are you still with me?

When I first began working with owls (was it really 42 years ago?), the acknowledged reference was Peter’s ‘Check-list of Birds of the World’ (1940) which listed 141 species of owl. In 1973 John Burton, in his splendid ‘Owls of the World’ reduced this figure to just 133. Five years later, in 1978, Clark, Smith & Kelso produced their opus ‘Working bibliography of Owls of the World’ and told us there were between 109 – 143 species owl – which gives you some idea of how difficult it was to answer the question only thirty years ago! Next came Sibley & Monroe’s ‘Distribution & Taxonomy of Birds of the World’ in 1990 which added a somewhat staggering 35 new species to Peter’s list, giving us a grand total of 176. Much better!

However, in 1991 along came Howard & Moore with their magnificent ‘A Complete Checklist of the Birds of the World’ - the first book to list the entire world’s subspecies along with the full species. Not surprisingly this was my ‘bible’ for many years (it has recently been revised and re-published, so things might have changed yet again!), so if you had asked me the question between 1991 – 1999, my answer would have been 175 – one less than Sibley & Monroe’s figure!

In 1992 John Burton revised his list for the second edition of his book, adding ten new species to give us a total as 143, but at 32 less than Howard & Moore, this suggests that some time had elapsed between completion of the second manuscript and actual publication, a not unusual circumstance with such books. As I have said, things were beginning to move fast in owl taxonomy by then.

In 1997 Hume & Boyer produced yet another ‘Owls of the World’, demonstrating the increasing popularity of these birds (thanks to the WOT?!) which listed a conservative 151 species, again far less than shown in Howard & Moore, but this proved to be the lull before the storm, for by the end of the 20th Century the fantastic DNA work of Prof. Michael Wink at Heidelberg University in Germany had begun to revolutionize our thinking regarding owl taxonomy.

In 1992 the Spanish publishers Lynx Editions had started to produce the first volumes of their incredible ‘Handbook of the Birds of the World’ which in my (and most other ornithologists) opinion, probably represent the finest books on birds ever published. They are fantastic. In 1999 Volume 5 appeared, and this was the volume which included all the world’s owls – 195 of them!

Almost simultaneously a new ‘Warburton bible’ was published – ‘Owls – A Guide to the Owls of the World’ by Claus Konig, Friedhelm Weick and Jan-Hendrik Becking (Pica Press. ISBN 90 – 74345 – 19 – 0). This book – the one I had been waiting for most of my life! – included a chapter by our friend Michael Wink and his colleague Petra Heidrich in which they went into great detail to explain the incredible discoveries they had made in the process of their DNA studies.

One of their findings which shook the owl world and confi rmed our suspicions (first raised by London Zoo’s Amanda Ferguson, the Owl Taxon Advisory Group’s Studbook Keeper for the species) was that the beautiful and popular white-faced scops owl was hiding a dark secret! Not only wasn’t it a ‘scops’ (i.e. an ‘otus’) owl, it was in fact not one full species, but two - the Southern white-faced owl Ptilopsis granti, and the Northern white-faced owl Ptilopsis leucotis! Hence, here we had yet another addition to our owl species total! Mind you, naming it correctly and getting owl keepers to start using the new name is another story. Evidently old habits die hard!

If that was to prove difficult, I suspect it will be nothing compared with another of Michael and Petra’s findings which confirms something that many of us have believed for many years – the snowy owl is nothing more than a superbly adapted ‘Arctic eagle owl’ minus ear tufts. Yes folks, it’s a Bubo not a Nyctea! Amidst all this mayhem came yet another new figure – the one I then accepted – i.e. a grand total of 212 full species of owl!


This was not the end of the story. In the last decade no less than five new owl species have been discovered or re-identified which are not mentioned as full species in my new ‘bible’.

These are the Serendib scops owl Otus thilhoffmanni discovered in Sri Lanka in February 2001; the Pernambuco pygmy owl Glaucidium mooreanum collected in northern Brazil in 1990, but only identified as a new species in 2000; the Little Sumba hawk owl Ninox sumbaensis found on Sumba Island, southern Indonesia, in December 2001; the Togian Island hawk owl Ninox burhani found on Togian Island, Sulawesi in 1999; and lastly, the Socotra scops owl Otus socotranus formerly thought to be a subspecies of the striated (pallid) scops owl Otus brucei, but since recognized as a species in its own right following two recent expeditions to the Yemen.

* For more details about these five new species see Newsletter 30 or contact us here or the office and we will send you the article. So, the answer to the thorny question, so far as it can be answered, is – 217 at the time of writing – BUT WATCH THIS SPACE!

Tony Warburton

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