Bijdragen tot de Dierkunde, 60 (3/4) 163-170 (1990) SPB Academie Publishing bv, The Hague Species boundaries in non-tropical Northern Hemisphere Owls K.H. Voous Institute of Taxonomie Zoology, University of Amsterdam, P.O. Box 4766, 1009 AT Amsterdam, The Netherlands Keywords: Northern Hemisphere Owls, species boundary, species concept will be made based North- Abstract attempt on non-tropical ern Hemisphere owls on which a comprehensive in non- book has been 1988). A survey is presented of the status of species boundaries published recently (Voous, Northern Hemisphere owls in order to investigate the restricted to discussion of tropical The survey will be a reality of the biological and geographicalspecies concept applied stages in the evolution of owl-species without mak- to these owls in current handbooks. At the same time the prac- ing special reference to expressions of doubt which ticability ofevolutionary systematics as opposed to phylogenetic in recent years have been raised against the objec- synthesis is elaborated on. of the tivity of the concept geographically polytypic species. Résumé 2. On passe en revue la situation des limites entre espèces chez les Monotypic genera Hiboux non-tropicaux du hémisphère Nord, afin d’examiner la réalité du et de concept biologique géographique l’espèce ap- Nyctea scandiaca - Snowy Owl - circumpolar arctic circulation pliqué à ces oiseaux dans les traités en courante. tundra D’autre on insiste sur la de la part, praticabilité systématique Surnia ulula - Northern Hawk Owl - circum- à la évolutive, en tant qu’approcheopposée synthèse phylogéné- global boreal forest tique. Micrathene whitneyi - Elf Owl - Sonoran Saguaro desert “Speotyto” cunicularia — Burrowing Owl - American grass- lands and semi-deserts 1. Introduction The taxonomie limits of species allocated to mono- the and Accepting that according to biological ge- typic genera offer no problems. In addition to the ographical species concept reproductive behaviour differential nature of their morphological charac- and geographical variationare the keystones of spe- ters, theirspecificity is supported by theirlife styles cies formation processes in terrestrial animals which are directly related to their relatively uncom- worthwhile (Mayr, 1953: 19), it seems to investigate plicated geographical and ecological distribution. of boundaries in selected the status species taxo- The Snowy Owl is an arctic descendant of the Eagle nomie groups on which enough knowledge on be- Owls Bubo; the NorthernHawk Owl is a somewhat haviour and distribution is available. In it aberrant of either Glaucidium Ninox fact, ecotype or or the of the in of means survey applicability nature a of both, and the Elf Owl is a minor deviation of still Years I have tried do important theory. ago to Pygmy Owl Glaucidium. this in relation to Northern Hemisphere ducks, The Burrowing Owl is a case by itself. Tradition- geese and swans (Voous, 1964); at present another ally placed in the monotypic genusSpeotyto with an 164 K.H. Voous - Species boundaries in non-tropical Northern Hemisphere Owls exclusively American distribution, there has been a body length 46 cm) of more than 1 Vi recent tendency of incorporating this species in the times its size. This situation is realized in the island World Athene 1988: of where small form Old genus (see Voous, 199). Hispaniola, a indigenous (T. DNA-analysis seems to indicate, however, that a. glaucops ) seems to be forced to pair up with, or relatives Burrowing Owls have no known close succomb under an alien giant recently arrived on its bio- USA (C.G. Sibley, pers. comm.). Thus, providing own from the Bahama Islands or the (T. a. chemical similarity is the ultimateindicator of rela- pratíncola) with a wing length almost 1 Vi times that tionship, the Burrowing Owl should be considered of the indigenous Barn Owl. In this case one could to represent a monotypic genus. If placed in the ge- wonder indeed whether these Barn Owls will ultimate terrestrial nus Athene, in which it is the manage to act as independently reproducing popu- of the and that This view representative, the application biological lations, is, as two separate species. geographical species concept remains equally clear has been advocated by Olson (1978). It is more like- and unchallenged. ly, however, that in the long run one of the Barn Owl types will oust the other (not necessarily the smallerone) and that only one survives, best adapt- 3. Monotypic species ed the local conditions of habitat and food to sup- ply, eliminating the local species problem in the Ketupa flavipes - Tawny Fish Owl - Sino-Himalayan sub- Another similar situation occurs on Lord montane mountain streams process. - Strix butleri - Hume's Owl Wadis in Middle East stone- Howe Island, halfway between Australia and New deserts Zealand, where large Barn Owls from California and smaller from Australia (T. a. pratincola) ones As in the monotypic genera the eco-geographical of (T. a. delicatula, body length about 72% the distributionsof these morphologically well-defined North American owls) have been introduced for ro- species are of a restricted nature and the species dent control, allegedly without interbreeding (see limits are unchallenged. Digging deeper into the Voous, 1988: 12). This, then, would be a case of a history of these species, the Tawny Fish Owl could first attempt to species duplication in an insular oc- be an ecoform of the early Asian fish owls Ketupa, currence of the Barn Owl. and more specifically of the Malay Fish OwlKetupa Indeed, it is rumbling within the Barn Owl com- is ketupu, whereas Hume's Owl most probably a plex of forms. The North American Barn Owl is at desert derivative of early palaearctic Tawny Owls least 20% larger in size than the corresponding Eu- Strix aluco. ropean form (T. a. alba). A reason for it has been recently explained. Mammal prey supply in North 4. Holarctic distributions America includes larger species than in Europe. In Europe no resident owl species in between the size (a) Holarctic species with wide global distributions of the Barn Owl and the Long-eared Owl Asio otus Tyto alba - Barn Owl - near-cosmopolitan exists, whereas in North America the parapatric Asio flammeus - Short-eared Owl - semi-cosmopolitan Western and Eastern Screech Owls Otus kennicottii The Barn Owl is the bird with the vir- among species and O. asio of intermediatesize are preying on widest Some 35-40 the same of the Barn global ranges. geographical tually types prey as Owl, press- from the Barn Owl take the races are currently recognized. Apart a gliding ing to on average larger prey variation in darkness of the plumage and spotting and growing to larger size in the process. Thus, the of the underparts, body size is the most obvious ge- body weights, and therefore the prédation forces, ographically varying character. One may wonder of the Barn Owl and the Long-eared Owl in Europe whether bird of the each other than a tiny race inhabiting Curaçao relate to as slightly more 1:1, as in the South Caribbean (T. a. bargei, body length against almost 2:1 in North America. Would this 29 would cm) have a chance to survive when con- situation permit or obstruct a mutual reproductive with Owls fronted a Barn Owl from the USA (T. a. behaviourof Old World and New WorldBarn pratincola, - 1990 165 Bijdragen tot de Dierkunde, 60 (3/4) underneath rather than in case these populations would ever meet? As it is barred longitudinally is As there is biogeographical evi- unlikely that this will happen, the problem more striped (Eck, 1968). academic than real. dencethat boreal forests have been continuous over of Another interesting point is the fact that differ- the Bering Sea area during one or more periods of feather lice extension in the Pleistocene, connecting the ent groups parasitic Strigiphilus glacial and northern of Asia and the (Mallophaga) occur on American, Australian parts America, conspeci- the hand and of boreal forest owls is understanda- south Asian Barn Owls on one on ficity present differences African, Middle East and European Barn Owls on ble (Voous, 1958). No behavioural are the other hand (Clay, 1966). This would indicate known to doubt this conclusion (see also Voous, that the geographical separation of these popula- 1988a on Asio otus). could tions is of old date. However, one hardly Holarctic of doubtful visualize where and when Old and New WorldBarn (c) species or species groups taxonomic status Owls have been in contact with each other. Is this, - - Owls and then, finally, a reason to split the Barn Owl into Otus scops/flammeolus Scops warm-temperate mountain forests the more than one species? I think not. But con- Glaucidium passerinum/ - Pygmy Owls - boreal and moun- cannot be either. specificity of the groups proved gnoma tain forests should realize that in than Instead, one more one Strix uralensis/ varia - Ural and Barred Owls - boreal place the Barn Owl seems to be on the verge of and temperate forests bursting out of its species limits. Old World In the Short-eared Owl no geographical differ- Though being a member of the mainly have been between of owl" rather than of the New World ences apparent population type "scops owls" der 1975; groups inhabiting the wide expanse of cold and "screech (Van Weijden, Hekstra, the the FlammulatedOwl has temperate Eurasia and North America. Even 1982), so many morpho- Short-eared Owls nesting in similar climates in logical, structural, behavioural and vocal charac- North Ameri- South American mountains and plains, as well as teristics of its own that its status as a endemic those in the tropical Galapagos islands, differ only can species is at present widely accepted from those 1966: 240; Voous, 1988: very slightly in their plumage characters (Marshall, 53-58).