The Chromosomal Phylogeny of Owls (Strigiformes) and New Karyotypes of Seven Species W

_??_1993 The Japan Mendel Society Cytologia 58: 403-416 , 1993

The Chromosomal Phylogeny of Owls (Strigiformes) and New Karyotypes of Seven Species W. E.R. Rebholz1*, L.E. M. De Boer2, M . Sasaki3, R.H. R. Belterman1, and C. Nishida-Umehara4 1Stichting Koninklijke Rotterdamse Diergaarde , P. O.Box 532, 3000AM Rotterdam, TheNetherlands 2National Foundati onfor Research inZoological Gardens, P. O. Box 20164, Amsterdam,TheNetherlands 3Sasaki Institute , 2-2,Kanda-Surugadai, Chiyoda-ku, Tokyo 101, Japan 4 ChromosomeResearch Unit, Hokkaido University, Sapporo 060, Japan

Accepted July 15, 1993

The order of Strigiformes (owls) consists of 134 species in 25 genera (Burton 1973). After decades of study taxonomic and phylogenetic relationships of this order are still a matter of discussion (Sibley and Ahlquist 1972: review). Phylogenetics of owls have been studied using egg-white protein data (Sibley and Ahlquist 1972), morphological data (Cracraft 1981), karyotypical data (Belterman and De Boer 1984, Schmutz and Moker 1991), DNA-DNA hybridization data (Sibley et al. 1988) and allozyme data (Randi et al. 1991). Unfortunately, these studies do not result in a uniform phylogeny, because they contradict each other in several aspects. Cracraft (1981) is the only one who put all owls (Tyto and Phodilius inclusive) in the family Strigidae, which he believes to be part of the order Falconiformes. All other recent publications believe the Strigiformes and Falconiformes to be separate orders. Two publica tions put all owls in the suborder Strigi (comprising two families: Tytonidae and Strigidae) and combine this suborder with the suborders Aegotheli and Caprimulgi in the order Strigiformes (Sibley et al. 1988, Randi et al. 1991), which is closely related to the Musophagidae and distantly related to the Falconidae. Some authors put all owls in one family (Sibley and Ahlquist 1972), others make a distinction between Tytonidae and Strigidae (Belterman and De Boer 1984, Sibley et al. 1988, Randi et al. 1991). From this information it is clear that it is still too early to arrive at a uniform phylogeny. The karyotypes of 26 species from 15 genera have been studied and recorded in the literature, but few subspecies and individuals per species are studied. Consequently, much about intraspecific variation or differences between subspecies is unknown. Different karyo types have been found within some single species of which enough individuals were studied, of which Asio otus, Pulsatrix perspicillata and Tyto alba are some examples. Some published karyotypes or karyotype dscriptions are of questionable quality and those species need to be reexamined. Most karyotypes have been published separately without comparing them with other owl karyotypes. Belterman and De Boer (1984) and Schmutz and Moker (1991) published reviews on the karyological phylogeny of owls. We try to establish a phylogenetic tree based on karyotypes studied to date and this should make it easier for other researchers to see where their results fit in. It could be helpful if future publications on karyology would refer to the phylogenetic tree published in this paper, to increase understanding about phylogeny of this order. It is convenient to use Bubo virginianus as reference for the ancestral Strigidae type because G-banded and C-banded karyotypes have been published (Biederman et al. 1980).

* Current address: Department of Chemical Pathology University of Cape Town, Cape Town, South Africa. 404 W. E. R. Rebholz et al. Cytologia 58

Materials and methods Blood samples used in this study were from Asio otus (2 males), Athene noctua (1 female), Bubo lacteus (1 male), Ketupa blakistoni (1 female), Ketupa ketupa (1 female), Otus scops (1 female), Pulsatrix perspicillata (1 male, 2 females), Speotyto cunicularia (2 males), Strix hylophila (1 male), Strix leptogrammica (1 male, 1 female), Strix nebulosa (2 males, 1 female), and Tyto alba (1 male, 2 females). Lymphocyte cultures were carried out as described by Belterman and De Boer (1984). C-banding was done as described by Sumner (1972). Chromosomes were stained with Orcein or Giemsa.

Observations

In karyotypes presented here a uniform system of chromosome numbering is used unless shown otherwise. This means that homologous chromosomes in different species have identical numbers, but homologies are based on Orcein stained macrochromosomes only. Pairs numbe red 5/7 indicate supposed fusion products of ancestral chromosomes 5 and 7. Microchromo somes are acrocentric or telocentric and the difference is often cryptic. The original chromo some numbering can be found in Belterman and De Boer (1984). The supposed ancestral Strigidae karyotype is deduced from comparison with other avian orders (Belterman and De Boer 1984) and the fact that four different genera all have an identical type seems to justify this. Karyotypes of the ancestral Strigidae type species consist of an acrocentric pair 1, acrocentric pairs 2 and 3 of comparable size, a submetacentric pair 4 half the size of pair 1, an acrocentric pair 5, one or two metacentric Z-chromosomes about the size of pair 4 and about 60 to 70 telocentric microchromosomes. W-chromosomes vary in size and form, but are smaller than Z-chromosomes. This supposed ancestral type is represented in the phylogenetic tree by 11 species studied so far: Asio flammeus (Sasaki et al. 1981, Biederman in Shields 1982, Bian et al. 1988, Bian and Li 1989: 2n=82), Bubo lacteus (this report Fig. 1: 2n= 80-84), Bubo poensis (Belterman unpublished data), Bubo virginianus (Krishan et al. 1965, Biederman et al. 1980: 2n=82), Ketupa blakistoni (Sasaki et al. 1981, this report Fig. 2: 2n= 82), Ketupa ketupa (Sasaki et al. 1981, this report Fig. 4: 2n=82), Ketupa zeylonensis (Belterman and De Boer 1984, Roy 1990: 2n=78-80), Nyctea scandiaca (Sasaki et al. 1981,

Fig. 1. Karyotype of a male Bubo lacteus (2n=80-84) with Z-chromosomes which are chosen tentatively, because only males were studied. 1993 The Chromosomal Phylogeny of Owls 405

Fig. 2. Karyotype of a female Ketupa blakistoni (2n=82) .

Fig. 3. A C-banded karyotype of a female Ketupa blakistoni (2n=82), with additional C-band material in pair 2.

Fig. 4. Karyotype of a female Ketupa ketupa (2n=82).

Belterman and De Boer 1984: 2n=82), Otus leucotis (Belterman and De Boer 1984: 2n=70 or higher), Otus bakkamoena (Sasaki et al. 1981: 2n=82, Bhunya and Mohanty 1987, Roy et al. 1987, Bian et al. 1988, Bian and Li 1989, Roy 1990: 2n=78), and Otus scops (This report Fig. 5: 2n=74-84). In the karyotype of O. scops the W-chromosome could not be identified 406 W. E. R. Rebholz et al. Cytologia 58

Fi.g 5. Karyotype of a female Otus scops (2n=74-84) in which the W-chromosome could not be identified amongst other microchromosomes.

amongst other microchromosomes. Schmutz and Moker (1991) argue that Asio otus also belongs to this group, but since there are three different types of this species, we did not include it in this group yet. K. blakistoni (Sasaki et al. 1981, this report Fig. 2: 2n=82) shows a somewhat different karyotype from others in that pair 2 is similar in length to pair 1, which is due to an extra large block of C-band material in pair 2 (Fig. 3). The five species of the genus Strix studied so far, S. aluco (Renzoni and Vegni-Talluri 1966, Hammar 1970: 2n=80), S. hylophila (Fig. 6: 2n=80), S. leptogrammica (Sasaki et al. 1981, this report Fig. 8: 2n=82?), S. nebulosa (Biederman in Shields 1982, this report Fig. 10: 2n= 80) and S. uralensis (Takagi and Sasaki 1974, Sasaki et al. 1981: 2n=82), are all very similar, having a characteristic fusion pair 5/7. Ciccaba woodfordii (Belterman and De Boer 1984: 2n= 82) also belongs to this group. Z-chromosomes and W-chromosomes vary in this group: the ancestral metacentric Z is found in S. aluco, S. leptogrammica and S. uralensis, a submetacentric Z, the same size as the ancestral one in S. nebulosa, a large metacentric Z in size between pairs 1 and 2 in S. hylophila and C. woodfordii. Z-chromosomes in the karyotype of S. hylophila (Fig.

Fig. 6. Karyotype of a male Strix hylophila (2n=80) having fusion pair 5/7 as a characteristic element. The unusually large Z-chromosomes are chosen after comparison with other Strix-species. 1993 Th e Chromosomal Phylogeny of Owls 407

Fig. 7. A C-banded karyotype of a male Strix hylophila showing that all centromeres a re extremely C-band positive.

Fig. 8. Karyotype of a female Strix leptogrammica (2n=82?) having fusion pair 5/7 as a characteristic element.

6), which are unusually large for owls, are chosen after comparison with other Strix species. W-chromosomes vary from metacentric (S. leptogrammica, S. uralensis japonica) and sub metacentric (S. nebulosa, S. uralensis hondoensis) to telocentric (S. aluco). The size of W-chromosomes is also variable between these species, with S. aluco having the smallest W-chromosome and S. uralensis japonica having the largest W-chromosome. The W chromosomes of S. leptogrammica, S. nebulosa, which are of the same size, are a little bit smaller than those of S. uralensis hondoensis. It should be noticed that the two subspecies of S. uralensis have different W-chromosomes. Now that several females per (sub)species have been studied, it seems evident that W-chromosomes do not vary in size within a subspecies. A C-banded karyotype of a male S. hylophila (Fig. 7) shows that all centromeres are extremely C-band positive. The additional C-band material found in the long arms of the Z-chromosomes could possibly be responsible for their exceptional size. A C-banded karyotype of a females. leptogrammica (Fig. 9) shows that all macrochromosomes and nearly all microchromosomes are C-band positive. Another group consists of Bubo bubo (De Boer 1976, Omura 1976, Sasaki et al. 1981, Belterman and De Boer 1984, Herzog 1985, Rebholz 1992: 2n=80 and B. b. nikolskii, Belterman unpublished data) and B. africanus (Belterman and De Boer 1984: 2n=76), characterized by pair 1/5, although both species have different Z-chromosomes and two forms of Z-chromosomes have been reported for B. bubo (Rebholz 1992). The karyotype of Glaucidium radiatum (Misra 1974, Misra and Srivastava 1974, Roy et al. 408 W. E. R. Rebholz et al. Cytologia 58

Fig. 9. A C-banded karyotype of a female S. leptogrammica (2n=82?) showing all macrochromosomes and nearly all microchromosomes to be C-band positive.

Fig. 10. Karyotype of a female Strix nebulosa (2n=80) having fusion pair 5/7 as a characteristic element.

1987, Roy 1990: 2n=82) is characterized by pair 8/9. Misra and Srivastava (1974) found that the W-chromosome of G. radiatum is slightly larger than the Z-chromosome, which is uncommon in birds. The group of the genus Ninox consists of N. novaeseelandiae (Belterman and De Boer 1984, Christidis 1985, 1990: 2n=80) and N. scutulata (Roy et al. 1987, Roy 1990: 2n=82) with pairs 2 inv and 8/9. In N. novaeseelandiae however, Z-chromosomes are smaller than ancestral Z-chromosomes, in size between pair 5 and 6. For Asio otus (Sasaki et al. 1981, Biederman in Shields 1982, Sasaki et al. 1983, this report Fig. 11: 2n=82, Schmutz and Moker 1991: 2n=76) three slightly different karyotypes have been reported. Schmutz and Moker (1991) found one specimen which was identical to the ancestral Strigidae, whereas Sasaki et al. (1983) reported polymorphism in pair 6, and here we present a specimen with inversions in both chromosomes of pair 6 (Fig. 11). The karyotype presented by Sasaki et al. (1983) seems to be the intermediate between the one of Schmutz and Moker (1991) and the one presented here. Otus kennicotti (Schmutz and Moker 1991, 2n=70) seems to be a single member of another group, since it is characterized by a large submetacentric chromosome, a large metacentric chromosome, and a small metacentric chromosome not seen in any other karyo 1993 The Chromosomal Phylogeny of Owls 409

Fig. 11. Karyotype of a male Asio otus (2n=82) , in which both chromosomes of pair 6 are inverted. type. Another uniform group comprises A. noctua (Renzoni and Vegni-Talluri 1966, Bian et al. 1988, Bian and Li 1989: 2n=82), A. brama (Ray-Chaudhuri et al. 1969, Misra 1974, Misra and Srivastava 1974, Roy et al. 1987, Roy 1990: 2n=80), and Surnia ulula (Schmutz and Moker 1991: 2n=66), having the characteristic pair 2/3, with an armratio of 1.1, and pair 8/9. The group comprising only Speotyto cunicularia (Rocha and De Lucca 1988, Schmutz and Moker 1991, this report Fig. 12: 2n=86) only differs from the ancestral Strigidae type in pairs 4 inv and 8/9 and a heteromorphic (acrocentric plus telocentric) pair 1. However, pair 1 seems to be submetacentric in a karyotype presented by Schmutz and Moker (1991). Pair 4 inv is of the same size as ancestral submetacentric pair 4 whereas pair 4 inv is metacentric, which could be due to a pericentric inversion. This karyotype is probably derived from Glaucidium radiatum. Pulsatrix perspicillata (Takagi and Sasaki 1974, Sasaki et al. 1984, this report Fig. 13: 2n= 76) forms a group on its own because it is completely different from other owl karyotypes, so our chromosome numbering is not comparable with that of other species. It consists of one subtelocentric pair (2), two submetacentric pairs (3 and 4) and four metacentric pairs (1, 6, 7 and sex-chromosomes). Pair 1, which is called 2/3 in Belterman and De Boer (1984) and Schmutz and Moker (1991), has an armratio of 1.3, which suggests that the two chromosomes are not identical. However, banding studies should confirm this difference. There are about 30 metacentric and 30 acrocentric microchromosomes and both sex chromosomes are metacentric: the Z-chromosome is fifth in length and the W-chromosome is somewhat larger than the

Fig. 12. Karyotype of a male Speotyto cunicularia (2n=82/86), with the characteristic pairs 4 inv. and 8/9. 410 W. E. R. Rebholz et al. Cytologia 58

Fig. 13. Karyotype of a female Pulsatrix perspicillata (2n=76). The numbering does not correspond with other species. smallest macrochromosome pair. The large number of metacentric microchromosomes found here is uncommon in owls but the other authors do not mention this finding. Takagi and Sasaki (1974) found all microchromosomes to be telocentric and Sasaki et al. (1984) show a few (less than 30) non-telocentric microchromosomes. Thus, three different karyotypes of P. perspicil lata are published, including the one presented here. Six subspecies of P. perspicillata are known (Burton 1973), so three different subspecies could have been studied, but this is difficult to prove because the origin of the animals used is unknown. Sampling animals of known subspecies could prove valuable. A C-banded karyotype of a female P. perspicillata (Fig. 14) shows that the entire W-chromosome is C-band positive while all other chromosomes have C-band positive centromeres. Similar results were obtained by Sasaki et al. (1984). Phodilius badius (Belterman and De Boer 1984: 2n=90), Tyto alba (Renzoni and Vegni-Talluri 1966, Ray-Chaudhuri 1973, Ray-Chaudhuri 1976, Belterman and De Boer 1984, Mayr and Auer 1988, this report Fig. 15: 2n=80-92) and Tyto capensis (Bian et al. 1991) are not included in the phylogenetic tree because their karyotypes are completely different from Strigidae karyotypes and thus clearly form a group on their own. The karyotypes mainly consist of telocentric microchromosomes and zero to three (T. alba) or three metacentric autosomal pairs (P. badius). To date, three different karyotypes of T. alba have been published by Renzoni and Vegni-Talluri (1966), Ray-Chaudhuri (1973, 1976) and Belterman and De Boer (1984). Renzoni and Vegni-Talluri's karyotype has 2n=approx. 92 and only one metacentric pair (38 in length), apart from the metacentric W-chromosome. Ray-Chaudhuri's

Fig. 14. A C-banded karyotype of a female Pulsatrix perspicillata showing that the entire W-chromosome is C-band positive while all other chromosomes have C-band positive centromeres. 1993 The Chromosomal Phylogeny of Owls 411

Fig. 15. Karyotype of a female Tyro alba (2n=90).

Fig. 16. A C-banded karyotype of a female Tyto alba, showing that the W-chromosome is a medium-sized telocentric chromosome

karyotype has 2n=approx. 80 and three metacentric pairs (4, 5 and 6 in length) and W-chromosomes are not shown as only males were studied. Belterman and De Boer's karyotype has 2n=approx. 90, only Z-chromosomes are metacentric and they are largest of all. Our data with karyotypes identical to that of Belterman and De Boer (1984) and Mayr and Auer (1988), suggest that the W-chromosome is a medium-sized telocentric chromosome, as shown in a C-banded cell (Fig. 16). These three different karyotypes could represent three different subspecies as 35 subspecies are known (Bunn et al. 1982). The subspecies examined by Ray-Chaudhuri (1973, 1976) is likely to be T. a. stertens, the only subspecies present in India. The mediterranean subspecies examined by Renzoni and Vegni-Talluri (1966) is probably T. a. alba, while Belterman and De Boer (1984), Mayr and Auer (1988) and we probably studied the north European subspecies T. a. guttata.

Discussion

The phylogenetic trees presented by Belterman and De Boer (1984) and Schmutz and Moker (1991) are basically correct, but a few additions and revisions should be incorporated 412 W. E. R. Rebholz et al. Cytologia 58

Fig. 17. The chromosomal phylogeny of all owls studied to date. Characteristic chromosomes are listed for each group. (m=metacentric, sm=submetacentric, Z=Z-chromosome, m/m= microchromosome, 1=large, s=small).

(Fig. 17). The ancestral Strigidae type is represented by 11 species from five genera: Asio flammeus, Bubo lacteus, B. poensis, B. virginianus, Ketupa blakistoni, K. ketupa, K. zeylonensis, Nyctea scandiaca, Otus bakkamoena, O. leucotis, and O. scops. Asio flammeus definitely needs to be included in the ancestral group, as mentioned by Schmutz and Moker (1991). The position of Asio otus still remains uncertain, since different karyotypes are reported. The phylogenetic trees presented by Belterman and De Boer (1984) and Schmutz and Moker (1991) suggest that P. perspicillata is identical to Athene, but our results show that two chromosome pairs (1 and 2/3 respectively) are not identical in the two genera. Therefore, Pulsatrix perspicillata needs to be separated from Athene noctua and A. brama, although P. perspicillata could have been evolved from Athene. Karyotypes of P. perspicillata presented by Takagi and Sasaki (1974) and Sasaki et al. (1984) may be identical to Athene, but they have to be examined better. Glaucidium radiatum could be ancestral to three groups: Speotyto, Athene and Ninox (Fig. 17). However, this definitely needs to be checked with banded chromosomes, since pair 8/9 is their only common feature. Speotyto cunicularia should not be included in the genus Athene, since their karyotypes are too different, which is also argued by Schmutz and Moker (1991). They also argue that this species has a submetacentric chromosome pair 1, which would be unique among the owl species studied to date. However, our data show that pair one is acrocentric, just like all other owls, so maybe there is a dimorphism in this chromosome pair for this species, which would be interesting to study. A minor detail in the phylogenetic tree presented here is that the units Strix/Ciccaba and Bubo bubo/B. africanus might need to be split into three and two separate ones respectively, because of variation in Z-chromosomes, but maybe this variation is too unimportant to justify separation. Schmutz and Moker (1991) also argue for a separation of Ciccaba and Strix, based on differences in chromosome pair 5 and 5/7, but our data show clearly that all five Strix species and Ciccaba have identical 5/7 chromosomes. However, our data also show that there is 1993 The Chromosomal Phylogeny of Owls 413 variation in Z-chromosomes, with the large Z-chromosomes of Ciccaba woodfordii and Strix hylophila derived from the ancestral type. The Z-chromosomes of Strix nebulosa might have evolved separately from the ancestral type. Finally, the species name Otus scops in the phylogenetic tree of Belterman and De Boer (1984) should be changed to O. sunia. The phylogenetic tree based on karyotypes is not in concordance with the phylogenetic tree based on allozymes (Randi et al. 1991). It has to be said that Randi et al. (1991) only studied seven owls (Asio flammeus, Asio otus, Athene noctua, Bubo bubo, Otus scops, Strix aluco, and Tyto alba) of which six belong to the Strigidae. They consider Tyto alba to be a sister lineage of the Strigidae. However, they consider Athene noctua to be ancestral to most Strigidae studied, Strix aluco is supposed to be ancestral to Asio, and Bubo bubo and Otus scops are supposed to be sister genera, which is not supported by chromosome data. The allozyme data presented by Randi et al. (1991) are not enough to establish a solid phylogenetic tree, although

Table 1. A list of owl species studied to date 414 W. E. R. Rebholz et al. Cytologia 58 some relationships can be resolved. An allozyme study on a larger number of owl species might be helpful to establish a better insight in the phylogenetics based on allozymes. Some genera need special attention in the future, e. g. Pulsatrix, Lophostrix, Ciccaba, Otus, Bubo and Tyto. Especially the species P. koeniswaldiana and P. melanota should be studied for their karyological relationship with P. perspicillata. Lophostrix should be studied because it is supposed to be closely related to Pulsatrix. Other species of Ciccaba would be very interesting to study, because C. woodfordii is the only representative of the genus in Africa, whereas all other species occur in Central America. The genus Otus contains 34 species and therefore would be worth a thorough study. Tyto alba and Bubo bubo both contain many subspecies which need investigating. As a general rule more individuals per species need to be studied to eliminate the possibility of scoring a variant karyotype as the normal karyotype of a species. At present, only 33 species from 15 genera have been studied (see Table 1), leaving 101 species and 10 genera to be investigated, and only few banded karyotypes have been published (Bubo virginianus in Biederman et al. 1980), so it still is difficult to compare karyotypes in detail. There really is a need for banded karyotypes, because variation caused by paracentric inversions is not detected in Giemsa stained chromosomes. Biederman (in: Shields 1982) claims B. virginianus and Nyctea scandiaca to have identical G-band patterns. He also claims this to be so for Asio otus and A. flammeus. This is not likely to be true, because even unbanded karyotypes are not completely identical. A complicating factor in avian phylogenetic studies is that only macrochromosomes can be used for comparisons because microchromosomes are too small to distinguish them individually. However, G-band patterns of avian macrochromosomes have been conservative during evolution (most chromosome changes involved Robertsonian translocations), so it is not impossible to construct a phylogenetic tree. It is striking in the phylogenetic tree that many groups evolved independently from the ancestral type. A rapid radiation at some stage could have been responsible for this, but only a minority of extant owl species has been investigated to date. Clearly, more species need to be studied to get a more complete picture of the phylogeny of the Strigiformes.

Summary The phylogeny of 33 owl species is studied karyologically. Karyotypes of seven owl species new to karyology (Bubo lacteus, Ketupa blakistoni, K. ketupa, Otus scops, Strix hylophila, S. leptogrammica and S. nebulosa) are described. Four other karyotypes (Asio otus, Pulsatrix perspicillata, Speotyto cunicularia, and Tyto alba) are presented to complete previous publica tions.

Acknowledgements We are indebted to Wuppertal Zoo, Krefeld Zoo, Roland van Bocxstaele, curator of birds at Antwerp Zoo, Joep Wensing at Burgers' Zoo Arnhem and Koos Stuster, curator of birds at Blijdorp Zoo Rotterdam for allowing us to bleed their owls. We are also grateful to Terry Dennett and Mandy Walton for printing the photographs.

References

Belterman, R. H. R. and De Boer, L. E. M. 1984. A karyological study of 55 species of birds, including karyotypes of 39 species new to cytology. Genetica 65: 39-82. Bhunya, S. P. and Mohanty, M. K. 1987. Distribution of constitutive heterochromatin in the collared scops owl. J. Heredity 78: 204-205. 1993 The Chromosomal Phylogeny of Owls 415

Bian, X. and Li, Q. 1989. Studies on the karyotypes of birds V. 20 species of climber birds (Ayes) . Zool. Res. 10: 310 -317. - , -and Zhang, H. 1988. Chromosome Atlas of Birds. DEC press, Dalian (China): pp. 1-238. - , -and -1991. Studies on the karyotypes of birds XII. 15 species of nonpasserine birds (Ayes). Zool. Res. 12: (in press). Biederman, B. M., Florence, D. and Lin, C. C. 1980. Cytogenetic analysis of great horned owls (Bubo virginianus). Cytogenet. Cell Genet. 28: 79-86 . Bunn, D. S., Warburton, A. B. and Wilson, R. D. S. 1982. The Barn Owl. T & AD Poyser Ltd, Calton, England . Burton, J. A., [ed]. 1973. Owls of the World . Peter Lowe/Eurobooks , London. Christidis, L. 1985. A rapid procedure for obtaining chromosome preparations from birds. The Auk 102: 892-893. - 1990. Animal Cytogenetics 4: Chordata 3B. Aves. Gebruder Berntraeger Berlin Stuttgart: pp. 1-116 . Chromosome Atlas: Fish, amphibians , reptiles and birds. Vol 1 1973. M. L. Becak, W. Becak, F. L. Roberts, R . N. Shoffner and E. P. Volpe (eds.). Springer , Berlin-Heidelberg-New York. Cracraft, J. 1981. Towards a phylogenetic classification of the recent birds of the world (class Aves). The Auk 98: 681-714. De Boer, L. E. M. 1976. The somatic chromosome complements of 16 species of Falconiformes (Aves) and the karyological relationships of the order . Genetica 46: 77-113. Hammar, B. 1970. The karyotypes of thirty-one birds. Hereditas 65: 29-58. Herzog, S. 1985. Sexing of birds without sex dimorphism with the aid of chromosome analysis described in the case of the long-eared owl Bubo bubo. Zeitschrift fur Jagdwissenschaft 31: 50-52 . Itoh, M., Ikeuchi, T., Shimba, H., Mori, M., Sasaki, M. and Makino , S. 1969. A comparative karyotype study in fourteen species of birds. Jap. J. Genet. 44: 163-170 . Krishan, A., Haiden, G. J. and Shoffner, R. N. 1965. Mitotic chromosomes and the W-sex chromosome of the great horned owl (Bubo v. virginianus). Chromosoma 17: 258-263 . Mayr, B. and Auer, H. 1988. A method to induce Giemsa staining resistance of avian W chromosomes: detection of an additional W chromosome in turkey. Genome 30: 395-398. Misra, M. 1974. Studies on the chromosomes of birds. PhD Thesis, University of Allahabad, Allahabad (India) .- and Srivastava, M. D. L. 1974. The W-chromosome in two species of Strigiformes. Chromosome Information Service 17: 28-29. Omura, Y. 1976. Sex determination by chromosomes in seven species of birds. Jap. J. Veterinary Sci. 38: 281-288 . Randi, E., Fusco, G., Lorenzini, R. and Spina, F. 1991. Allozyme divergence and phylogenetic relationships within the Strigiformes. Condor 93: 295-301. Ray-Chaudhuri, R. 1973. Cytotaxonomy and chromosome evolution in birds. In A. B. Chiarelli and A. Capanna [eds.], Cytotaxonomy and Vertebrate Evolution. Academic Press. London, New York. - 1976. Karyotype studies in some Indian birds. The Nucleus 19: 86-91.-, Sharma, T. and Ray-Chaudhuri, S. P. 1969. A comparative study of the chromosomes of birds. Chromosoma 26: 148-168. Robholz, W. E. R. 1992. Z-chromosome dimorphism in Eagle Owls. Zoo Biology 11: 291-295. Renzoni, A. and Vegni-Talluri, M. 1966. The karyotypes of some Falconiformes and Strigiformes. Chromosoma 20: 133-150. Rocha, G. T. and De Lucca, E. J. 1988. Nucleolar organizer regions in somatic chromosomes of some species of birds. Caryologia 41: 299-308. Roy, S., Ansari, H. A. and Kaul, D. 1987. Karyological relationships of five species of owls (Aves: Strigiformes: Strigidae). The Nucleus 30: 54-56. -1990. Chromosomal studies in birds. PhD Thesis, University of Allahabad, Allahabad (India). Sasaki, M., Nishida, C. and Tsuchiya, K. 1981. Comparative karyotype studies in ten species of owls (Abstract). (Abstract of 53rd Annual Meeting of the Genetics Society of Japan) Jap. Genet. 56: 633. -, - and -1983. Autosomal polymorphism in the long-eared owl Asio otus (Strigiformes: Aves). Chromosome Information Service 34: 17-18. - , Takagi, N. and Nishida, C. 1984. Current profiles of avian cytogenetics, with notes on chromosomal diagnosis of sex in birds. The Nucleus 27: 63-73. Schmutz, S. M. and Moker, J. S. 1991. A cytogenetic comparison of some North American owl species. Genome 34: 714-717. Shields, G. F. 1982. Comparative avian cytogenetics: a review. Condor 84: 45-58. Sibley, G. C. and Ahlquist, J. E. 1972. A comparative study of non-passerine birds. Peabody Mus. Nat. Hist. Yale Univ. Bull. 39, New Haven, CT. pp. 1-276. -, - and Monroe, B. L. 1988. A classification of the living birds of the world based on DNA-DNA hybridization studies, The Auk 105: 409-423. 416 W . E. R. Rebholz et al . Cytologi a 58

Sumner, A. T. 1972 . A simple technique for demonstrating ce ntromeric heterochromatin . Exp. Cell Res , M. 1974. A phylogenetic study of bird karyotyp . 75: 304-306Takagi,N.and Sasaki es. Chromosoma 46: 91-120 .