Contents. Preface 7 Acknowledgements 11

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2 Contents Preface 7 Acknowledgements Introducing the Tertiary The changing ecology of the Palearctic in the Pleistocene Origins of Palearctic birds Corvoidea shrikes, crows and orioles Sylvioidea hirundines, warblers and larks Paroidea tits Muscicapoidea chats, thrushes, flycatchers and allies Passeroidea sparrows, finches, pipits and buntings Falcons Terrestrial non-passerines Owls Raptors Gulls, terns, auks and waders Divers, tubenoses, and waterbirds Cranes, rails, bustards and cuckoos Nightjars and swifts Pigeons, sandgrouse, tropicbirds, flamingos and grebes Geese, swans, ducks and gamebirds Climate and the history of the birds of the Palearctic Surviving climate change characteristics of survivors The Palearctic avifauna of yesterday, today and tomorrow 235 Appendix 1. Species covered in this book: bioclimatic and ecological features 242 Appendix 2. European Pleistocene fossil birds 268 References 279 Index 289

3 112 Chapter 11 Owls Group 1, subgroup e The barn owls are an ancient lineage that diverged from the rest of the owls early in the Oligocene (Ericson et al., 26). The true barn owls diverged from the bay owls, the other subfamily of the Tytonidae, in the mid-miocene, over 1 mya (Wink and Heidrich, 1999; Wink et al., 29). The radiation of the different species of Tyto followed shortly after and its centre of origin appears to be Southeast Asia and New Guinea, where most species are found today. There is evidence of two separate settlements of the Australasian region (Wink et al., 29). The next stage of divergence involves the Common Barn Owl in the Old World, from which a later branch leads to the New World taxon (now sometimes considered a discrete species). The New World was presumably colonised from Asia at a point where the climate was relatively mild, as barn owls are essentially species of warm climates. Barn owls are absent from large areas of the Palearctic, especially the dry interior, the more humid Western Palearctic being exceptional in this respect. They must have once been present in northern Asia (from where the New World would have been colonised) but have since become extinct during Plio-Pleistocene aridification. The Striginae The separation of the large Striginae subfamily from the hawk and pygmy owls (the Surninae) predates the split of the barn and bay owls (Wink et al., 29) which, as we have seen, dates to over 1 mya. The group of owls that include the Otus scops owls also separated within the Striginae prior to 1 mya. The other three major groups in the subfamily, the Strix wood owls, the Bubo eagle owls and the Asio eared owls, diverged some time later, probably during the mid-miocene. Within the wood owls, Hume s Owl S. butleri is most closely related to the African Wood Owl S. woodfordi, with these taxa separating at some point between the split of the New and Old World Strix owls (5-6 mya) and the separation of the Old World species (Tawny S. aluco and Ural S. uralensis Owls, around 4 mya). The separation of the Holarctic Great Grey Owl, S. nebulosa, would seem to predate that of Tawny from Ural Owl (Wink et al., 29). Hume s Owl is a geographical counterpart of the African Wood Owl in the Middle East, where it occupies desert and open country. The Tawny and Ural Owls are also geographical counterparts of each other; the Tawny in the oceanic west and the warm south of the Palearctic and the Ural in the continental north, with an area of overlap in southern Scandinavia and eastern Europe. The larger Great Grey Owl occurs to the north of the Ural Owl, with which it overlaps across a large belt of the northern Palearctic. The size difference between the two presumably permits coexistence. The eagle owls, Bubo, constitute a sister group to the Strix owls, with a divergence date of around 1 mya (Wink et al., 29). Within this group, a number of species separated at an early stage to form a loose cluster that includes African and south-east Asian forest and fish-eating species. Within this group, the fish owls (formerly Ketupa) include the Brown Fish Owl B. zeylonensis, which reaches the Western Palearctic in the Middle East, and Blakiston s Fish Owl B. blakistoni in the Eastern Palearctic. The remaining species separate out into an American cluster, which includes the Holarctic Snowy Owl B. scandiacus, a southern African cluster, and a Palearctic North and East African group. This latter group includes the widespread Eurasian Eagle Owl B. bubo, and its geographical counterparts, the Cape Eagle Owl B.capensis, which

4 Owls occupies the Rift Valley down to South Africa, and the Pharaoh Eagle Owl B. ascalaphus of North Africa, the Sahara and Arabia. The eared owls, Asio, are a small and homogeneous group within the Striginae. They separated from the rest of the group around 6 8 mya. Eight species make up this group, with three occurring in the Western Palearctic. The eared owls separate into two groups. The long-eared owls (Eurasian A. otus, African A. abyssinicus, Madagascar A. madagascariensis and Stygian A. stygius) are geographical counterparts that between them span the Palearctic, the New World and Africa. The Neotropical Striped Owl, A. clamator, is closely related. The second group (Short-eared Owl A. flammeus, Marsh Owl A. capensis and Galápagos Owl A. galapagoensis) are also geographical counterparts, with the first species widespread across the Holarctic and large parts of South America, and capensis replacing it in Africa. This second group is characterised by preferring open ground and marshland, and is absent from the Neotropical and African rain forests. The eared owls are absent from South-east Asia and Australia. The fourth owl group, the scops owls Otus, separated from the North American Megascops screech owls around 6 8 mya. The split must have followed a period of contact when warm forests would have connected the two worlds. Many Otus are South-east Asian or Indian Ocean island endemics. The four Western Palearctic species (Eurasian Scops Owl O. scops, Pallid Scops Owl O. brucei, Arabian Scops Owl O. pamelae and Socotra Scops Owl O. socotranus) are closely related and geographical counterparts Eurasian Scops across a wide area of the southern and Central Palearctic, O. brucei within a warm, dry region of the southcentral Palearctic, and the other two localised within the Arabian peninsula. This group is closely-related to the Oriental Scops Owl O. sunia of southern and eastern Asia and the African Scops Owl O. senegalensis of sub-saharan Africa. The Surninae Three major clusters make up the Surninae. The first group that separates from the rest are South-east Asian and Australasian hawk owls of the genus Ninox. There are no Western Palearctic species in this group (though there is one in the Eastern Palearctic). The second major cluster is composed of the four species in the genus Aegolius. All occur in the New World, where they must have originated, and the most northerly species, Tengmalm s Owl A. funereus, has a wide distribution across the Holarctic west to Scandinavia and the Pyrenees. The separation between this species and the Nearctic Northern Saw-whet Owl A. acadicus is older than 6 mya (Wink et al., 29). The third major cluster is subdivided into two subgroups, one containing the genus Athene and the other the genera Taenioglaux, Surnia and Glaucidium (Wink et al., 29). Athene consists of six species that are geographical counterparts: Burrowing Owl A. cunicularia in the New World, Little Owl A. noctua across much of the mid-latitude belt, Lilith Owlet A. lilith in south-eastern Europe and the Middle East, Ethiopian Little Owl A. spilogaster in north-east Africa, Spotted Owlet A. brama in south and South-east Asia, and Forest Owlet A. blewitti in central India. In the second subgroup, the New and Old World pygmy owls separated from each other around 6 8 mya (Wink and Heidrich, 1999). The three Old World species are geographical counterparts, with the Western Palearctic species, the Eurasian Pygmy Owl Glaucidium passerinum, occupying a wide belt of forest north of the mid-latitude belt from Scandinavia to eastern Russia. The other two species are African and are separated from that of the Palearctic by desert, steppe and savanna and must have diverged from a common ancestor with a larger distribution in the Miocene, when forests were continuous between Africa and the Palearctic. The Northern Hawk Owl Surnia ulula has a widespread Holarctic distribution across the boreal forests, from north-east Canada to Scandinavia, generally north of Glaucidium, from which the genus must have diverged in the mid-miocene. Climate The barn owls are overwhelmingly species of warm, wet/humid climates, with a small number of species having managed to occupy the dry end of the warm climatic spectrum (Figures combine T ytonidae 113

5 avian survivors and Strigidae). Occupation of cooler climates is rare and limited to a single species in each climatic type. The Western Palearctic is occupied by the Common Barn Owl Tyto alba, the barn owl with the widest bioclimatic tolerance, occupying a more central position on the temperature and humidity gradients than any other barn owl (Appendix 1). Like the barn owls, the striginine owls are largely species of warm, wet/humid climates (Figures ). A significant number of species have become specialists of mountain climates. Otherwise, small numbers have occupied temperate and cool bioclimates, dry as well as humid. Palearctic species include four with the widest bioclimatic tolerances in the group, and comparable to the most bioclimatically tolerant of all birds: Eurasian Eagle, Tawny, Eurasian Long-eared and Short-eared Owls. A second group includes three species with relatively broad tolerances and tendencies towards cool and wet bioclimates (Ural Owl), cool and dry (Great Grey Owl), and warm and dry (Eurasian Scops Owl). An exceptional species in the group is the Snowy Owl, which has become a specialist of the coldest and driest bioclimates. The remaining Palearctic species are all specialists of warm climates with restricted distributions in the south of the region. Two are in dry climates, in south-west and Central Asia: Hume s and Pallid Scops Owls. Two others are species of warm climates but occupy a wetter part of the humidity gradient: Brown Fish Owl and Marsh Owl. The surninine owls are, as all other owls, species of warm, wet/humid, climates. It is the four genera that have reached the Palearctic that have the widest climatic tolerance and have managed to occupy temperate and cool climates (Appendix 1). Even so, the surninine owls do not reach the bioclimatic breadth of the most generalised striginine owls. The Little Owl stands out as the species with the broadest tolerance, occupying a central position in the temperature and humidity gradients. The Northern Hawk, Eurasian Pygmy and Tengmalm s Owls are species with fairly broad tolerance to climates at the cool and dry end of the spectrum. The Lilith Owlet is a specialist of warm, dry climates. number of species % Palearctic total species Palearctic species % Palearctic a b c d e bioclimatic tolerance Figure 11.1 Bioclimatic tolerance of owls. Definitions as on Figure 4.1 (see p. 38). i ii number of species a b c d e temperature % Palearctic number of species a b c d e humidity % Palearctic Figure 11.2 Temperature (i) and humidity (ii) tolerance of owls. Definitions as in Figure 4.2 (see p. 38). Key as in Figure

6 Owls Habitat Barn owls are birds of forest, with a few species occupying more open habitats, including grasslands (Figure 11.3). The striginine owls are predominantly species of forest (Figure 11.3). Very few species have abandoned forest habitats to occupy savanna, shrubland and wetland, with even fewer being successful in treeless habitats, including tundra and desert. The 15 Western Palearctic species deviate from this pattern. Even though seven species are typical in that they are forest inhabitants, a wide range of habitats is occupied: savanna (5), shrubland (4), treeless (2), tundra (2), desert (6), rocky areas (6) and wetlands (3). The forest dwellers include those of the temperate and boreal forests that lie north of the mid-latitude belt, and these species have uninterrupted distributions either across the Palearctic (Ural Owl) or across the Holarctic (Great Grey, Eurasian Long-eared and Short-eared Owls). A notable subset is of species that occupy open habitats in the warm and arid part along the south of the mid-latitude belt (Pharaoh s Eagle, Hume s, Pallid Scops, Arabian Scops and Socotra Scops Owls). The surninine owls are predominantly birds of forests, with a significant number of species in savanna. The Athene owls appear to have managed to break away from the forest theme and have become at home in savanna and treeless habitats (including desert and rocky). Palearctic species follow this trend of forestdwelling, with Athene in more open habitats. Although owls are heavily dependent on forests, the occupation of rocky habitats (Figure 11.3) is a feature that characterises some Palearctic owls. This ability to occupy rocky habitats has ensured the success of some species where forests were absent. number of species % Palearctic forest mix open rocky wetlands habitat Figure 11.3 Habitat occupation by owls. Definitions as in Figure 4.3 (see p. 39). Key as in Figure Migratory behaviour Barn owls are strictly resident species. There are no migratory species of barn owl and such a limitation may have been a major contributory factor to their absence from the more continental environments of the Palearctic. The striginine owls include the few species of owl that exhibit migratory behaviour. All seven migratory species occur in the Palearctic: Snowy, Eurasian Scops, Oriental Scops, Pallid Scops, Brown Hawk, Eurasian Long-eared and Short-eared Owls. In addition, a number of other species show irruptive behaviour related to breeding output which is, in turn, related to prey abundance. The Snowy and Eurasian Scops Owls are fully migratory, the former moving to areas immediately to the south and the latter to tropical Africa. Pallid Scops Owls in the south of their limited range are resident, with populations in the continental interiors being migratory. Oriental Scops and Brown Hawk Owls are migratory in the Eastern Palearctic with sedentary populations to the south. Short-eared Owls are almost wholly migratory but populations in the extreme south and west of the breeding range are resident. The Eurasian Long-eared Owl, by contrast, is mainly sedentary with only populations in the northernmost continental areas being migratory. This difference between two closely related owls would suggest that forest habitats (occupied by Long-eared) are possible to occupy throughout the year, whereas open ones (used by Short-eared, and incidentally also Snowy) are not. This suggestion is reinforced by the behaviour of owls of the temperate and boreal forests, all of which are 115

7 avian survivors resident. Their success, without having to migrate south for the winter, lies in their ability to exploit small mammals during the long, dark northern winter. Migratory behaviour is scarce in this group and is virtually absent from Western Palearctic species which are, at most, irruptive (the exceptions are the striginine owls discussed above). Overall, 247 of 25 species have sedentary populations, contrasting with only 1 with migrants, 7 of which are Palearctic. Fossil owls Barn owls first appear in the fossil record of Europe in the Oligocene, and Tyto is present from the Early Miocene (Mlíkovský, 22). This observation is in keeping with an early split of the Tytonidae from the Strigidae during the Oligocene, which must have been followed by a rapid radiation and geographical expansion. Fossil striginine owls are certainly present in Europe from the Early Miocene (Asio, Strix) and modern species from at least the Early Pliocene (B. bubo, B. zeylonensis; Mlíkovský, 22). Eleven species are all present from the Early Pleistocene (Appendix 2). Noteworthy among these records is the presence of northern species well to the south of the present range. Snowy Owls are common in France and many other central and western European countries, reaching south to Gibraltar. Ural Owls also reach Italy, France and Spain, while Great Grey Owls occur in central and eastern Europe, west to Italy (Tyrberg, 1998, 28). These observations indicate a significant southward and westward extension of boreal forest and tundra during the Pleistocene glaciations. Compared to other owls, surninine owls appear rather later in the fossil record of Europe: Aegolius in the Late Miocene, and Surnia, Glaucidium and Athene in the Late Pliocene. All Western Palearctic species are present in the fossil record throughout the Pleistocene (Appendix 2), the Little Owl being the most frequently recorded. As with the previous group, the more northerly surninine owls are recorded south and west of their present range during the Pleistocene. The Northern Hawk Owl has been found in deposits from Germany, Italy, Austria, Switzerland, Hungary, Ukraine, France and the United Kingdom; the Eurasian Pygmy Owl in France, Italy, Greece and Spain; and Tengmalm s Owl in the United Kingdom, Italy and Spain. TYTONIDAE Taxa in the Palearctic Tyto The Common Barn Owl T. alba is the sole Palearctic representative of this genus of tropical forest owls. The Barn Owl itself has a wide tropical distribution, in the Americas, Africa, southern Asia and Australia, but outside the tropics it has only succeeded in North America and the Western Palearctic. It is absent from the Central and Eastern Palearctic. It is a bioclimatic multi-latitude (Latitude Category F) semi-generalist but avoids cold and arid conditions so it would have been prevented from surviving in the harsh conditions of the Central Palearctic. Its absence from the Eastern Palearctic which, like North America, once had connections with southern tropical forests, is harder to understand. It may be that conditions in the oceanic Western Palearctic permit the survival of this sedentary owl but the harshness of Eastern Palearctic winters does not. If so, the answer would lie in the bird s inability to migrate. STRIGIDAE Otus Five (9.8%) of the world s scops owls breed in the Western Palearctic. Otus are overwhelmingly bioclimatic specialists of warm and wet forests. The Palearctic species include the two most bioclimatically generalised of the genus European Scops (moderate, Latitude Category D) of the Western and Central Palearctic, and its Eastern Palearctic counterpart, the Oriental Scops Owl (moderate, multi-latitude, Category F). 116

8 Owls These two species have the largest ranges of the Palearctic scops owls; they are successful because they are migratory. The only other migratory scops owl is Pallid Scops Owl, which has a restricted range in the Central Palearctic and the eastern part of the Western. To the south resident populations occur. This is a bioclimatic specialist of the mid-latitude belt (Latitude Category D) so, in spite of its migratory habits, its bioclimatic intolerance has restricted it much more than the two previously discussed species. The other species are resident Eastern Palearctic bioclimatic specialists Collared Scops O. lettia (multi-latitude, Category F) and Japanese Scops O. semitorques (mid-latitude, Category D). Strix Four species (16.6%) of Strix owls breed in the Palearctic. They are mainly tropical forest owls with two major clusters, one in southern Asia and the Himalayas, which may have been the centre of radiation of the genus, and the second in the New World. The colonisation of the Palearctic may have followed the launchpad model that we have described for other, particularly forest, genera (see p. 41). Entry into the Americas would have been during a mild climatic phase, when forests provided habitat continuity. Three of the four species have pan-palearctic ranges. The Tawny Owl is a generalist with a continuous, multi-latitude (Latitude Category F), range in the Western Palearctic and discontinuous, as we would expect with the fragmentation of forests, in the Central and Eastern Palearctic. In this respect the Tawny Owl resembles the Barn Owl in having a wide distribution in the west and a restricted one in the east. Great Grey and Ural Owls are bioclimatic moderates that owe their success to having occupied the Boreal (Latitude Category B) forest belt. They have continuous pan-palearctic ranges except in the west, where they are marginal. The Great Grey Owl s range continues in the Nearctic. A limited southern area (Latitude Category D) in the Western Palearctic range of the Ural Owl indicates a larger range that became disconnected with global warming. Finally, Hume s Owl S. butleri is a specialist of the subtropical belt of the Western Palearctic, which has adapted to arid treeless environments by adopting a rocky habitat lifestyle. Its range is consequently restricted. This genus conforms with the single generalist per genus pattern (see p. 46). Bubo Four species (16%) of largely Afro-Asian tropical forest eagle owls breed in the Palearctic. Eurasian Eagle Owl is a bioclimatic generalist with a multi-latitude (Latitude Category F) pan-palearctic range that is discontinuous in the west. In spite of its large range, this owl never managed to colonise the Nearctic. Its success has been due in part to its ability to breed in rocky, as well as forested, habitats. The Snowy Owl is a semi-specialist of open Arctic (latitude Category A) habitats and has a Holarctic distribution. It is the Bubo solution to life on the tundra, and involves migration; the Snowy Owl is the only migratory owl of the genus. Two bioclimatic semi-specialists, with the unusual habit of catching fish, occupy limited areas of the Western (Brown Fish Owl Latitude Category E) and Eastern (Blakiston s Fish Owl Latitude Category C) Palearctic. Asio Three species (37.5% of the species in this genus) breed in the Palearctic. The genus is globally widespread. The Palearctic species include two generalists, which would appear to form a break from the single generalist per genus rule. But the two species belong to the two major lineages within Asio and differ hugely in behaviour. The Eurasian Long-eared Owl is a forest bird with a multi-latitude (Latitude Category F) panpalearctic range. It is sedentary across this range but northernmost populations are migratory; the Shorteared Owl A. flammeus is a Boreal (Latitude Category B) pan-palearctic species and, like the Long-eared, its range is fragmented in the west. It is a species of open, treeless habitats and is highly migratory. These major ecological and behavioural differences, in species that belong to different lineages within the genus, would seem sufficient to permit two widespread generalist congeners to overlap widely in range. The third species Marsh Owl is African and reaches the southern fringe of the Western Palearctic where it is on the northern tip of its range. It is a sedentary semi-specialist of the subtropical (Latitude Category E) belt, and is a species of wetlands. 117

9 avian survivors Ninox The Brown Hawk Owl N. scutulata is the only species (4%) of this large south-east Asian and Australasian genus to occur in the Palearctic. It is the most bioclimatically tolerant (moderate) of all the species in its genus and occupies a multi-latitude (Latitude Category F) in the Eastern Palearctic. It is a migratory forest insectivore that appears to have been confined to the east, as is the case for a number of other forest insectivores. Aegolius This is a New World genus of four species, one of which Tengmalm s (or Boreal) Owl has a Holarctic range. It is the most bioclimatically tolerant (semi-generalist) in the genus and it has a split-category (B/D) pan-palearctic range that is discontinuous in the west. It follows the pattern observed in a number of other forest species that must have had a wider latitudinal spread during colder climatic phases. Athene Two (33.33%) of the little owls breed in the Palearctic. The Little Owl A. noctua is a semi-generalist with a pan-palearctic range across the mid-latitude belt (Latitude Category D). An inhabitant of rocky habitats, it has spread right across this belt as other species have done (e.g. choughs, wheatears). The Lilith Owlet A. lilith is confined to south-eastern Europe and the Middle East where it must have speciated during a period of climatic isolation. It is a specialist of warm and dry habitats of the mid-latitude belt (Latitude Category D). The little owls seem good candidates for a launch-pad range expansion from south or south-east Asia via the Himalayas, with a gradual abandonment of forest for open and rocky habitats. Little Owl spread across the belt and two species emerged in isolation within this range, Lilith and Ethiopian Little Owl in north-east Africa. There must have been a wider range during a warmer past, which allowed the genus to enter the New World. It is represented there today by the widespread Burrowing Owl. Glaucidium The Eurasian Pygmy Owl is the only Palearctic representative (4%) of this large New World genus of warm and wet climate forest owls. Along with the Nearctic Northern Pygmy Owl G. californicum, it is the most bioclimatically tolerant (moderate) of the genus. Its range is Boreal (Latitude Category B) pan-palearctic, discontinuous in the west. Surnia This single-species Holarctic genus is a Miocene offshoot of Glaucidium. The Northern Hawk Owl S. ulula is a bioclimatic moderate with a continuous pan-palearctic range, split between Boreal (B) and mid-latitude (D), as in a number of other forest birds (including Tengmalm s and Ural Owls). 118 CONCLUSIONS (a) Bioclimatic generalisation. Bioclimatic generalists and semi-generalists make up a large proportion of the Palearctic owls 7 species, 29.17%. It appears to have been the solution among birds that have not developed migratory strategies: 16 (66.67%) of the Palearctic owls are sedentary. Four species have multilatitude (Latitude Category F) ranges, three of them pan-palearctic. The other bioclimatically tolerant species have Boreal (Latitude Category B, 1 species), mid-latitude (Latitude Category D, 1 species) and split (Latitude Category B/D, 21 species) ranges. (b) Mid-latitude belt representation. Five species have ranges centred on 4 N, and they are all little and scops owls. To these we may add three with split boreal/warm (B/D) ranges. In fact, other than the multilatitude species (6) most owls are either warm (Category D), split boreal/warm or Boreal (B, 4 species). In contrast there is only one Temperate species (Category C), which seems to indicate that ideal conditions for owls, other than multi-latitude ones, lie in the 4th and 6th parallel belts. (c) Geographical nature of the genera. Several genera fit into the launch-pad model of South-east Asian species penetrating the Palearctic via Himalayan altitude belts. This would seem to apply to Strix and

10 Owls Athene, and possibly also to Bubo and Otus. Two, possibly three, genera reveal a different kind of launchpad spread, one we have come across occasionally so far (e.g. in Troglodytes); the dispersal of a single species in a genus (usually bioclimatically tolerant) from the Nearctic. The genera in question are Aegolius, Glaucidium and, possibly, Surnia. In such cases the Palearctic is dominated by one species, a situation akin to the south-east Asian Himalayan model. In both cases the sources of species have connections with the tropical south. (d) Habitat and diet modification. A feature among the owls has been the ability to move away from forest habitats and exploit a range of other habitats available to them in the Palearctic. Rocky habitats are exploited for breeding in three genera Athene (Little Owl, Lilith Owlet), Strix (Hume s Owl) and Bubo (Eurasian Eagle Owl). There is also adaptation to the open habitats of the north in Bubo (Snowy) and Asio (Short-eared), and movement into wetland habitats in Asio (Marsh Owl) and among the fish-eating eagle owls (Brown and Blakiston s Fish Owls). (e) Representation in the Western Palearctic. The sub-region with fewest owls is, not unsurprisingly given the great loss of forests there, the Central Palearctic (13). There are 15 species in the Eastern Palearctic, but the sub-region with most species is the Western Palearctic with 18. The reason for this may be that the Western Palearctic contains the greatest range of owl habitats (forest and rocky), more than the forested Eastern Palearctic or the forest-sparse Central Palearctic. 119