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Molt Stage, Wing Bar Patterns and Digital Photography As Tools for Assessing Age Distribution and Recognizing Individuals of Great Grey and Snowy Owls

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Molt Stage, Wing Bar Patterns and Digital Photography As Tools for Assessing Age Distribution and Recognizing Individuals of Great Grey and Snowy Owls Roar Solheim Molt stage, wing bar patterns and digital photography as tools for assessing age distribution and recognizing individuals of Great Grey and Snowy Owls PhD Thesis 2019 Faculty of Applied Ecology, Agricultural Sciences and Biotechnology 1 2 Preface My interest for owls started shortly after birds captured my fascination, when a small Pygmy Owl perched in a birch tree outside my classroom window. I was twelve, I was lost, and I have been lost to the world of owls ever since. I have been fortunate to meet all ten species of owls which regularly breed in Norway, and have had the opportunity to study several of them at close range. Since 1995 I have been employed as a Senior Curator in Zoology at the Agder Natural His­ tory Museum in Kristiansand, which in 2017 became an integrated university museum under Agder University. My position has made it possible to work in the border zone between life and death, combining studies of free living owls with skin studies in scientific museum collec­ tions. I am grately indepted for the opportunity my employers have granted me for these studies, and finally giving me time to compile my work into this PhD thesis. Petter Wabakken at Evenstad, Inland Norway University, has been a great friend and ispirator for many years, and we have shared passion and fascination for wildlife since our student days at the University of Oslo. He strongly urged me to appl y for the PhD studies at Evenstad, and I am very thankful for his thrust, and interest in my work. This PhD might never have seen the light of day without him. I also wish to thank Evenstad for taking me in as a PhD candidate. It has been a pleasure to return to student mode, follow courses and get to know the other PhD­students, professors and teachers. The staff at Evenstad have been very nice, and I have always felt welcome at this campus. I especially thank Kjartan Østbye for accepting an old «dinosaur» among his PhD­students. I thank all the museums which granted me access to their skin collections; Tromsø Museum, Bergen Museum, Natural History Museum in Oslo (former Zoological Museum Oslo), Swed­ ish Natural History Museum in Stockholm (NRM), Helsinki Museum, Copenhagen Zoo­ logical Museum, Smithsonian Museum in Washington and the Natural History Museum in New York. I also thank the many people who kindly helped me at these museums. The material from the field studies could not have been collected without the help of many co­workers and friends. I first thank my colleagues and co­researchers in the Norwegian Snowy Owl Project: Karl­Otto Jacobsen, Ingar Jostein Øien and Tomas Aarvak, with whom I have shared many magnificent and exclusive owl moments! My co­workers of Snowy Owl studies in Canada and USA collected a vast number of wing images of Snowy Owls captured on the great prairies. These images have been paramount to un tangle the moult sequences 3 for aging Snowy Owls. I am thus greatly in debt to Tom Mc Donal d, Dan Zaze lenchuk, Mike Blom and Marten Stoffel who sent me photos. Karen Wiebe at the Saskatoon University has also been a valuable co­worker in the Snowy Owl studies. I also thank Aleksandr Sokolov for letting me use his owl images from Beliy Island in 2015 to test the applicability of my method s on Snowy Owls, and for co­authoring paper IV. Each spring brings excitement and high hopes, as field season and time to inspect the owl forests in Hedmark, Värmland and Dalarna approaches. Steinar Myhr has been my close asso ciate and co­worker on most of this field work since 2008, and has been of great help and support. We have shared many exciting and splendid moments in the borea l forests of central Scandinavia, and I am very thankful for his company and friendship. Many ornithologists have shared information and work on the Great Grey Owl adventure in Hedmark. Trond Berg has collected the majority of wing images of captured owls, and also compiled the nest data into readable Excel­sheets. I am very thankful for his cooperation and field efforts. Many people have contributed with localities and information on the Great Grey Owls. With the danger of missing someone I would especially thank the support provided by Roar Svenkerud, Steinar Kråbøl, Carl Knoff, Rune Bjørnstad, Robert Huldt and Egil Østby. Antonio B. S. Poleo at Evenstad helped me arrange the blind test of Great Grey Owl wings. Kjartan Østbye and Geir A. Sonerud have kindly read and given valuable comments to the PhD synopsis. I am grately thankful for their corrections and support. Geir A. Sonerud also co­authored paper V on the Great Grey Owl age studies in Hedmark, and greatly enhanced the quality of this paper. I am very thankful for his help, lifelong friendship and shared fascination for owls. Roar Solheim Grimstad and Evenstad September 2019 4 Contents Preface ......................................................................................................................... 3 Sammendrag (Norwegian summary) .......................................................................... 7 Abstract ....................................................................................................................... 9 List of papers ............................................................................................................... 12 1 Introduction ..................................................................................................... 13 1.1 Snowy Owl and Great Grey Owl ­ the species ............................................... 13 1.2 Population status of the Snowy Owl and the Great Grey Owl ....................... 14 1.2.1 Snowy Owl ..................................................................................................... 14 1.2.2 Great Grey Owl .............................................................................................. 15 1.3 Prey choice ..................................................................................................... 16 1.4 Hunting behaviour ......................................................................................... 17 1.5 Hunting voles on tundra and taiga ................................................................. 18 1.5.1 Landscape constraints .................................................................................... 18 1.5.2 Fluctuating prey populations ......................................................................... 18 1.5.3 Theories of vole population fluctuations ....................................................... 19 1.5.4 Are cole cycles levelling off? ........................................................................ 21 1.6 Owls, voles and climate ................................................................................ 22 2. Monitoring Snowy Owls and Great Grey Owls ............................................ 24 2.1 Searching for nests and nest sites .................................................................. 24 2.2 Surveilling age structure ............................................................................... 25 3 Moult, plumage and age ............................................................................... 25 4 Objectives ..................................................................................................... 26 5 Material and methods ................................................................................... 26 5.1 Terminology and numbering of feathers ...................................................... 26 5.2 Terminology of age and moult ..................................................................... 29 5.3 Wear and bleaching of feathers .................................................................... 29 5.4 Differences between juvenile and adult feathers .......................................... 30 5.5 Sampling wing images ................................................................................. 34 5.6 Comparing bar patterns on wing images ...................................................... 36 5.7 Sample sizes ................................................................................................. 38 5.7.1 Great Grey Owl ............................................................................................ 38 5.7.2 Snowy Owl .................................................................................................. 38 6 Results and discussion ................................................................................. 40 6.1 Moult (paper I and II) ................................................................................... 40 6.2 Feather bar patterns and individuality (paper III) ........................................ 46 6.3 Applying moult and feather bar patterns in population studies ..................... 47 5 Contents (continued) 6.3.1 Snowy Owl summer invasion (paper IV) ...................................................... 47 6.3.2 Great Grey Owl breeding population (paper V) ............................................ 48 6.3.3 Great Grey Owls reported through public sciences (paper VI) ..................... 50 6.4 Photography as a non­invasive technique ..................................................... 51 7 Conclusion .................................................................................................... 52 8 Future perspectives and work ....................................................................... 53 9 References .................................................................................................... 54 Paper I .....................................................................................................................
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