Relative magnitude of two Northern Hawk-Owl (Surnia ulula) irruptions to southern Norway: comparison of citizen data and survey data
Cover photo:Northern Hawk-Owl Surnia ulula. Photo: Terje Lislevand. The Northern Hawk-Owl Surnia ululaoccurs as an irruptive species to southern parts of Fennoscandia. Large numbers of individuals were recorded in the autumns of 2016 and 2020 but assessing the relative magnitude of irruptions is cha...
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BirdLife Norway
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ftboapojs:oai:boap.uib.no:article/3425 2023-05-15T16:12:08+02:00 Relative magnitude of two Northern Hawk-Owl (Surnia ulula) irruptions to southern Norway: comparison of citizen data and survey data Dale, Svein 2022-01-18 application/pdf https://boap.uib.no/index.php/ornis/article/view/3425 https://doi.org/10.15845/on.v45i0.3425 eng eng BirdLife Norway https://boap.uib.no/index.php/ornis/article/view/3425/3363 https://boap.uib.no/index.php/ornis/article/view/3425 doi:10.15845/on.v45i0.3425 Copyright (c) 2022 Svein Dale http://creativecommons.org/licenses/by/4.0 CC-BY Ornis Norvegica; Årg 45 (2022); 1-9 info:eu-repo/semantics/article info:eu-repo/semantics/publishedVersion 2022 ftboapojs https://doi.org/10.15845/on.v45i0.3425 2022-01-19T23:35:43Z Cover photo:Northern Hawk-Owl Surnia ulula. Photo: Terje Lislevand. The Northern Hawk-Owl Surnia ululaoccurs as an irruptive species to southern parts of Fennoscandia. Large numbers of individuals were recorded in the autumns of 2016 and 2020 but assessing the relative magnitude of irruptions is challenging. Systematic surveys allow direct comparisons but are time-consuming and will therefore be limited in time and space. Citizen data may provide large amounts of information for wide areas but may in particular suffer from spatial biases in the observation effort of birdwatchers. I compared the 2016 and 2020 irruptions of Northern Hawk-Owls to southern Norway, and found that citizen data indicated that numbers in 2016 were ca. 2–3 times larger than in 2020. However, the relative magnitude differed geographically, and the 2016 irruption was larger in western and southern counties, whereas the difference was smaller in eastern counties (in particular in Innlandet county). Systematic surveys in eastern regions (Oslo and Akershus) indicated that Northern Hawk-Owl densities were similar in the two irruption years. Overall, Northern Hawk-Owls were recorded at the same rate (approximately one owl per 16 km), and density was estimated to be 0.09–0.18 individuals/km2 in 2016 and 0.08–0.13 individuals/km2 in 2020. Thus, citizen data and survey data from the same geographical region concurred. However, due to the geographical variation in relative irruption size and spatial variation in observer density and biases in observation effort, the overall difference between the two years is difficult to assess. The 2016 irruption was likely larger than the 2020 irruption, but the difference was probably smaller than suggested by citizen data. Article in Journal/Newspaper Fennoscandia Bergen Open Access Publishing (University of Bergen Library) Norway Ornis Norvegica 45 1 9 |
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Open Polar |
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Bergen Open Access Publishing (University of Bergen Library) |
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ftboapojs |
language |
English |
description |
Cover photo:Northern Hawk-Owl Surnia ulula. Photo: Terje Lislevand. The Northern Hawk-Owl Surnia ululaoccurs as an irruptive species to southern parts of Fennoscandia. Large numbers of individuals were recorded in the autumns of 2016 and 2020 but assessing the relative magnitude of irruptions is challenging. Systematic surveys allow direct comparisons but are time-consuming and will therefore be limited in time and space. Citizen data may provide large amounts of information for wide areas but may in particular suffer from spatial biases in the observation effort of birdwatchers. I compared the 2016 and 2020 irruptions of Northern Hawk-Owls to southern Norway, and found that citizen data indicated that numbers in 2016 were ca. 2–3 times larger than in 2020. However, the relative magnitude differed geographically, and the 2016 irruption was larger in western and southern counties, whereas the difference was smaller in eastern counties (in particular in Innlandet county). Systematic surveys in eastern regions (Oslo and Akershus) indicated that Northern Hawk-Owl densities were similar in the two irruption years. Overall, Northern Hawk-Owls were recorded at the same rate (approximately one owl per 16 km), and density was estimated to be 0.09–0.18 individuals/km2 in 2016 and 0.08–0.13 individuals/km2 in 2020. Thus, citizen data and survey data from the same geographical region concurred. However, due to the geographical variation in relative irruption size and spatial variation in observer density and biases in observation effort, the overall difference between the two years is difficult to assess. The 2016 irruption was likely larger than the 2020 irruption, but the difference was probably smaller than suggested by citizen data. |
format |
Article in Journal/Newspaper |
author |
Dale, Svein |
spellingShingle |
Dale, Svein Relative magnitude of two Northern Hawk-Owl (Surnia ulula) irruptions to southern Norway: comparison of citizen data and survey data |
author_facet |
Dale, Svein |
author_sort |
Dale, Svein |
title |
Relative magnitude of two Northern Hawk-Owl (Surnia ulula) irruptions to southern Norway: comparison of citizen data and survey data |
title_short |
Relative magnitude of two Northern Hawk-Owl (Surnia ulula) irruptions to southern Norway: comparison of citizen data and survey data |
title_full |
Relative magnitude of two Northern Hawk-Owl (Surnia ulula) irruptions to southern Norway: comparison of citizen data and survey data |
title_fullStr |
Relative magnitude of two Northern Hawk-Owl (Surnia ulula) irruptions to southern Norway: comparison of citizen data and survey data |
title_full_unstemmed |
Relative magnitude of two Northern Hawk-Owl (Surnia ulula) irruptions to southern Norway: comparison of citizen data and survey data |
title_sort |
relative magnitude of two northern hawk-owl (surnia ulula) irruptions to southern norway: comparison of citizen data and survey data |
publisher |
BirdLife Norway |
publishDate |
2022 |
url |
https://boap.uib.no/index.php/ornis/article/view/3425 https://doi.org/10.15845/on.v45i0.3425 |
geographic |
Norway |
geographic_facet |
Norway |
genre |
Fennoscandia |
genre_facet |
Fennoscandia |
op_source |
Ornis Norvegica; Årg 45 (2022); 1-9 |
op_relation |
https://boap.uib.no/index.php/ornis/article/view/3425/3363 https://boap.uib.no/index.php/ornis/article/view/3425 doi:10.15845/on.v45i0.3425 |
op_rights |
Copyright (c) 2022 Svein Dale http://creativecommons.org/licenses/by/4.0 |
op_rightsnorm |
CC-BY |
op_doi |
https://doi.org/10.15845/on.v45i0.3425 |
container_title |
Ornis Norvegica |
container_volume |
45 |
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1 |
op_container_end_page |
9 |
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1765997384352923648 |