An automated procedure (v2.0) to obtain positions from light-level geolocators in large-scale tracking of seabirds. A method description for the SEATRACK project
Bråthen, V.S., Moe, B., Amélineau, F., Ekker, M., Fauchald, P.,Helgason, H.H., Johansen, M. K., Merkel, B., Tarroux, A., Åström, J. & Strøm, H. 2021. An automated procedure (v2.0) to obtain positions from light-level geolocators in large-scale tracking of seabirds. A method description for the S...
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Format: | Report |
Language: | English |
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Norwegian Institute for Nature Research (NINA)
2021
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Online Access: | https://hdl.handle.net/11250/2735757 |
id |
ftninstnf:oai:brage.nina.no:11250/2735757 |
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record_format |
openpolar |
institution |
Open Polar |
collection |
Norwegian Institute for Nature Research: Brage NINA |
op_collection_id |
ftninstnf |
language |
English |
topic |
Seabirds Alcids Atlantic puffin Black-legged kittiwake Brünnich’s guillemot Common eider Common guillemot European shag Glaucous gull Herring gull Northern fulmar Lesser-black-backed gull Little Auk Light-level geolocators Global location sensing GLS Migration Non-breeding season |
spellingShingle |
Seabirds Alcids Atlantic puffin Black-legged kittiwake Brünnich’s guillemot Common eider Common guillemot European shag Glaucous gull Herring gull Northern fulmar Lesser-black-backed gull Little Auk Light-level geolocators Global location sensing GLS Migration Non-breeding season Bråthen, Vegard Sandøy Moe, Børge Amélineau, Françoise Ekker, Morten Fauchald, Per Helgason, Hálfdán Helgi Johansen, Malin Kjellstadli Merkel, Benjamin Tarroux, Arnaud Åström, Jens Strøm, Hallvard An automated procedure (v2.0) to obtain positions from light-level geolocators in large-scale tracking of seabirds. A method description for the SEATRACK project |
topic_facet |
Seabirds Alcids Atlantic puffin Black-legged kittiwake Brünnich’s guillemot Common eider Common guillemot European shag Glaucous gull Herring gull Northern fulmar Lesser-black-backed gull Little Auk Light-level geolocators Global location sensing GLS Migration Non-breeding season |
description |
Bråthen, V.S., Moe, B., Amélineau, F., Ekker, M., Fauchald, P.,Helgason, H.H., Johansen, M. K., Merkel, B., Tarroux, A., Åström, J. & Strøm, H. 2021. An automated procedure (v2.0) to obtain positions from light-level geolocators in large-scale tracking of seabirds. A method description for the SEATRACK project. NINA Report 1893. Norwegian Institute for Nature Research. Partners in the SEATRACK project have since 2014 deployed >14 000 light-level geolocators on 11 species of seabirds to study their non-breeding distribution in the North Atlantic. Geolocator tags are ideal for large-scale tracking of seabirds being cheap and small. The tags contains a clock and a light sensor that register light levels at fixed intervals. These data are stored in the internal memory and are obtained when the tag is recovered from the bird. From these data two positions per day are calculated by estimating latitude from the length of day and night, and longitude from time of mid-day and mid-night. However, positions cannot be obtained from recorded light-data during the polar night or midnight sun. Further, the latitudinal accuracy is unreliable close to spring and autumn equinox when the length of day and night is similar across the earth. Using a threshold method, we first identify twilight events, which is the time when light-levels cross a predefined threshold that separate day from night. However, the light-level recordings are affected by environmental factors and the behaviour of the bird that may shade the geolocator or expose it to artificial light. As such, the accuracy is low compared to GPS or Argos tracking devices. A common approach has therefore been to improve the identification of these twilight events by manually inspecting the light-level data. This process is, however, time-consuming and prone to not being fully consistent and reproducible among different persons applying it. In this report, we describe an automated procedure (v2.0) for obtaining the basic positional dataset in SEATRACK from raw light-level data. The procedure automatically filters and edits the twilight events used for calculating positions. It further removes unrealistic positions using filters on equinox periods, speed, distribution, angle, distance, variation in timing of twilights and midnight sun periods, and produces double smoothed positions. Calibration of sun elevation angles, crucial for producing the final positions, is performed on each track and is the only part involving subjective assessment, but we show that it can be performed consistently and with a high repeatability. SEATRACK processes light data from >1000 geolocators after each field season, and the database has become one of the largest seabird tracking databases in the world. The automated procedure (v2.0) is a very cost-efficient method for such large-scale tracking and is consistent and reproducible. We have recently updated the entire database using this procedure, replacing all previous data based on the manual procedure and the first version of the automated procedure (v1.0). This report describes the methods used to obtain positions from geolocators in the SEATRACK project. As the described procedure replace our previous manual method, we show comparisons of the two procedures. The report also provides examples of how to read and visualize the positional data and can serve as the reference for the methods and as a tool for using the data. |
format |
Report |
author |
Bråthen, Vegard Sandøy Moe, Børge Amélineau, Françoise Ekker, Morten Fauchald, Per Helgason, Hálfdán Helgi Johansen, Malin Kjellstadli Merkel, Benjamin Tarroux, Arnaud Åström, Jens Strøm, Hallvard |
author_facet |
Bråthen, Vegard Sandøy Moe, Børge Amélineau, Françoise Ekker, Morten Fauchald, Per Helgason, Hálfdán Helgi Johansen, Malin Kjellstadli Merkel, Benjamin Tarroux, Arnaud Åström, Jens Strøm, Hallvard |
author_sort |
Bråthen, Vegard Sandøy |
title |
An automated procedure (v2.0) to obtain positions from light-level geolocators in large-scale tracking of seabirds. A method description for the SEATRACK project |
title_short |
An automated procedure (v2.0) to obtain positions from light-level geolocators in large-scale tracking of seabirds. A method description for the SEATRACK project |
title_full |
An automated procedure (v2.0) to obtain positions from light-level geolocators in large-scale tracking of seabirds. A method description for the SEATRACK project |
title_fullStr |
An automated procedure (v2.0) to obtain positions from light-level geolocators in large-scale tracking of seabirds. A method description for the SEATRACK project |
title_full_unstemmed |
An automated procedure (v2.0) to obtain positions from light-level geolocators in large-scale tracking of seabirds. A method description for the SEATRACK project |
title_sort |
automated procedure (v2.0) to obtain positions from light-level geolocators in large-scale tracking of seabirds. a method description for the seatrack project |
publisher |
Norwegian Institute for Nature Research (NINA) |
publishDate |
2021 |
url |
https://hdl.handle.net/11250/2735757 |
op_coverage |
Barents Sea, Norwegian Sea, North Sea, Svalbard, NortheastAtlantic Ocean, Arctic |
long_lat |
ENVELOPE(-46.016,-46.016,-60.616,-60.616) ENVELOPE(67.217,67.217,-70.544,-70.544) ENVELOPE(-45.683,-45.683,-60.733,-60.733) |
geographic |
Arctic Barents Sea Fulmar Johansen Moe Norwegian Sea Svalbard |
geographic_facet |
Arctic Barents Sea Fulmar Johansen Moe Norwegian Sea Svalbard |
genre |
Arctic Atlantic puffin Barents Sea Black-legged Kittiwake Common Eider common guillemot Glaucous Gull Lesser black-backed gull little auk North Atlantic Northern Fulmar Norwegian Sea polar night Svalbard midnight sun |
genre_facet |
Arctic Atlantic puffin Barents Sea Black-legged Kittiwake Common Eider common guillemot Glaucous Gull Lesser black-backed gull little auk North Atlantic Northern Fulmar Norwegian Sea polar night Svalbard midnight sun |
op_source |
50 |
op_relation |
NINA Report;1893 urn:isbn:978-82-426-4666-8 urn:issn:1504-3312 https://hdl.handle.net/11250/2735757 |
op_rights |
© Norwegian Institute for Nature Research The publication may be freely cited where the source is acknowledged |
_version_ |
1766350353249337344 |
spelling |
ftninstnf:oai:brage.nina.no:11250/2735757 2023-05-15T15:20:08+02:00 An automated procedure (v2.0) to obtain positions from light-level geolocators in large-scale tracking of seabirds. A method description for the SEATRACK project Bråthen, Vegard Sandøy Moe, Børge Amélineau, Françoise Ekker, Morten Fauchald, Per Helgason, Hálfdán Helgi Johansen, Malin Kjellstadli Merkel, Benjamin Tarroux, Arnaud Åström, Jens Strøm, Hallvard Barents Sea, Norwegian Sea, North Sea, Svalbard, NortheastAtlantic Ocean, Arctic 2021 application/pdf https://hdl.handle.net/11250/2735757 eng eng Norwegian Institute for Nature Research (NINA) NINA Report;1893 urn:isbn:978-82-426-4666-8 urn:issn:1504-3312 https://hdl.handle.net/11250/2735757 © Norwegian Institute for Nature Research The publication may be freely cited where the source is acknowledged 50 Seabirds Alcids Atlantic puffin Black-legged kittiwake Brünnich’s guillemot Common eider Common guillemot European shag Glaucous gull Herring gull Northern fulmar Lesser-black-backed gull Little Auk Light-level geolocators Global location sensing GLS Migration Non-breeding season Research report 2021 ftninstnf 2021-12-23T07:17:02Z Bråthen, V.S., Moe, B., Amélineau, F., Ekker, M., Fauchald, P.,Helgason, H.H., Johansen, M. K., Merkel, B., Tarroux, A., Åström, J. & Strøm, H. 2021. An automated procedure (v2.0) to obtain positions from light-level geolocators in large-scale tracking of seabirds. A method description for the SEATRACK project. NINA Report 1893. Norwegian Institute for Nature Research. Partners in the SEATRACK project have since 2014 deployed >14 000 light-level geolocators on 11 species of seabirds to study their non-breeding distribution in the North Atlantic. Geolocator tags are ideal for large-scale tracking of seabirds being cheap and small. The tags contains a clock and a light sensor that register light levels at fixed intervals. These data are stored in the internal memory and are obtained when the tag is recovered from the bird. From these data two positions per day are calculated by estimating latitude from the length of day and night, and longitude from time of mid-day and mid-night. However, positions cannot be obtained from recorded light-data during the polar night or midnight sun. Further, the latitudinal accuracy is unreliable close to spring and autumn equinox when the length of day and night is similar across the earth. Using a threshold method, we first identify twilight events, which is the time when light-levels cross a predefined threshold that separate day from night. However, the light-level recordings are affected by environmental factors and the behaviour of the bird that may shade the geolocator or expose it to artificial light. As such, the accuracy is low compared to GPS or Argos tracking devices. A common approach has therefore been to improve the identification of these twilight events by manually inspecting the light-level data. This process is, however, time-consuming and prone to not being fully consistent and reproducible among different persons applying it. In this report, we describe an automated procedure (v2.0) for obtaining the basic positional dataset in SEATRACK from raw light-level data. The procedure automatically filters and edits the twilight events used for calculating positions. It further removes unrealistic positions using filters on equinox periods, speed, distribution, angle, distance, variation in timing of twilights and midnight sun periods, and produces double smoothed positions. Calibration of sun elevation angles, crucial for producing the final positions, is performed on each track and is the only part involving subjective assessment, but we show that it can be performed consistently and with a high repeatability. SEATRACK processes light data from >1000 geolocators after each field season, and the database has become one of the largest seabird tracking databases in the world. The automated procedure (v2.0) is a very cost-efficient method for such large-scale tracking and is consistent and reproducible. We have recently updated the entire database using this procedure, replacing all previous data based on the manual procedure and the first version of the automated procedure (v1.0). This report describes the methods used to obtain positions from geolocators in the SEATRACK project. As the described procedure replace our previous manual method, we show comparisons of the two procedures. The report also provides examples of how to read and visualize the positional data and can serve as the reference for the methods and as a tool for using the data. Report Arctic Atlantic puffin Barents Sea Black-legged Kittiwake Common Eider common guillemot Glaucous Gull Lesser black-backed gull little auk North Atlantic Northern Fulmar Norwegian Sea polar night Svalbard midnight sun Norwegian Institute for Nature Research: Brage NINA Arctic Barents Sea Fulmar ENVELOPE(-46.016,-46.016,-60.616,-60.616) Johansen ENVELOPE(67.217,67.217,-70.544,-70.544) Moe ENVELOPE(-45.683,-45.683,-60.733,-60.733) Norwegian Sea Svalbard |