Diet and activity pattern of the white-tailed eagle (Haliaeetus albicilla) under the midnight sun
I recorded prey deliveries at two nests of the white-tailed eagle (Haliaeetus albicilla) during the nestling period in May – July in Troms county in northern Norway. A total of 74 prey items were recorded delivered during 866 h monitoring time. Among the prey, 74.3 % were fish, 18.9 % birds, 5.4 % u...
Main Author: | |
---|---|
Other Authors: | |
Format: | Master Thesis |
Language: | English |
Published: |
Norwegian University of Life Sciences, Ås
2016
|
Subjects: | |
Online Access: | http://hdl.handle.net/11250/2404149 |
id |
ftunivmob:oai:nmbu.brage.unit.no:11250/2404149 |
---|---|
record_format |
openpolar |
institution |
Open Polar |
collection |
Open archive Norwegian University of Life Sciences: Brage NMBU |
op_collection_id |
ftunivmob |
language |
English |
topic |
white-tailed eagle haliaeetus albicilla havørn Balsfjord Malangen diet activity pattern siblicide VDP::Mathematics and natural science: 400::Zoology and botany: 480::Ecology: 488 |
spellingShingle |
white-tailed eagle haliaeetus albicilla havørn Balsfjord Malangen diet activity pattern siblicide VDP::Mathematics and natural science: 400::Zoology and botany: 480::Ecology: 488 Eriksen, Einar Diet and activity pattern of the white-tailed eagle (Haliaeetus albicilla) under the midnight sun |
topic_facet |
white-tailed eagle haliaeetus albicilla havørn Balsfjord Malangen diet activity pattern siblicide VDP::Mathematics and natural science: 400::Zoology and botany: 480::Ecology: 488 |
description |
I recorded prey deliveries at two nests of the white-tailed eagle (Haliaeetus albicilla) during the nestling period in May – July in Troms county in northern Norway. A total of 74 prey items were recorded delivered during 866 h monitoring time. Among the prey, 74.3 % were fish, 18.9 % birds, 5.4 % unidentifiable and one (1.4 %) was a tailfin from a harbour porpoise (Phocoena phocoena). Average mass of the prey items delivered was estimated to 425~g. Righteyed flounders (Pleuronectidae) constituted a larger share of the diet at the nest located near the shallow bay of Kobbevågen than at the nest at Brokskar, both located on the same peninsula with 12 km distance between. This suggests an element of functional response in the foraging strategy of the eagles. To measure the activity level, I used a logical factor of whether or not at least one prey was delivered within each hour-block. The eagles were most active when the tide was ebbing. Furthermore, they had an activity acrophase around 7 am and bathyphase around 7 pm not corresponding to studies on white-tailed eagles farther south, where white-tailed eagles have been regarded as strictly diurnal with an acrophase at midday. The eagles were also more active on low tidal levels when the tide was ebbing and somewhat opposite at flooding tide. Precipitation did not explain activity levels, but suggested there was a trend with higher activity levels at low precipitation. The estimated total prey mass delivered per day per nestling was 432 g. I recorded an event of siblicide, which are common in several other birds of prey but viewed as very rare in white-tailed eagles in Norway. One plausible explanation for this event can be found in the sibling rivalry hypothesis. Video monitoring is a precise way of exploring the diet of birds of prey in the breeding season. Feeding habitat and diet are relevant to the white-tailed eagles survival and reproduction, thus also for the conservation of the species. The noticeable local variation of the individual diets over short distance suggests that more studies are needed in other locations to better understand the feeding behaviour. Jeg videoovervåket reirene til to havørn (Haliaeetus albicilla ) fra mai til juli på Malangshalv øya i Troms. Totalt ble det levert 74 byttedyrenheter til ungene i reiret i løpet av 866 t video. Av disse var 74,3 % sk, 18,9 % fugl, 5,4 % uidenti serbare og ett byttedyr (1,4 %) var en hale nne fra en nise (Phocoena phocoena). Gjennomsnittlig masse for byttedyrene ble estimert til 425 g. Flyndre sk (Pleuronectidae) utgjorde en større del av dietten i reiret lokalisert ved langgrunne Kobbevågen sammenlignet med reiret på Brokskar 12 km lengre nordøst på den samme halvøyen. Dette tyder på et element av funksjonell respons i ørnens furasjeringsstrategi. For å måle aktivitetsnivået brukte jeg en logisk faktor for om minst ett byttedyr ble levert innenfor en timesblokk eller ei. Ørnene viste seg å være mest aktive ved fellende tidevann. Videre hadde de høyest aktivitet omtrent kl. 7 på morgenkvisten og var minst aktive rundt kl. 7 om kvelden. De var også mer aktive ved lavt tidevann ved fellende havnivå, og til en viss grad motsatt ved øende havnivå. Nedbør forklarte ikke aktivitetsnivået, men viser likevel en trend hvor det er høyere aktivitet når det er lite nedbør og varmt i luften. Den estimerte totale byttedyrmassen per dag per unge var 432 g. Jeg kk også opptak av et søskendrap, siblicid, som er vanlig hos mange andre rovfugler men ansett som veldig sjeldent blant havørn i Norge. En plausibel forklaring på hendelsen presenteres i søskenrivaliseringshypotesen. Videoovervåkning er en presis måte å undersøke dietten til rovfugler på i hekkesesongen. Furasjeringshabitat og diett er relevant for havørnens overlevelse og reproduksjon, og dermed også i bevaringsøyemed. Den bemerkelsesverdige variasjonen i diettene til individer geogra sk nærme hverandre taler for at ere studier bør gjennomføres andre steder for å bedre kartlegge havørnens furasjeringsadferd. Viltfondet (Miljødirektoratet) M-NF |
author2 |
Sonerud, Geir A. |
format |
Master Thesis |
author |
Eriksen, Einar |
author_facet |
Eriksen, Einar |
author_sort |
Eriksen, Einar |
title |
Diet and activity pattern of the white-tailed eagle (Haliaeetus albicilla) under the midnight sun |
title_short |
Diet and activity pattern of the white-tailed eagle (Haliaeetus albicilla) under the midnight sun |
title_full |
Diet and activity pattern of the white-tailed eagle (Haliaeetus albicilla) under the midnight sun |
title_fullStr |
Diet and activity pattern of the white-tailed eagle (Haliaeetus albicilla) under the midnight sun |
title_full_unstemmed |
Diet and activity pattern of the white-tailed eagle (Haliaeetus albicilla) under the midnight sun |
title_sort |
diet and activity pattern of the white-tailed eagle (haliaeetus albicilla) under the midnight sun |
publisher |
Norwegian University of Life Sciences, Ås |
publishDate |
2016 |
url |
http://hdl.handle.net/11250/2404149 |
op_coverage |
Norway, Tromsø |
long_lat |
ENVELOPE(19.227,19.227,69.240,69.240) ENVELOPE(-86.317,-86.317,-78.067,-78.067) ENVELOPE(18.598,18.598,69.400,69.400) ENVELOPE(67.467,67.467,-67.817,-67.817) ENVELOPE(12.760,12.760,67.756,67.756) ENVELOPE(18.537,18.537,69.519,69.519) ENVELOPE(18.808,18.808,70.104,70.104) |
geographic |
Norway Tromsø Balsfjord Hale Malangen Shallow Bay Reiret Brokskar Kobbevågen |
geographic_facet |
Norway Tromsø Balsfjord Hale Malangen Shallow Bay Reiret Brokskar Kobbevågen |
genre |
Balsfjord Haliaeetus albicilla Harbour porpoise Havørn Malangen Northern Norway Phocoena phocoena Tromsø White-tailed eagle midnight sun Troms |
genre_facet |
Balsfjord Haliaeetus albicilla Harbour porpoise Havørn Malangen Northern Norway Phocoena phocoena Tromsø White-tailed eagle midnight sun Troms |
op_source |
46 |
op_relation |
http://hdl.handle.net/11250/2404149 |
_version_ |
1766368031325290496 |
spelling |
ftunivmob:oai:nmbu.brage.unit.no:11250/2404149 2023-05-15T15:37:28+02:00 Diet and activity pattern of the white-tailed eagle (Haliaeetus albicilla) under the midnight sun Eriksen, Einar Sonerud, Geir A. Norway, Tromsø 2016-09-05 application/pdf http://hdl.handle.net/11250/2404149 eng eng Norwegian University of Life Sciences, Ås http://hdl.handle.net/11250/2404149 46 white-tailed eagle haliaeetus albicilla havørn Balsfjord Malangen diet activity pattern siblicide VDP::Mathematics and natural science: 400::Zoology and botany: 480::Ecology: 488 Master thesis 2016 ftunivmob 2021-09-23T20:15:27Z I recorded prey deliveries at two nests of the white-tailed eagle (Haliaeetus albicilla) during the nestling period in May – July in Troms county in northern Norway. A total of 74 prey items were recorded delivered during 866 h monitoring time. Among the prey, 74.3 % were fish, 18.9 % birds, 5.4 % unidentifiable and one (1.4 %) was a tailfin from a harbour porpoise (Phocoena phocoena). Average mass of the prey items delivered was estimated to 425~g. Righteyed flounders (Pleuronectidae) constituted a larger share of the diet at the nest located near the shallow bay of Kobbevågen than at the nest at Brokskar, both located on the same peninsula with 12 km distance between. This suggests an element of functional response in the foraging strategy of the eagles. To measure the activity level, I used a logical factor of whether or not at least one prey was delivered within each hour-block. The eagles were most active when the tide was ebbing. Furthermore, they had an activity acrophase around 7 am and bathyphase around 7 pm not corresponding to studies on white-tailed eagles farther south, where white-tailed eagles have been regarded as strictly diurnal with an acrophase at midday. The eagles were also more active on low tidal levels when the tide was ebbing and somewhat opposite at flooding tide. Precipitation did not explain activity levels, but suggested there was a trend with higher activity levels at low precipitation. The estimated total prey mass delivered per day per nestling was 432 g. I recorded an event of siblicide, which are common in several other birds of prey but viewed as very rare in white-tailed eagles in Norway. One plausible explanation for this event can be found in the sibling rivalry hypothesis. Video monitoring is a precise way of exploring the diet of birds of prey in the breeding season. Feeding habitat and diet are relevant to the white-tailed eagles survival and reproduction, thus also for the conservation of the species. The noticeable local variation of the individual diets over short distance suggests that more studies are needed in other locations to better understand the feeding behaviour. Jeg videoovervåket reirene til to havørn (Haliaeetus albicilla ) fra mai til juli på Malangshalv øya i Troms. Totalt ble det levert 74 byttedyrenheter til ungene i reiret i løpet av 866 t video. Av disse var 74,3 % sk, 18,9 % fugl, 5,4 % uidenti serbare og ett byttedyr (1,4 %) var en hale nne fra en nise (Phocoena phocoena). Gjennomsnittlig masse for byttedyrene ble estimert til 425 g. Flyndre sk (Pleuronectidae) utgjorde en større del av dietten i reiret lokalisert ved langgrunne Kobbevågen sammenlignet med reiret på Brokskar 12 km lengre nordøst på den samme halvøyen. Dette tyder på et element av funksjonell respons i ørnens furasjeringsstrategi. For å måle aktivitetsnivået brukte jeg en logisk faktor for om minst ett byttedyr ble levert innenfor en timesblokk eller ei. Ørnene viste seg å være mest aktive ved fellende tidevann. Videre hadde de høyest aktivitet omtrent kl. 7 på morgenkvisten og var minst aktive rundt kl. 7 om kvelden. De var også mer aktive ved lavt tidevann ved fellende havnivå, og til en viss grad motsatt ved øende havnivå. Nedbør forklarte ikke aktivitetsnivået, men viser likevel en trend hvor det er høyere aktivitet når det er lite nedbør og varmt i luften. Den estimerte totale byttedyrmassen per dag per unge var 432 g. Jeg kk også opptak av et søskendrap, siblicid, som er vanlig hos mange andre rovfugler men ansett som veldig sjeldent blant havørn i Norge. En plausibel forklaring på hendelsen presenteres i søskenrivaliseringshypotesen. Videoovervåkning er en presis måte å undersøke dietten til rovfugler på i hekkesesongen. Furasjeringshabitat og diett er relevant for havørnens overlevelse og reproduksjon, og dermed også i bevaringsøyemed. Den bemerkelsesverdige variasjonen i diettene til individer geogra sk nærme hverandre taler for at ere studier bør gjennomføres andre steder for å bedre kartlegge havørnens furasjeringsadferd. Viltfondet (Miljødirektoratet) M-NF Master Thesis Balsfjord Haliaeetus albicilla Harbour porpoise Havørn Malangen Northern Norway Phocoena phocoena Tromsø White-tailed eagle midnight sun Troms Open archive Norwegian University of Life Sciences: Brage NMBU Norway Tromsø Balsfjord ENVELOPE(19.227,19.227,69.240,69.240) Hale ENVELOPE(-86.317,-86.317,-78.067,-78.067) Malangen ENVELOPE(18.598,18.598,69.400,69.400) Shallow Bay ENVELOPE(67.467,67.467,-67.817,-67.817) Reiret ENVELOPE(12.760,12.760,67.756,67.756) Brokskar ENVELOPE(18.537,18.537,69.519,69.519) Kobbevågen ENVELOPE(18.808,18.808,70.104,70.104) |