Diet and breeding success of great skuas (Catharacta skua) on Bjørnøya, Norway
The last 40 years there has been a marked increase in the number of Great skuas (Catharacta skua) in Norwegian territory, and it seems as if the core distribution area is shifting, from Iceland and Shetland, northwards to the Barents Sea region. As a generalist and top predator in the marine ecosyst...
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Norwegian University of Life Sciences, Ås
2010
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ftunivmob:oai:nmbu.brage.unit.no:11250/186706 2023-05-15T15:39:12+02:00 Diet and breeding success of great skuas (Catharacta skua) on Bjørnøya, Norway Diett og hekkesuksess for storjo (Catharacta skua) på Bjørnøya, Norge Knutsen, Arnstein Engemyr 2010-12-27T13:36:45Z application/pdf http://hdl.handle.net/11250/186706 eng eng Norwegian University of Life Sciences, Ås http://hdl.handle.net/11250/186706 25 great skuas Catharacta skua storjo diet diett breeding success hekkesuksess VDP::Mathematics and natural science: 400::Zoology and botany: 480::Ecology: 488 Master thesis 2010 ftunivmob 2021-09-23T20:14:54Z The last 40 years there has been a marked increase in the number of Great skuas (Catharacta skua) in Norwegian territory, and it seems as if the core distribution area is shifting, from Iceland and Shetland, northwards to the Barents Sea region. As a generalist and top predator in the marine ecosystem the Great skua has a broad range of available prey, and their impact on prey species, particularly other seabirds, is poorly understood. The diet of Great skuas during winter is largely unknown, because they live mostly out in the open ocean. As they come to shore to breed, it is possible to obtain an estimate of the diet during the breeding season through analysis of regurgitated pellets. The pellets were collected from a total of 25 Great skua nests in 2008 and 2009. Each nest was visited every fifth day from hatching, and chicks were weighed and measured at each visit. Almost all pellets contained remains from birds while 38 % contained remains from fish. On average, 62 ± 3.7 % of pellets from a pair contained only seabird remains. In 2008, dietary specialization toward seabirds was found in 33 % of the pairs, compared to 62 % in 2009. The overall diet composition did not differ between years, but the proportion of fish in pellets varied between pairs within years. As the breeding season progressed the probability of fish being found in pellets decreased. Body mass, tarsus length and wing length of chicks were negatively correlated with the proportion of pellets with only fish. Hatching dates varied between years, being delayed in 2009. Breeding success was higher in 2008 than in 2009. There was no relationship between the number of chick survival to age 15 days (D (15) = fledging success) and differences in specialization, but in 2009 there was a positive relationship between the survival of chicks at the end of the field work and a specialist diet. This indicates that dietary specialization among Great skua pairs on Bjørnøya can have positive effects on fledging success, and hence also breeding success. Master Thesis Barents Sea Bjørnøya Catharacta skua Great skua Iceland Storjo Open archive Norwegian University of Life Sciences: Brage NMBU Barents Sea Norway Bjørnøya ENVELOPE(-67.250,-67.250,-68.151,-68.151) |
institution |
Open Polar |
collection |
Open archive Norwegian University of Life Sciences: Brage NMBU |
op_collection_id |
ftunivmob |
language |
English |
topic |
great skuas Catharacta skua storjo diet diett breeding success hekkesuksess VDP::Mathematics and natural science: 400::Zoology and botany: 480::Ecology: 488 |
spellingShingle |
great skuas Catharacta skua storjo diet diett breeding success hekkesuksess VDP::Mathematics and natural science: 400::Zoology and botany: 480::Ecology: 488 Knutsen, Arnstein Engemyr Diet and breeding success of great skuas (Catharacta skua) on Bjørnøya, Norway |
topic_facet |
great skuas Catharacta skua storjo diet diett breeding success hekkesuksess VDP::Mathematics and natural science: 400::Zoology and botany: 480::Ecology: 488 |
description |
The last 40 years there has been a marked increase in the number of Great skuas (Catharacta skua) in Norwegian territory, and it seems as if the core distribution area is shifting, from Iceland and Shetland, northwards to the Barents Sea region. As a generalist and top predator in the marine ecosystem the Great skua has a broad range of available prey, and their impact on prey species, particularly other seabirds, is poorly understood. The diet of Great skuas during winter is largely unknown, because they live mostly out in the open ocean. As they come to shore to breed, it is possible to obtain an estimate of the diet during the breeding season through analysis of regurgitated pellets. The pellets were collected from a total of 25 Great skua nests in 2008 and 2009. Each nest was visited every fifth day from hatching, and chicks were weighed and measured at each visit. Almost all pellets contained remains from birds while 38 % contained remains from fish. On average, 62 ± 3.7 % of pellets from a pair contained only seabird remains. In 2008, dietary specialization toward seabirds was found in 33 % of the pairs, compared to 62 % in 2009. The overall diet composition did not differ between years, but the proportion of fish in pellets varied between pairs within years. As the breeding season progressed the probability of fish being found in pellets decreased. Body mass, tarsus length and wing length of chicks were negatively correlated with the proportion of pellets with only fish. Hatching dates varied between years, being delayed in 2009. Breeding success was higher in 2008 than in 2009. There was no relationship between the number of chick survival to age 15 days (D (15) = fledging success) and differences in specialization, but in 2009 there was a positive relationship between the survival of chicks at the end of the field work and a specialist diet. This indicates that dietary specialization among Great skua pairs on Bjørnøya can have positive effects on fledging success, and hence also breeding success. |
format |
Master Thesis |
author |
Knutsen, Arnstein Engemyr |
author_facet |
Knutsen, Arnstein Engemyr |
author_sort |
Knutsen, Arnstein Engemyr |
title |
Diet and breeding success of great skuas (Catharacta skua) on Bjørnøya, Norway |
title_short |
Diet and breeding success of great skuas (Catharacta skua) on Bjørnøya, Norway |
title_full |
Diet and breeding success of great skuas (Catharacta skua) on Bjørnøya, Norway |
title_fullStr |
Diet and breeding success of great skuas (Catharacta skua) on Bjørnøya, Norway |
title_full_unstemmed |
Diet and breeding success of great skuas (Catharacta skua) on Bjørnøya, Norway |
title_sort |
diet and breeding success of great skuas (catharacta skua) on bjørnøya, norway |
publisher |
Norwegian University of Life Sciences, Ås |
publishDate |
2010 |
url |
http://hdl.handle.net/11250/186706 |
long_lat |
ENVELOPE(-67.250,-67.250,-68.151,-68.151) |
geographic |
Barents Sea Norway Bjørnøya |
geographic_facet |
Barents Sea Norway Bjørnøya |
genre |
Barents Sea Bjørnøya Catharacta skua Great skua Iceland Storjo |
genre_facet |
Barents Sea Bjørnøya Catharacta skua Great skua Iceland Storjo |
op_source |
25 |
op_relation |
http://hdl.handle.net/11250/186706 |
_version_ |
1766370682227130368 |