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- Pöysä, Hannu, et al.
(author)
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Recovering Whooper Swans do not cause a decline in Eurasian Wigeon via their grazing impact on habitat
- 2018
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In: Journal of Ornithology = Journal fur Ornithologie. - : Springer Science Business Media. - 0021-8375 .- 1439-0361. ; 159, s. 447-455
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Journal article (peer-reviewed)abstract
- The Whooper Swan (Cygnus cygnus) is a good example of successful conservation, with rapidly growing numbers in Fennoscandia in recent decades. To the contrary, Eurasian Wigeon (Mareca penelope) shows a strong negative trend in breeding numbers, which raises conservation concerns. Previous research suggests a causal link between recent population trajectories of the two species. Both preferentially breed on wetlands with abundant horsetail (Equisetum spp.), a plant providing food for Whooper Swan and crucial feeding microhabitat for Eurasian Wigeon broods. We here test predictions based on the hypothesis that grazing on Equisetum by Whooper Swan reduces breeding habitat or breeding habitat quality for Eurasian Wigeon. We use data from 60 lakes in which waterfowl were counted in 1990–1991 and 2016, and Equisetum was mapped in 1990–1991 and 2013–2014. Lakes colonized by Whooper Swan typically had more abundant Equisetum vegetation in the past than lakes not colonized. Lake-specific decrease of Equisetum was not associated with colonization by Whooper Swan. The number of lakes occupied by Eurasian Wigeon decreased, but the decrease was not stronger on lakes colonized by Whooper Swan than on those that were not. Contrary to our prediction, current Eurasian Wigeon abundance was positively associated with Whooper Swan abundance. Moreover, Eurasian Wigeon did not decrease more on lakes from which Equisetum disappeared than on lakes in which there was still Equisetum left. This study does not support the idea that Whooper Swan affects Eurasian Wigeon negatively by grazing on Equisetum.
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| 3. |
- Almgren, Kjell
(author)
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Detail Surveying with GPS
- 1995
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Licentiate thesis (other academic/artistic)abstract
- Abstract In the past ten years, the Global Positioning System (GPS) has revolutionized navigation and positioning at or near the surface of the Earth. Even though it is developed and authorized by the US military forces, it has found a remarkable civilian use. In most uses of GPS, the position accuracy is in the order of metres. To achieve better accuracy (i.e. at the centimetre level), the position determination is somewhat more complicated. Firstly, centimetre accuracy can not be established with a single receiver since too many errors will affect the observations. At least two receivers have to be used, and it is the vector between the receivers which can be accurately determined. Secondly, the integer numbers of whole cycles between each satellite and receiver, called cycle ambiguities, have to be determined. This is a rather complicated procedure, which will delay the time to get a solution. Many papers have been written in the last decade about different methods for resolution of ambiguities as fast as possible and the emphasis of this thesis is put at a description of some of these theories. Ambiguities can either be determined while the receiver is at rest or while it is in motion. The latter case is called ambiguity resolution on the fly and it gives in several ways a more complicated model to solve. To aid the users, this thesis starts with a short description of the system, its history and use today followed by a list of different measuring techniques and the plans for an operational reference system in Sweden. Furthermore, observation techniques and error sources are briefly discussed together with other factors affecting the measurements such as satellite geometry and distances between receivers. In order to validate the theoretical part, some practical tests is carried out and calculated by a RlNEX-based software developed by the author for this special purpose. Parameters such as receiver compatibility, distance between receivers, number of frequencies, number of satellites and multipath effects are investigated. To enable setting out using GPS, a radio link has to send corrections to the roving receiver. This is one of the most interesting utilities for GPS in the future. To enable set outs, a real-time system has to be used. This utility is briefly explained and investigated. From the practical part, some conclusions can be drawn. Firstly, a dual-frequency receiver is superior compared to a single frequency unit when a fast solution is wanted. However, there might be some problems when initializing the second frequency due to encryption. Secondly, the time of ambiguity resolution is highly dependent of the number of satellites in view since redundant satellites give the possibility to reject false solutions at an early stage. Finally, real- time observations will significantly improve the use of GPS since otherwise, there are no possibilities to tell the user in the field when ambiguities are solved.
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| 5. |
- Arzel, Céline, et al.
(author)
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Does changing spring phenology affect short and long distance migratory waterfowl similarly?
- 2010
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In: The abstract book. ; , s. 43-
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Conference paper (other academic/artistic)abstract
- Among waterfowl, most ducks may be considered income breeders due to their small body size and their limited capacity to store energy. Therefore limited access to resources on their breeding grounds is likely to affect their breeding schedule and potentially output. At northern latitudes, ice break up dictates the access to the breeding lakes. An early ice break up allows for early access to the breeding site and its feeding resources, and potentially leading to higher breeding output than after a late ice break up. Short distance migrants are thus more likely to adapt to ice break up conditions than long distance migrants which have to cope with weather conditions en route and local resource accessibility along the migratory path. Using 20 years of data on breeding phenology and success of 3 species of ducks differing in their migratory strategy - Teal Anas crecca, Mallard Anas platyrhynchos and Common Goldeneye Bucephala clangula - in a watershed in Finland, we test the idea that variation in spring phenology affects the reproductive performance of duck species differently depending on their migration pattern.
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| 6. |
- Arzel, Céline, et al.
(author)
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Does changing spring phenology affect short and long distance migratory waterfowl similarly?
- 2010
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Conference paper (other academic/artistic)abstract
- Among waterfowl, most ducks may be considered income breeders due to their small body size and their limited capacity to store energy. Therefore limited access to resources on their breeding grounds is likely to affect their breeding schedule and potentially output. At northern latitudes, ice break up dictates the access to the breeding lakes. An early ice break up allows for early access to the breeding site and its feeding resources, and potentially leading to higher breeding output than after a late ice break up. Short distance migrants are thus more likely to adapt to ice break up conditions than long distance migrants which have to cope with weather conditions en route and local resource accessibility along the migratory path. Using 20 years of data on breeding phenology and success of 3 species of ducks differing in their migratory strategy - Teal Anas crecca, Mallard Anas platyrhynchos and Common Goldeneye Bucephala clangula - in a watershed in Finland, we test the idea that variation in spring phenology affects the reproductive performance of duck species differently depending on their migration pattern.
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| 7. |
- Arzel, Céline, et al.
(author)
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Early springs and breeding performance in two sympatric duck species with different migration strategies
- 2014
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In: Ibis. - : Wiley: 12 months. - 0019-1019 .- 1474-919X. ; 156:2, s. 288-298
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Journal article (peer-reviewed)abstract
- The capacity of migratory species to adapt to climate change may depend on their migratory and reproductive strategies. For example, reproductive output is likely to be influenced by how well migration and nesting are timed to temporal patterns of food abundance, or by temperature variations during the brood rearing phase. Based on two decades (1988–2009) of waterfowl counts from a boreal catchment in southern Finland we assessed how variation in ice break-up date affected nesting phenology and breeding success in two sympatric duck species, Mallard Anas platyrhynchos and Eurasian Teal Anas crecca. In Fennoscandia these species have similar breeding habitat requirements but differ in migration distance; Teal migrate roughly seven times as far as do Mallard. Annual ice break-up date was used as a proxy of spring ‘earliness’ to test the potential effect of climate change on hatching timing and breeding performance. Both species were capable of adapting their nesting phenology, and bred earlier in years when spring was early. However, the interval from ice break-up to hatching tended to be longer in early springs in both species, so that broods hatched relatively later than in late springs. Ice break-up date did not appear to influence annual number of broods per pair or annual mean brood size in either species. Our study therefore does not suggest that breeding performance in Teal and Mallard is negatively affected by advancement of ice break-up at the population level. However, both species showed a within-season decline in brood size with increasing interval between ice break-up and hatching. Our study therefore highlights a disparity between individuals in their capacity to adjust to ice break-up date, late breeders having a lower breeding success than early breeders. We speculate that breeding success of both species may therefore decline should a consistent trend towards earlier springs occur.
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| 8. |
- Arzel, Céline, et al.
(author)
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Early springs and breeding performance in two sympatric duck species with different migration strategies
- 2014
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In: Ibis. - : Wiley-Blackwell Publishing Ltd. - 0019-1019 .- 1474-919X. ; 156:2, s. 288-298
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Journal article (peer-reviewed)abstract
- The capacity of migratory species to adapt to climate change may depend on their migratory and reproductive strategies. For example, reproductive output is likely to be influenced by how well migration and nesting are timed to temporal patterns of food abundance, or by temperature variations during the brood rearing phase. Based on two decades (1988–2009) of waterfowl counts from a boreal catchment in southern Finland we assessed how variation in ice break-up date affected nesting phenology and breeding success in two sympatric duck species, Mallard Anas platyrhynchos and Eurasian Teal Anas crecca. In Fennoscandia these species have similar breeding habitat requirements but differ in migration distance; Teal migrate roughly seven times as far as do Mallard. Annual ice break-up date was used as a proxy of spring ‘earliness’ to test the potential effect of climate change on hatching timing and breeding performance. Both species were capable of adapting their nesting phenology, and bred earlier in years when spring was early. However, the interval from ice break-up to hatching tended to be longer in early springs in both species, so that broods hatched relatively later than in late springs. Ice break-up date did not appear to influence annual number of broods per pair or annual mean brood size in either species. Our study therefore does not suggest that breeding performance in Teal and Mallard is negatively affected by advancement of ice break-up at the population level. However, both species showed a within-season decline in brood size with increasing interval between ice break-up and hatching. Our study therefore highlights a disparity between individuals in their capacity to adjust to ice break-up date, late breeders having a lower breeding success than early breeders. We speculate that breeding success of both species may therefore decline should a consistent trend towards earlier springs occur.
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