| 1. |
- Ekroos, Johan, et al.
(författare)
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Declines amongst breeding Eider Somateria mollissima numbers in the Baltic/Wadden Sea flyway
- 2012
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Ingår i: Ornis Fennica. - 0030-5685. ; 89:2, s. 81-90
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Tidskriftsartikel (refereegranskat)abstract
- We report on the status of the Baltic/Wadden Sea flyway Eider population based on trends in breeding and wintering numbers throughout the region, supplemented by changes in the sex ratio and proportion of young Eiders as monitored in the Danish hunting bag. At the flyway scale, total numbers of breeding pairs decreased by 48% during 2000-2009, after relatively stable breeding numbers in 1991-2000. The majority of the population nest in Finland and Sweden, where the number of breeding pairs has halved over the same period. After initial declines in winter numbers between 1991 and 2000, during 2000-2009, national wintering numbers increased in the Baltic Sea, but decreased in the Wadden Sea. The annual proportion of adult females in the Danish hunting bag data decreased from ca. 45% (1982) to ca. 25% (2009) and simultaneously the proportion of first-winter birds fell from ca. 70% to ca. 30%, indicating dramatic structural changes in the Danish wintering numbers. These results suggest that the total flyway population will experience further declines, unless productivity increases and the factors responsible for decreasing adult female survival are identified and ameliorated. We discuss potential population drivers and present some recommendations for improved flyway-level monitoring and management of Eiders.
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| 2. |
- Ekroos, Johan, et al.
(författare)
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Philopatric predisposition to predation-induced ecological traps: habitat-dependent mortality of breeding eiders
- 2012
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Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 1432-1939 .- 0029-8549. ; 170:4, s. 979-986
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Tidskriftsartikel (refereegranskat)abstract
- Because population size is sensitive to changes in adult survival, adult survival may be buffered against environmental variability. Philopatry may be adaptive in changing environments, but it could also constrain breeding habitat selection under changing conditions such as shifting predation regimes. Habitat preference and quality could become decoupled in long-lived philopatric species that evolved in stable environments when suddenly faced by increased adult predation risk, as dispersal may be triggered by past reproductive failure. We evaluated whether the Baltic eider (Somateria m. mollissima) population may currently face a predation-induced ecological trap. Eiders are philopatric and nest on open and forested islands. We hypothesized that open-nesting females would be disproportionately affected by increased predation. We compared female annual survival in these two habitats in 1996-2010. We also tested for effects of time trends, winter severity (NAO), female body condition, and habitat-specific predation pressure on survival. Our results revealed the lowest survival recorded for this species (I broken vertical bar = 0.720), and survival on open islands was significantly lower (I broken vertical bar = 0.679) than on forested islands (I broken vertical bar = 0.761). Nonetheless, only 0.7 % of females changed breeding habitat type despite ample availability of alternative islands, and breeding phenology in both habitats was similar. Female survival increased with body condition, while it was unrelated to winter climate and stable over time. Open islands had a higher predation pressure on incubating females. Breeding philopatry results in a predator-mediated ecological trap for open-nesting eiders. Our results contribute to explaining the drastic decline of the Baltic eider population.
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| 3. |
- Hillström, Lars, et al.
(författare)
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Is asynchronous hatching adaptive in herring gulls ( Larus argentatus )?
- 2000
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Ingår i: Behavioral Ecology and Sociobiology. - : Springer Science and Business Media LLC. - 0340-5443 .- 1432-0762. ; 47:5, s. 304-311
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Tidskriftsartikel (refereegranskat)abstract
- Hatching asynchrony commonly induces a size hierarchy among siblings and the resultant competition for food between siblings can often lead to starvation of the smallest chicks within a brood. We created herring gull (Larus argentatus) broods with varying degrees of hatching synchrony by manipulating the timing of incubation while maintaining the originally laid eggs. The degree of hatching asynchrony affected sibling size hierarchy at the time of hatching of the last-hatched ”c-chick.” In unmanipulated broods, there was no disadvantage of being a c-chick. However, when asynchrony was experimentally increased, we found reduced survival of the c-chick only in the exaggerated asynchronous experimental group. The effects were observable only during the first 10 days of chick life. We recorded no cases of the chicks dying of starvation. Furthermore, behavioral observations indicated that there was no sibling competition, and no selective feeding of larger sibs in the study colony. We propose that the observed lower survival rates of c-chicks in exaggerated asynchronous broods resulted from their lesser motor abilities, affecting their chances of escaping predators. Fledging success for the whole colony was generally high and almost half of all pairs fledged all three chicks, which is indicative of a good feeding environment. We argue that normal hatching asynchrony is a favorable solution in a good feeding environment, but that increased asynchrony reduces breeding success. We do not view asynchrony in the herring gull as an adaptation for brood reduction and propose instead that it may come about because there has been selection for incubation to start before clutch completion.
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| 4. |
- Larsson, Kjell, et al.
(författare)
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Effects of an extensive Prymnesium polylepis bloom on breeding eiders in the Baltic Sea
- 2014
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Ingår i: Journal of Sea Research. - : Elsevier. - 1385-1101 .- 1873-1414. ; 88, s. 21-28
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Tidskriftsartikel (refereegranskat)abstract
- The effects of an extensive bloom of the potentially toxic Prymnesium polylepis (Haptophyta) on breeding eiders (Somateria mollissima) in the Baltic Sea were analysed. Increasing abundances of the alternate stage P. polylepis was detected by a marine monitoring programme in the autumn 2007. The bloom peaked between March and May 2008 in the southern, central and northwestern Baltic Proper and abundances of up to 5 x 106 cells l- 1 were recorded. At several sites P. polylepis constituted between 30 and 90% of the total phytoplankton biovolume. The flagellate was only recorded in low numbers in the northeastern Baltic Proper and Gulf of Finland. The abundances were low in 2007, 2009 and 2010. In 28 eider colonies situated in the southern and central Baltic Proper, sharp and synchronous declines in the number of nesting eiders were observed from 2007 to 2008. In colonies on Gotland in the central Baltic Proper, a 76% decrease, from 6650 nests to 1620 nests, was followed by increases in 2009 and 2010, although not up to numbers observed in 2007. At Utklippan and Ertholmene in the southern Baltic Proper, the observed decreases of 55%, from 144 to 65 nests, and 36%, from 1660 to 1060 nests, respectively, between 2007 and 2008, were followed by increases in 2009 and 2010 up to the level observed in 2007. By contrast, no general decline of the number of nesting eiders was observed from 2007 to 2008 in 75 colonies in the northeastern Baltic Proper and Gulf of Finland. Hence, the spatial distribution of the P. polylepis bloom in 2008 closely matched the observed distribution of extensive non-breeding of female eiders. We suggest that the intensive spring bloom of P. polylepis, either through a toxic or non-toxic pathway, affected the main benthic food of eiders, i.e. blue mussels (Mytilus trossulus x Mytilus edulis), at pre-breeding foraging sites close to the breeding sites, and, subsequently, the body condition of adult female eiders and their breeding propensity.
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| 5. |
- Westerbom, Mats, et al.
(författare)
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Population Dynamics at the Range Margin : Implications of Climate Change on Sublittoral Blue Mussels (Mytilus trossulus)
- 2019
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Ingår i: Frontiers in Marine Science. - : Frontiers Media SA. - 2296-7745. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Examining changes in abundance and demographic rates at species distribution margins may provide the first signs of broader species responses to environmental change. Still, the joint impact of space and time have remained relatively unstudied in most marginal regions. In order to examine the influence of climate variability on mussel distribution patterns, we monitored three sublittoral and marginal blue mussel (Mytilus trossulus) populations, spaced along a salinity gradient. Densities and biomasses peaked toward the saltier parts of the study area and showed relatively larger variations toward the low saline edge. Temporally, the areas showed a consistent increase in abundance after a synchronized large-scale recruitment event, which was followed by a decline in population size, occurring much faster toward the very range edge. Salinity, temperature, winter severity, and wave exposure explained most of the spatiotemporal variation in mussel abundances and adults showed positive effects on recruit abundance. We show empirically that the dynamics of edge populations are not driven by large changes in climate variables but that small spatial and temporal changes in key environmental variables have large and non-linear population level effects. Our results also show that fluctuating recruitment is a key factor for population stability affecting the storage potential of marginal populations, which dramatically decrease toward the edge. Our study provides a window into future population patterns and processes that drive marginal mussel populations in an altered sea characterized by rising temperature and declining salinity.
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