| 61. |
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| 62. |
- Olsson, Camilla, et al.
(författare)
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Field preference of Greylag geese Anser anser during the breeding season
- 2017
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Ingår i: European Journal of Wildlife Research. - 1612-4642 .- 1439-0574. ; 63
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Tidskriftsartikel (refereegranskat)abstract
- Few studies address food preference of geese on agricultural land (utilization related to availability) and only a handful so for the breeding season. We studied Greylag geese Anser anser during the breeding season in an intensively farmed area in southern Sweden. Few of 22 available field types were truly preferred. Pastureland was the most consistently preferred, by goslings (with parents) as well as by nonbreeders. In some sampling periods, goslings also preferred grazed hay, ley, and carrot fields. Non-breeders exploited a greater variety of crops/fields, feeding also on barley, fallow, grazed hay, lettuce, oats, potatoes, and carrots. Most of these crops were preferred on at least one sampling occasion, except for fallow, grazed hay, and wheat, which were always used less than expected from availability. GLMs revealed that goslings rested more than they fed and preferred shorter vegetation before higher. Moreover, goslings occurred in higher densities in younger age classes than in older and preferred nearshore areas. In contrast, density of non-breeders was only related to field type and sampling occasion (higher densities as the season progressed). The maximum number of broods observed (106) implies a breeding success of 34% based on311 active nests earlier in the season. Brood size decreased from 3.5 to 2.1 during the study period. Our study shows that goose management during the breeding season should consider goslings and their parents separately from non-breeders, and it implies little potential conflict between Greylag geese and agriculture during the breeding period.
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| 63. |
- Olsson, Camilla, 1991-, et al.
(författare)
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Long-distance and local movements of greylag geese in present-day agricultural landscapes
- 2018
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Ingår i: 18th Conference of Goose Specialist Group. - : Marine Institute of Klaipeda University. - 9789955189794 ; , s. 77-
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Konferensbidrag (refereegranskat)abstract
- Recent changes in environmental conditions together with increasing goose populations have completely changed the ballgame for geese in Europe. To better understand their current distribution and foraging patterns, this project will explore how geese utilize the agricultural landscape, with focus on their movements, field selection and foraging patterns. We fitted 199 Greylag geese with neck-collars and 64 with GPS transmitters at 5 locations in Sweden. The tagged geese will be used for studying movement patterns at a field-tofield level. However, the GPS transmitters also deliver data that can be used together with re-sightnings of neck-collared geese to unravel large-scale movement patterns of the Swedish Greylag goose population. Preliminary results from GPS positions received June--November 2017 indicate a varation in migration patterns and wintering grounds, depending on the origin of the geese. Geese breeding and molting in the southern parts of Sweden seem to migrate shorter distances, and have spent most of their time during the autumn months in Denmark, or in the southernmost parts of Sweden, while the geese marked farther north migrated earlier and moved longer distances, with the majority spending the autumn in Germany and the Netherlands.
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| 64. |
- Petersen, Robert C., et al.
(författare)
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Influence of velocity and food availability on catchnet dimensions of Neureclipsis bimaculata (Trichoptera: Polycentropodidae)
- 1984
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Ingår i: Holarctic Ecology. - 0105-9327. ; 7:4, s. 380-389
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Tidskriftsartikel (refereegranskat)abstract
- Larvae of Neureclipsis bimaculata (Trichoptera: Polycentropodidae) construct elaborate catchnets in lotic habitats to trap small drifting invertebrate prey. Three populations located at two oligotrophic and one eutrophic site were studied in southern Sweden. Measurements were made of larval weight, net size, seston quality and quantity, and stream velocity.Neureclipsis larvae alter their net dimensions in response to both velocity and seston concentration. This was determined by comparing net structure and seston at the three locations. Larvae from the eutrophic, high quality seston site attain a significantly (P < 0.001) heavier instar V dry weight, spin a smaller catchnet, filter a volume of water dependent on body size, and slightly alter their catchnet dimensions with velocity. Larvae from the two oligothrophic sites are significantly smaller than those from the eutrophic site, spin a larger net at comparable velocities, filter a larger volume of water at comparable weights, and alter net dimensions with velocity.Estimates of silk production indicate that the net cost is minimized by spinning a very fine silken strand and by adding silk over a period of time. The cost while large is offset by a large capture rate of prey.The structure of Neureclipsis nets appears to be the result of a trade-off between maximizing food capture and minimizing hydraulic stress on the net.
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| 65. |
- Pöysä, Hannu, et al.
(författare)
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Changes in species richness and composition of boreal waterbird communities : a comparison between two time periods 25 years apart
- 2019
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Ingår i: Scientific Reports. - : Nature Publishing Group: Open Access Journals - Option C / Nature Publishing Group. - 2045-2322. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- Global measures of biodiversity indicate consistent decline, but trends reported for local communitiesare more varied. Therefore, we need better understanding of mechanisms that drive changes in diversity of local communities and of differences in temporal trends between components of local diversity, such as species richness and species turnover rate. Freshwater ecosystems are vulnerable to multiple stressors, and severe impacts on their biodiversity have been documented. We studied species richness and composition of local boreal waterbird communities in 1990/1991 and 2016 at 58 lakes distributed over six regions in Finland and Sweden. The study lakes represented not only local trophic gradients but also a latitudinal gradient in the boreal biome. While species richness tended to be lower in 2016 than in 1990/1991, species turnover was relatively high. Within foraging guilds, local species richness of diving ducks and surface feeding waterbirds decreased, whereas that of large herbivores increased. The number of species gained in local communities was higher in lakes with rich vegetation than in lakes with sparse vegetation. Conservation of boreal freshwater ecosystems would benefit from recognizing hat large-scale environmental changes can affect local diversity via processes operating atfiner scales.
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| 66. |
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| 67. |
- Sjöberg, Kjell, et al.
(författare)
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Born to cope with climate change? : experimentally manipulated hatching time does not affect duckling survival in the mallard Anas platyrhynchos
- 2011
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Ingår i: European Journal of Wildlife Research. - 1612-4642 .- 1439-0574. ; 57:3, s. 505-516
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Tidskriftsartikel (refereegranskat)abstract
- Two main hypotheses proposed to explain the seasonal decline in reproductive performance in birds are (1) deterioration of environmental conditions and (2) lower parental quality of late breeders. Previous experimental work addressing these hypotheses generally have problematic biases pertaining to delay of hatching, costs of re-laying and incubation, as well as variation in the quality of eggs, territories, offspring and parental traits. We address these biases in an experimental test of the timing hypothesis (i.e. (1) above) in a precocial bird. Using a 2-year cross-over design and game-farm mallard (Anas platyrhynchos) eggs originating from a number of hens and a standardised delay procedure, we introduced early and late broods with a foster female onto boreal oligotrophic lakes and monitored subsequent duckling survival. Standardised invertebrate sampling was done concurrently to get a measure of lake-level abundance of aquatic prey, a likely causative agent of putative seasonal difference in duckling survival. Survival data and covariates (duckling age; days) were analysed by an information theoretic approach. There was no effect of treatment (i.e. manipulation of hatching date) on duckling survival, which was higher in 2005 than in 2004. In contrast to observational studies from more seasonal wetlands, our experiment demonstrates that duckling survival on boreal lakes was not affected by a 12-day delay in hatching date. Since we did not find any consistent trends in abundance of aquatic prey, i.e. neither clear peaks nor differences between treatment periods, we hypothesise that moderate climate change has minor effects on resource abundance and hence also on mallard duckling survival in boreal environments.
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| 68. |
- Sjöberg, Kjell, et al.
(författare)
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Density dependent survival of mallard ducklings in boreal lakes : a field experiment
- 2003
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Konferensbidrag (refereegranskat)abstract
- From earlier field studies and experiments we have found that the nutrient status of lakes in the boreal region of northern Europe might influence the production of ducklings among dabbling ducks. For ducks, this might be important in the choice of breeding strategy. In this study we created a 2-year cross-over field experiment in northern Sweden where mallard hens and broods (10 ducklings) were introduced on 10 oligotrophic lakes (i.e. poor lakes) in two different densities; 4 hens with broods (high density) on 5 lakes and 1 hen with brood (low density) on the remaining 5 lakes. The adult ducks were wild birds, caught and brought to a game farm where they hatched their eggs. Within a few days after hatching they were released on the lakes in the beginning of June when wild mallards have their hatching peak. After introductions the survival of broods, ducklings and hens were monitored daily the first 12 days and then every third day until day 24. The second year there was a switch of treatments in the lakes. The results after one year indicate that the survival rates of broods, ducklings and hens are density dependent. In lakes with high densities of introduced mallards the survival rates was higher compared to low density lakes.
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| 69. |
- Sjöberg, Kjell, et al.
(författare)
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Experimentally manipulating early and late breeding in mallards
- 2006
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Konferensbidrag (refereegranskat)abstract
- We used imprinted ducklings and wing-clipped female mallards with broods as a complement to observational field studies. Because mallard ducklings search for food by themselves, the food searching efficiency and behaviour of imprinted ducklings and ducklings together with a wing-clipped female ought to reflect the general conditions in the lake they search for food, if not in a strict quantitative way, at least it should reflect the relative differences in conditions for the lakes used in the experiments. We were interested in why mallards start breeding so early and how climate change might influence early and late breeding ducks. In a cross over experiment conducted 2004 and 2005, we studied the result of releasing two sets of female mallards with ducklings. The first one was done close to the same time as wild mallards normally started their breeding season in the region. The other set of broods was delayed 12 days. The eggs for the late release of ducklings were kept at low temperature and 12 days later they were put under sitting mallard females. The hens and broods were subsequently released with an interval of 12 days (one brood in each of 10 lakes in the first release, and the late release in ten other lakes). The next year the lakes were reversed. Survival of ducklings was followed every day during the first 12 days, and later every 4 days up till 24 days. Invertebrates in the lakes were sampled as well (of both benthic and pelagic origins). The data are analyzed in relation to food abundance during the early and late part of the two breeding seasons.
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| 70. |
- Söderquist, Pär, et al.
(författare)
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Effects of released farmed mallards on species richness of breeding waterbirds and amphibians in natural, restored and constructed wetlands
- 2021
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Ingår i: Wildlife Biology. - 0909-6396 .- 1903-220X. ; 2021, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- Common practices in current game management are wetland restoration and creation, as well as releases of quarry species. We studied the impact of releases of mallard ducklings on species richness of wild waterbirds and amphibians on three types of wetlands: natural, constructed and restored. Data on species richness, macrophyte cover and water characteristics (total phosphorous and pH) were collected at 32 sites in an agricultural landscape in southern Sweden. In total, 14 species of waterbirds were recorded, ranging from zero to seven per wetland and survey. Amphibians were present in 24 of the 32 wetlands; in total five species were found, ranging from zero to three per wetland. By using generalized linear modelling we found that wetland type best predicted waterbird species richness. Constructed wetlands had significantly more waterbird species, regardless of whether they were used for mallard releases or not. There were breeding amphibians in 62% of natural, 100% of restored and 77% of constructed wetlands. Breeding amphibians were present in 84% of wetlands without, and in 62% of wetlands with releases. However, included variables did not explain amphibian species richness in the wetlands. Releasing large numbers of mallards on a wetland and providing food ad libitum is likely to affect water quality, nutrient availability and predation pressure. Indeed, phosphorous levels were significantly higher in release wetlands, but no differences were found between wetland types.This means that mallard releases may increase nutrient loads in environments that are already eutrophied. However, in our study system releases did not influence species richness of waterbirds and amphibians locally. Constructing wetlands for mallard releases can thus have positive local effects on species richness.
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