Karsten Laursen

Factors affecting escape distances of staging waterbirds

Abstract Escape distances (EDs) have been used to study sensitivity of waterbirds to different sources of disturbance, to design reserves for waterbirds, and to define eco-targets for the Wadden Sea management plan. However, the use of ED as an index of sensitivity has been criticised because it can be highly variable. Although some factors affecting variation in the EDs of species have been studied, there is still a need for further analysis of factors that may affect it. In this study, we analysed the EDs of 19 waterbird species (geese, ducks, waders and gulls) exposed to a walking person (N = 1,371) during autumn and spring 1980–1984 under controlled conditions in the Danish Wadden Sea. We analysed how EDs varied between species in relation to body mass and hunting and within species in relation to flock size and weather conditions. EDs increased significantly with species body mass, and quarry species (dabbling ducks, curlew Numenius arquata, golden plover Pluvialis apricaria, common gull Larus canus and black-headed gull L. ridibundus) had longer EDs than non-quarry species when corrected for body mass. EDs increased with flock size in dabbling ducks and nine waterbird species in autumn and two waterbird species in spring. In autumn an inverse relationship was found between visibility and ED for dabbling ducks and five wader species. An inverse relationship was also found between wind force and ED for three wader species, but this relationship was found to be positive for two wader species. Several factors affected EDs, and EDs measured in one region may not apply to other regions. Based on our results it is recommended that reserve borders (core area and buffer zones) are designed to take into account mean EDs as well as variation in EDs, with respect to local disturbance levels, flock size and target species.

Accuracy of ‘total counts’ of waterbirds from aircraft in coastal waters

Abstract Estimating ‘total counts’ of waterbirds from aircraft is a widely used survey method, and we assessed the effectiveness of this method for geese, ducks, waders and gulls by comparing the results of counts from aircraft with ground counts in the Danish Wadden Sea during 1984–1998. In total, 47 counts were carried out in 12 counting sites and the results were compared for 18 waterbird species, which varied in abundance, flock size and degree of aggregation. Significantly greater numbers of waterbird species were identified from the ground than from aircraft (mean number: 16.1 vs 10.6 species). Depending on the accuracy of aerial counts compared to ground counts, the species were divided into three categories: a) brent goose Branta bernicla, shelduck Tadorna tadorna, mallard Anas platyrhynuchos, eider Somateria mollissima and oystercatcher Haematopus ostralegus had a high level of correspondence between densities obtained from ground and aerial counts (detection rate of >80% with no statistical difference between slopes and intercepts of the observed regression lines and the ideal lines (x=y), differences between mean densities of ground and aerial counts being <15%); b) wigeon Anas penelope, teal A. crecca, grey plover Pluvialis squatarola, dunlin Calidris alpine, bar-tailed godwit Limosa lapponica, black-headed gull Larus ridibundus, common gull L. canus, herring gull L. argentatus, great black-backed gull L. marinus and common/arctic tern Sterna hirundo and S. paradisaea had a medium correspondence between densities obtained from the two platforms (detection rate of >55% with differences between the mean densities of ground and aerial counts of <30%; and c) redshank Tringa totanus, greenshank T. nebularia arquata and curlew Numenius arquata had a low correspondence between the densities obtained from the two platforms (detection rate of <55% and differences between the mean densities of ground and aerial counts of >30%). Species with a high and medium level of correspondence between the two platforms are mostly species that are numerous, of widespread occurrence, and found in large flocks. Species with a low correspondence are minority species, occurring scattered or in small flocks. We recommend to supplement aerial counts with ground counts at sites with mixed flocks of more dabbling duck species present to increase the accuracy of the count results.

Long-Term Changes in Nutrients and Mussel Stocks Are Related to Numbers of Breeding Eiders Somateria mollissima at a Large Baltic Colony

Background The Baltic/Wadden Sea eider Somateria mollissima flyway population is decreasing, and this trend is also reflected in the large eider colony at Christiansø situated in the Baltic Sea. This colony showed a 15-fold increase from 1925 until the mid-1990s, followed by a rapid decline in recent years, although the causes of this trend remain unknown. Most birds from the colony winter in the Wadden Sea, from which environmental data and information on the size of the main diet, the mussel Mytilus edulis stock exists. We hypothesised that changes in nutrients and water temperature in the Wadden Sea had an effect on the ecosystem affecting the size of mussel stocks, the principal food item for eiders, thereby influencing the number of breeding eider in the Christiansø colony. Methodology/Principal Finding A positive relationship between the amount of fertilizer used by farmers and the concentration of phosphorus in the Wadden Sea (with a time lag of one year) allowed analysis of the predictions concerning effects of nutrients for the period 1925–2010. There was (1) increasing amounts of fertilizer used in agriculture and this increased the amount of nutrients in the marine environment thereby increasing the mussel stocks in the Wadden Sea. (2) The number of eiders at Christiansø increased when the amount of fertilizer increased. Finally (3) the number of eiders in the colony at Christiansø increased with the amount of mussel stocks in the Wadden Sea. Conclusions/Significance The trend in the number of eiders at Christiansø is representative for the entire flyway population, and since nutrient reduction in the marine environment occurs in most parts of Northwest Europe, we hypothesize that this environmental candidate parameter is involved in the overall regulation of the Baltic/Wadden Sea eider population during recent decades.

Assessment of Blue Mussel Mytilus edulis Fisheries and Waterbird Shellfish-predator Management in the Danish Wadden Sea

We assessed the blue mussel Mytilus edulis fishery management scheme introduced in 1994 in the Danish Wadden Sea that regulate fishing vessels, fishery quota, set-aside for mussel-eating birds and established zones closed to mussel fishery. The results showed (i) a reduction in the blue mussel biomass and mussel bed areas in zones closed to fishery, (ii) decrease in eiders Somateria mollissima numbers and increase or stable numbers for oystercatcher Haematopus ostralegus and herring gull Larus argentatus and (iii) that energy estimations based on ecological food requirements for the mussel-eating birds should be at least three times larger, than the amount set-aside in the mussel management scheme. It is concluded that the mussel management scheme had been unable to stabilize or increase the blue mussel stocks and to secure stable or increasing numbers for all target bird species. Thus, it is recommended to revise the present blue mussel management scheme in the Danish Wadden Sea, to continue and improve mussel stock and bird surveys, and to consider novel studies of the mussel-eating birds’ energetics for improved set-aside estimates and future assessments.

Current and Potential Threats to Nordic Duck Populations — A Horizon Scanning Exercise

We review the current and future threats to duck populations that breed, stage, moult and/or winter in the Nordic countries. Migratory duck species are sensitive indicators of their changing environment, and their societal value confirms the need to translate signals from changes in their distribution, status and abundance into a better understanding of changes occurring in their wetland environments. We used expert opinion to highlight 25 major areas of anthropogenic change (and touch briefly on potential mitigation measures through nature restoration and reserve management projects) that we consider key issues likely to influence Nordic duck populations now and in the near future to stimulate debate, discussion and further research. We believe such reviews are essential in contributing to development of successful management policy as well as stimulating specific research to support the maintenance of duck species in favourable future conservation status in the face of multiple population pressures and drivers.

Fertilizer Leakage to the Marine Environment, Ecosystem Effects and Population Trends of Waterbirds in Denmark

Abstract Leakage of nutrients from farmland to freshwater and marine environments results in fertilization that increases primary production with cascading effects in the ecosystem. Leakage of fertilizers may initially increase availability of food for primary and secondary consumers, although part of this effect may subsequently be followed by a reduction in food abundance caused by hypoxia. We hypothesized that leakage of nutrients from farmland increased primary and secondary production and subsequently the population size of waterbirds. The amount of phosphorus in the marine environment in Denmark during 1975–2010 increased with fertilizer use on farmland and this effect was stronger when winter precipitation was high. Leakage of fertilizer had ecosystem effects on phytoplankton, zooplankton, and ultimately biodiversity in the marine environment. We found linear relationships between fertilizer use and population size of breeding and wintering waterbirds, with additional quadratic relationships with fertilizer use and linear effects of temperature. The linear effect of fertilizer use depended on the diet of waterbirds with stronger effects in herbivorous and piscivorous species than in species eating benthos. These findings have implications for management of waterbird populations because a reduction in fertilizer use should result in increasing populations of herbivores and piscivores.

Car traffic along hedgerows affects breeding success of Great Tits Parus major

Capsule In hedgerows near roads with fast and frequent traffic, the mortality of Great Tit Parus major broods was higher than in hedgerows with less traffic and hedgerows with no disturbance.

Hunting from motorboats displaces Wadden Sea eiders Somateria mollissima from their favoured feeding distribution

Abstract Hunting of eiders Somateria mollissima from motorboats is common in Danish marine waters, and to reduce hunting pressure on eiders and other diving duck species in Denmark, motorboat hunting was banned within 42 marine sites covering an area of 2,934 km2, although the effects of this regulation have to date not been examined. Our case study analyses the effects of excluding motorboat hunting from an area of 682 km2 of the Danish Wadden Sea (hereafter the ‘Study Area’) which also supported a large area of blue mussel beds, the preferred food for eiders. Our study covered the entire Danish Wadden Sea (total area 1,225 km2) during the hunting seasons (October-February) of 1980–2003 using 85 aerial surveys of eiders and motorboats used by hunters. Eider numbers increased by 56% in the Study Area following the ban on motorboat hunting despite a 50% reduction in the eider flyway population over the same period. There was a significant negative relationship between the density of hunter motorboats and that of eiders on a small geographical scale (1.8–2.5 km). Motorboat hunting in the Study Area also affected eider distribution at larger geographical scales (4–12 km), displacing eiders from the Study Area offshore from the Wadden Sea into the North Sea. Following the ban on motorboat hunting, most eiders occurred in the Study Area. Winter (21 December-31 January) body condition of eiders was greater in the Study Area than the body condition of eiders in the Offshore Area during autumn (20 October-20 December). Eider abundance relative to blue mussel biomass significantly increased after motorboat hunting was banned in the Study Area, but there was no such change during winter after the hunting ban. Since the ban on motorboat hunting in the Study Area, eider numbers throughout the entire Danish Wadden Sea seem to be regulated by total blue mussel biomass.

The integrated programme for commodities

Abstract The gains from stabilizing commodity prices are likely to be rather small. The distribution of such gains among producers and consumers is uncertain. Compensatory financing is a cheaper and more effective means of dealing with the problem of fluctuating export earnings. The developing countries have some scope for cartel pricing in the tropical beverages, but hardly in any of the other ten ‘core’ commodities. A common fund is not an economically essential feature of the commodity programme, and will not lead to savings in terms of resources. As a group the ‘core’ commodities do not face serious import barriers in the developed countries. In sum, the integrated commodity programme, if implemented, may produce some, but probably rather limited benefits to the developing countries. Some of these could be at the cost of the developed countries, and it is not clear if the whole scheme is a positive-negative-, or zero-sum game.

The feeding ecology and distribution of Common Coots Fulica atra are affected by hunting taking place in adjacent areas

Capsule Birds using a shooting-free area are markedly influenced by close-by shooting. Aims To examine changes in distribution, feeding ecology and food supply of Common Coots before and after the beginning of hunting on adjacent salt marshes. Methods Common Coots were counted and mapped in October and November, i.e. before and after the start of hunting. In both months, activity budgets for the Coots were determined. To quantify the food supply, macrophyte biomass samples and depth measures were taken along four parallel transects in the areas used by the birds for foraging. Results Before the start of hunting in October, 45% of all Coots were observed within 400 m of the hunting area. In November (when hunting had started) the birds redistributed themselves away from the hunting area, reducing the number of birds within 400 m to 5%. Because of this redistribution, Coots were observed in deeper-water areas of the lagoon during November compared to October, and foraging by diving increased significantly from 14 to 35%. The average biomass of submerged macrophytes in the lagoon was 155.01 g dry weight/m2, which corresponds to a total of 302 250 kg in the whole lagoon. The food requirement of each Coot is 52.3 g/day, which is equivalent to 104 kg/day for the autumn peak number at this lagoon (1989 Coots). Conclusion Hunting disturbance outside the shooting-free area displaced Coots from their preferred feeding grounds inside the reserve, causing their redistribution into sub-optimal habitat at greater water depths where Coot feeding costs were higher. Submerged macrophyte biomass showed that food was abundant in the area and therefore unlikely to be a limiting factor that influenced the redistribution of Coots during the shooting season. We suggest that at this particular site the feeding ecology of Coots could be improved by incorporating an appropriate buffer zone between the protected area and the hunted area. This may be of value not only to Coots, but also for other bird species that exploit shallow water.