Common Scoter Melanitta Nigra Research Articles

Breeding Common Scoters Melanitta nigra in Scotland’s Flow Country: a population in decline despite productivity being stable

ABSTRACT Capsule The breeding productivity of the Common Scoter population in Scotland’s Flow Country remained relatively stable during a 44% population decline in Britain and Ireland. Aim To investigate breeding productivity changes in the eastern Flow Country’s Common Scoter population over 22 years and identify possible threats and causes of change during a period of national population decline. Methods Common Scoters from 32 breeding sites were surveyed annually between 2002 and 2023. Each site was visited two to three times in May (pre-nesting period) and two to three times in July and August (post-hatching period) to record the numbers of adult and juvenile Common Scoters. Results Between 2002 and 2023, whilst the Common Scoter population declined (approximately 44% from 27 to 15 breeding pairs) across the study area, breeding productivity (defined as large ducklings per female) remained stable, averaging 0.44 (range of annual means 0.00–1.06) large ducklings per female. The number of small ducklings per female also remained relatively stable. A year of higher breeding productivity did not result in an increase in the number of breeding females in the following years, suggesting that the cause of the population decline lies away from the breeding region. Conclusion Breeding productivity needs to increase, and poor breeding seasons need to be prevented to help maintain this population. The causes of the Common Scoter’s decline away from the breeding area need to be resolved to prevent local extinction. This could be assisted with the removal of non-native forestry plantations in the area, which has been observed to benefit other ground-nesting species by alleviating predation pressure, and by maintaining lake habitat quality, as reflected in shallow water and abundant large invertebrates.

Recent increase in annual survival of nesting female Common Scoter Melanitta nigra in Iceland

Despite their unfavourable conservation status, little is known about the population status, trends and demography of Common Scoter Melanitta nigra. Capture-mark-recapture (CMR) data from 154 recapture events of 88 individually marked breeding female Common Scoter Melanitta nigra in the Aðaldalur valley, northeast Iceland, during 2009–2018 generated an estimated annual apparent survival probability of 0.848 (95% CL 0.775–0.901). This exceeds a previous Icelandic CMR estimate (0.783, 95% CL 0.715–0.839) from nesting females during 1925–1958 at the nearby Mývatn (45 km to the SSE) when the population was declining at c. 2% per annum. Spring count data from Mývatn show that numbers of male and female Common Scoter at this important breeding site (thought to constitute over 80% of the Icelandic breeding national total) have increased by c. 1.8% per annum since 1974, and by 4–5% per annum since 2009. A population model showed that the observed change in survival corresponded well with the observed change in population growth rate. We reflect on causes of the increase in mean expected lifespan (from 4.1 to 6.1 years) between 1925–1958 and 2009–2018, speculating whether changes in food supply and/or reduction in gill-net fishing on Mývatn in the last 25 years could have been contributing factors to explain recent increases in breeding females there. An alternative, not necessarily mutually exclusive explanation could also be that the dramatic declines in chronic marine oil spill pollution in European waters could have contributed to higher recent female annual survival. While fully recognising the challenges of comparing survival rates from two sites in two different periods, survival rate has increased significantly between the two studies in a way that could potentially explain the increase in abundance at Mývatn. This could indicate that female survival has increased in the population as a whole. We strongly recommend demographic monitoring as a contribution to monitoring sea duck populations, species that are difficult to count and otherwise monitor annual changes in abundance in any meaningful way across large geographical ranges.

From a research study to a conservation partnership: Developing approaches to restoring common scoter populations

Abstract Like many sea‐duck populations, the British breeding population of common scoters Melanitta nigra has declined markedly. In 2009, a study was established to measure factors affecting lake use by breeding scoters, to inform conservation measures. That study, published in Aquatic Conservation: Marine and Freshwater Ecosystems (AQC) in 2016, showed that lakes used by scoters had relatively more shallow water and large invertebrates. Furthermore, lakes with abundant large invertebrates had relatively few brown trout Salmo trutta. These results probably reflect the importance of foraging habitat (shallow water), prey abundance (large invertebrates), and competition for prey (trout abundance) in influencing scoter lake use. To develop this study, additional research, and scoter conservation measures, we formed a long‐term partnership, comprising nature conservation non‐governmental organizations, statutory agencies, fisheries managers and the regional hydropower company. The partnership meets regularly to coordinate and review research and develop conservation measures, building on the earlier lake‐use study. At key scoter lakes managed for hydropower, the partnership negotiated a revised water level management regime, favouring shallow water availability in the breeding season. This regime was informed by additional research, showing the value of certain islands for nesting scoters, and water level requirements to maintain these as islands. In a different key scoter area — an extensive near‐natural peatland where recreational angling takes place — the partnership established a trial of increased brown trout angling, with increased fish removal, to determine whether this would increase invertebrate prey abundance and benefit breeding scoters. Both conservation interventions are currently being evaluated by detailed monitoring. Overall, the earlier study published in AQC, was important in strengthening and informing our researcher–practitioner partnership, as we collaborated within an adaptive management framework to reverse scoter declines. Long‐term interdisciplinary partnerships are likely to have an important role to play in general, for the successful conservation of aquatic biodiversity.

Comparison of bivalve communities between moulting and wintering areas used by Common Scoter Melanitta nigra in the German North Sea

The Common Scoter (Melanitta nigra) is a common sea duck, which predominantly feeds on sedentary benthic bivalve prey and occurs in large late-summer moulting concentrations in the German North Sea in areas which differ from those used by later wintering concentrations. Assuming scoters distribute in response to prey accessibility, abundance and profitability, we hypothesis that their contrasting distribution during moult compared to winter potentially reflects differences in prey type and distribution. We compared benthic bivalve community composition, abundance, ash-free dry mass and flesh-to-shell ratios between both areas to investigate factors influencing the seasonal difference in areas used by scoters. The American Razor Clam (Ensis leei) was the most common bivalve in the moulting area (mean abundance 1004 ± 1681 ind. m−2, mean ± SD) with the highest flesh-to-shell ratio (0.341 g m−2 ± 0.729 g m−2), whereas the American Piddock (Petricolaria pholadiformis) showed the highest ash-free dry mass (0.635 g m−2 ± 0.392 g m−2). In the wintering area, the most common bivalve was the Bean-like Tellin (Fabulina fabula, 13 ± 17 ind. m−2), Spisula solida had the highest ash-free dry mass (1.639 g m−2 ± 1.262 g m−2) and F. fabula and Abra alba had the highest flesh-to-shell ratios. Overall benthic species community composition differed considerably between moulting and wintering areas, with fewer species and lower abundances in the wintering area. The high abundance and food quality (flesh-to-shell ratio) of E. leei (an invasive alien to the German North Sea since the 1980s) in the moulting area suggests its relative importance and potentially explains the seasonal differences of Common Scoter distributions.

Trematode fauna (Platyhelminthes: Digenea) of some sea ducks wintering on the southern Baltic coast (NW Poland) – a general comparison

ABSTRACTThe common scoter Melanitta nigra, velvet scoter M. fusca and long-tailed duck Clangula hyemalis (Aves: Anatidae) are among the more abundant sea ducks on the southern coast of the Baltic in winter, but their parasitic trematode fauna (Platyhelminthes, Digenea) in this region is little known. The aim of this study, conducted in 2007–2009, was a general comparison of the trematode fauna of these ducks in NW Poland. The prevalence and intensity of trematode infection were 68.3% and 119.9 in common scoter (101 examined), 77.6% and 13.1 in velvet scoter (58 examined) and 70.6% and 23.7 in long-tailed duck (68 examined). The following trematodes were found: Diplostomum pungitii, Apatemon gracilis, Australapatemon minor, Typhlocoelum sisowi, Echinochasmus spinulosus, Echinoparyphium recurvatum, Psilostomum brevicolle, Psilotrema simillimum, Catatropis verrucosa, Notocotylus attenuatus, N. gibbus, Paramonostomum alveatum, Prosthogonimus ovatus, Levinseniella propinqua, Gymnophallus bursicola and Cryptocotyle concava. The common scoter differs from the velvet scoter and long-tailed duck in its statistically significantly higher prevalence of G. bursicola; from long-tailed duck in its higher prevalence and greater intensity of infection with P. alveatum; and from velvet scoter in its greater intensity of infection with C. concava. The velvet scoter is distinguished from the long-tailed duck by its greater intensity of infection with P. brevicolle, lower prevalence of L. propinqua and lower intensity of infection with C. concava. Links between the differences found and the biology and ecology of the hosts, as well as the means of transmission of the parasites, are also discussed.

Correlates of lake use by breeding common scoters in Scotland

Abstract1. Many populations of sea‐ducks, which typically winter at sea but breed on fresh water, are declining. Numbers of common scoters Melanitta nigra (L.) breeding in Scotland halved between 1995 and 2007, despite most breeding sites having special conservation status. To identify potential conservation measures, a 3‐year study was conducted, investigating correlates of lake use by scoters.2. At 26 scoter breeding lakes, food abundance (macroinvertebrates) and foraging habitats (substrates, water depth) were measured, and their associations with scoter lake use explored using multi‐model inference. Correlates of macroinvertebrate abundance (water quality, fish abundance) were also investigated.3. Averaged over 3 years (2009–2011), these lakes held 26.7 (SE 6.3) females, around half the Scottish breeding population. Scoters occurred more often at lakes having abundant large‐bodied invertebrates and extensive shallow water. Lakes where the average weight of the largest invertebrate in each sample exceeded 4 mg had 9.2 times (females) or 27 times (broods) more scoter records than other lakes. Lakes where water depths (10 m from the shore) averaged less than 1.3 m had 2.5 times (females) or 12 times (broods) more scoter records than other lakes.4. The abundance of large‐bodied invertebrates was greater where small fish species (mostly three‐spined sticklebacks Gasterosteus aculeatus) were more common and brown trout Salmo trutta were scarcer.5. Results suggest two approaches to scoter conservation. At lakes used for hydro‐electricity generation, water level regimes that provide extensive shallow water should be tested to see if these benefit scoters. At lakes used for trout fishing, trout reduction by increased angling should be trialled, to see if this increases large‐invertebrate abundance and scoter use. Copyright © 2015 John Wiley & Sons, Ltd.

The importance of offshore areas in southern Öresund, Sweden, for staging and wintering sea ducks

The occurrence of wintering and spring-staging sea ducks in the southern part of Swedish Öresund was surveyed from air and ship during the period 2001–2011. Altogether 22 air and 20 boat surveys were made during the months November–May and here we present the results regarding five commonly recorded sea ducks. We present the numbers recorded and the general time pattern of occurrence during winter and spring in the area. Recorded numbers are then used for evaluating the importance of the area, both in relation to national wintering totals as well as to international (Baltic) totals. Southern Swedish Öresund is of no larger importance for Long-tailed Duck Clangula hyemalis in winter and spring. The area is however of national importance for both Velvet Scoter Melanitta fusca and Common Scoter Melanitta nigra in winter. Peak numbers of Common Scoters do also reach international importance. Southern Swedish Öresund is of large national and international importance for both wintering and spring-staging Eider Somateria mollissima and Red-breasted Merganser Mergus merganser.

Diversity and abundance of water birds in a subarctic lake during three decades

The numbers of divers, ducks, gulls, terns and waders in the 15 km2 oligotrophic lake Takvatn, North Norway were estimated six times during 1983-2012. Systematic mapping surveys were done by boat within the first week after ice-break in June. Twenty-one species were observed over the years and 12 were regarded as breeding on the lake. Red-breasted merganser Mergus serrator was the dominant diving bird, with estimated minimum number of pairs varying from 15 to 39 among years. Black-throated diver Gavia arctica (1-3 pairs), tufted duck Aythya fuligula (2-15 pairs) and common scoter Melanitta nigra (1-5 pairs) bred regularly, while velvet scoter Melanitta fusca (1-2) and goldeneye Bucephala clangula (2-4) were found in some years and mallard Anas platyrhynchos (1 pair) and wigeon Anas penelope (1 pair) in one year. Common gull Larus canus (6-30 pairs) and arctic tern Sterna paradisaea (2-35 pairs) bred in all years. Common sandpiper Tringa hypoleucos (3-9 pairs) and redshank Tringa totanus (1-4 pairs) were regular waders. Density variations of mergansers, gulls and terns are possibly related to density variations of three-spined sticklebacks Gasterosteus aculeatus, their dominant fish prey. The water birds are important links in the food web of the lake.

The effects of shoreface nourishments on Spisula and scoters in The Netherlands

The coast of The Netherlands is protected by nourishing sand. Generally, two different techniques are used, beach nourishment and shoreface nourishment. The latter technique supplies sand at a water depth of about 5–8 m in the surf zone, and has been used on a regular basis since 1997 with increasing volumes since 2001. Observations on the bivalve mollusc Spisula subtruncata that was abundant before 1997 and a key food species for wintering seaduck show a decline since 2001. This coincided with a decrease in the abundance of the Common Scoter Melanitta nigra, the most numerous wintering seaduck off the Dutch coast. These observations raised concern about shoreface nourishments. This study analyses the timing and locations of shoreface nourishments in combination with S. subtruncata abundance and spatial distribution. Against the expectation, no causal relationship was found between the decline of S. subtruncata and shoreface nourishments. Other causes, such as climate change, fisheries, unsuccessful settlement or predation of spatfall are more likely behind the decline of Spisula along the Dutch coast.

The Sea Empress oil spill (Wales, UK): Effects on Common Scoter Melanitta nigra in Carmarthen Bay and status ten years later

Carmarthen Bay, UK, regularly supports internationally important numbers (>16,000) of non-breeding Common Scoters Melanitta nigra. The spill of 72,000 tonnes of crude oil from the Sea Empress in 1996 affected birds both through direct mortality and likely pollution of key food resources. Numbers were greatly reduced following the spill, whilst changes in the distribution of birds within Carmarthen Bay suggested that potentially sub-optimal foraging zones were used. However, ten years after the incident, numbers of Common Scoter were no different to those recorded immediately before the spill. Compared to some other spills, rapid revival is evident. Numbers increased to pre-spill levels within three winters and distributional changes suggested a concurrent return to previously contaminated feeding areas, implying that the ecosystem had regenerated sufficiently to support its top predator. The importance of prolonged, standardised monitoring of bird numbers and distribution as indicators of ecological recovery from environmental damage is emphasised.

Changes in body mass and organ size during remigial moult in common scoter Melanitta nigra

The “cost‐benefit” hypothesis states that avian body organs show mass changes consistent with the trade‐off between their functional importance and maintenance cost, which may vary throughout the annual cycle. Flightless moulting common scoter Melanitta nigra in Danish marine waters select rich undisturbed offshore feeding areas lacking predators, suggesting active feeding during moult. We tested four predictions relating to organ size during flightlessness in moulting male common scoter under this hypothesis. Namely that (i) pectoral muscles would show atrophy followed by hypertrophy, but that there would be no change in (ii) leg muscles and heart (the locomotory architecture required to sustain diving for food), (iii) digestive organs and liver (required to process food), or (iv) fat deposits (because birds could fulfil daily energy requirements from locally abundant food resources). Dissection of scoters collected at different stages during wing moult south of the Danish island of Læsø provided data on organ size that were consistent with these predictions. Pectoral muscle mass showed a c.23% atrophy during the middle of the flightless period relative to that at the end of moult. There was no significant loss in leg muscle, heart, digestive organs (except gizzard mass), liver, fat reserves or body mass with remigial growth. These findings are consistent with the hypothesis that common scoter moult in a rich feeding area, and rely on their diet to meet the nutritional requirements of remigial moult. These results differ in detail from those of a similar study of terrestrial feeding moulting greylag geese Anser anser, but because of the widely differing ecology of the species concerned, both sets of findings provide strong support for the hypothesis that variations in phenotypic plasticity in size of fat stores, locomotor and digestive organs can be interpreted as evolutionary adaptations to meet the conflicting needs (feather growth, nutritional challenges and predator avoidance) of the flightless moult period in different Anatidae species.

Changes in body mass and organ size during remigial moult in common scoter Melanitta nigra

Changes in body mass and organ size during remigial moult in common scoter Melanitta nigra

Seabirds Foraging at Floating Seaweeds in the Northeast Atlantic

The influence of floating seaweed patches on the distribution and behaviour of seabirds was investigated using the European Seabirds At Sea database (ESAS). The percentage of observations that seabirds were observed with floating seaweed differed among species, depending on the mode of foraging. The results indicate that surface feeding species that make shallow dives (terns and Red-breasted Mergansers Mergus serrator) benefit most from the presence of floating seaweeds and their associated macro- and ichthyofauna. Species hunting for pelagic and bottom-dwelling prey (divers, Guillemots Uria aalge, Razorbills Alca torda, Puffins Fratercula arctica, Gannets Sula bassana and Cormorants Phalacrocorax carbo), and especially benthos feeders (Common Scoters Melanitta nigra and Eiders Somateria mollissima) were frequently seen in association with floating seaweeds, while opportunists and scavengers like gulls and skuas were recorded on few occasions. Petrels and shearwaters (surface-seizing, pursuit-plunging, pursuit-diving) were seldomly seen in association with floating seaweeds. The most common behavioural activities of the birds associated with floating seaweed were found to be surface pecking, actively searching, and pursuit plunging.

Distribution and behaviour of Common Scoter Melanitta nigra relative to prey resources and environmental parameters

Offshore wind farms are proposed around the coast of the UK and elsewhere in Europe. These sites tend to be located in shallow coastal waters that often coincide with areas used by over‐wintering Common Scoter Melanitta nigra. A large‐scale study was undertaken to ascertain the relationship of the spatial distribution of Common Scoter in Liverpool Bay with prey abundance and environmental and anthropogenic variables that may affect foraging efficiency. The highest numbers of Common Scoter coincided with sites that had a high abundance and biomass of bivalve prey species. There was strong evidence that the maximum observed biomass of bivalves occurred at a mean depth of c. 14 m off the Lancashire coast and at c. 8 m off the north Wales coast. This coincided well with the distribution of Common Scoter at Shell Flat, but less well with the distribution of birds off North Wales. Common Scoters were observed in lowest numbers or were absent from areas in which anthropogenic disturbance (shipping activity) was relatively intense, even when these areas held a high prey biomass. Commercial fishing activities did not appear to contribute to this disturbance.

Changes in abundance and at-sea distribution of seabirds in the Bay of Biscay prior to, and following the “Erika” oil spill

We investigated the impact of the Erika oil spill in the Bay of Biscay (France) on seabird populations. Relative abundance and spatial distribution at sea between 1980−1999 and 2000−2002 periods were compared. This study took place in a standardized monitoring at sea carried out with Coast Guard vessels following the line transect method. This work rests on 107 551 standardized counts of one minute before Erika and 23 449 after the oil spill. There was not a simple correlation between the number of individuals found oiled and the numerical variation of the populations at sea during the two years following the accident. The guillemot Uria aalge, the most frequently collected species in the north of the Bay of Biscay, showed no decrease in at sea abundance during the two years following the pollution. Conversely, some species found in small numbers on the coast (e.g. divers Gavia sp., razorbill Alca torda, common scoter Melanitta nigra) decreased significantly at sea (20 to 80%). Overall, marine bird populations declined significantly in the northern sector of the Bay of Biscay (48 ◦ 32 � to 46 ◦ 58 � north) and increased in the southern sector (45 ◦ 13 � to 43 ◦ 15 � north), whereas decreases and increases occurred in the central sector (46 ◦ 57 � to 45 ◦ 14 � north). Changes in the spatial distribution of the species after the Erika oil spill occurred through disappearance or retraction (Bay of Vilaine, Houat-Hoedic archipelago), or through displacement and reinforcement (Gouf of Capbreton). Overall, this suggests a redistribution of the populations within the Bay of Biscay, depending on the level of injuries to the ecosystems caused by the pollution.

Seabirds in the North Sea Demobilized and Killed by Polyisobutylene (C4H8)n (PIB)

This paper reports on a mass stranding of seabirds in the North Sea in December 1998. Hundreds of birds were washed ashore alive in Zeeland (SW Netherlands), covered in a whitish, sticky substance, and were transported to a rehabilitation centre. About 10 days later, more (dead) casualties washed ashore further to the north on Texel and along the mainland coast, again covered in a glue-like substance. Common guillemots Uria aalge, northern fulmars Fulmarusglacialis and common scoters Melanitta nigra were the most numerous birds affected in this incident. Both strandings were temporarily (10 days) and geographically separated (ca. 120 km apart), but were apparently caused by a single source of pollution. The meteorology at the time was consistent with the course of a single incident. At least 1100 seabirds were affected by this substance, soon identified as polyisobutylene (C4H8)n. PIB is known as a non-toxic, non-aggressive substance. Volunteers cleaning the birds in the rehabilitation centre reported serious discomfort and dizziness and the soft parts of the PIB-affected birds found dead (bill, eye, throat, feet, webs) appeared to dissolve in a few days time. Both effects cannot be attributed to PIB, and are therefore unexplained. Although the dumping of PIB in the marine environment is not explicitly prohibited under MARPOL, the effects on wildlife observed are enough to plead for counter-measures.

Identifying inter‐dive intervals in time‐activity budget studies of diving ducks

In order to identify inter‐dive intervals in diving ducks, i.e. the time spent regaining breath between consecutive feeding dives, the position of the tail, carpal joints and head was recorded in different behavioural categories for eight species on the southwestern coast of Norway in March. Inter‐dive intervals are part of the feeding behaviour and are easily confused with the behavioural categories of swimming and loafing. During inter‐dive intervals the ducks adopt a more or less hunch‐backed position, preparing for the next dive. In this position the tail touches the water surface and the head is held in a more forward position than during loafing and swimming. Some species expose carpal joints in inter‐dive intervals, while most of the wings are covered by the flank feathers during non‐feeding behaviour. Logistic regressions showed that a near perfect classification was obtained from the position of the wings alone in common eider Somateria mollissima, velvet scoter Melanitta fusca, and long‐tailed duck Clangula hyemalis. An almost equally good classification was obtained for the two last mentioned on the position of the tail, for scaup Aythya marila on the position of the head, and for red‐breasted merganser Mergus merganser on the position of the head and the stretching of the neck. Less reliable classifications were obtained for goldeneye Bucephala clangula and tufted duck Aythya fuligula, whereas in common scoter Melanitta nigra none of the variables fulfilled the criteria for entering a logistic regression function.

Wildfowl of Islay

SynopsisThe island of Islay posssesses by far the largest population of wintering wildflowl in the Inner Hebrides; there are 18,000-20,000 barnacle geese Branta leucopsis and 4,000 Greenland white-fronted geese Anser albifrons jiavirostris. There is also a small flock of greylag geese A. anser. Most of the commoner dabbling and diving ducks spend the winter in small numbers, with a flock of 1,000 scaup Aythya marila the most important. A few hundred pairs of eider Somateria mollissima breed, and up to 3,000 wintering or moulting birds have occurred offshore. Other breeding duck are few in number, including up to five pairs of common scoter Melanitta nigra. Whooper swans Cygnus cygnus spent the winter in the past but are now common on passage only. Barnacle geese have trebled in numbers in the last twenty years, leading to complaints of agricultural damage, and a subsequent increase in shooting and disturbance followed by a recent decline in numbers. Annual data on populations, productivity and losses are presented. Greenland white-fronted geese have varied less in numbers, but shooting has increased and the situation is reviewed. All other wildfowl occurring on the island are dealt with briefly.