Red-throated Diver Gavia Stellata Research Articles

The status of breeding Red-throated Divers Gavia stellata and Black-throated Divers Gavia arctica in Kintyre, Scotland, 2016–2020

ABSTRACT Capsule An onshore wind farm monitoring programme carried out across Kintyre, Scotland from 2016 to 2020 provided an insight into the status of the area’s breeding Red-throated Diver Gavia stellata and Black-throated Diver Gavia arctica populations and their current threats. Aims This study provides an example of targeted monitoring undertaken for a renewables development which can inform conservation decision-making at a population and species level. The aims were to: (i) determine the population status of the breeding diver populations; (ii) determine whether the Cour Wind Farm, or other wind farms in Kintyre, have had any effects on the populations; and (iii) identify the most likely conservation threats to breeding divers within Kintyre. Methods Annual breeding diver surveys across Kintyre recorded presence, breeding activity and productivity. Within the Cour Wind Farm site carcass searches were conducted to record any incidences of diver collisions with wind turbines. Results Divers were recorded on approximately one third of waterbodies monitored in each year. The current Kintyre breeding populations are estimated to be 18–23 Red-throated Diver pairs, and between two and six Black-throated Diver pairs. The Kintyre Red-throated Diver population appears to have lower productivity rates than the UK average. Predation and interspecific competition may be limiting breeding success. No Black-throated Divers were observed to have successfully bred in Kintyre from 2016 to 2020, which may be partly due to a shortage of waterbodies with preferred conditions for nesting. No diver collisions were recorded during carcass searches and there is no evidence to suggest that the Cour Wind Farm is influencing the numbers or distribution of divers. Conclusion The Kintyre Red-throated Diver population may be, and the Black-throated Diver population is likely to be, in unfavourable condition. Opportunities for conservation should be considered, particularly to manage waterbodies so that they are optimal for breeding.

Prevalence of Haemosporidian Parasites in an Arctic Breeding Seabird Species-The Red-Throated Diver (Gavia stellata).

Haemosporida, vector-transmitted blood parasites, can have various effects and may also exert selection pressures on their hosts. In this study we analyse the presence of Haemosporida in a previously unstudied migratory seabird species, the red-throated diver Gavia stellata. Red-throated divers were sampled during winter and spring in the eastern German Bight (North Sea). We used molecular methods and data from a related tracking study to reveal (i) if red-throated divers are infected with Haemosporida of the genera Leucocytozoon, Plasmodium and Haemoproteus, and (ii) how infection and prevalence are linked with the breeding regions of infected individuals. Divers in this study were assigned to western Palearctic breeding grounds, namely Greenland, Svalbard, Norway and Arctic Russia. We found a prevalence of Leucocytozoon of 11.0% in all birds sampled (n = 45), of 33.0% in birds breeding in Norway (n = 3) and of 8.3% in birds breeding in Arctic Russia (n = 25). For two birds that were infected no breeding regions could be assigned. We identified two previously unknown lineages, one each of Plasmodium and Leucocytozoon. Haemosporida have not been detected in birds from Greenland (n = 2) and Svalbard (n = 2). In summary, this study presents the first record of Haemosporida in red-throated divers and reports a new lineage of each, Plasmodium and Leucocytozoon GAVSTE01 and GAVSTE02, respectively.

Behavioural responses of non-breeding waterbirds to marine traffic in the near-shore environment

ABSTRACT Capsule Recording of behavioural responses to ferry traffic for 11 target species showed that Red-throated Diver Gavia stellata, Slavonian Grebe Podiceps auratus, and Black-throated Diver Gavia arctica were most likely to react to passing vessels. Aim To provide information on how responses to marine traffic vary between waterbird species to inform marine spatial planning and environmental impact assessments in the near-shore environment. Methods We recorded behavioural responses to ferry traffic for 11 target species in near-shore waters: Common Eider Somateria mollissima, Goldeneye Bucephala clangula, Long-tailed Duck Clangula hyemalis, Velvet Scoter Melanitta fusca, Red-breasted Merganser Mergus serrator, Black-throated Diver, Great Northern Diver Gavia immer, Red-throated Diver, European Shag Gulosus aristotelis, Slavonian Grebe and Black Guillemot Cepphus grylle. Responses were analysed using generalized linear models and mixed models. Results Red-throated Diver, Black-throated Diver and Slavonian Grebe were the most likely species to exhibit a response to passing vessels. While Red-throated Divers and Slavonian Grebes were highly likely to flush, Black-throated Divers and Great Northern Divers rarely took flight, instead favouring swim or dive responses. In rougher sea conditions birds were more likely to take flight, and the propensity to respond declined across the wintering period. Conclusions This research provides comparative evidence on the behavioural responses of waterbirds to marine traffic. The results support previous studies which highlighted the high sensitivity of diver species to disturbance and provide new evidence that Slavonian Grebe may also be a high sensitivity species.

New information on the bar-tailed godwit Limosa lapponica (Linnaeus, 1758) and red-throated diver Gavia stellata (Pontoppidan, 1763) on the Crimean Peninsula (the Black Sea)

New data on the distribution of the bar-tailed godwit Limosa lapponica (Linnaeus, 1758) and red-throated diver Gavia stellata (Pontoppidan, 1763) on the Crimean Peninsula are presented. Against the backdrop of aquatic and coastal ecosystems’ transformation under natural and anthropogenic impact, even single finds of hydrophilic avifauna representatives in atypical spatiotemporal conditions are of interest for the analysis of emerging trends in migration phenology and abundance of both separate species and taxonomic and ecological groups of birds. The aim of the study was to clarify the distribution boundaries and terms of stay on the Crimean Peninsula of two hydrophilic bird species: semiaquatic species, bar-tailed godwit, and true water bird, red-throated diver. Bird observations were carried out during scheduled accountings on the Isthmus of Ak-Monay (March 2012) and in the Kruglaya Bay (Sevastopol) (July 2019). The bar-tailed godwit is registered in Crimea during spring and autumn migration periods. For the first time, it was found in the north of the Crimean Peninsula in 1972; later, there were an increase in its abundance and expansion of a distribution area. Recent records of this species in southern Crimea significantly expanded the known boundaries of its distribution on the peninsula during the migration period. The observation of the bar-tailed godwit in eastern Crimea on 14 March, 2012, specified the date its spring migration begins; the observation in Sevastopol (western foothill) on 27 July, 2019, was the first one in Mountain Crimea. Off the Crimean coast, the red-throated diver is a rare overwintering and migratory bird. The find of the red-throated diver individual in the Kruglaya Bay on 19 January, 2020, was the third reliable record of this species overwintering in Crimea and the first one in Sevastopol area. The registration of the red-throated diver at a considerable distance from its usual overwintering areas (off the southwestern coast of the Black Sea), along with numerous facts of the expansion of nesting or winter ranges of different bird species northward, confirms the ongoing climatic and ecological changes. Particular attention should be focused on the problem, associated with low ecological culture of the use and disposal of fishing tackles, which have a detrimental effect on hydrophilic birds. Measures have to be developed to regulate fishing with nets, hooks, and line tackles in the areas of bird mass overwintering and seasonal migrations.

Behaviour of Black-throated Diver Gavia arctica and Red-throated Diver Gavia stellata during autumn migration stopover

The stopover behaviour of Black-throated Divers Gavia arctica and Red-throated Divers Gavia stellata during autumn migration was observed in two sites in Poland. Differences in time-activity budget and diving pattern were recorded from mid-October to mid-January of 2004 and 2005. A total of 1,516 minutes of observation was achieved. Birds spent their time diving (60.7%), followed by preening (14.8%), surface swimming (12.5%), and other activities (12%). The feeding pattern of Red-throated Divers and Black-throated Divers was similar. Immature birds had significantly longer dives than adults and they made longer dive-pause intervals. This is suggested to be caused by the differences between age classes in detecting and capturing prey. Moreover, our results show that, in autumn, first-year divers spent less time foraging than adult birds, instead spending more time resting and surface swimming.

Changes in the breeding bird communities on mires and in surrounding forests in southeastern Norway during a 40-year period (1976–2015)

The breeding bird communities of 18 mires and surrounding forests in southeastern Norway were censused in 1976–77 and in 2015. We found that 53% of the mire species with sufficient data for analyses showed significant changes. Red-throated Diver Gavia stellata, Common Crane Grus grus, Wood Sandpiper Tringa glareola and Tree Pipit Anthus trivialis increased, whereas Northern Lapwing Vanellus vanellus, Black-headed Gull Chroicocephalus ridibundus, Meadow Pipit Anthus pratensis and Yellow Wagtail Motacilla flava decreased. There were also near significant decreases of Eurasian Curlew Numenius arquata and Eurasian Skylark Alauda arvensis. Population changes did not differ between short- and long-distance migrants. Species with marginal populations on mires declined more than mire specialist species, suggesting an indirect negative influence of problems in other habitats. Overall, there was a significant 19% decline in number of mire species, but a non-significant 7% increase in number of individuals. The bird community in the forests surrounding the mires showed significant population changes for 42% of the species with sufficient data for analyses, with increases in many resident forest species, but less so for migrants. Overall, there was a near significant 12% increase in number of forest species, and a significant 28% increase in number of individuals. Mire- and forest-associated species did not differ in population trends. Among short-distance migrants (mire and forest species combined), species wintering in agricultural habitats had more negative population changes than species wintering in other habitats. Thus, the breeding bird community on and around mires in this part of Norway has undergone large changes during the last 40 years. We discuss our results in relation to general trends of bird communities in northern Europe.

Diet of red-throated divers Gavia stellata reflects the seasonal availability of Atlantic herring Clupea harengus in the southwestern Baltic Sea

Red-throated divers are piscivorous seabirds considered to be opportunistic feeders. The overall knowledge about their diet at sea is scarce. A large sample size of 82 by-caught red-throated divers from two winter (2001–02 and 2002–03) and three spring periods (2003, 2004 and 2005) offered the unique opportunity to analyse their dietary composition in the Pomeranian Bight. This area represents a hot spot in their winter distribution in the southwestern Baltic Sea and a marine protected area has been established due to its importance for the divers and other seabird species. Diet composition was analysed based on stomach and gut contents. The comparison of the different prey species was mainly based on reconstructed biomass using regressions between skeletal hard parts such as otoliths and original fish length and weight. The diet of the divers comprised eleven different fish species and nine different families. No interannual differences in the consumption of the nine most important prey species could be observed. However, in contrast to the other fish species the consumption of Atlantic herring and zander differed significantly between seasons. Herring supplied the majority of prey biomass in all three spring periods and zander in both winter periods. Moreover, the average length of herring consumed differed significantly between seasons. In winter, smaller herring was consumed compared to spring. The distinct seasonal changes in the diet composition were paralleled and most probably evoked by the migration pattern of the Western Baltic spring spawning herring which has its main spawning grounds adjacent to the study area. Based on the habitat requirements of the different prey species it could be inferred that mostly the coastal waters of the bight were used for foraging. Its function as spawning, nursery area and feeding ground with numerous resident and migrating fish species available might explain the important role of the Pomeranian Bight as wintering and staging area for red-throated divers in the southwestern Baltic Sea.

Revised estimate of numbers of wintering Red-throated Divers Gavia stellata in Great Britain

Capsule An estimated 17 000 Red-throated Divers winter around Great Britain. Aim To produce an up-to-date assessment of the numbers of Red-throated Divers wintering around Great Britain. Methods A revised Great Britain (GB) wintering population estimate for Red-throated Divers was compiled using data primarily from systematic line transect surveys by aircraft over marine nearshore areas conducted during 2001–06, supplemented with county bird records and Wetland Bird Survey (WeBS) counts, both from 1995 to 2005. Population estimates for each survey area around GB were calculated as the mean of either annual means (aerial surveys) or annual maxima (WeBS, county bird records) of all data collected within January and February of each year. These were summed to give a revised GB wintering population estimate. Results A total of 17116 (13198–21034, 95% confidence interval) Red-throated Divers were estimated to winter around GB. Distribution was uneven. By far the greatest numbers were found off southeast and east Britain (59.3% of the total was between Flamborough Head, Yorkshire, and Dungeness, Kent), with large concentrations off the English south coast (10.9%), north Wales and Liverpool Bay (9.8%), and eastern Scotland (6.1%). Conclusion This is a minimum plausible population estimate and the true population size may be larger. The new 1% of population threshold for statutory conservation work is 170 birds.

Smålommens Gavia stellata häckningsframgång i relation till vattenkemi och fiskbeståndens sammansättning i olika fiskevatten

Breeding performance by Red-throated Diver Gavia stellata was compared to water chemistry, light penetration and density of fish in 34 freshwater lakes used for foraging in South and Central Sweden. The study covered around 25% of the breeding population in these parts of the country. Fishing lakes were overall nutrient-poor, and some of them were also acidic and had a poor buffering capacity. There were no relationships between breeding success and water chemistry (pH, alkalinity, total phosphorus), light penetration or impact of acidification. Species composition of the fish communities was characteristic for nutrient-poor lakes: on average 6.6 fish species per lake and dominance of Perca fluviatilis, Rutilus rutilus, Esox lucius and Coregonus albula. The survival of chicks was correlated to high abundance of cyprinid and salmonid fish, i.e. the dominant prey delivered to non-fledged chicks. Around 300 freshwater lakes are judged to be of importance as foraging sites for breeding Red-throated Divers in Sweden. Continuous and long-term liming is a prerequisite in order to maintain viable fish stocks in those lakes that are acid or have a poor buffering capacity.

Kvicksilverbelastningen hos svenska smålommar Gavia stellata och storlommar Gavia arctica

We investigated concentration of mercury in eggs of Red-throated Diver Gavia stellata and Black-throated Diver Gavia arctica collected in South and Central Sweden, 1981—1997. In South Sweden (Sydsvenska Höglandet), mean concentration in Red-throated Diver eggs was remarkably high (6.84 ppm dry weight, 5 pairs), or more than three times as high as in Black-throated Diver eggs (2.11 ppm dry weight, 16 pairs). In Central Sweden (Svealand), the concentration in Red-throated Diver eggs (3.04 ppm dry weight, 8 pairs) was significantly lower than in South Sweden, but still higher than in Black-throated Diver eggs (1.21 ppm dry weight, 5 pairs). In Black-throated, but not in Red-throated Diver, there was higher mercury concentrations in eggs from pairs fishing in lakes affected by acidification. We found no relationship between mercury and breeding success, although concentrations in single Red-throated Diver eggs exceeded the level associated with high risk of impaired reproduction. We recommend that mercury concentration of diver eggs should be further monitored, with reference to the risks of increased exposure, related to leakage from terrestrial deposits of air-borne transmissions to freshwater habitats.

Smålommens Gavia stellata häckningsframgång i artens svenska kärnområde

We investigated the breeding success of a Red-throated Diver Gavia stellata population of approximately 70 pairs during ten seasons, 1991–2000, in a 1820 km2 study area, dominated by coniferous forests and mires in Malung, Dalarna in Central Sweden. The majority of the pairs bred in tarns smaller than 1.0 ha and foraged in larger freshwater lakes or rivers up to a distance of 4.6 km. Average breeding success was 0.76 “large” chicks per pair and year, with a declining trend over the study period accompanied by a decline in the proportion of broods with two “large” chicks. Breeding success was higher in seasons with an average early start of incubation and could be related to higher hatching success and survival of chicks. Predation during incubation was probably an important reason for breeding failures, and abandoning or change of breeding tarns were related to breeding failures. The annual variation of the percentage of broods with two “large” chicks was synchronised between pairs foraging at different fishing lakes, which indicates the influence of some large-scale regional factors linked to the availability of food. Chick survival in two-chicks broods was significantly lower than in one-chick broods. The declining trend in breeding success is an incitement for future monitoring, and any link to impaired foraging conditions needs to be more closely addressed.

The status and distribution of the Red-throated Diver Gavia stellata in Britain in 1994

The first national survey of breeding Red-throated Divers Gavia stellata in Britain was carried out in 1994. It was based on two visits to all standing freshwater in Shetland and Orkney, and to a sample elsewhere in the species' range in Scotland (Inner and Outer Hebrides and mainland). The survey located an estimated 855 breeding pairs (95% CI 735–990) and 1295 (95% CI 1075–1525) non-breeding adults. About 12% of birds that were recorded as non-breeding probably bred, but were not proved to do so; taking these into account the corrected total population for Scotland was estimated at 935 breeding pairs, with approximately 430 (46%) of these in Shetland, 105 (11%) in Orkney and 400 (43%) elsewhere in Scotland. In total, there were an estimated 3010 (95% CI 2685–3360) adult Red-throated Divers in Scotland during summer 1994. The Red-throated Diver population in Shetland has declined by more than a third since 1983, that in Orkney is probably stable and trends elsewhere are unknown. A comparison with Red-throated Diver populations on the Northern Isles showed that on the mainland densities were very much lower, that a smaller proportion of the birds present bred, that they did so on much larger lochs and that when they did breed they were less successful. In Shetland, breeding pairs on small lochs were more successful than those on large lochs; some potential reasons for this are discussed.

The effects of aero-generators on moorland bird populations in the Orkney Islands, Scotland

In order to ascertain the effects of aero-generators on breeding birds, two moorland plots in Orkney's West Mainland were censused each year between 1981 and 1989. One plot was immediately adjacent to the aero genera for site while the other acted as a control. Although the bird populations in the plots were not large enough to state categorically that the aero-generators caused no declines, their effects appear to have been minimal. The only species to have been adversely affected by the development of the site was Red-throated Diver Gavia stellata and its decline was probably the result of factors other than the operation of the aerogenerators.

Levels of mercury in eggs of Red-throated Diver Gavia stellata and Black-throated Diver G. arctica in Southwest Sweden

In connection with surveys of breeding populations of Gavia stellata and G. arctica in Southwest Sweden 1978—91, unhatched eggs in abandoned nests were collected and analysed for mercury. In the investigated area, divers of both species primarily fish in oligotrophic lakes, many of them affected by air-borne acidifying pollutants. The level of mercury in G. stellata eggs was extremely high; in a sample of seven eggs from four breeding sites the mean concentration was 9.5 ppm dry weight with a range of 6.2–14.2 ppm, which is among the highest levels recorded for any bird species in Sweden. The concentrations in G. arctica eggs were lower: 1.0–2.4 ppm dry weight in samples from four breeding sites at circumneutral lakes, and on average 4.0 ppm (range 1.8–5.9 ppm) in a sample from four breeding sites at lakes affected by acidification. For G. stellata, all eggs contained mercury at levels where reproductive impairment is to be expected, and also single G. arctica eggs were so heavily contaminated that the risk of impairment must be considered. Fish samples from seven lakes indicated that potential prey fish (Rutilus rutilus and Coregonus albula, <20 cm) for G. stellata feeding chicks contained higher concentrations of mercury in lakes affected by acidification. In one lake, fish contained levels about twice those reported to be associated with behavioural and reproductive disturbances in fish-eating birds. Also, single fish in two other lakes contained high concentrations of mercury. The results indicate that especially G. stellata, but also G. arctica in their breeding grounds in Southwest Sweden are exposed to levels of dietary mercury, sufficiently high for reproductive impairment to be expected, and that a connection exists to high levels of mercury in prey fish from freshwaters affected by acidification.