bluuebunny/crossref_metadata_2025 huggingface dataset:
Skuas on the Canadian tundra in 1999: relative occurrence of species, ages and colour phases
Authors: Kjellén Nils
Published: March 2023

During the Swedish Tundra Ecology Expedition to northern Canada in 1999 the age and colour phase of Pomarine S. pomarinus, Arctic S. parasiticus and Long-tailed S. longicaudus Skuas were recorded along a transect across 72° longitude from Nuuk, Greenland in the east to Banks Island in the west. Pomarine Skua comprised 4% of the 302 recorded skuas, with 77% Long-tailed Skua and 19% Arctic Skua. Measured indices of lemming numbers were low in the whole visited region. A similar study in 1994 along the Russian tundra from the Kola Peninsula in the west to Wrangel Island in the east was made in a peak lemming year. This resulted in a total of 1,587 skuas, with 52% Pomarine, 10% Arctic and 38% Long-tailed. The Arctic Skua occurred in fairly low densities all along both transects, but was absent from the most northerly sites. The much lower proportion of Pomarine compared to Long-tailed Skua in Canada may be explained by a higher proportion of Pomarines leaving the breeding areas early, since this species obviously did not breed at all this year. It is however possible that lemming peaks on the Canadian Islands are generally less pronounced in the lack of Lemmus species. This would mean that breeding conditions for Pomarine Skuas, being totally dependent on lemmings, are generally less favourable. No skuas in second year plumage were observed and a few immatures of the two smaller species were all recorded in Davis Strait, between Greenland and Baffin Island. This indicates that only a smaller proportion of younger non-breeders reach the breeding grounds. Compared to 25% dark Arctic Skuas in Nuuk, Greenland only 3% of the birds observed on the Canadian Islands were dark. The same total dominance of light birds seem to prevail among all solitarily nesting Arctic Skuas in the arctic region.
Two migratory flights of Sedge Warblers Acrocephalus schoenobaenus from Finland to Estonia
Authors: Bulyuk Victor , Chernetsov Nikita
Published: March 2023

We examined two cases of first-year Sedge Warblers Acrocephalus schoenobaenus which were ringed in Finland and recovered in Estonia on the following day. Environmental/meteorological conditions during the nights of the migratory flights are discussed, together with the possible ground speed of birds. The birds lost 1.0 and 1.2 g, respectively, probably entirely from their fat reserves. On the basis of the estimated ground speed of the birds, energy expenditure for migratory flight is discussed. One estimate, 10.9 times BMR, is very close to generally accepted values (10–12 times BMR). The other, 20.6 times BMR, may be an overestimate, but we speculate that it reflects in increased cost of flight in a cold front.
Påverkar kanadagässen Branta canadensis häckningsresultatet för smålom Gavia stellata och storlom G. arctica?
Authors: Eriksson Mats O G , Lindberg Peter
Published: March 2023

During the latest decades, Canada Geese have increased in numbers and expanded over large parts of north-western Europe. Hitherto, the risk for adverse effects on the native bird fauna has been assessed to be negligible, although there are single records of divers (Gavia spp.) having failed or abandoned the breeding site after the establishment of Canada Geese. Therefore, we initiated an inquiry about breeding success and nest locations of divers and geese in Sweden. For Red-throated Diver, we compared the breeding success for pairs nesting at tarns with and without breeding Canada Geese. We found no indication of any negative effects on breeding success: The average production was 0.82 “large” chicks per pair and year for pairs at tarns with breeding Canada Geese, compared to 0.75 at tarns without breeding geese. For Black-throated Diver, the average hatching success for pairs with and without nesting Canada Geese on the same islet was 46% and 47%, respectively. But the average distance to the closest goose nest (on another islet) was lower for failed nests compared to successful ones. We judge, that the expansion of the Canada Goose is not a threat on a national or regional scale, although single diver pairs certainly suffer from having Canada Geese as close neighbours. Among both species of divers there are also indications of adaptations to the geese, e.g. through moving to new nesting sites at the same breeding lake. Finally, potential benefits from the presence of Canada Geese, e.g. if the geese keep other potential predators away, should not be overlooked.
Storlommens Gavia arctica häckningsframgång i relation till vattenkemi, försurning, kvicksilverhalt i fisk och sjöyta i sydsvenska sjöar
Authors: Eriksson Mats O G , Hake Mikael
Published: March 2023

We investigated the breeding success of Black-throated Divers in relation to water chemistry, acidification status, mercury content in Pike Esox lucius, and surface area in two study areas in South Sweden with 44 and 30 lakes, respectively. In both areas, divers nest at oligotrophic clear-water lakes and normally forage in their breeding lake. In one area, the majority of lakes was affected by acidification, but also target for liming since the early 1980’s in order to restore and maintain viable fish stocks. In the other area, most lakes were not affected by acidification. Average breeding success in the two areas in 1994–1997 was 0.46 and 0.66 ‘large’ chicks per pair, year and lake, respectively. This is on the same level or slightly higher than recorded in previous studies in South Sweden. In one of the areas there was an indication of lower breeding success in lakes affected by acidification. The difference was not significant but it should still be considered as no such tendencies were found in earlier studies in the same area in the 1970’s and 1980’s. The water chemistry parameters investigated were pH, alkalinity, total-phosphorus and water colour. None of them was significantly correlated to breeding success, nor was exposure of mercury, measured as content in muscle tissue of Pike. We conclude that variation in breeding success of Black-throated Divers between lakes rarely can be ascribed to variations in water chemistry, at least within the range normally observed in oligotrophic clear-water lakes in Scandinavia. Instead, other factors such as flooding of nests, predation and disturbance from recreation may be more important than any influence of water chemistry. We will not exclude, however, the risk of a slow but long-term decline in the breeding success in lakes affected by acidification. This potential problem needs closer monitoring.
Inventering av labb Stercorarius parasiticus i Södermanlands läns skärgård 1999 samt ett försök till utvärdering av framtida förekomst i Sverige
Authors: Andersson Arne
Published: March 2023

In 1999, I made a complete census of the Arctic Skua population in the archipelago of Södermanland. I surveyed all parts at least three times between 10 May and 13 July. I found 15 breeding pairs (5 pairs with young, 2 incubating pairs, and 8 stationary pairs with unmistakable breeding behaviour), and two resident birds (probably a pair) that did not breed. The Södermanland population was estimated at 25 pairs in the 1970’s. This decline is different from the assumption that the total Swedish population has increased. The population of Stockholm archipelago was estimated at 200 pairs in the mid 1980’s and 300 pairs in the mid 1990’s, and that of Västerbotten in the north of Sweden at about 10 pairs in the early 1980’s and 40–45 pairs in 1994. The total Swedish population was estimated to be 370–380 pairs in the mid 1980’s. Compiling the most recent estimates (most from the late 1990’s), I found that the total population now is 546–571 pairs. In spite of this, I am not certain that these figures represent a real increase. The general ornithological activity in the archipelagos has also increased much, and some ornithologists have recently been particularly interested in skuas. Hence it is possible that the increase is only apparent. All skuas bred near gull colonies, and almost all gull colonies had a skua pair. This makes it unlikely that the skua population will increase unless the gull populations do the same.
Learning the task: age-related differences in the proficiency of Black-headed Gulls kleptoparasitising Lapwings
Authors: Källander Hans
Published: March 2023

How Black-headed Gulls’ Larus ridibundus skill at kleptoparasitising Lapwings Vanellus vanellus improved during the course of the autumn was studied in southernmost Sweden from 1988 to 1997. Relative to adults, whose success rate remained constant, that of juveniles increased rapidly from late July to early August and more slowly thereafter. Overall success rate of adults was c. 63% and that of juveniles c. 45% based on about 5,000 attacks by each age category. In contrast to kleptoparasitism, the feeding rates of adults and juveniles did not differ when they used some other feeding methods, not even when catching flying insects on the wing about a month after the young birds fledged. This suggests that kleptoparasitism is a difficult feeding method that takes time to perfect.
Wing moult duration for the Reed Bunting Emberiza schoeniclus at Kvismaren, central Sweden, with regard to data representativeness and weather influence
Authors: Sondell Jan
Published: March 2023

I have analysed 1,777 moult records of the Reed Buntings Emberiza schoeniclus, collected at Kvismaren, central Sweden, in 1973–1995. When evaluating moult with regression techniques it is important that the data are representative primarily with respect to the start and the end of the moult period. Otherwise a too short period is obtained. The mean moult duration was estimated to be 63 days, starting on 10 July. The females started to moult 6 days later and finished moult 3 days later than the males. Weather conditions significantly affected the moult performance. The variation in mean annual onset of moult ranged from 3 to 17 July. The temperature in April, May and to some extent also in July had a significant influence on the onset. Warm versus cold summers introduced a variation of only about 3 days in the duration of the moult but under extreme conditions (snow in spring and warm summer versus warm spring and cold summer) the variation between years in the mean duration of the moult was as much as 10 days.
Changes in numbers and distribution of staging and wintering goose populations in Sweden, 1977/78—1998/99
Authors: Nilsson Leif
Published: March 2023

Regular goose counts have been undertaken in Sweden since 1977/78 as a part of the International Goose Counts organised by Wetlands International. The main counts are undertaken in October and November, covering all sites of importance for Bean Goose Anser fabalis and in January when all sites are covered. September counts of Greylag Goose Anser anser will be published separately. In October, the major part of the World population of the Taiga Bean Goose Anser fabalis fabalis is found in Sweden. The population increased from about 20,000 in 1960 to 80,000 in 1989, after that it has decreased to about 50,000. During the study period Bean Goose numbers decreased markedly in the southernmost part of Sweden, whereas numbers increased at sites further north in southern Sweden. The species also established new important staging areas. This change in distribution was probably related to differences in hunting pressure between different regions and to changes in agriculture. Staging populations of White-fronted Goose Anser albifrons also increased during the period reflecting changes in the much bigger population south of the Baltic. Marked increase in numbers and a spread to new sites were also noted among staging Greylag Geese, Canada Geese Branta canadensis and Barnacle Geese Branta leucopsis reflecting increased breeding populations in south Sweden.
Sträckvägar och sträckbeteende hos labbar Stercorarius
Authors: Jakobsson Gunnar , Johansson Bjorn
Published: March 2023

Observations of migrating skuas Stercorarius in Sweden 1982—1995  have been analysed with respect to numbers observed, as well as their seasonal and regional occurrence during spring and autumn migration. Numbers of observed skuas have risen during this period. Increased knowledge of identification of younger birds, increased field activity at optimal weather conditions and for Arctic Skua S. parasiticus probably also a larger breeding population in Northern Scandinavia are the supposed reasons for this. Food shortage along the traditional migration routes for Pomarine S. pomarinus and Long-tailed S. longicaudus Skua may have caused them to change their routes in early 1980's. All three species showed a peak in numbers every third year, coinciding with the lemming cycle on the tundra of Arctic Russia.
Häckfagelfaunan i östra Smålands ytterskärgård 1990—2000
Authors: Johansson Thomas , Larsson Tommy
Published: March 2023

The numbers of breeding birds were surveyed in the Baltic archipelago of Småland, southeastern Sweden, during 1984 and 1990—2000. The species included in the survey were Podiceps cristatus, Phalacrocorax carbo, Ardea cinerea, swans, ducks and geese (Anatidae), waders (Haematopus ostralegus and Charadridae), skuas, gulls and terns (Laridae), auks (Alcidae) and the passerine Anthus petrosus. The surveyed area is a narrow belt in the outer archipelago. It is 90 km long and ranges from Mönsterås in the south to Västervik in the north. Breeding birds were recorded from 54 islands or groups of islands. On average, 7,572 pairs were recorded each year from a total of 39 breeding species. The species population trends were analysed for the period 1990—2000. Three species showed a significant increase in number of pairs: Mergus serrator, Larus marinus, and Sterna caspia. Ten species showed a significant decrease in number of pairs: Tadorna tadorna, Melanitta fusca, Haematopus ostralegus, Arenaria interpres, Larus canus, Larus fuscus, Sterna paradisaea, Cepphus grylle, Alca torda and Anthus petrosus.
The occurrence of the Great Cormorant Phalacrocorax carbo in Sweden, with special emphasis on the recent population growth
Authors: Engström Henri
Published: March 2023

The population of Great Cormorants Phalacrocorax carbo sinensis in Sweden has increased considerably in size during recent decades and currently Sweden holds about a quarter of the total Northwest European population. In 1999, the population contained an estimate of 25,600 pairs, distributed over about 154 colonies. The increase was particularly strong between 1986 and 1994 (mean annual increase 31%), and the population grew from 1,800 to 15,500 pairs. After the mid-1990s, the population increase within most of the core area appear to have levelled off, while now fluctuating in size. However, in some northern breeding areas (including the coasts of Södermanland, Uppland, Gotland and several lakes) the population continued to grow at a high rate. With growing cormorant numbers, conflicts with human interests, mainly fishery, have increased. Hunting and egg pricking have frequently been used as methods to reduce cormorant densities locally and to solve fishery related problems. It seems, however, as these measures, in most areas, only have had limited effects in terms of stabilising or reducing population size of cormorants.
Large gulls as predators of passerine landbirds migrating across the southeastern North Sea
Authors: Dierschke Volker
Published: March 2023

The predation by large gulls on passerines migrating across the southeastern North Sea was studied on the offshore island Helgoland throughout 1999; 15,307 pellets of Herring Gull Larus argentatus and Great Black-backed Gull L. marinus were examined. The main prey was fish and crustaceans, but during migratory seasons of passerines (March to May, August to November) up to 7% of the pellets contained remnants of passerines (mainly thrushes Turdus spp. and Starlings Sturnus vulgaris, but few species of <50 g body mass). For half-month periods, the number of pellets containing passerines correlated with the number of passerines stopping over on Helgoland for both size categories of <50 g and >50 g. Pellets containing passerines were mainly found during weather conditions favourable for migration, when many birds were aloft, rather than during adverse conditions. Based on the number of large gulls present, an estimated 5,200 passerines might have fallen victim to gulls during the year. Although some passerines may be scavenged rather than captured, gulls must be important potential predators for passerines migrating across the sea.
Migration patterns of Nordic Greylag Geese Anser anser
Authors: Andersson Åke , Follestad Arne , Nilsson Leif , Persson Hakon
Published: March 2023

Migration patterns of Nordic Greylag Geese Anser anser were studied by means of neck-collaring. A total of 4,173 birds (738 breeders, 1,999 goslings and 1,436 moulters; most moulters subsequently identified as belonging to a specified breeding population) was marked throughout Norway, Sweden, Denmark and Finland during 1984–1994. This report is based on observations made up to 30 June 1995. In general, Norwegian Greylag Geese left their breeding areas rapidly for staging areas in Denmark and/or the Netherlands during the period late August–early September, but the most northerly breeding populations migrated south much later and not so rapidly. After a long refuelling period most Norwegian Greylags left the Netherlands for wintering areas in Spain during November. The Guadalquivir Marismas in the south-western part of the country was the main wintering area, but sites in the Duero Basin in the north-central part gained importance throughout the study period. Normally, the geese left Spain in February, for a long stop-over in the Netherlands. Breeders returned to Vega in Norway in April, but to Troms and Finnmark not until May. Most Greylags from Scania and Denmark, all belonging to the West Baltic population, remained in the breeding area until October, merging into larger and larger flocks, together with returning moulters and birds from more northern breeding grounds. The majority made only a short stop-over in the Netherlands en-route to their main winter quarter, the Guadalquivir Marismas, Spain. An increasing proportion wintered in the Dutch Delta. In general, West Baltic Greylags left their winter quarters during the first two weeks of February and migrated rapidly to the breeding grounds. Largely, Norwegian and West Baltic Greylags used different staging areas in the Netherlands and non-overlapping feeding areas in Spain. Outside the Atlantic flyway there is a few re-sightings from England of Norwegian and Swedish birds as well as one re-sighting each from Scotland and Hungary of a Swedish Greylag. Finnish Greylags were found along both the Atlantic flyway, down to the Guadalquivir Marismas, and the Continental flyway, down to Tunisia and Algeria. Winter quarters of the two studied naturalised populations were situated apart from the main ones; Greylags from the Oslo area wintered in the Netherlands and the majority from Södermanland at Lac du Der, east of Paris.
Offspring sex ratio and male quality in Goshawk Accipiter gentilis
Authors: Ryttman Hans
Published: March 2023

In some bird species, brood sex ratios have been shown to vary with male quality and time of season. Sex ratio adjustment in favour of males would be adaptive if sons inherit their fathers characters that increased their attractiveness to females. In species without obvious sexual ornaments, as in Goshawks, female choice must be based on other characters. One possible male quality character is his ability to defend and protect a good territory. Brood sex ratios skewed towards males have been reported in Goshawks, but only in broods of four young did the male/ female ratio differ significantly. In the present study of Goshawks in Sweden I registered a total number of 953 females and 1,054 males (=52.5% males) in 745 broods, which is significantly different from parity. However, in the 116 broods with four young I did not find any evidence for my hypothesis about different sex ratio among clutches or territories.
Breeding success of Great Crested Grebe Podiceps cristatus on fishponds
Authors: Vogrin Milan
Published: March 2023

Between 1993 and 2000, breeding success of Great Crested Grebe Podiceps cristatus was monitored at two fishpond localities, Vrbje in central and Race in north-eastern Slovenia. During the study 50 and 23 nests with eggs were found, respectively. On average, 1.3 chicks per territorial pair survived until fledged in September. Between the two localities, there was no difference in number of fledged chicks per pair in September but a difference existed in number of hatched chicks per territorial pair (Mann-Whitney U test = 13.5; P<0.05). At both localities, the number of fledglings per nest was positively density-dependent. Young mortality was low, only 12%, in no year above 33%, and did not differ between the localities. Correlation between number of pairs and number of pairs known to have hatched chicks, and correlation between number of pairs and number of fledglings per pair in September varied between localities. In comparison with other studies nest losses were very low (4.3%, all predation, at Vrbje, and 18% by all causes, 4,0% by predation, at Race).
Changes in numbers of migrating birds at Falsterbo, South Sweden, during 1980—1999, as reflected by ringing totals
Authors: Karlsson Lennart , Ehnbom Sophie , Persson Karin , Walinder Göran
Published: March 2023

Ringing totals from 1980—1999, a twenty-year long period of standardized trapping at Falsterbo Bird Observatory, S. Sweden, are presented. Nearly all birds are passerines and most species are nocturnal migrants. There are three series of data: spring and autumn totals from the Lighthouse Garden and autumn totals from the Flommen reedbed Each series was treated separately. We used the seasonal totals in a sample of 50 regularly occurring species for monitoring purposes. Among long-distance migrants, 15 of 24 species showed significantly negative trends and only one was positive. The largest decrease in numbers occurred around 1990 in most cases. Among medium/ short-distance or partial migrants the pattern was different with fewer significant trends, which were either increasing or decreasing. Analyses of different environmental factors, which may have affected the trends, as well as comparisons with other monitoring programmes, were not made in this paper. Instead, possible biases in the results caused by errors in the methods of standardized trapping are discussed. Fixed seasons, trapping sites and trapping equipment are essential parts of the standardization. Necessary attention must be paid to influences of topography, weather, migration periods and the behaviour of the birds in the trapping area when interpreting the data.
Duvhökens Accipiter gentilis beståndsutveckling i Sverige sedan 1975
Authors: Svensson Sören
Published: March 2023

I have used data, mainly from south of 62°N, collected within the Breeding Bird Survey and the Winter Bird Count (1975—2001) to describe the population development of the Goshawk Accipiter gentilis in Sweden. The data from the breeding season indicate a considerable population increase. The winter data show a stable population for the winters 1975/1976—1993/94, then six winters with lower values, and a return to the former mean level in 2000/2001. The linear trend for the whole period shows a decline of almost 20%. The winter data are difficult to interpret in terms of breeding population since a large proportion of the hawks are wintering birds from northern Sweden and Finland. The conclusion is that the number of overwintering Goshawks in southern Sweden has declined, especially in recent years, but that the breeding population has increased, or – considering the weak summer data – at least not declined during the last quarter of a century.
Abundance of owls and Bramblings Fringilla montifringilla in relation to mast seeding in south-eastern Sweden
Authors: Lithner Stefan , Jönsson K Ingemar
Published: March 2023

We investigated the relationship between mast seeding in beech Fagus sylvaticus and oak Quercus spp., and the occurrence of the rodent-dependent predators Tengmalm’s Owl Aegolius funereus, Long-eared Owl Asio otus and Tawny Owl Strix aluco in south-eastern Sweden (Blekinge) 1992—2000. We also compared available data on seed production with data on winter flocks of Brambling Fringilla montifringilla, mainly depending on beech seeds as winter food. Years of good beech mast production were followed by years of high frequency of Tengmalm’s Owl and Long-eared Owl, indicating a rapid numerical response to improved food conditions. The Tawny Owl did not respond in the same way, but tended to reach high densities two years after mast seeding. These results suggest that mast seed production may influence the populations of rodent-feeding predators, and that the numerical response may be very rapid in potentially nomadic specialist predators. This was indicated particularly for the Tengmalm´s Owls arriving in Blekinge rather late in spring of 1999. Winters following good beech mast production normally held large numbers of Bramblings. However Bramblings were absent in Blekinge during the winter of 1992/93 despite the very good year for beechnut production in 1992. Thus, low number of Bramblings was no reliable indication for low numbers of owls the following spring.
Wood quality and the Tawny Owl Strix aluco in different forest types of central Italy
Authors: Salvati Luca , Manganaro Alberto , Ranazzi Lamberto
Published: March 2023

We correlated breeding density and proportion of wooded area per territory of Tawny Owl Strix aluco measured in four deciduous forest types with forest elevation and songbird abundance, both regarded as estimators of forest productivity. The proportion of wooded area was positively correlated to forest elevation, being low in coastal thermophilous oak woods and increasing in hilly mesophilous oak woods and in mountain beech woods. Songbird abundance showed a reverse pattern as the proportion of wooded area per owl territory was negatively correlated to songbird abundance. No correlation was observed between these variables and the breeding density of owls. The low proportion of wooded area per territory in coastal thermophilous oak forests likely depends on that this wood type provides old trees with suitable cavities for nesting and large prey availability, thus representing the optimal habitat for the Tawny Owl in central Italy. We suggest that wooded area per owl territory may be used to predict the quality of different forest types.
Changes in feeding behaviour and reproductive success in the Common Guillemot Uria aalge on the island of Stora Karlsö
Authors: Österblom Henrik , Olsson Olof
Published: March 2023

We studied the feeding behaviour and reproductive success in Common Guillemots Uria aalge at the island of Stora Karlsö to reveal effects of an increased density of the prey fish Sprat Sprattus sprattus. Feeding rates were almost twice as high in 1998 (4.3 feeds/chick/day) as in 1975 (2.2 feeds/chick/day), and feeding trips were short. The adult birds spent a large proportion of the day together at the site during the chick–rearing period, indicating that the birds were not under significant food stress. Contrary to what we had expected, reproductive success was lower in 1998 and 1999 (0.671, SE = ±0.045, n = 2) than in 1974–1977 (0.803, SE = ±0.010, n = 4) and chick survival and age at fledging was unchanged despite the increase of available prey. We speculate that the condition (nutritional value), rather than the abundance of Sprat, has been important in changing the Guillemots feeding behaviour. The study indicates that the reason for the observed lower reproductive success was lower egg survival, most likely an effect of an increased predation pressure from Herring Gulls Larus argentatus.
Density fluctuations in an urban population of Tawny Owl Strix aluco: a long-term study in Rome, Italy
Authors: Ranazzi Lamberto , Manganaro Alberto , Salvati Luca
Published: March 2023

The population of Tawny Owls Strix aluco breeding in urban Rome, Italy, was studied from 1992 to 2001. Yearly density (range: 0.9–1.1 territories km-2) was rather stable compared with data from central Europe, likely due to mild weather conditions and abundant food supply. The rate of territory occupation, regarded as estimator of density fluctuations, was non-linearly correlated with density and proportion of wooded and farmland areas, and not correlated with the proportion of built-up areas. In plots with owl density ranging from 2–4 territories km-2 all the breeding territories were stable over ten years. At decreasing density the lower rate of territory occupation was attributable to the large proportion of unsuitable habitat. Competition with neighbours and the consequent reduction of mean territory size may account for the lower territory stability at high densities, where the proportion of wooded areas is high. The proportion of farmland areas, which is a poor habitat for breeding but represent a suitable hunting ground, explains additional variance of the density fluctuations.
Population dynamics of the Swedish Ornithological Society
Authors: Jonzén Niclas , Waldenström Jonas , Svensson Sören
Published: March 2023

It has recently been recognized that there is declining interest in ornithology among the younger generations. In this paper we analyse the short and long-term dynamics of the Swedish Ornithological Society (SOF) and the Swedish Society for Nature Conservation (SNF) by using analytical tools from population ecology. We first show that the increasing number of SOF and SNF members is not the result of a constant proportion of ornithologists or people interested in nature conservation among a growing Swedish population. Hence, the number of members most likely reflects the true interest in joining organizations such as SOF. We also demonstrate that the growth rate of SOF can be fairly well estimated, but the possible equilibrium size is uncertain. Removing the long-term trend reveals a cyclic pattern with a period of 23 years. This pattern was not found when analysing the SNF data and we discuss the observed patterns in relation to human and member generation time. Finally, we present an improved population model based on data up to 1998 and show how model predictions compare with the observed number of members in year 2002.
Birds in the cold: The effects of plumage structure and environment on operative temperature, shown by spherical models
Authors: Stoutjesdijk Flip
Published: March 2023

question I photographed free-living birds in such a way that the total volume of the bird could be estimated. It was then assumed that the bird could be represented by a sphere of the measured volume with a core (kept at 40 °C) of which the volume in cm3 was equal to the bird’s mass in g. The overall thermal conductance of the spherical model was calculated and compared with what could be expected for real birds based on metabolic data from the literature. The conductance calculated for the models was consistently lower than predictions from the literature. The discrepancy was as could be expected, and became smaller with decreasing size. For small birds the fit was quite good and the relative plumage thickness approached the value where further increase would have a relatively small effect. The model suggests that the operative temperature of a small bird perching in the sun on a cold winter day can exceed the air temperature by more than 20 °C on thermally favoured sites. Alternatively expressed, the energy saved can exceed the basal metabolic rate. For a plumage penetrable for solar radiation the excess may be still higher, even when the reflectivity is rather high. It is estimated that the operative temperature may exceed the preferred range already with an air temperature of 10 °C.
Habitat quality, breeding success and density in Tawny Owl Strix aluco
Authors: Persson Martin
Published: March 2023

Habitat categories and songbird availability as a predictor of forest productivity were compared between Tawny Owl territories and areas not occupied by Tawny Owls near Gothenburg, south-western Sweden. There was no significant difference with regard to habitat categories. There was a significant positive correlation between density of territories and proportion of forest cover for each territory. With regard to songbird availability, there was a significant difference between occupied and not occupied sites. Tawny Owl population density and chick production was positively correlated with songbird availability. Prey remnants from nest boxes were investigated to find out the importance of birds in the diet.
Why is the Water Rail Rallus aquaticus a very scarce breeder north of 61° N?
Authors: De Kroon G H J , Mommers M H J
Published: March 2023

Along a transect from just north of Uppsala (c. 60° N) to Luleå (c. 65°30'N), the eastern coast of Sweden, we searched for Water rails Rallus aquaticus. Rails were found at four of twenty-four visited sites, the northernmost site at 61°08'N. The reason for the absence of rails further north we assume to be a transition of the marsh vegetation from one dominated by dense Phragmites australis and Carex elata with a layer of shallow water above the bottom to one dominated by Potentilla palustris and increasing amount of Sphagnaceae and Polytrichaceae mosses without any water above the vegetation mat. The former vegetation, high and dense but with open space at the bottom, provide both shelter and nest sites and permit the rails to move easily without being exposed to predators. The latter vegetation is too dense and too low for the rails to be able to move without exposing themselves to predators.
Stopover of Northern Wheatears Oenanthe oenanthe at Helgoland: where do the migratory routes of Scandinavian and Nearctic birds join and split?
Authors: Dierschke Volker , Delingat Julia
Published: March 2023

According to measurements from bird ringing, Northern Wheatears of both Scandinavian (subspecies oenanthe) and Nearctic (subspecies leucorhoa) origin stopover on Helgoland (southeastern North Sea) during spring and autumn migration. Although with a large overlap, leucorhoa birds migrate earlier in spring and later in autumn compared to oenanthe. In release experiments during spring migration, Scandinavian birds headed in directions between northwest and northeast, while Nearctic birds departed in directions between southwest and north. Most Nearctic Wheatears are assumed to switch their direction to northwest already west of Helgoland, some do this on Helgoland but some continue on a northerly course and then head northwestwards in southern Norway. Only very few leucorhoa birds occur east of Helgoland in spring as well as in autumn (shown by birds captured at Greifswalder Oie, 390 km east of Helgoland). Some long-winged Wheatears are found much further east at Rybachy (Courish Spit), most probably belonging to Siberian breeding populations. Owing to the gap in the occurrence of long-winged Wheatears in the western Baltic it is unlikely that long-winged individuals at the German North Sea coast are of Siberian origin.
Factors affecting different spatial distribution of wintering Tufted Duck Aythya fuligula and Goldeneye Bucephala clangula in the western part of the Gulf of Gdańsk (Poland)
Authors: Jakubas Dariusz
Published: March 2023

Tufted Duck and Goldeneye wintering in the western part of the Gulf of Gdańsk (Poland) were counted in January 1988—1999. In all seasons, the concentrations of the two species were observed in different places. Tufted Ducks gathered in areas well protected against waves and winds (in harbours, near breakwaters, in the river mouths). Goldeneyes preferred areas abundant in food and with shallow water. This distribution difference of the species could be affected by their behaviour. Tufted Duck searched quiet resting places by day when Goldeneye mainly foraged in the same time. During all seasons, adult male ratio of both species was similar. Adult males were the most numerous group during severe winters (with ice-cover in part of the study area). This could be a result of arrival of birds from frozen wintering areas in northern Europe (predominance of males) and of abandonment of the study area by females and young birds, which are less resistant to bad conditions. In mild winters, individuals in female plumage predominated in the majority of the coastal sectors.
Foraging and diving patterns of the Great Crested Grebe Podiceps cristatus in a fishpond
Authors: Vogrin Milan
Published: March 2023

Diving and foraging patterns of the Great Crested Grebe Podiceps cristatus were studied on Vrbje fishpond in Central Slovenia. Three pairs and their 10 young were studied. The duration of 348 dives of the six adults before hatching, 295 dives of the three pairs of adults with young, and 185 dives of the immature birds were recorded during the breeding season in 1998 (from June through October). Mean dive duration was 31 sec for adults before hatching, 41 sec for adults with young, and 25 sec for immatures. Diving success varied significantly between groups, the most successful were grebes with young. Adult grebes without young caught a higher proportion of large fish than the other groups did. Fish size was negatively correlated with duration of dives in adult grebes without young and in adults with young but not in immatures.
Könsfördelning hos övervintrande brunand Aythya ferinai Erstaviken, Sörmland
Authors: Söderholm Svante
Published: March 2023

Data on the sex ratio of Pochard Aythya ferina have been collected during eleven consecutive winters (December—February) at Erstaviken (59° 16'N, 18° 15'E) in the vicinity of Stockholm, Sweden. The average fraction of males was 0.89±0.054. No difference in sex ratio was found between different winters or between mild and cold winters, i.e. if the bay froze or not during the winter. Neither was there any difference between different months. Flock size did not affect sex ratio either. The high proportion of males at Erstavik fits with a general pattern of declining sex ratios from north to south in Europe. However, presence or absence of seasonal variation in sex ratio and its dependence on flock size seem to vary from site to site in Europe.
Breeding success of Wryneck Jynx torquilla during the last 40 years in Sweden
Authors: Ryttman Hans
Published: March 2023

The Swedish population of Wrynecks Jynx torquilla has decreased at least during the last decades. The reason can be worse breeding success, fewer breeding places, or problems in the wintering areas. This study compares brood size at ringing and number of ringed broods between the periods 1962—1981 and 1982—2001. Breeding success did not decrease. On the contrary, a small but significant increase was shown, from 6.7 to 7.1 young per brood. Despite this the number of ringed broods declined from 1,016 to 449. Deducting an observed 15% loss between ringing and fledging, 5.7–5.8 young would fledge from broods that were not deserted before ringing. Wrynecks lay about 10 eggs, so the loss to fledging is high, but despite this the observed brood size ought to be enough to maintain a stable population if mortality alone were to be compensated, indicating that habitat loss is the most likely explanation for the decline, probably diminishing area of pasture with fewer grazing cattle which in turn decrease the abundance of the ant species on which the Wrynecks feed.
Start of egg-laying in relation to latitude and elevation among Swedish Starlings Sturnus vulgaris in 1988—2003
Authors: Svensson Sören
Published: March 2023

The Starlings Sturnus vulgaris breeding in sixteen nestbox groups, three in northern and thirteen in southern Sweden, were monitored in 1988—2003. Date of the first egg was found to correlate with both latitude and elevation when all sites were included (13 degrees of latitude; 5–430 m elevation). Restricting the analysis to only the south Swedish sites (4 degrees of latitude; 5–230 m elevation), only elevation had any effect. The absence of an effect of latitude in southern Sweden is interpreted as an effect of the large-scale Atlantic low-pressure systems that rapidly pass Sweden and bring mild spring weather to that whole area almost simultaneously, making local climate as determined by elevation more important than effects of latitude. Onset of laying at the sites in northern Sweden did not differ with more than two days in spite of one site being at the coast and the other two in mountain valleys at 380 and 430 m, possibly because the western birds winter at the Norwegian coast only c. 70 km away.
Wintering of Finnish Taiga Geese Anser f. fabalis in Skåne, South Sweden: time-budget differences among age groups
Authors: Kampe-Persson Hakon
Published: March 2023

European Taiga Geese Anser fabalis fabalis, wintering in Skåne, South Sweden, were studied while grazing winter wheat seedlings. The activities of individually marked birds were continuously observed from the time they left their night roost in the morning until they returned in the evening. Each time the bird changed from one activity to another, the change was noted on a continuously running cassette tape recorder. In autumn and early spring, adults allocated an average of 40% of their time to grazing, 27% to staying alert, and 25% to resting/sleeping. In winter, adults increased the proportion of the day devoted to grazing to 52%, whereas the time spent staying alert decreased correspondingly. Adults, subadults, and juveniles devoted similar proportions of the average day to grazing in winter, whereas juveniles spent less time staying alert and more time to resting/sleeping compared with adults. In autumn and winter, the geese grazed 4.0–4.1 hours/day.
Does food supply affect egg size in Dunlin Calidris alpina schinzii?
Authors: Flodin Lars-Åke , Hirsimäki Henry
Published: March 2023

Food supply in relation to egg volume was studied in Dunlins Calidris alpina schinzii in the Getterön area, southwest Sweden 1995—1997. Food supply generally decreased from 1995 to 1996, and tended to increase from 1996 to 1997. Within a year, food supply generally increased over the breeding season. Mean egg volume followed the food supply pattern, i.e. egg volume decreased between 1995 and 1996, and increased between 1996 and 1997. However, within a year there was no change in egg volume over the season despite an increased food supply. The latter result may be a consequence of later breeding females investing less in their clutches, or that a seasonal increase in food supply compensated a lower potential for egg volume in late females (that may be of lower quality).
Starlings Sturnus vulgaris and cattle—a widespread feeding association
Authors: Källander Hans
Published: March 2023

Most of this study was made in the extensive grasslands at Revinge, southernmost Sweden, but some data were also obtained in other parts of South Sweden. Starlings occurred significantly more often in pastures with than without cattle and also more often with active than resting cattle. Starlings were associated with cattle during all months from May to October, but predominantly in July and August. The birds followed grazing animals and pecked small insects from the vegetation close to the cattle’s feet and mouth. There was a positive relationship between number of Starlings and the size of the herd they accompanied. Starlings arriving at a herd spread out among the cattle and, when the total number of birds was high, often some birds left and formed flocks that foraged independently in the grass. Both observations suggest that the benefit of the association may be density-dependent. Pecking rates were higher, and speed of movement lower, for Starlings that associated with cattle than for those that foraged independently. In hot weather Starlings sometimes used a sit-and-wait tactic; when cattle were grazing in tall vegetation short flights after flushed insects were common.
Bruna kärrhökens Circus aeruginosus predation på en skrattmåskoloni Larus ridibundus
Authors: Karlsson Thomas
Published: March 2023

During 1992—1994, I recorded the predation by the Marsh Harrier Circus aeruginosus on a colony of Black-headed Gulls Larus ridibundus at Hornborgasjön in southwestern Sweden. The number of Marsh Harriers varied between 21 and 34 pairs and the size of the gull colony between 2,500 and 5,500 pairs. The female harriers caught more gulls, both adults and juveniles, than the males. Females succeeded in 15.2% and males in 1.3% of the attacks. The females spent more time in the colony and made more attacks during their nestling period. There was no significant difference in the number of attacks during their nest building and incubation periods. The female showed a peak in the number of attacks between 10 and 12 hours, whereas there was no difference in the number of attacks made by the male over the day. There was no difference in prey-catching between morning and afternoon. Between 158 and 221 Black-headed Gulls were estimated to be taken every year, which is a small fraction of all gulls.
Storlommens Gavia arctica häckningsframgång innanför och utanför fågelskyddsområden i sjöarna Fegen och Sottern
Authors: Eriksson Mats O G , Dahlgren Tomas , Holmer Arne , Lindberg Peter , Åhlund Matti
Published: March 2023

We compared the breeding success of Black-throated Divers Gavia arctica inside and outside bird sanctuaries with restricted public access during the incubation period in Lake Fegen-Svansjöarna and Lake Sottern, South Sweden. Both lakes held populations of approximately 15–20 pairs. At Fegen-Svansjöarna, average breeding success was 0.51 large chicks per pair and year inside and 0.27 outside the sanctuaries (field surveys in 1983—1984 and 1997—2000). The difference was not statistically significant, however, and in two out of the six study years breeding success was higher outside the bird sanctuaries. At Sottern, breeding success was 0.39 and 0.25 large chicks per pair and year inside and outside the bird sanctuary, but breeding success was higher inside the sanctuary only in four out of nine years, 1997—2005. The results from the two lakes together indicated an overall positive effect (P = 0.08). We recommend keeping a constant water-level during incubation to be the primary measure to enhance breeding success. Sanctuaries with limited access may be an additional benefit at lakes highly frequented for out-door recreation.
Populationsutveckling och häckningsframgång för brunand Aythya ferina vid Angarnsjöängen, Uppland, 1995—2005
Authors: Söderholm Svante
Published: March 2023

Abundance of wildfowl has been censused annually since 1978 at Angarnsjöängen, a shallow formerly drained eutrophic lake near Stockholm, Sweden. It was extensively restored 1992—1993. Breeding success has been monitored since 1995. Here breeding data on Pochard Aythya ferina, collected 1995—2005, are presented. The population showed large fluctuations between 1978 and 2005 and they were not related to the status of the lake. The population varied between 2 and 14 breeding pairs. In four of the eleven years no broods were observed. It is suggested that the main causes for an absence of reproductive success are water level and/or lack of nesting sites. Mean brood size per successful pair was 5.6 pulli, similar to that in Central Europe. Breeding success (number of broods or pulli per breeding pair) was not related to the number of breeding pairs. Mean brood size was positively correlated with breeding success, but mean brood size was not related to the number of breeding pairs, neither was there a correlation between the total production of pulli and the number of breeding pairs.