bluuebunny/crossref_metadata_2025 huggingface dataset:
The spring migration of Sanderling Calidris alba, Little Stint C. minuta and Curlew Sandpiper C. ferruginea in Sweden
Authors: Blomqvist Sven , Lindström Åke
Published: March 2023

The timing and regional distribution of the spring migration of Sanderling Calidris alba, Little Stint C. minuta and Curlew Sandpiper C. ferruginea in Sweden are reported. Few birds were observed before May. The migration period was unimodal in all three species, with a median date of 29 May for Sanderling (n=1,939), 24 May for Little Stint (n=1,851) and 25 May for Curlew Sandpiper (n=674). Curlew Sandpipers appeared significantly earlier in the north of Sweden than in the south. In all three species, the majority of birds were observed in southern Sweden. However, a considerable proportion (almost one third) of the Little Stints were recorded in northern Sweden. In the Sanderling, 28% of the birds were sightings of single individuals or parties of 25 birds. A sizable proportion (40%) of the Sanderlings occurred in flocks of 20 birds or more. The large flocks were mainly seen in early June. Most records of Little Stints and Curlew Sandpipers referred to 1–5 birds (61% and 74%, respectively). The majority of the birds observed in southern Sweden were most likely en route for breeding areas on the Taimyr peninsula. Little Stints recorded in northern Sweden were, however, more likely bound for northern Norway and northwestern Russia. The movements through Sweden are discussed in relation to the overall migration patterns of these species through the western Palaearctic.
Stopover and fat accumulation in passerine birds in autumn at Ottenby, southeastern Sweden
Authors: Åkesson Susanne , Hedenström Anders , Hasselquist Dennis
Published: March 2023

Stopover duration and fat accumulation were studied during autumn migration at two sites near Ottenby, Öland, southeastern Sweden in 1985 and 1986. The species are Thrush Nightingale, Barred Warbler, Lesser Whitethroat, Whitethroat, Willow Warbler and Red-backed Shrike. We captured the birds in mist nets between 10 July and 20 August and recorded visually the fat class and measured the body mass. Post juvenile moult was scored on juvenile birds. In several of the species fat class and body mass increased with day of season (Thrush Nightingale, Barred Warbler and Whitethroat), while in the Lesser Whitethroat there was a reduction in fat class and body mass with day of season. Recaptures revealed that the highest daily increase in body mass was 2.7% in a Willow Warbler and a Red-backed Shrike, while a Barred Warbler showed a maximum daily body mass increase of 2.4%. The duration of stopover in migrants varied between 2 and 7 days.
Kungsfågelns Regulus regulus höstflyttning över Stora Fjäderägg
Authors: Grenmyr Urban , Olsén Björn
Published: March 2023

During the period 1985 to 1992 a total of 18,520 Goldcrests Regulus regulus were ringed in the autumn at Stora Fjäderägg Bird Observatory (63°49'N, 21°00'E). The mean migratory period, defined as the period including 90% of the bird trapped over these years was 39 days. The mean of median dates was 22 September compared to 14 October at Falsterbo. Goldcrest migration speed through Sweden was estimated to 47 km/day according to the difference in mean median date from Stora Fjäderägg and Falsterbo bird observatories. The average migratory direction in the autumn was southwest (230.5°). The migratory direction of the passing Goldcrests at Stora Fjäderägg seems to be more uniform than at bird observatories in southern Sweden. According to the few controls of ringed birds at Stora Fjäderägg, the source area for Goldcrests passing Stora Fjäderägg seems to be on the east side of the northern part of the Baltic sea.
The Red-backed Shrike Lanius collurio in southeastern Sweden: Habitat and territory
Authors: Olsson Viking
Published: March 2023

The population of Red-backed Shrike Lanius collurio in Sweden has declined considerably over the last two decades. Changes in agricultural practices and forestry management have been suggested to be the main reasons for this decline. Territory and habitat of a population of Red-backed Shrikes were studied extensively for four decades, and more intensively during the last 5 years, in Gryt, southeastern Sweden. Territories were fairly small, 0.5–1 ha. Characteristics of the habitat and the shrikes' use of habitat are described. Open sunny areas with plenty of well-spread perches were important. About 1,000 prey items were recorded mainly by analysing food remains in nests and in pellets below perches. Hymenoptera (55% by number) and Coleoptera (36%) dominated strongly in the shrikes' diet, vertebrates making up only 2.3%. The studied population appears to have remained stable over the four decades. However, a decline is likely to start soon also in this area, mainly as a consequence of the fact that cattle-grazing of natural, scrub-rich pastures is ceasing at a fast rate. Possible measures to protect different kinds of habitat essential to Red-backed Shrikes are discussed.
The autumn migration of Willow Warblers Phylloscopus trochilus in Sweden: results from a nation-wide co-operative project
Authors: Lindström Åke , Hedenström Anders , Pettersson Jan
Published: March 2023

The result of a nation-wide co-operative project studying the autumn migration of Willow Warblers Phylloscopus trochilus in Sweden is presented. This involved 18 bird observatories and private ringers during 1988–1990, at both coastal and inland sites, with data on more than 36,000 birds analysed. Data on age, wing length, fat and body mass were collected in a standardised way, as was scoring of post-juvenile moult (used as a measure of juvenile age). Each bird observatory made a basic compilation of data into weekly averages, upon which the present analysis builds. The proportion of juveniles (93%) was much higher than expected (c. 75%), at both inland and coastal sites. Adults migrated a few days later than juveniles. There was no sex difference in the timing of migration in adults. Juveniles of Ph. t. acredula started migration at an earlier age (35–40 days old) than juveniles of Ph. t. trochilus (50–55 days old). Average wing length increased during the season at many sites, suggesting that birds belonging to the longer-winged Ph. t. acredula passed later in season. Juvenile energy stores were small during mid post-juvenile moult, but higher in the last moult stage, especially at coastal sites. Generally, Willow Warblers in Sweden in autumn carry only small to moderate fat loads, which supports earlier findings that the commencement of migration involves short flights. Conclusions on energy stores were based on data from visual fat score. Because both moulting and migrating birds occurred at most sites, and moulting birds have a different composition of their lean body, body mass does not reflect the seasonal changes in fat loads. Body mass averages of 8.2–9.3 g were similar to averages from other parts of northern Europe, but below the values reported for birds prior to trans-Sahara flights and maximum masses of birds in captivity.
Occupation and breeding parameters in the Great Tit Parus major and the Italian Sparrow Passer italiae in nest-boxes of different size
Authors: Sorace Alberto , Carere Claudio
Published: March 2023

This study examined the preference for nest-boxes of two different dimensions (14x14x22 cm, hole diameter 3.7 cm, 'normal'; 25x25x35 cm, hole diameter 6 cm, 'large') for three breeding seasons in the Great Tit and the Italian Sparrow together with specific reproductive parameters. Sparrows showed a significant preference for normal boxes while tits seemed not to discriminate between large and normal boxes although in the large ones the breeding success was impaired by higher predation rates. For both species no differences between the two kinds of boxes were found for date of laying. As regards clutch size, data suggest that in large boxes tits laid larger clutches.
The timing of post-juvenile moult and fuel deposition in relation to the onset of autumn migration in Reed Warblers Acrocephalus scirpaceus and Sedge Warblers Acrocephalus schoenobaenus
Authors: Hall Susanna
Published: March 2023

The extent of post-juvenile moult and fuel deposition prior to migration in Reed Warblers Acrocephalus scirpaceus and Sedge Warblers A. schoenobaenus were analysed using 11 years ringing data from Lake Kvismaren in South Central Sweden. Re-trap data showed that Reed Warblers acquired their first winter plumage in 34 days, compared to 22 days in Sedge Warblers. The moult pattern of the two species differed due to Sedge Warblers only undertaking a fill-in moult of bare body areas. Fuel deposition rates for the two species were similar, 0.38 g/day for Reed Warblers and 0.34 g/day for Sedge Warblers. The estimated average fuel stores at departure from Lake Kvismaren differed, with Reed Warblers found to leave with a fuel store of 21% (in relation to lean body mass) compared to 6.2% in Sedge Warblers. The median date of departure from Lake Kvismaren was estimated to 30 August for Reed Warblers and 12 August for Sedge Warblers. The earlier departure of Sedge Warblers, with smaller fuel stores, may reflect different migration strategies between the species.
Biometri och könsbestämning av rosenfink Carpodachus erythrinus under häckningsid med hjälp av kloakens utseende
Authors: Ström Kåre , Niklasson Aimon
Published: March 2023

The Scarlet Rosefinch Carpodacus erythrinus was studied in a Swedish west coast area in 1988—1995 in order to evaluate sex-related differences between subadult (2K, 2nd calendar year) males and females (2nd calendar year or older). Biometric examination included weight, wing length, and height, diameter and form of the cloacal protuberance. Subadult "green" males lack the red colour of older males, and are very difficult to separate from females . We found the cloacal protuberance in both "green" and "red" males to differ significantly from that of females of all ages. The cloacal protuberance in both "green" and "red" males was of the "bulbous" type. The size and the form of the cloacal protuberance changed during the breeding cycle. Subadult males had a less well-developed cloacal protuberance than adult males. Subadult males had a smaller protuberance at time of arrival than adult males. The protuberance in both groups of males regressed late in the breeding period. The height of the cloacal protuberance was found to give better sex separation than wing length with nearly no overlap between "green" males and females during the main breeding period. Mean wing length differed significantly between the sexes, but considerable overlap makes this feature unreliable for single individuals. No significant sex- or age-related difference in weight was found.
Flyttvägar och övervintringsplatser for svenska skrattmåspopulationer
Authors: Bengtsson Kenneth
Published: March 2023

A total of 1,508 recoveries of Black-headed Gulls Lorus ridibundus ringed as young in Sweden is analysed. There was hardly any evidence of a non-directional juvenile dispersal. Rather young gulls seemed to leave colonies and start migrating in the predominantly southwesterly direction soon after fledging. The recovery data suggest two main migratory routes for Swedish Black-headed Gulls, one along the Baltic coast and across the Danish Isles, the other across Sweden, mainly in the South Central Lowlands, and later along the coasts of Jutland. There are some indications that more northerly populations spend the winter slightly further to the north than more southerly ones. Although a few recoveries were from as far south as Morocco and some from Central Europe, the main wintering areas of Swedish Black-headed Gulls are Britain, The Netherlands, Belgium and France.
Recent trends of the Black-headed Gull Larus ridibundus population in Latvia
Authors: Viksne Janis , Janaus Mara , Stipniece Antra
Published: March 2023

The Black-headed Gull population in Latvia increased from 10,000 pairs in the early 1940s to 110,000 pairs in 1986, then decreased to about 40,000 pairs in 1994 and continues declining. The population changes have been more pronounced at coastal sites than at inland ones. Simultaneous changes in breeding success (a significant decline of average number of fledglings/pair since 1974), diet and feeding flights have taken place. Changes in the availability of anthropogenic food, appearance of new predators (mainly the American mink Mustela vison) and decrease of suitable nesting habitat are considered local reasons for the recent population decline.
Mass and wing length of young Black-headed Gulls Larus ridibundus as predictors of age and survival
Authors: Bensch Staffan , Källander Hans , Lager Robert
Published: March 2023

This study of Black-headed Gulls aims at finding methods for estimating the condition of gull chicks at the colony level, a measure that could be used to identify colonies exposed to poor and good feeding conditions, respectively. In enclosed parts of two colonies in South Central Sweden, we ringed hatchlings and measured wing length and mass of chicks throughout their pre-fledging period (≤25 days old). Chicks with a high mass relative to age were more likely to survive between visits to the enclosures suggesting that this measure can be used to estimate condition. From the age of two weeks wing length is a relatively accurate predictor of age and from this time mass relative to wing length and mass relative to age are closely correlated. We therefore propose that one can obtain data on the condition of chicks from a single visit at a colony, by estimating individual condition as the deviation in mass from that expected from the chick's wing length. This is important in that many colonies can be studied with relatively little effort.
Predation och störningar i skrattmåskolonier
Authors: Bensch Steffan , Karlsson Thomas , Källander Hans , Lager Robert
Published: March 2023

The frequency of disturbance and predation was studied during one breeding season at six Black-headed Gull Larus ridibundus colonies and during two breeding seasons at four colonies. The level of disturbance, i.e. when at least part of the gulls were put on the wing, varied from just above once an hour to nearly ten times an hour. Marsh Harriers Circus aeruginosus elicited the strongest response with respect to number of gulls leaving the nest (mean 57% of colony) while mink Mustela vison caused the longest disturbances (mean 4.6 min). Among the frequently occurring potential predators of Black-headed Gull eggs and chicks, large gulls (L. argentatus, L. marinus) normally caused disturbance much less often than once an hour and Hooded Crows Corvus corone cornix less often than once an hour (except at one locality in 1992 when a breeding pair entered a colony as often as 5.5 times an hour). Marsh Harriers were lacking at three, caused disturbance c. 0.1-1.2 times per hour at eight, and up to three times an hour at three colonies. On average 3% of predation attempts by large gulls were successful versus 14% for both crows and Marsh Harriers (neither the frequency of visits nor predation by mink could be estimated because of difficulties in observing this species). A crude estimate of the number of gull eggs and chicks taken by the three avian predators showed that large gulls had a negligible impact in all colonies, crows normally took less than 10% of eggs laid (33% in one colony) and Marsh Harriers mostly 0-10%. Even though predation by crows and/or Marsh Harriers can be considerable, it is concluded that increased avian predation cannot explain the decrease in Black-headed Gull numbers in Sweden; the mink's role remains to be evaluated.
Revirtäthet och artdiversitet bland fåglar häckande i Ångermanländsk skogsmark
Authors: Risberg Birger
Published: March 2023

The aim of this study was to estimate density and diversity of breeding birds in ordinary managed forests in the northern Swedish province of Ångermanland. The field work was performed during four breeding seasons within the period of 1989 to 1994. A territorial survey method, with fixed study areas, was used. 41 survey areas with a total area of 623.8 ha were censused representing 0.4 per mile of the woodland in Ångermanland. The mean density was 139 breeding pairs/km2 (median 124 pairs/km2). 53 different bird species were considered breeding in the 41 survey areas. Chaffinch, Willow Warbler and Robin were the most abundant species. These three species accounted for 36% of the total amount of territories. The lowest density and diversity was found in clear cuts and plant stands (90 pairs/km2; 21 different species) while the highest was recorded in middle aged stands (165 pairs/km2; 34 species). Game birds and birds of prey were found breeding only in mature and middle aged stands. The abundance of most tits and woodpeckers were highest in mature stands.
The egg size variation of the Treecreeper Certhia familiaris in south-western Sweden
Authors: Enemar Anders
Published: March 2023

Egg measurements were in 1994—1996 collected on a Treecreeper population nesting in artificial nest sites erected in deciduous forests in south-western Sweden. The mean egg volume was 1.21±0.091(SD)cm3 (n=533) and the mean weight was 1.26±0.100g (n=133). The mean volume decreased as the clutch size increased from 1.26±0.091cm3 (4-egg clutch) to 1.16±0.079cm3 (7-egg clutch). Within clutches, the volume showed on average an 8% increase from first to last laid egg, and the size and laying order coincided for about 50% of the eggs on each separate day in the laying sequence. The egg sizes of neighbouring clutches with laying start on the same day tended to vary in parallel from first to last egg, indicating a constraining influence of environmental origin on egg formation. The size of an egg was positively correlated with the ambient temperature of the first two or three days before laying. This relation was less clear during periods of falling temperature, probably because the temperature influence was counteracted by the tendency of the female to successively increase egg investments in the laying sequence. The consequences and adaptive value of this trait are discussed.
Population size, migration routes and breeding origin of Purple Sandpipers Calidris maritima wintering in Sweden
Authors: Hake Mikael , Blomqvist Donald , Pierce Elin P , Järås Tommy , Johansson Olof C
Published: March 2023

We analysed the occurrence and breeding origin of Purple Sandpipers Calidris maritima wintering in Sweden, using data from long-term surveys along the Swedish west coast, sightings in other parts of the country, and ringing data from Sweden, Svalbard and the Baltic Sea coasts. About 2,000 Purple Sandpipers were estimated to winter in Sweden. Most of them (75%) occurred in the outer archipelago off the west coast, where birds arrived in October and November. This arrival coincided with the migration of birds along the east coast and across Sweden. Sightings and ringing recoveries confirmed that some wintering birds followed a migration route along the Swedish east coast and across northern Finland, but the data also showed that some wintering birds originated from Svalbard and migrated along the Norwegian coast. Accordingly, bill-length distribution of birds captured at the Swedish west coast indicated that at least two populations regularly occur here. Most birds had bill-lengths similar to Svalbard breeders, but several had bills longer than the maximum measurement recorded at Svalbard. Bill-lengths of migrating Purple Sandpipers captured at the Baltic Sea coasts, as well as sightings and recoveries of birds ringed in Sweden, suggested that the long-billed Purple Sandpipers use the migration route along the Swedish east coast. Probably, these birds originate from breeding grounds on the Taymyr Peninsula.
Breeding success, dispersal, and long-term changes in a population of Eagle Owls Bubo bubo in southeastern Sweden 1952–1996
Authors: Olsson Viking
Published: March 2023

In 1950 when the Eagle Owl became legally protected in Sweden, the species was nearly extinct in most parts of the country and survived only with a small population in the southeastern part of the country, along the Baltic Sea coast. This population has been studied in 1952–1996. Recoveries of birds ringed in the study area demonstrated that dispersal was limited; post-fledging dispersal was on average 56.8 km in the first year of life. In birds older than one year the mean distance from the hatching site to the site of recovery was 47.7 km. The mean brood size in successful nests was 1.47 young. However, the mean reproductive success calculated for all occupied territories was only 0.68 young per pair and year. Among all pairs, 43.7% bred successfully and 24.7% failed. Thus, each year 31.6% of the pairs stayed in the territory without breeding. For an extended part of this long term study, reproduction seems to have been just enough to maintain a stable population size in the study area. Only in the years 1986–90, there seemed to be a surplus of young produced in the study population resulting in new breeding pairs, predominantly outside the old study area. From a national project with captive breeding, 2,759 young Eagle Owls have been released in nearly all parts of Sweden. Around 1982, the number of pairs originating from the released birds was in equilibrium with the original "wild" population, and in 1995 the released birds and their descendants were about twice as many. In recent years probably many pairs are of mixed origin, and the mixing of the two populations is likely to increase in the future. In total, there were about 400 territories occupied by Eagle Owls in Sweden in 1996.
Importance of a bird migration hot spot: proportion of the Swedish population of various raptors observed on autumn migration at Falsterbo 1986–1995 and population changes reflected by the migration figures
Authors: Kjellén Nils
Published: March 2023

The importance of Falsterbo, Sweden, as a concentration site for migrating raptors was assessed by recording total numbers of various species during ten autumns 1986–1995. Population estimates and number of fledged young per pair were taken from the literature to estimate the Swedish autumn population. These estimates were compared with the average numbers of migrants at Falsterbo to see how large proportion was recorded there and if there was any difference between adults and juveniles. The proportion observed at Falsterbo varied from below 1% in Goshawk Accipiter gentilis to 38% in Red Kite Milvus milvus. Species with more southerly distribution (breeding closer to Falsterbo), like Red Kite and Marsh Harrier Circus aeruginosus were recorded to a higher degree compared to northerly species like Northern Harrier Circus cyaneus and Rough-legged Buzzard Buteo lagopus. Thermal migrants like Honey Buzzard Peris apivorus, Red Kite and Common Buzzard Buteo buteo were more concentrated at Falsterbo compared to active flyers like harriers and falcons, which are less inclined to follow leading lines. In most species a higher proportion of juveniles was recorded. This may be due to adults generally wintering further north or being less inclined to follow leading lines. Three species (Honey Buzzard, Rough-legged Buzzard and Peregrine Falco peregrinus) showed a higher percentage of adults. In these species I suggest the adults use their previous experience to follow established safe and efficient routes to their known winter quarters. Systematic autumn counts of migrating birds at Falsterbo have been conducted since 1973. The correlation of annual numbers with these standardised counts is significant in all species, although the average figures are between 38 and 214 percent higher in this study due to a better coverage. Most species are at the moment stable or increasing. Recent population increases in Red Kite, Marsh Harrier and Peregrine are very well reflected by the counts. Standardised migration counts at Falsterbo are presently the best way to follow long-time changes in the Swedish raptor populations.
Is there a viable population of Corncrakes Crex crex on Öland, southeastern Sweden?: habitat preference in relation to hay-mowing activities
Authors: Ottvall Richard , Pettersson Jan
Published: March 2023

Corncrake Crex crex numbers have declined on Öland, southeastern Sweden from 239 singing males in 1972—75 to 90 singing males in 1997. During the same period, the median date for the harvesting of silage and hay advanced about two weeks from late to early June. A census conducted in 1997 revealed that 86% of Corncrake males used silage or hay fields as calling sites before harvest. Alternative habitats after mowing were set-aside fields with Phleum pratense, meadows dominated by grass, and on southern Öland vegetation with herbs such as Anthriscus sylvestris, Urtica dioica and Filipendula ulmaria. Between the early 1970s and 1997, the number of singing males had decreased in almost all parishes that previously held large number of Corncrakes. The only exception was Löt where 24 males were registered in late June 1997 (26 in the early 1970s). This area probably attracted birds that had failed elsewhere. Later mowing at Löt in 1997 allowed survival to hatching of a small proportion of first broods in silage fields . However, successful reproduction in silage or hay fields of repeat and replacement broods was not likely as all fields were mown before 20 July. This study indicates that the breeding success of Corncrakes on Öland is below what is needed for a viable population.
Density and flock size of the Magpie Pica pica on the agricultural landscape during winter period
Authors: Vogrin Milan
Published: March 2023

On the agricultural landscape (346 ha) in northeastern Slovenia (46°25'N, 15°45'E) the Magpie Pica pica was studied during the winter period (December–February) 1997/98. The average density was 8.38 individuals/km2. The Magpies foraged mainly single or in pairs. Differences in flock size between months were significant only on arable land (Kruskal-Wallis test, Chi-square = 7.98, df = 2, P < 0.05) but not in urban areas.
Age structure of passerine migrants at the eastern Baltic coast: the analysis of the "coastal effect"
Authors: Payevsky Vladimir A
Published: March 2023

The trapping data of 12 migrant passerine species comprising more than 1,025,000 birds were used to determine age structure of migrants. The data were collected at the Courish Spit of the Baltic Sea during 1972—1995. Six species which are predominantly nocturnal migrants showed the "coastal effect", that is a disproportionately high percentage of immature birds, as opposed to diurnal migrants. The comparison of these results with the data from other studies in the Baltic region incline us to think that the coastal effect is caused by differential behaviour of adults and immatures during landfall after a nocturnal flight over large bodies of water.
Egg size of the Common Tern Sterna hirundo in Slovenia
Authors: Vogrin Milan
Published: March 2023

Clutch size and egg size of the Common Tern Sterna hirundo was studied in Slovenia. The total number of eggs measured was 242 from 90 nests. Among 90 complete clutches, 53.7% had three eggs. Density of breeding pairs had no effect on the clutch size. The largest eggs were found in clutches with two eggs. Egg length averaged 41.23 mm, egg breadth 30.07 mm, egg volume 19.52 cm3 and egg shape 0.73. No significant relationship was found between egg size (volume, breadth, length) and latitude and longitude (this study and literature data) within Europe.
Spring migration of Barnacle Goose Branta leucopsis and Dark-bellied Brent Goose B. bernicla bernicla over Sweden
Authors: Green Martin
Published: March 2023

Numbers of migrants, flock sizes, influence of winds, geographical pattern, and timing of spring migration of Barnacle Goose Branta leucopsis and Dark-bellied Brent Goose Branta bernicla bernicla over Sweden during 1981–1995 are reported. Both species showed a general increase in passing numbers during the period, in good agreement with overall population trends. Flock sizes of Brent Geese in Sweden were larger than those at departure from the Wadden Sea while flock sizes of Barnacle Geese were similar in Sweden and at the Wadden Sea. Flocks migrating overland were larger than flocks following the coast for both species. There was a preference for migrating in tailwinds. Normally 70–90% of all observed birds (both species) were recorded in the most southern provinces. Median dates of passage was 19 April for Barnacle Goose and 25 May for Brent Goose. The time pattern of Barnacle Goose changed during the period with a higher proportion passing in May during the later years of the study. Timing of Brent Goose passage did not change, although it was delayed in headwind years.
Length of stay and volume of autumn staging Dunlins Calidris alpina at the Tipperne reserve, Denmark
Authors: Desholm Mark
Published: March 2023

Resightings of dyed, staging Dunlins showed that the mean length of stay was 23.4 days. Applying this figure on data from the running bird counts I estimated that 33,928 Dunlins used the area during autumn 1996. Hence Tipperne qualify as a site of international importance with 1% of the flyway population using the area. The maximum number of Dunlins observed in a single autumn count in 1996 was 12,172 individuals. This substantial discrepancy suggests that maximum number is an inadequate measure of volume and with that of site quality. Analysis of a ten years period showed that maximum numbers do not correlate with bird-days, which further underline maximum number as a controversial measure of site quality. Length of stay at six different staging areas in Northern Europe declined with increasing distance to the Wadden Sea; once arrived in its vicinity the migratory urge is reduced and the length of stay is considerably increased. This increasing length of stay will result in an undervaluation of site quality of the eastern staging areas if the criterion is based on maximum numbers from simple head counts.
Sexing Serin Serinus serinus fledglings by plumage colour and morphometric variables
Authors: Senar Juan Carlos , Domenech Jordi , Conroy Michael J
Published: March 2023

Identifying the sex of fledglings may be crucial in many ecological bird studies. However, in many passerine species, fledglings show a typically streaked, brownish plumage which prevents discrimination of sexes. In this paper we test the usefulness of plumage colour (in conjunction with morphometric variables) to sex Serin fledglings. The data are based on 904 Serin fledglings (EURING age 3J) captured in the suburban area of Barcelona (NE Spain) from 1993 to 1996. Of these, 175 were recaptured and the sex confirmed. Variables used included: plumage colour (a six values visual score from very greyish-brown to very ochreous-brown, and quantitative data from a digital chromameter), days since 1st of March (to compensate for incomplete feather growth), length of wing, tail and culmen, width and depth of bill, body mass, length of first and third primary, and the five first components of a Principal Components Analysis of the biometric variables. We also included the interaction between the variables. The results showed that female fledglings tend to have a greyish-brown plumage colour, whereas males display an ochreous- brown plumage, characterised by a higher saturation of colour on back and breast, and a generally more yellowish hue. According to logistic regression, 83% of Serin fledglings can be correctly sexed by wing length, plumage colour, date and the interaction between wing-length and date.
Migratory pattern in the genus Circus: sex and age differential migration in Italy
Authors: Gustin Marco , Pizzari Tommaso
Published: March 2023

The migratory patterns of Marsh Circus aeruginosus, Pallid C. macrourus, and Montagu's C. pygargus Harrier were studied in spring in south-east Italy. Differences in the time of passage during the season were found between sexes and age classes in all three species. Adult males showed a significant tendency to migrate earlier than females and the latter earlier than juveniles. Also, adult Marsh and Montagu's Harriers passed significantly earlier during the day than second calendar year individuals. Such patterns are explained in the light of the selective pressure exerted on adults to reach the breeding territories early in the reproductive season.
Kornknarrens Crex crex biotopval, revirstorlek och ortstrohet på Öland: en radiosändarstudie
Authors: Ottvall Richard , Pettersson Jan
Published: March 2023

A radio telemetry study of the Corncrake Crex crex was carried out on Öland, southeastern Sweden in 1992—1997. The aim was to study the breeding biology and habitat selection of this globally threatened species. 73 males were ringed and to 43 of these males we attached radio transmitters for more detailed monitoring. The number of singing males was counted regularly. Most frequented habitats were (1) wet meadows dominated by grass, (2) abandoned marginal zones with tall herb vegetation like Anthriscus sylvestris and Urtica dioica and (3) silage fields. Cereals were seldom used. The home range was about 5 ha at each calling site, but some males changed territories and moved up to 7 km the same season. The majority, or 59%, of captured birds were aged as second year birds. Site fidelity between years was 13%. The apparent low site tenacity does not necessarily indicate low reproduction of young. A low return rate could instead be explained by the high annual mortality observed in this species. Several breedings were confirmed in the study area but the relative reproductive success was unknown. There are, however, indications of a 50% decline on Öland since the 1970s. Keeping a habitat mosaic is important to prevent further declines.
Flockstorlek och tidspann hos inflygande starar Sturnus vulgaris till övernattningsplatsen
Authors: Karlsson Thomas , Lerner Henrik
Published: March 2023

We studied a small communal roost of starlings situated in an urban area. On 14 evenings between 16 June 1993 and 7 July 1994 we recorded 824 flocks with 11,388 individuals. The roost had most starlings per night (more than 3,000) just after the breeding season. In spring, arriving flocks were mostly small (mean 8 birds) while they were larger (18 birds) in autumn. Most flocks arrived close to the mean arrival time. On 12 of the 14 days mean arrival time fell before sunset. The duration of the arrival period was positively related to day length. In early spring 1994, no starlings at all arrived at the roost. During the first observations in June, we also noticed that the starlings were unwilling to land in the reedbeds. We guess that juvenile starlings arriving at the roost for the first time learnt the behaviour. We also guess that adult starlings in early spring have the same behaviour.
An apparatus for photographing whole clutches of passerine birds in transmitted light
Authors: Enemar Anders
Published: March 2023

Single eggs have since long been examined in transmitted light in various ways in the field to obtain information on the incubation stage of a clutch. This technique can be rendered more effective by combining it with photographing whole clutches. An apparatus for this purpose is described, dimensioned for work with clutches of small passerines up to the size of thrushes. The photographs reveal more details than is possible to discern during direct examination in the field. Further, the presence of all eggs of the clutch on the same photo facilitates the interpretation in order to estimate certain breeding biology data, such as the time of incubation start and the developmental or hatching asynchrony.
Inventering av häckande simänder vid Angarnsjöängen 1978–1998 och sjörestaureringens inverkan på resultatet
Authors: Söderholm Svante , Eriksson Kjell
Published: March 2023

Angarnsjöängen is a shallow lake 25 km north-east of Stockholm. It was famous for its bird life already in the 1930s, but the conditions have deteriorated in recent years because of expansion of high emergent vegetation and willows along the shores. A restoration plan was implemented in 1992 involving creation of large areas of open water and increase of the annual water level amplitude, especially spring flooding. The breeding dabbling ducks (Anas species) had been censused annually since 1978. Hence the effects of the restoration could be accurately estimated. After restoration there was a rapid increase of the duck population. Two species, A. querquedula and A. crecca showed the strongest response. Three other species also increased, A. strepera, A. platyrhynchos and A. clypeata, although it was less clear that the restoration was the only cause. For A. strepera the lake also became an excellent autumn site. The study shows that long-term monitoring of important bird lakes is necessary both for detection of deterioration and for assessment of restoration results.
Gulärlans Motacilla f. flava häckningsbiologi i strandängsmiljö i nordöstra Skåne
Authors: Flyckt Greger
Published: March 2023

The subspecies Motacilla flava flava of the Yellow Wagtail has shown a decreasing breeding population trend in southern Sweden. A contributory cause could be the extensive use of wetlands, the most preferred breeding habitat. This habitat is successively disappearing from modern Swedish farmland. To get more information about the breeding biology in southern Sweden a study was started in 1991. Data from a total of 81 nests from shore meadows were collected during 1991—1996. The birds showed a preference for breeding in grazed areas (63–70%) in comparison with mowed meadows. The average breeding success in grazed areas differed from the mowed areas (4.26 vs. 4.68 fledged young per nest). Out of 13 unsuccessful breeding attempts, 8 failures were directly caused by grazing cattle.
Symmetrical location of White Stork Ciconia ciconia nests in hightension poles
Authors: Lima-De-Faria Antonio
Published: March 2023

The white stork Ciconia ciconia was found to build 24 nests on high-tension poles located in marshy fields near the city of Coimbra, Portugal. The metal poles consist of a central frame with three platforms, which ramifies into two arms in nearly vertical position. These arms are connected by a large horizontal frame. The nests were only situated on the high-tension poles. The number of nests in a single pole was found to be: 1, 2, 5, 6 or 7. In most cases the nests were located at the extreme ends of the metal frames whether these had a horizontal or a nearly vertical position. When two or more nests were present, a symmetrical pattern emerged in all cases observed, irrespective of the different nest locations. Four factors are considered when interpreting these findings: (1) The shape of the poles, (2) the size of the stork’s wings, (3) the presence of a high magnetic field, and (4) the mental behaviour of the birds. The last aspect seems to be the most probable explanation but it demands further study.
Bar-tailed Godwits Limosa lapponica on south Swedish shores in spring—emergency stopovers or a regular occurrence?
Authors: Green Martin
Published: March 2023

The occurrence of spring staging Bar-tailed Godwits Limosa lapponica in two bays in Öresund, southwestern Sweden, was monitored in 1996—1998. Godwits were present in the area from early April to early June with a peak in the first half of May, when several hundred birds were present at one time. The timing of the occurrence indicates that the birds belong to the ”European population”. Total number of birds involved per season could maximally be a few thousand, constituting 1–3% of the total population in northern Europe. Numbers of birds present was not significantly correlated to weather variables as wind, cloud cover or precipitation. The birds foraged intensively but no large scale accumulation of fuel stores was observed (i.e. by the use of abdominal profile scores), indicating a relatively rapid turnover of individuals in the area. More females than males were observed which indicate differences in migration strategies between the sexes. It is concluded that the two bays are a regular, but small-scale, stopover area for Bar-tailed Godwits during spring migration.
Assessment of the zoobenthos biomass consumed yearly by diving ducks wintering in the Gulf of Gdańsk (southern Baltic Sea)
Authors: Stempniewicz Lech , Meissner Włodzimierz
Published: March 2023

Numbers, distribution and food contents of seven common diving ducks (Clangula hyemalis, Melanitta fusca, Melanitta nigra, Aythya marila, Aythya fuligula, Bucephala clangula, Somateria mollissima) and Fulica atra were studied in the Gulf of Gdańsk during September–April, 1987/88–1996/97. The number of animal food taxa consumed was at least 23. The birds fed mainly on bivalves (79.4% of the food volume), and fish (7.1%), gastropods (6.7%) and crustaceans (5.0%) constituted the remaining significant prey. Mya arenaria, Cerastoderma glaucum and Hydrobia sp. were preferred, while Mytilus trossulus, dominating in the shallow parts of the gulf, was taken in lower proportions. Small ducks (Aythya, Clangula) selected bivalves of shell length 7–14 mm regardless of their different average size in zoobenthos. The two biggest ducks (Somateria mollissima and Melanitta fusca) selected the largest (above 30 mm) of the available Mya arenaria specimens. Birds consumed proportionally more bivalves in December and January than later in the season. Fish (mainly fish eggs) increased their share in spring. Diving ducks and Coot function generally as first to forth-order carnivores in the food web. As a consequence of their high numbers and long period of stay, annual biomass consumption is considerable: 25,000 tonnes, including 20,000 tonnes bivalves, 1,800 tonnes fish, 1,700 tonnes gastropods and 1,270 tonnes crustaceans. For bivalves this is ca 13 % of the total biomass in the Gulf. The strongest exploitation of bivalves takes place in December–February, when their proportion in the diet is highest and the birds are most numerous, and concerns the shallow water areas where ducks and coots concentrate. In such areas they can exert significant predatory pressure on preferred size classes of their most important prey.
Nest-leaving in the Starling Sturnus vulgaris: an example of parent-offspring conflict?
Authors: Ottosson Ulf
Published: March 2023

It has been suggested that there will be a conflict not only between parent-offspring but also between siblings, about when to leave the nest. To investigate which part of the family initiates nest-leaving Starling nestboxes, with individually marked nestlings, were observed prior to, during and after nestlings had started to leave the nest. Parents may initiate nest-leaving by decreasing the provisioning rate. It is suggested that the time of fledging is determined by sibling competition and the trade off between the possibility to be fed inside the nestbox or outside.
Egg sizes of nine passerine bird species in a subalpine birch forest, Swedish Lapland
Authors: Enemar Anders , Arheimer Ola
Published: March 2023

Egg measurements together with calculated volumes are presented for nine passerine species (Prunella modularis, Luscinia svecica, Phoenicurus phoenicurus, Turdus pilaris, Turdus philomelos, Turdus iliacus, Phylloscopus trochilus, Fringilla montifringilla, and Carduelis flammea), breeding in rich subalpine birch forests on a south-faced mountain slope in southern Swedish Lapland. There were no clear regional size trends in comparisons with egg collections from other parts of Europe. There was a significant increase in egg size in the latter part of the laying sequence. The ultimate egg is from 2.1% (F. montifringilla) to 6.5% (Ph. trochilus) larger than the mean of the clutch. According to several years’ measurements of T. pilaris and T. iliacus eggs there was no significant size variation between seasons. This constancy together with the relatively large egg sizes might be a consequence of the productive breeding habitat of the study area.
Migration of Garganey Anas querquedula and Teal Anas crecca in north-eastern Slovenia
Authors: Vogrin Milan
Published: March 2023

Migration patterns and occurrence of Teal Anas crecca and Garganey Anas querquedula were studied in the fishpond complex Racki ribniki (35 ha) in northeastern Slovenia between 1985 and 1996. Peak numbers of Teal in spring occurred in February and in autumn during November. Spring peak numbers of Garganey occurred in April, whereas in autumn the migration was less pronounced. During the spring migration the differences in numbers between months were highly significant. In spring, males were significantly more common than females. Comparisons with other localities in Slovenia showed that the Racki ribniki ponds are important sites for both species during migration.
The Swedish Reed Warbler Acrocephalus scirpaceus population estimated by a capture-recapture technique
Authors: Stolt Bengt-Olov
Published: March 2023

The number of Reed Warblers Acrocephalus scirpaceus leaving Sweden on autumn migration was estimated by a capture-recapture technique. A large number of Reed Warblers are ringed annually, mainly in July–September. During the same period, shortly after ringing, these birds leave Sweden on autumn migration directed south-west. One sample is recaptured at the south-western corner of Sweden, at Falsterbo Bird Observatory, and the capture-recapture technique can be used to estimate the size of the total population. The result of the calculation for the total number of Reed Warblers leaving Sweden each autumn was 3.3 million (95 % confidence interval ±0.86 million). The corresponding number for the juvenile birds was 1.8 million (±0.63 million). Due to a low rate of recaptures of ringed adult birds at Falsterbo, the calculated total number may be too high, whereas the number achieved for juvenile birds was judged to be more correct. Detailed analyses of available data support that about 1.8 million juvenile birds leave Sweden on autumn migration. Among them, 5.7 % are assumed to be of Finnish origin and 1 % are assumed to come from other areas outside Sweden. On the basis of available data on survival, breeding success, pair density and reed areas, the mean annual breeding population of Reed Warblers in Sweden, 1988–1993, was estimated to be about 500,000 to 600,000 pairs, which is a larger population than previously assumed.
Strömstaren Cinclus cinclus och försurningen: beståndsutveckling, häckningsresultat och födoval i sydvästra Sverige
Authors: Åhlund Matti , Börjesson Roland , Engblom Eva , Eriksson Mats O G , Lingdell Pär-Erik , Ström Kåre , Åhlund Ingemar
Published: March 2023

Breeding Dippers were surveyed at 45 streams in southwestern Sweden in 1974—1978 and in 1990—1992. Dippers bred at 37 streams (65 sites) in 1974—1978 and 38 streams (74 sites) in 1990—1992. The breeding frequency, and the change in breeding frequency from 1974—1978 to 1990—1992, did not differ between streams with different history of acidity. Also, clutch size and brood size were similar along neutral, formerly acidic, and acidic streams. We analysed by faeces the diet of adult Dippers in 30 breeding pairs in 1991. Their diet at neutral, formerly acidic and acidic streams showed no clear differences; preferred prey seemed to be available even on acidic streams. So, in contrast to studies in Scotland and Wales, we found no apparent effects of stream acidity on breeding Dippers in this pilot study.
Do Mynahs prefer Peacock feathers of more regular pattern?
Authors: Kobayashi Tomomichi
Published: March 2023

The “sensory exploitation hypothesis” and the “quality assessment hypothesis”, aimed at explaining female preferences of symmetrical male sexual ornaments, were tested on Mynahs. In the first experiment, two birds were allowed to select between two abstract patterns, one regular and one irregular. The birds preferred the regular patterns but only significantly so in one individual. In the other experiment two other Mynahs were allowed to select between two images of male Peacock tails, a sexual ornament of an unrelated species. Both birds showed a significant preference for the image with a more regular Peacock tail. The results are discussed in the light of the limited sample size. The value of the technique to separate between the hypotheses of female preference for symmetric male characters is discussed.