bluuebunny/crossref_metadata_2025 huggingface dataset:
Spring staging of Taiga Bean Goose Anser f. fabalis in southern Sweden 2007—estimate of the size of populations using the western and central flyways
Authors: Skyllberg Ulf , Tjernberg Martin
Published: March 2023

The Taiga Bean Goose Anser fabalis fabalis is one of few goose species under current decline. The species uses three flyways: the Scandinavian population migrates west of the Baltic Sea and the Bothnian Bay, the Finnish and western Russian populations take a central flyway, and the central Russian population migrates east of the Baltic Sea. On 17–21 March 2007, the number of birds using the western and the central flyways were counted at all staging sites in southern Sweden. During the count, practically the whole western and central flyway populations were concentrated in southern Sweden. We estimated the number of birds at 56,000. Recent estimates suggest that 5,000–6,000 of these birds breed in Scandinavia and use the western flyway. This means that approximately 50,000 birds used the central flyway. Assuming that a maximum of 30,000 birds wintered in Germany and used the eastern flyway, the global population of the Taiga Bean Goose amounted to a maximum of 85,000 birds. This is about 15,000 birds less than an estimate from 1999.
Breeding performance of the Fieldfare Turdus pilaris in the subalpine birch zone in southern Lapland: a 20 year study
Authors: Arheimer Ola , Svensson Sören
Published: March 2023

A Fieldfare population, on average c. 160 pairs, was studied in subalpine birch forest in southern Lapland (c. 66°N; 500–600 m.a.s.l.) in 1983–2002. Onset of egg-laying showed no temporal trend, consistent with absence of spring temperature trend. Eggs were laid with an interval of c. 21 hours and 45 minutes, not 24 hours as normal in passerines. This reduces the exposure time to depredation during egg-laying with 9%. Egg hatchability was 96%. Egg parasitism never occurred. Depredation of nests was 46%, but very variable. Replacement and second clutches did not occur. Although an average of 4.45 young fledged from successful nests (≥1 fledgling), only 2.11 fledglings were produced per pair and year. The population varied without trend over the study period. Adult survival, estimated by the proportion of adults at the start of breeding, was 58%. This infers that first year survival must be at least c. 40%. Since this is a likely value, it seems that the Fieldfare population of the subalpine birch forest is selfsustained and not dependent upon immigration.
En långtidsstudie av talgoxens Parus major häckningsbiologi i ett mellansvenskt blandskogsområde
Authors: Schölin Karl Gustav
Published: March 2023

A nestbox-breeding population of Great Tits Parus major was studied from 1948 to 2008 in a mixed coniferous-deciduous forest near Örebro, South Central Sweden. The population was relatively stable around 20 pairs until the mid-1980s after which it increased markedly. Mean laying date was advanced by almost 5 days over the 60-year period, with most of the change taking place after 1985. The mean size of first clutches was 8.72 and was negatively related to number of breeding pairs. Mainly because of Pine Marten Martes martes predation, the mean number of fledged young was only 5.76 (all nests) and 7.37 (nests with at least one fledgling). The proportion of second clutches varied from zero to c.20%. Second clutches had a mean size of 7.00 eggs, slightly less than that of replacement clutches (7.29). The mean number of young fledging from these two categories of broods combined was 5.5. Both the clutch size and fledging success found in this study are similar to those in other Swedish studies at similar latitudes.
Population trends for Swedish breeding birds
Authors: Ottvall Richard , Edenius Lars , Elmberg Johan , Engström Henri , Green Martin , Holmqvist Niklas , Lindström Åke , Pärt Tomas , Tjernberg Martin
Published: March 2023

We have assessed the population trends for the 255 bird species breeding in Sweden (including distinct subspecies), based on data for the last 30 and 10 years, respectively. Over the past 30 years more species have decreased (38%) than increased (32%) in numbers. In particular, formerly common farmland species have fared poorly but this is also true for some forest species. Over the past 10 years there are more species with increasing trends (29%) than there are species with decreasing trends (19%). Trends for several species in long-term decline have levelled off and have in some cases even started to increase. It is not known whether this recent change is a result of conservation efforts or simply that population numbers have stabilised at lower levels now permitted by the environment. It is therefore essential to initiate research devoted to finding factors directly linked to ongoing population changes, particularly for species in long-term decline. To cover population trends for all Swedish species additional monitoring programmes are needed, in particular on owls and in mountain habitats.
Waterbird dynamics at the shallow Lake Krankesjön, southern Sweden: a long-term study
Authors: Källander Hans , Hansson Lars-Anders , Brönmark Christer , Nicolle Alice
Published: March 2023

This paper reports the within-year and between-year variations in the number of waterbirds at Lake Krankesjön, southern Sweden based on counts carried out during 1985 to 2007. The background to these counts was a dramatic decrease in the number of Great Crested Grebe Podiceps cristatus, Mute Swan Cygnus olor and Common Coot Fulica atra from 1974 to 1976, concurrent with a deterioration of water transparency and a nearly total disappearance of submerged vegetation. In 1985, when the regular counts of waterbirds started, the lake had just begun to recover. Numbers of moulting and staging waterbirds increased rapidly as the conditions improved. Numbers of grebes, swans and coots over the two decades correlated with limnological variables, and it is concluded that their numbers depend on the amount of submerged vegetation, in turn determined by water transparency.
Differences in foraging ecology of Wood Sandpiper Tringa glareola and Ruff Philomachus pugnax during spring migration in Sajna River valley (nor thern Poland)
Authors: Krupa Małgorzata , Ściborski Mateusz , Krupa Robert , Popis Rafał , Wołoszyn Justyna
Published: March 2023

The research was conducted in 2002, in Sajna River valley (NE Poland). It was aimed at foraging ecology of two wader species not specialised in terms of feeding techniques. We found that while foraging on a stopover site during spring migration Ruffs used different ecological niche than Wood Sandpipers. Ruffs foraged significantly more often in medium and deep water and made also more medium and deep probes, what indicates preference in random probing. High intensity and proportionally low efficiency of foraging may confirm it. Contrary, Wood Sandpiper foraged less intensively but much more effectively; this, together with frequent changes of feeding places in terms of water level indicate that Wood Sandpiper to greater extent uses visual detection of prey than Ruff.
Territoriality in the Willow Warbler Phylloscopus trochilus in its winter quarter in Lesotho
Authors: Kopij Grzegorz
Published: March 2023

Territorial behaviour of the Willow Warbler Phylloscopus trochilus was studied in an urbanised habitat in Lesotho, southern Africa, in three consecutive wintering seasons (November–March 1999–2002). Contrary to expectation, the Willow Warblers were holding territories. As many as 34% of all territories were held permanently throughout the wintering season, and 33% were located at the same site for the three consecutive years. The intensity of territoriality (singing) tended to increase as spring migration was approaching (February–March). This was assumed to be a response to an increasing need to defend food resources required for fat deposition before departure. The birds showed a strong preference for feeding in Salix babylonica and Acacia dealbata.
Images of Barnacle Goose Branta leucopsis hybrids – a photo documentation of some crosses with different Anser species
Authors: Gustavsson C G
Published: March 2023

This article presents full-body and close-up photographs of hybrids between Barnacle Goose and some Anser goose species. The second parent was in one case a Snow Goose, in five cases a Greylag Goose, in one case a domestic Swan Goose and in one case a Bar-headed Goose. Parentage is considered proven in the Snow Goose and the Greylag Goose hybrids. These hybrids are all rare. The number of individuals is in the magnitude of the estimated total Swedish populations and this is apparently the first report of a Barnacle Goose x domestic Swan Goose hybrid in Sweden. The bill colour pattern varied markedly between the five Greylag Goose hybrid siblings but little from one year to another. In the autumn, Greylag Goose hybrids and to some degree also the Swan Goose hybrid developed a transient white area of the front head next to the bill but a darker and browner colour of the pale cheek area. The various expressions of features inherited from the two parent species are exemplified in the Greylag Goose hybrids.
Brood size of twelve farmland bird species in Sweden during 1962—2001
Authors: Ryttman Hans , Hall-Karlsson K Susanna S
Published: March 2023

Several farmland bird species are declining in Sweden. We investigated if the population decreases are linked to smaller broods or a higher rate of unhatched eggs. The number of broods ringed and the average number of nestlings in these broods from 1962 to 2001 were analysed for twelve species: Skylark Alauda arvensis, Swallow Hirundo rustica, House Martin Delichon urbica, Meadow Pipit Anthus pratensis, White Wagtail Motacilla alba, Wheatear Oenanthe oenanthe, Whitethroat Sylvia communis, Starling Sturnus vulgaris, House Sparrow Passer domesticus, Tree Sparrow Passer montanus, Linnet Carduelis cannabina and Yellowhammer Emberiza citrinella. Only two of the investigated species, the Tree Sparrow and the Yellowhammer, showed a statistically significant decline in average brood size over time. We conclude that changes in brood size alone cannot explain the decline in several farmland bird species. The House Sparrow showed an increase in the number of dead nestlings and data for House Sparrow, Tree Sparrow and Whitethroat indicated that a higher rate of unhatched eggs might be a problem.
Breeding Skylarks Alauda arvensis on organic set-asides—effects of time of cutting, vegetation structure and landscape composition
Authors: Berg Åke , Kvarnbäck Olle , Gustafsson Åsa
Published: March 2023

We assessed the quality of organic set-asides as habitat for breeding Skylarks. We evaluated (i) density in relation to vegetation structure and landscape composition, (ii) reproductive success on set-asides cut at normal time (1 June) and with delayed cutting (15 June), and (iii) nest predation and destruction by using artificial nests. Skylark density was negatively associated with vegetation height and cover, and it was three times higher on fields without forest than with more than 50% forest in the surrounding landscape. Of the artificial nests, 56% were destroyed by cutting that also increased predation on surviving nests. Delayed cutting resulted in higher reproductive success; mean number of fledged broods per territory increased from 0.42 to 0.52. The negative effects of early cutting seemed to be largest on fields with sparse vegetation. Based on fledging dates we suggest that 20 June is a reasonable date for first cutting in south-central Sweden. Reproductive success on organic set-asides could probably be further improved if less dense vegetation (or unsown patches or strips) is combined with a delayed cutting.
Laying and clutch size of the Treecreeper Certhia familiaris in south-western Sweden
Authors: Enemar Anders
Published: March 2023

Breeding data were collected on an unringed Treecreeper population nesting in artificial nest sites (nest pockets) of two sizes, erected in predominantly deciduous forests in southwestern Sweden. From 1982 through 1992, 459 breeding attempts were recorded. The earliest and latest dates of laying were 29 March and 26 June. The distribution of first egg dates showed three peaks: one in April and early May (first clutches), one from late May through June (probable second clutches), with a narrow peak in between (replacement clutches). Clutch size was related to laying date in a curved fashion peaking in early May with a mean of 5.93. Overall mean clutch size was 5.48 with a range of 3-7. About a third of the successful breeding attempts (n=37) were followed by another attempt in a nest pocket nearby, considered to be genuine second clutches. The sizes of these first and probable second clutches were 5.46 and 5.03, respectively. Clutch size in large and small nest pockets did not differ although the large pockets were preferred as nest sites.
Low reproductive success in a colony of Black-headed Gulls Larus ridibundus—mass starvation of nestlings?
Authors: Bensch Staffan
Published: March 2023

The Black-headed Gull Larus ridibundus has declined in Sweden during the last twenty years, locally with as much as 75%. The factors causing this decline are unknown, and we lack data on reproductive success and mortality. In 1992, I recorded breeding success of a colony of 818 pairs on Lilla Karlso in the Baltic Sea. Only 0.37 fledglings per pair were produced. No predation was observed. When the surviving young had left the colony a search revealed at least 151 dead young (>14 days old). Five of them were recently dead. They were very thin with atrophied pectoral muscles, indicating starvation as the cause of death. The reproductive rate that I observed is lower than in other European studies, but similar to the one found in a declining colony in Britain. May and June of 1992 were very dry, possibly making the main food, earth worms, unavailable. Hence, 0.37 young per pair may not be typical for an average weather situation. None the less, it is urgent to carry out further studies on the breeding success of the Black-headed Gull in the Nordic and Baltic countries in order to determine whether starvation or any other factor contributes to the population decline of the species.
Interspecific variation in time budgets among sympatric dabbling ducks
Authors: Åström M¨årten
Published: March 2023

The effect of some of the ecological differences among Swedish dabbling ducks, population densities and sex ratios on the proportion of time allocated to foraging was studied during the breeding season 1986 and 1987. Time budget data were collected at southern Gotland, Sweden, and correlation analyses were done with ecological differences determined from the literature and from observations. Increasing male bias in the sex ratios increased the amount of time spent vigilant early in the breeding season for both sexes in April 1987 and for males in May 1987, and also increased the amount of movements of males in April 1987 and of females in May 1986, but decreased movements of males in June 1986. The amount of time spent vigilant did also decrease with increasing male bias for females in June 1986. The proportion of time spent foraging by females in May 1986, but also in May 1987 and June 1986, decreased as the male bias increased. In early breeding season (April), the proportion of time devoted to aggressions (for males) and movements (for females) were positively correlated with the population densities. This did not, however, lead to decreased foraging time. In late season (July) the foraging time was positively correlated with population densities, indicating intraspecific exploitative competition for prey. Migration distance and degree of carnivory did not influence amount of time allocated to foraging. In conclusion, it was shown that sex ratios and population densities did influence time allocation among dabbling ducks during some parts of the breeding season.
The importance of mires as breeding habitat for wetland birds in Sweden
Authors: Arvidsson Björn L , Boström Ulf , Dahlén Börje , De Jong Adjan , Kolmodin Ulf , Nilsson Sven G
Published: March 2023

During the last 15 years the bird fauna was censused on 2,250 km2 of mires, which is 10–15% of the estimated total area of larger, treeless mires (>0.5 km2) in Sweden. The total number of bird species breeding on mires increases from 25 in the most southern region (Götaland) to 43 in the most northern region (N. Norrland), but more of the northern species breed at very low densities. Among taxonomic groups, species richness of wildfowl and shorebirds increases with latitude while that of passerines shows no clear trend. One possible explanation for the increased species diversity towards the north may be that northern mires generally have a more complex habitat structure, making more niches available. There was no general geographic pattern in the population density of different species. Wildfowl, birds of prey (including owls) and shorebirds (including the Crane) breed at higher densities in the north while passerines have lower densities. One reason for the higher breeding densities of wildfowl and shorebirds in the north is that mires there to a larger extent consist of fens than do mires in the south. Also, a lower nest predation in the north is a probable reason. Combining all species there was no trend in breeding density. Calculations of population sizes show that 25% of the 44 species recorded have breeding populations of more than 10,000 pairs while 25% have less than 1,000 pairs on mires. Estimates of population sizes in Sweden as a whole for all species breeding on mires show that 11 species have more than 50%, and four have more than 75% of their total Swedish population on mires. These species are especially interesting from a conservation point of view since they may be used as indicators of valuable mires.
Feeding areas and local movement patterns of post-breeding Greylag Geese Anser anser in South Sweden
Authors: Nilsson Leif , Persson Hakon
Published: March 2023

Greylag Geese Anser anser mostly selected one field type, neglecting all other available types. After the breeding season they started to feed on grasslands, turned to peas during the end of July or the middle of August, and then shifted to wheat stubble in the first half of September. Only two other field types, barley stubble and newly-sown cereals, were occasionally selected. Most of the time they never showed any interest in oat stubble, newly-sown cereals and newly-sown rape. Rape stubble and ploughed fields were never used. Fields with high-energy food accounted for about 95% of all goosedays each autumn. The exploitation rate of large fields (>17 ha) with peas or wheat stubble was much higher than that of smaller fields with the same crop. Distances between roosts and feeding areas were normally less than 5 km. In October the activity pattern, characterized by two daily feeding periods, began to weaken, with some geese staying on the feeding grounds all day. In November all geese spent the whole day on the feeding grounds. The length of time spent on the feeding grounds per day increased from about 200 min. in mid-August to more than 400 min. in early October. The marked families not only stayed in the study area the whole autumn but moreover, they rarely moved between different gathering areas. There were no significant differences between families and pairs without young with respect to the time they were present and the number of times they moved between different gathering areas. Subadults moved between gathering areas significantly more often than did mature birds.
Requirements by the Great Spotted Woodpecker Dendrocopos major for a suburban life
Authors: Hannsson Lennart
Published: March 2023

The Great Spotted Woodpecker Dendrocopos major has expanded its habitat range to include suburban areas in Sweden. This range expansion may affect entire communities of hole-nesters by proficient excavation of nest holes. Numbers, habitat and nest site selection were studied in a 3 km2 suburban area in south-central Sweden during the years 1983—91 and in several forest landscapes without houses. Densities were much higher in various habitats within the suburban landscape but in such areas woodpeckers preferred to nest in woodland areas that were fairly distant from houses and in large trees. Nest heights and the number of nest holes per tree increased with distance from houses, while the proportion of Aspens among nest trees decreased with distance from houses. Aspens still dominated strongly among nest trees. The proportions of new nests and trees with single nests were lower in the suburban area than in remote forests. It is concluded that nest sites, and possibly breeding densities, are constrained by the few old or decaying trees left when new housing areas are built. Retainment of old trees and different-sized young Aspens would promote higher densities of woodpeckers and other hole-nesters and maintain a high diversity of hole-nesting species.
Variation in wing length in relation to sex and age of Marsh Tits Parus palustris
Authors: Nilsson Jan-Åke
Published: March 2023

Wing length of juvenile and adult Marsh Tits Parus palustris was measured during autumn and winter. Individuals later sexed during breeding were used to study a possible sexual dimorphism in wing length. Males of both juveniles and adults had significantly longer wings than females, the difference between the sexes being around 5.5%. Using wing length as the only criterion, between 97.4% and 88.6% of juveniles and between 98.0% and 93.4% of adults can be unambiguously sexed during autumn/winter. Individuals measured during their second or later autumn/winter had significantly longer wings than those measured as juveniles. No evidence for selection against short-winged individuals was found. Each individual increased its wing length during the first complete moult. Hypotheses explaining an increase in wing length with age are discussed and I argue that the best explanation encompasses some sort of nutritional constraint during the nestling and/or early fledgling phase.
Levels of mercury in eggs of Red-throated Diver Gavia stellata and Black-throated Diver G. arctica in Southwest Sweden
Authors: Eriksson Mats O G , Johansson Ingemar , Ahlgren Claes-Göran
Published: March 2023

In connection with surveys of breeding populations of Gavia stellata and G. arctica in Southwest Sweden 1978—91, unhatched eggs in abandoned nests were collected and analysed for mercury. In the investigated area, divers of both species primarily fish in oligotrophic lakes, many of them affected by air-borne acidifying pollutants. The level of mercury in G. stellata eggs was extremely high; in a sample of seven eggs from four breeding sites the mean concentration was 9.5 ppm dry weight with a range of 6.2–14.2 ppm, which is among the highest levels recorded for any bird species in Sweden. The concentrations in G. arctica eggs were lower: 1.0–2.4 ppm dry weight in samples from four breeding sites at circumneutral lakes, and on average 4.0 ppm (range 1.8–5.9 ppm) in a sample from four breeding sites at lakes affected by acidification. For G. stellata, all eggs contained mercury at levels where reproductive impairment is to be expected, and also single G. arctica eggs were so heavily contaminated that the risk of impairment must be considered. Fish samples from seven lakes indicated that potential prey fish (Rutilus rutilus and Coregonus albula, <20 cm) for G. stellata feeding chicks contained higher concentrations of mercury in lakes affected by acidification. In one lake, fish contained levels about twice those reported to be associated with behavioural and reproductive disturbances in fish-eating birds. Also, single fish in two other lakes contained high concentrations of mercury. The results indicate that especially G. stellata, but also G. arctica in their breeding grounds in Southwest Sweden are exposed to levels of dietary mercury, sufficiently high for reproductive impairment to be expected, and that a connection exists to high levels of mercury in prey fish from freshwaters affected by acidification.
Spring migration of the Taiga Bean Goose Anser f. fabalis along the “Western Flyway” in northern Sweden: numbers in 2003—2008 and timing in comparison with the “Central Flyway” in Finland
Authors: Skyllberg Ulf , Nousiainen Ismo , Hansson Per , Bernhardtson Per , Andersson Östen , Nordlund Mattias
Published: March 2023

Daily counts and conservative estimates of turn-over showed that at least 3,000 Taiga Bean Geese regularly used the Ume River Delta as the major staging site along the Western Flyway (following the west coast of the Gulf of Bothnia) during spring 2003—2008. Counts across all staging sites yielded 2,700–3,700 geese in southern Västerbotten and 4,000–4,800 at all sites in Västerbotten and Norrbotten. We estimate that 5,000–6,000 geese currently use the Western Flyway. Migration along the Central Flyway (Ostrobothnia, Finland) culminated on average about ten days earlier, meaning that the vast majority of geese using this flyway had left southern Sweden when the Western Flyway was activated. Counts of active migration on 15 April 2007 indicated that geese arriving in the Ume River Delta in late afternoon had passed Alirs öga, Söderhamn, 340 km to the south, five hours earlier. Assuming the same ground speed (68 km h-1) south of Söderhamn, these geese ought to have left either Lake Östen and/or Lake Kvismaren at sunrise, reaching the staging sites in Västerbotten after a 600–700 km non-stop flight.
Moult strategies of White Wagtail Motacilla alba and Yellow Wagtail Motacilla flava in central Sweden
Authors: Sondell Jan
Published: March 2023

The wing moult of the White Wagtail Motacilla a. alba and the Yellow Wagtail M. f .flava has been recorded since 1973 at Kvismaren, central Sweden. Based on data from 558 White and 78 Yellow Wagtails in active moult the wing moult duration of the former was estimated at 55–65 days and of the latter at 35–40 days. The moult sequence was the same in both species. The only significant difference  was the speed of the moult. The reason for this difference in moult strategy is probably the difference in migration  destination of the two species. The Yellow Wagtail arrives later than the White Wagtail, stays a shorter time in central Sweden and starts the migration towards tropical Africa  just before finishing the moult in the middle of August. Swedish White Wagtails winter in the east Mediterranean, arrive almost a month earlier and leave a month later. It is difficult to compare the present results with data from other parts of Europe as there are plenty of misrepresentations  published some decades ago and quoted in later works. Therefore, methods of moult data evaluation are also briefly discussed.
Diurnal song pattern in the Great Reed Warbler Acrocephalus arundinaceus
Authors: Hasselquist Dennis , Bensch Staffan , Ottosson Ulf
Published: March 2023

The diurnal song pattern of the Great Reed Warbler Acrocephalus arundinaceus was studied at Lake Kvismaren in South Central Sweden between 1985 and 1989. Males sing two types of song, a long song when attracting females and a short song when guarding fertile females. Seven males were studied over full 24-hour periods. The diurnal song pattern of males singing long song was characterized by a sharp peak in song rate at sunrise when they sang 70% of the time. In late morning song rate reached a plateau of about 55% of the time up till noon whereafter it slowly dropped to cease almost completely at sunset. An average male produced between 7,000 and 8,000 song strophes in a day. The song rate of individual males in noon and afternoon was clearly predictable from morning values, i.e. a male that had a high song rate in the morning was also likely to have a high song rate later the same day. In contrast to the long song, the short song was produced at a rather steady low level throughout the day and also appeared to be more variable in intensity over short time periods (i.e. showed a higher variance). The decline in the rate of long song over the day seemed to be paralleled by a decline in number of unmated females, suggesting that profitability of singing is highest during early morning whereafter it levels off. These results are discussed in relation to several hypotheses explaining diurnal song pattern in birds.
Different ecology in male and female wintering Snowy Owls Nyctea scaandiaca L. in Sweden due to colour and size dimorphism
Authors: Lind Henrik
Published: March 2023

Wintering Snowy Owls Nyctea scandiaca were studied in southern Sweden during four consecutive winters (November—March, 1989—1993). 85% of the known individuals (9–11 males, 11–12 females) in the provinces of Öland and Skåne were considered properly aged and sexed. They were observed for 92 h during daytime roosting and for an additional 29 h during hunting activity. Males were more often mobbed (p<0.001) during snowfree conditions, more often roosted in forests (p<0.01), left fewer pellets (p>0.05), preferred higher perch sites, and stayed shorter periods in the same area (p<0.01), as compared to females. First to second winter females were mobbed more often during snowcover compared to bare ground conditions (p<0.05), and were mainly selecting medium-sized prey (Oryctolagus, Anas, Perdix.) Two older owls (adult female/sub-adult male) were selecting smaller prey (Microtus, Apodermus, Passerinidae) compared to first second winter females (p<0.001). In conclusion, due to their smaller size and contrasting colouration, males were considered less well adapted to the mainly snowfree conditions in the area, because of a less favourable energy budget due to mobbing, presumed lower hunting success and smaller/less abundant prey. Females, due to their larger size and contrast reducing colouration, were considered better adapted to the same area, due to lower mobbing frequency, presumed higher hunting success and selection of larger prey.
Food caching in the European Nuthatch Sitta europaea
Authors: Källander Hans
Published: March 2023

The behaviour and cache sites of European Nuthatches storing naturally occurring beech Fagus sylvatica and hazel Corylus avellana nuts in a South Swedish wood are described. Data are also given on the retrieval of cached nuts in winter and on recaching. On average it took a Nuthatch about 1 min to cache a beech nut. A third of all caches were below 1 m, 20% in the ground. Of those in trees, most were at heights between 5 and 15 m and less than 20% on branches thinner than 4 cm; of caches made above ground, 43% were in dead, often rotten wood. The choice of cache site was related to the kind of item to be cached: a higher proportion of hazel than beech nuts was cached in the ground. Oak was used proportionally more, and other species of tree proportionally less for caching than suggested by their abundance, perhaps because oak presented much dead wood which was extensively used for caching. More than 80% of all caches were covered with material from the immediate surroundings of the cache site. The Nuthatches removed the seed coat from a high proportion of the beech nuts before caching them; however, none of those cached in the ground and similar sites were shelled. During the coldest part of the winter, 1.1 nut per hour was retrieved in a winter following a poor mast crop vs 4.6 in a winter following a rich one. Recaching was common at all times but less so in winter.
Differences in bird habitat quality between plantations of Scots and Lodgepole Pine measured in terms of Pied Flycaatcher Ficedula hypoleuca breeding success
Authors: Sjöberg Kjell , Pettersson Roger , Atlegrim Ola
Published: March 2023

The breeding density and reproductive performance of Pied Flycatchers Ficedula hypoleuca inhabiting nest boxes were studied in ca. 20 year-old plantations in Sweden of two pine species: the native Scots Pine Pinus sylvestris and the introduced North American Lodgepole Pine P. contorta. The analyses are based on data from 35 nest boxes placed within each of three Scots Pine and three Lodgepole Pine plantations. The plantations were distributed pairwise at each of three different sites. During the 4 year study (1989—1992), a total of 126 and 107 clutches were found in Scots and Lodgepole plantations, respectively. There was no significant difference in number of breeding pairs between the two types of pine plantations. However, reproductive success, as regards number of nestlings, tended to be higher in Scots than Lodgepole Pine habitats, and clutch size was significantly larger in Scots Pine plantations. Flycatcher food abundance in the trees was indexed by measuring insect larval droppings under pines during the nestling period in 1989. There were no significant differences in number of droppings between the habitat types. Although the Pied Flycatcher clutch size was higher in the Scots Pine habitats, it did not result in a higher number or weight of nestlings. Our results indicate that this was due to a high within habitat and between-site variation in flycatcher breeding success. The reasons for these variations are discussed.
Ageing of Tree Pipits Anthus t. trivialis
Authors: Karlsson Lennart , Persson Karin , Walinder Göran
Published: March 2023

Ageing criteria in Tree Pipits Anthus t. trivialis were studied and photographed at Falsterbo Bird Observatory, SW Sweden, during autumn and spring migration. Several characteristics useful for ageing were found and documented. Iris colour and the pattern on the second outermost tail-feather are valid all year, while other characteristics on wing-feathers (moult contrasts, degree of wear) are valid either in autumn or in spring/summer, depending on the moult of these feather tracts. Moult and ageing criteria are briefly commented on along with some statistics.
Distribution of Sylvia warblers at a stopover site during spring
Authors: Berglund Hasse , Fransson Thord
Published: March 2023

In this study the vertical and horizontal distribution of four Sylvia warblers at a spring stopover site on southernmost Gotland in the Baltic was investigated. The results show that there is some species specificity in micro-habitat choice, though small differences were found concerning the vertical distribution. During the breeding season, Sylvia warblers exhibit interspecific interactions to some degree, especially between the Garden Warbler S. borin and the Blackcap S. atricapilla. No change in habitat choice was noted in the distribution of Blackcaps after the arrival of Garden Warblers. This does not indicate that there is interspecific competition between these species during migration. However, the birds pass quickly through this stopover site and the situation may be different at a site where they stay longer. Some bird species were concentrated in particular nets, or groups of nets, which could be a warning when interpreting ringing results between years, since removal or addition of critical nets could highly affect the number of birds captured between years.
Bivråkens Pernis apivorus boplatsval
Authors: Amcoff Martin , Tjernberg Martin , Berg Åke
Published: March 2023

At 30 Honey Buzzard nests in southwest Uppland (59°45'N) data were collected concerning different parameters of the forest (tree species composition, age, density, site quality class, silviculture, history etc.). These data were compared with the same parameters collected from a random sample of 32 spots in forests from the same area. The results show that the Honey Buzzard Pernis apivorus preferred to nest in diversified forest with high site quality class, and the preferred forests were often neglected concerning forestry measures and were also often affected by earlier wood pasturage. Old forests with a high proportion of deciduous trees and with a high mixture of tree species were preferred, while no nests were found in pine forest despite this forest type being the most common in the study area. The nests of Honey Buzzard were not randomly situated in the landscape but tended to be congregated along lakes, where also the highest site quality class forests were found.
Överlevnadsberäkningar och försök att skatta populationsutvecklingen hos fiskgjuse Pandion haliaetus, ormvråk Buteo buteo och sparvhök Accipiter nisus i Sverige
Authors: Ryttman Hans
Published: March 2023

I have used ring recoveries to estimate survival rate and population trends for the Osprey, Common Buzzard and Sparrowhawk in Sweden. About 65% of the Ospreys survive their first year and about 81% the years thereafter. The same estimates for the Common Buzzard are 48% in the first year and 76% in the other years and for the Sparrowhawk 36% in the first year and 64% in the other years. With these figures the Osprey and the Sparrowhawk ought to increase their breeding populations in Sweden. However, the population of the Osprey is not at all or very slowly increasing, perhaps depending on shortage of breeding sites in natural trees and/or a higher first breeding age than assumed. The population trend in the Sparrowhawk depends mostly on cold winters and the population fluctuates accordingly. The Common Buzzard population seem to decline because of bad breeding results.
The wintering of Blackcaps Sylvia atricapilla (L.) in Sweden
Authors: Fransson Thord , Stolt Bengt-Olov
Published: March 2023

A total of 688 winter observations of Black caps in Sweden were compiled for an analysis of distribution, trend in numbers and winter survival. During the last 30 years wintering Blackcaps have been observed annually, with a maximum of 72 individuals reported during the winter 1982/83. The number of reports of wintering Blackcaps increased markedly from the 1960s to the early 1980s. Some possible explanations for this increase are discussed, including a new migratory habit in continental Blackcaps to move northward during autumn. Early winter observations occur over almost the whole country. In northern Sweden, nearly all the Blackcaps (98%) disappeared during the course of the winter, indicating a high mortality. In the southern part of the country, the decrease from November to March was 69%, which means that in this area about one out of three Blackcaps survived the winter, if we assume losses to be mortality. For the country as a whole, the decrease was 72% for males and 81% for females. The habit to feed at bird-tables is widespread. Some Blackcaps were stationary for longer periods, and 19 birds stayed for more than three months.
Marine birds drowning in fishing nets in the Gulf of Gdańsk (southern Baltic): numbers, species composition, age and sex structure
Authors: Stempniewicz Lech
Published: March 2023

During 8 seasons (1972–1976 and 1986–1990) 1,254 marine birds of 24 species, drowned in fishing nets in the Gulf of Gdańsk, were collected and studied. As a rule, the most numerous bird species in the Gulf constituted the most common bycatch. The exceptions are the Goldeneye Bucephala clangula, Tufted Duck Aythya fuligula and Coot Fulica atra, the numbers drowned being incommensurably low compared with those observed in the Gulf. The reverse is the case in the Eider Somateria mollissima. The percentage share of the Long-tailed Ducks Clangula hyemalis and Eiders in bycatches increased in general and that of the Velvet Melanitta fusca and Common Scoters Melanitta nigra decreased during successive years of the study. The number of birds drowned in nets in different months roughly reflects the seasonal changes in their numbers in the Gulf. Adult birds, particularly males, predominated among the Long-tailed Ducks (68% and 47% respectively) and Velvet Scoters (65% and 46% respectively). The opposite was the case among the Common Scoters and Eiders, where immature birds constituted as much as 71% and 67% respectively. With the passage of the season, these proportions changed in a species specific way. Adult birds became entangled in fishing nets less frequently than expected, considering their percentage share in the wintering population. It is estimated that about 17,500 birds (10–20% of the number observed in the area) die annually in nets. These include Long-tailed Ducks (about 8 400), Velvet Scoters (about 4,000), Scaups Aythya marila (about 1,300), Common Scoters and Eiders (each about 1,000).
Bivråkens Pernis apivorus överlevnad och beståndsutveckling i Sverige
Authors: Tjernberg Martin , Ryttman Hans
Published: March 2023

The survival rate of the Honey Buzzard Pernis apivorus was estimated using recovery data from 140 ringed nestlings that later were found dead or shot. The annual survival rate was 48.8% in the first year, 85.8% in the second year and 86.0% thereafter. By only including a subset of 53 Honey Buzzards found dead, the survival was 58.1% in the first year, 85.5% in the second year and 91.7% thereafter. For a stable population and under the assumption that Honey Buzzards breed for the first time when two years old, the reproduction must be 0.67 young/ pair and year. Without hunting, however, a reproductive rate of 0.34 young per pair is enough for keeping a stable population. With knowledge of reproduction and survival rates, the stability of the population can be estimated. In Uppland, central Sweden, the reproductive rate was 0.60 fledged young per established pair in 1986–91. However, figures from counts of migrating Honey Buzzards at Falsterbo indicate a lower reproductive rate– possibly around 0.30 fledged young/pair –and this is probably a more representative reproduction value for the total Swedish population. A reproductive rate around 0.3 young/pair and year is close to the estimated value for a stable population without hunting.
Moult in relation to migration in birds—a review
Authors: Kjellén Nils
Published: March 2023

This study reviews different ways of combining the moult with other essential activities like breeding and migration. Most species tend to avoid moult during the breeding. A majority of short-distance migrants change their feathers in summer before autumn migration, while most long-distance migrants perform a winter moult in the tropics after autumn migration. A complete moult both in summer and winter has only been recorded in a few passerines. Birds like albatrosses and larger eagles have a serial moult, changing only a number of their primaries every year. Another strategy common among long-distance migrants is to change some feathers on the breeding grounds, suspend moult, and complete it in the winter quarters. A special adaptation allowing faster moult is the simultaneous shedding of all wing quills. During this time birds are flightless and many species perform spectacular moult migrations to congregate in areas rich in food and free of predators. The moult strategy may vary between closely related species and a comparative study of three different groups (raptors, waders and warblers) is presented. The most clear differences in strategy seem to be related to migration distance.
The role of naturally stored food supplies in the winter diet of the boreal Willow Tit Parus montanus
Authors: Brodin Anders
Published: March 2023

The average amount of food that was stored during an autumn by Willow Tits Porus montanus was estimated by sampling hoarding intensities and analysing the energetic contents of the stored items. Measurements of retrieval and losses of the stored food made it possible to calculate how much of the stored food that actually was used by the hoarder. Also the chemical composition of the stored food was analysed, and a comparison of the energy contents of the food eaten with the energy requirements of the birds made it possible to assess the importance of hoarded food in the winter diet. According to the calculations, hoarded food can be assumed to account for almost all food that was consumed during December, whereas it was estimated to constitute around 24% of the food eaten from January to March. During colder winters, with higher energetical stress, it is possible that stored supplies could be more important during this part of the winter, perhaps of the magnitude of 45% of the total food consumed.
Response of female Great Tits Parus major to photoperiodic stimulation and the presence of a male
Authors: Jonsson Pernilla
Published: March 2023

The response of female Great Tits Parus major to photoperiodic stimulation was investigated by measuring the plasma concentration of oestradiol and the growth of the ovary in caged and in free-living birds. Stimuli from the male and from the nest-building labour are assumed to promote the ovaries to complete maturation. Two groups of females were kept on long days (20L:4D), one group consisting of female/male pairs with access to nest-building facilities, and one containing female/female pairs. Another group of female/female pairs was kept on short days (8L:16D). A reference group consisted of free-living females, caught during February—April. The oestradiol concentrations of the caged females on both light regimens remained low and at the same level as that of the free-living females prior to the nest-building. The hormone level peaked only among free-living females during the egg-laying period. The females kept on long day regimen only reached incomplete egg follicle growth which peaked at about the same size as that of the free-living females in the early nest-building period. The presence of a male stimulated neither the oestradiol secretion, nor the ovarian growth.
Incubation, hatching, and clutch desertion of the Treecreeper Certhia familiaris in south-western Sweden
Authors: Enemar Anders
Published: March 2023

Breeding data were collected on a Treecreeper population nesting in artificial nest sites, erected in deciduous forests in south-western Sweden. From 1982 through 1994, 74 incubation periods were estimated by measuring the time from laying of the last egg to either the hatching of that egg or the appearance of the last hatchling. The mean period was 15.7±1.44 (SD) days, showing a negative relation to laying date from about 17 days for clutches laid in early April to about 14 days in late June, as well as to the mean ambient temperature of the egg-laying period and the first five days of incubation. Mean hatching asynchrony was 1.0±0.37 days (n=38). Approximately 90% of the eggs surviving until hatching produced viable chicks. A third of the losses were perished hatchlings, the rest unhatched egg . Out of 443 clutches with at least one egg, 13% were abandoned without signs of robbing or other destruction. Part of the desertions occurred in connection with heavy rain soaking the nests. —The concept of incubation period is discussed.
Post-fledging movements of juvenile Reed Warblers Acrocephalus scirpaceus and Sedge Warblers Acrocephalus schoenobaenus
Authors: Nielsen Bo , Bensch Staffan
Published: March 2023

We have studied post-fledging movements among Reed Warblers and Sedge Warblers by comparing recapture rates between three different ringing sites in South Central Sweden. The positions of these three sites forms a triangle with Kvismaren in the west, Essön in the north and Segersjö in the east. Each side of the triangle is approximately 10 kilometres. A canal connects Kvismaren and Segersjö enabling the birds to move in their natural habitat between these sites. Lake Kvismaren and Essön has no such connection. Segersjö and Essön are both situated at the southern shoreline of lake Hjälmaren but bays and peninsulas make the distance of the shoreline 26 kilometres long, i.e. 16 kilometres longer than the linear distance. We discuss different hypotheses that may explain the post-fledging dispersal. Our results indicate that there is a higher recapture rate of birds between Segersjö and Kvismaren than between Essön and Kvismaren. Both Reed and Sedge Warblers feed primarily in reed beds or similar habitats near water. This suggests that the post-fledging dispersal is an exploratory movement within the birds' main habitat rather than longer flights in random directions. The predominant direction of the dispersal might correspond to the general migratory direction.