Cover photo: Common Loon Gavia immer with prey. Photo: Torborg Berge. Diet and aspects of feeding behaviour of Yellow-billed Loons Gavia adamsii and Common Loons G. immer were compared during the non-breeding season in coastal Norway. Stomach contents from 14 Common Loons and 13 Yellow-billed Loons showed that fishes constituted the main prey of both species. However, saithe Pollachius virens constituted a major component of the diet of the Yellow-billed Loon, whereas wrasses (Labridae), flatfish (Pleuronectidae), and sandeel Ammodytes tobianus were important prey for Common Loons. Common Loons also frequently included crustaceans and sometimes molluscs in their diet. We tested the hypothesis that the Yellow-billed Loon, with its more upturned bill, feed more on bottom-living prey than the Common Loon. Contrary to the hypothesis, stomach contents indicated that more bottom-living prey were taken by Common Loons, and Yellow-billed Loons seemed to prey more on pelagic fish. A difference in prey selection was consistent with field observations that Yellow-billed Loons often fed in water judged too deep for bottom-feeding, social groups were often synchronized when feeding, and their stomach contents contained only a few gastroliths compared to Common Loons. Species differences in number of gastroliths indicate that Yellow-billed Loons are feeding on softer food such as pelagic fish, whereas Common Loons are feeding on crustaceans and the more armoured and spiny fishes occurring in bottom habitats.
Cover photo: Golden Eagle Aquila chrysaetos. Photo: Henning Dunker. During breeding, most birds have to visit and leave the nest regularly to forage or to provision young. Nesting activity may help competitors or predators to locate the nest and offspring, selecting for parents to behave secretively. The present study reports observations of secretive flight behaviour of Golden Eagles Aquila chrysaetos during a long-term study in Norway based on more than 1500 hours of observation in the nesting areas of 16 pairs of eagles. By a combination of absence from the nest and secretive flights, the eagles seemed to avoid being observed near their nest, as shown by observations of 14 cases of secretive flights from 10 nesting areas. Silhouettes against the sky near the nest seemed to be avoided by the eagles, either by downhill flight in the forest below the nest and skyline, or by a fast approach to the nest, the latter either by a sideway descent or by falling like a stone from a high altitude above the nest within a few seconds. Secretive behaviour may help to avoid long-distance discovery and nest predation, in particular by intruding non-territorial eagles, but also by other raptors and Ravens Corvus corax, as well as to avoid disturbance by humans. Secretive behaviour creates serious challenges for monitoring of Golden Eagle populations, where each pair of eagles usually have several nest sites and where often less than 50% of the pairs are breeding in a given year.
Cover photo: A Peregrine Falcon Falco peregrinus landing on a radio antenna. Photo: Bjarne Emil Time. In November-December 2019, a Peregrine Falcon Falco peregrinus hunted close to the center of Bryne, a small town in southwest Norway. During winter, several thousand corvids normally roosted together in the city’s park area. The hunts took place in the dark, after sunset and before sunrise. In this 30-day study, the falcon used a sit-and-wait strategy to hunt roosting corvids. The hunt started each time from the top of a 43 m high antenna near to the park and my apartment. The falcon then brought prey items to a balcony on a tall office building in the city centre, and to the same plucking and eating site after each kill. Sensitive cameras documented the activity of the falcon and its prey which were always Jackdaws Corvus monedula. One camera was mounted by the antenna and two cameras were deployed on the balcony. The attacks were registered as successful if the falcon returned with prey, or otherwise as unsuccessful. The falcon made a total of 42 attacks. A subset of 18 attacks ended with a return to the balcony, of which 13 were successful, resulting in a hunting success of 31% (13/42). Overall, 54% of all kills occurred in the dark before sunrise, and most of the prey were killed in December (77%). The ratio of time spent on successful hunting to total hunting time was 79 to 308 minutes, giving a hunting time efficiency of 26%. On average, the falcon used 6 minutes per successful kill, with a range between 1 to 16 minutes.
Cover photo: Great Skua Catharacta skua. Photo: Terje Lislevand. A better understanding of how birdwatchers identify species of birds in flight may support the development of machine learning algorithms for automated identification from camera-tracking systems for bird monitoring and mitigation. Norwegian birdwatchers scored the importance of 18 criteria for identifying species of birds in flight in an online anonymous survey. Responses were analysed using an Analytical Hierarchy Process and Bayesian Belief Networks. Species identification was first affected by a seasonal expectation as to which species may be observed during a birding trip. Criteria linked to bird’s appearance were most important for species identification, including plumage colouration or patterns; body and wing shape; beak, neck and tail shape. However, flight pattern and speed may provide additional information. A hierarchical approach to categorisation and species identification may improve processing time of automated algorithms.
Cover photo: Hooded Crow Corvus cornix. Photo: Terje Lislevand. Non-vocal sounds made by rapid closing of the bill are well known among many bird species, including several corvids. However, this is the first documentation of bill clapping by a Hooded Crow Corvus cornix during aggressive encounters with a conspecific. The aggression level was low, and the bill clapping was accompanied by a weak rolling ‘r’ sound.
Climate change is expected to force species to move upwards and polewards. Mountain species are at particular risk because upward elevational shifts may be limited by the maximum height of mountain ranges. The Horned Lark Eremophila alpestris breeds in the high mountains of southern Norway. Two previous studies recorded the elevation of breeding territories of Horned Larks in two regions of Dovrefjell, central Norway. In mountains around Grimsdalen (Dovre municipality) territories had a mean elevation of 1329 m (range = 1200–1450 m, n = 15) in 1969, and in mountains around Einunndalen (Folldal and Oppdal municipalities) the mean was 1339 m (range = 1240–1430 m, n = 15) in 1992. The same mountain areas were resurveyed 30–53 years later in 2022. In Grimsdalen, mean elevation of lark territories was now 1426 m (range = 1260–1570 m, n = 23) and in Einunndalen 1415 m (range = 1196–1523 m, n = 42). Overall, the data suggested a mean upward elevational shift of 2.2 m/year. The shift in elevation suggests that climate change has influenced the elevational range of the Horned Lark in the mountains of central Norway, with potential population consequences if the upward shift continues.
Cover photo: Eurasian Goshawk Accipiter gentilis eating a Hooded Crow Corvus cornix. Photo: Kjetil Salomonsen. In southern Norway, the breeding density of Eurasian Goshawk Accipiter gentilis has typically ranged between 2–4 pairs per 100 km2. However, not all territorial pairs attempt to nest each year. In a ca. 2000 km2 forest-dominated study area in central parts of Telemark County, the highest number of nesting attempts recorded per year during 1991–2022 was 46, and the highest number of successful nesting attempts was 40. The nesting success of Goshawks increased with age and was 66.7% for juveniles (n = 12), 79.3% for subadults (n = 82) and 89.4% for adult females (n = 736). The annual proportion of young Goshawk females (juveniles and subadults) depended on the annual proportion of recorded replacements of old females and was positively related to mean temperatures in April. The annual proportion of recorded substitutions was positively correlated with population indices of several important prey species, particularly forest grouse, and without a time-lag. In a multiple regression model, the relative change in the recorded number of Goshawk nesting attempts, compared to the previous year, was positively correlated with a population index for thrush spp. and a combined index for Wood Pigeon Columba palumbus and Hooded Crow Corvus cornix, without a time-lag, and with a combined index for Capercaillie Tetrao urogallus and Black Grouse Lyrurus tetrix, with a one-year time-lag. The one-year time-lag with grouse was most evident when only successful nesting attempts were considered. We conclude that the breeding densities of Goshawk in Telemark are rather stable, and we conclude that annual variation in the number of recorded nesting attempts to a large extent reflects the effects of variation in prey density on the body condition of female Goshawks.
Cover photo: Male Great Tit Parus major. Photo: Bjørn Aksel Bjerke. Recently, there has been increasing interest in the ecological consequences of artificial light on wildlife. At northern latitudes, winter is characterized by short days and low temperatures. Under these conditions, resident birds need to consume more food in a shorter time to sustain their metabolism and maintain body temperature. Access to artificial light may prolong foraging opportunities for resident birds during winter. Here, we used a field experiment to test whether Great Tits Parus major benefit from artificial light to start foraging before sunrise. Further, we conducted a meta-analysis to test if onset of foraging was correlated with latitude in the Great Tit. A feeding station with artificial light was placed in a forest area in Ås, SE Norway, at nearly 60° north. A camera was placed in front of the feeding station to record daily activity of the Great Tit in December and February. In December, Great Tits started foraging earlier relative to sunrise when artificial light was available. In February, Great Tits were not stimulated by artificial light to start foraging before sunrise. The onset of foraging in Great Tits was also correlated with latitude. At the northernmost location, Great Tits started foraging several hours before sunrise, whereas at the southernmost location, Great Tits started foraging only a few minutes before sunrise. The results suggest that resident Great Tits may utilize artificial light to prolong their foraging activity during midwinter, and that onset of foraging is advanced relative to sunrise with decreasing daylength further north. Our findings contribute to the understanding of how short days during northern winters can limit foraging activity in resident birds.
Cover photo: Adult Great Cormorant of the subspecies Phalacrocorax carbo sinensis in breeding plumage. Photo: Frode Falkenberg. Great Cormorants Phalacrocorax carbo are now regularly seen in inland watercourses in southeast Norway, after the P. c. sinensis subspecies first established breeding colonies in coastal south Norway in 1996. Although both the sinensis and carbo subspecies occur, the ratio between them is unknown. We tested the accuracy of subspecific identification based on biometrics and genetic analyses in 75 Great Cormorants that drowned in fishing nets in a lake in southeast Norway during the period 2009-2020. Primarily based on the gular pouch angle (GPA), we classified 40 individuals to the carbo subspecies and 35 individuals to the sinensis subspecies. Eight of the carbo individuals and 14 of the sinensis individuals were within the overlapping range of GPA and were therefore classified to subspecies by supplementary measurements (bill depth minimum and bill length). Genetic analyses were based on seven polymorphic microsatellite markers. Assuming one panmictic population, we performed Structure analyses to separate the genotypes into two assumed genetic clusters. The two clusters, carbo and sinensis, could only be separated when adding information about morphological subspecies identities for the carbo, sinensis and carbo/sinensis groups. The sinensis and the carbo/sinensis groups belonged almost entirely to one genetic cluster, whereas the carbo group consisted of individuals with varying proportions of mixed ancestry. Furthermore, we found significant genetic differentiation between the carbo and sinensis groups, and between the carbo and the carbo/sinensis groups, but no significant differentiation between the sinensis and the carbo/sinensis groups. Our results suggest that gene flow is more common from sinensis into carbo than vice-versa, and that the use of GPA < 73° has limitations for the identification of Great Cormorant subspecies in areas where both forms occur. We conclude that the numbers of carbo vs. sinensis individuals in our sample were 32 and 43, respectively.
Cover photo: Singing Reed Bunting Emberiza schoeniclus at Årnestangen, Nordre Øyeren nature reserve. Photo: Øyvind Hagen. The Reed Bunting Emberiza schoeniclus is considered the most common of the five species of Emberiza buntings breeding in Norway and is currently listed as a species of Least Concern. However, a complete census of territorial male Reed Buntings conducted in the Nordre Øyeren nature reserve in 2019 showed a decline in the local breeding population of 67% compared to the last counts completed 40 years ago. Censuses were conducted in 1976 and 1981 in the same area and with the same methods. Analyses of citizen science data from the Norwegian Biodiversity Information Centre also show a similar decreasing trend (-66%) for the Reed Bunting breeding population in Nordre Øyeren from 1976 to 2019. Moreover, image analyses of the census maps show that that the number and density of Reed Bunting territories have decreased locally and probably has done so since early 1980s. Interestingly, a subset of localities within the survey area still have the same territory densities as the 1976 and 1981 censuses. We suggest that changes in habitat, vegetation and farming practice, especially grazing, could be the underlying cause of variation in bird numbers. Our results indicate a negative population trend for the Reed Bunting locally, a tendency that is also observed regionally in the Nordic countries. Taken together, local and regional declines raise concerns about the conservation status of the Reed Bunting in Norway.
Cover photo: Great Tit male. Photo: Alf Tore Mjøs. Birds may sing to defend a territory and to attract a mate. However, despite many studies clear conclusions remain on how ecological conditions affect the song, such as physical obstacles that may reduce the sound transmission, and anthropogenic noise that may mask the signal. The social environment of the local populations may also be important, such as breeding density and sex ratio, influencing the number of competing males with which to song match, and the distances to the neighbouring males and to prospecting females. During 2016-19, we counted the number of syllables (notes) per phrase of singing male Great Tits Parus major by visiting seven countries in Europe and one in North Africa. A total of 946 songs were observed by visiting 554 territories. We also recorded study year, anthropogenic noise, calendar date, time of day, type of habitat and vegetation density, latitude, longitude and altitude. The most important explanatory variables were anthropogenic noise and the latitude of the focal site; the number of syllables per phrase decreasing both with increasing anthropogenic noise and with the latitude. The latter result was also supported when analysing sonograms of the species found on the Internet (Xeno-canto), namely fewer syllables per phrase in Norway than in Spain and Portugal. We suggest that repetition of a short phrase is fast interpreted by conspecifics in noisy environments, and that such signals are more readily detected by conspecifics over a wider area where the density of the tits is low.
Cover photo: Adult White-tailed Eagle. Photo: Karl-Otto Jacobsen. Interspecific takeovers of nests are thought to be rare in birds. A female White-tailed Eagle Haliaeetus albicilla was observed incubating a nest of a Greylag Goose Anser anser with five eggs at Reinøya, Troms County, Norway in 2021. There were no signs of any killed geese in the area around the nest, and there had been no observations of interactions between the two species at the site before the eagle started incubating the eggs. The nest was discovered in the middle of May but was abandoned around midsummer. A similar case reported from the Isle of Mull, Scotland in 2017 was the first of its kind and originally believed to be unique, but the new case in Norway in 2021 suggests that interspecific nest takeover may not be as unusual as previously believed.
Cover photo: Male Lapland Longspur in its breeding habitat. Photo: Vegard B. Fjeldheim. The population of Lapland Longspur Calcarius lapponicus has declined drastically in the Scandinavian mountains over the last decades. One hypothesis is that the population decline has been caused by a change in vegetation composition, specifically an increase in lichen cover leading to a possible decrease in seed-producing plants. We tested the hypothesis by recording vegetation composition inside and outside Lapland Longspur territories in a 10 km2 study area at Hardangervidda, southern Norway, where longspurs previously bred in high numbers. Vegetation composition was recorded by percentage coverage in 295 1 x 1 m quadrats laid out evenly over the study area and compared to a similar treatment of 85 points inside 17 territories of Lapland Longspurs. No difference in lichen coverage or coverage by seed-producing plants was found inside versus outside territories. Instead, Lapland Longspurs were found to establish their territories in the upper part of the study area, where the snow melts earlier. Also, the occupied territories had an orientation towards the sun (sector S–W). Precipitation has increased strongly in the western parts of the Scandinavian Peninsula in recent decades. Falling as snow in the mountains, the increased precipitation leads to delays in spring thaw which could reduce the availability of breeding habitat for Lapland Longspurs during territorial establishment. We suggest that changes in spring conditions could be responsible for the species’ population decline in the western parts of the Scandinavian Peninsula.
Cover photo: Male Ortolan Bunting. Photo: Frode Falkenberg. In small, isolated or fragmented bird populations, past studies have shown that there can be a high proportion of unpaired males. Low male pairing success is suggested to be the result of female-biased natal dispersal and low female recruitment. Indirect evidence indicates that such an effect operates among populations with different degrees of isolation, but little is known of how isolation affects male pairing success within populations. The Norwegian population of Ortolan Buntings (Emberiza hortulana) is distributed in about 50 discrete patches in an area of nearly 500 km2. In this study, we examined whether patch isolation and individual male isolation affected male pairing success. The population has a strongly male-biased sex ratio, with almost half of all males being unpaired. We found that male pairing successs was negatively related to isolation of patches and isolation of individual males in most analyses, and with significant effects in particular in some analyses of individual isolation. Patch population size was measured as the total number of males observed in a particular patch in a specific year and did not have an effect on male pairing success, and was not related to patch isolation. Even though some tests were statistically significant, the magnitude of effects were small and there was large variance in male pairing success. Variance in success suggests that other factors than isolation such as male age or experience may be just as important for male fitness within our study population. Furthermore, we suggest that small effects of isolation were due to the ability of Ortolan Buntings to move large distances within the breeding season, and that isolation effects on small spatial scales are more likely for species with restricted dispersal, such as resident species or species with high population density.
Cover photo: Adult Golden Eagle. Photo: Kristian Henriksen. The characteristics of cliff nest sites of the Golden Eagle Aquila chrysaetos were evaluated from a sample of 57 nests, located during 2000–2020 in the forested valley of Valdres in southeast Norway. About 80% of nests were facing to the south and east, but availability of nest ledges seemed largely a consequence of cliff structure and orientation. Among the 57 nest sites, 4% were placed in a corner with vertical walls, 33% on a ledge with overhang, 10% on a ledge with a vertical back wall, 2% on a ledge with a reclining wall, 49% within a cavity and 2% within a cave. Thus, about 83% of the nest sites were sheltered by an overhang, a cavity or a cave in the cliff within 0.5–2 meters from the nest, and only 16% of sites lacked shelter from above. Heavy snowfall in early spring, torrential rain or strong winds in spring and summer may increase mortality among the nestlings unless the nest site is well sheltered. Moreover, a dry and snowless nest may allow the eagles to start early incubation in late March, thereby increasing fledgling survival. Cavitynests are sheltered sites with less visibility that might protect from attacks from other raptors and Ravens Corax corax.
Cover photo: A male Lapland Longspur Calcarius lapponicus. Photo: Terje Lislevand. Stomach samples of Lapland Longspur Calcarius lapponicus, Snow Bunting Plectrophenax nivalis, and Horned Lark Eremophila alpestris were collected at Hardangervidda in an early phase of the breeding season (during egg-laying and onset of incubation) in 1974. Our analyses of diet composition found that plant material, mainly seeds, made up 90, 95 and 97% by number of items, and 49, 66 and 83% by dry mass, in the diets of Lapland Longspur, Horned Lark, and Snow Bunting, respectively. Seeds of Potentilla, Luzula, different Caryophyllaceae, and Omalotheca were important foods for all three species. Seeds of Empetrum were only found in longspurs and buntings, and fragments of Bryophyta were abundant only in the Horned Larks. Arthropoda were dominated by adult Coleoptera (in particular Patrobus spp., Helophorus glacialis, and Otiorrhynchus dubius) and Diptera larvae (notably Tipulidae), and were taken by all three species in small quantities by number of items but made up 51, 34 and 17% by dry mass in the diets of Lapland Longspur, Horned Lark, and Snow Bunting. Food overlap compared asymmetrically between the species ranged from 0.49 to 0.74 by number of items and from 0.43 to 0.74 by dry mass (scale from 0 to 1.0). Recent population declines in Lapland Longspur and Snow Bunting but increases in Horned Larks may have affected interspecific food competition among the three species early in the breeding season. The food overlap has presumably increased over the last decades due to a longer-lasting snow cover over the nesting habitats of longspurs and buntings which has been a result of increased precipitation due to climate change.
Cover photo: Northern Hawk-Owl Surnia ulula. Photo: Terje Lislevand. The Northern Hawk-Owl Surnia ulula occurs as an irruptive species to southern parts of Fennoscandia. Large numbers of individuals were recorded in the autumns of 2016 and 2020 but assessing the relative magnitude of irruptions is challenging. Systematic surveys allow direct comparisons but are time-consuming and will therefore be limited in time and space. Citizen data may provide large amounts of information for wide areas but may in particular suffer from spatial biases in the observation effort of birdwatchers. I compared the 2016 and 2020 irruptions of Northern Hawk-Owls to southern Norway, and found that citizen data indicated that numbers in 2016 were ca. 2–3 times larger than in 2020. However, the relative magnitude differed geographically, and the 2016 irruption was larger in western and southern counties, whereas the difference was smaller in eastern counties (in particular in Innlandet county). Systematic surveys in eastern regions (Oslo and Akershus) indicated that Northern Hawk-Owl densities were similar in the two irruption years. Overall, Northern Hawk-Owls were recorded at the same rate (approximately one owl per 16 km), and density was estimated to be 0.09–0.18 individuals/km2 in 2016 and 0.08–0.13 individuals/km2 in 2020. Thus, citizen data and survey data from the same geographical region concurred. However, due to the geographical variation in relative irruption size and spatial variation in observer density and biases in observation effort, the overall difference between the two years is difficult to assess. The 2016 irruption was likely larger than the 2020 irruption, but the difference was probably smaller than suggested by citizen data.
Cover photo: Female Horned Lark Eremophila alpestris. Photo: Terje Lislevand. Strong declines in number of breeding Horned Larks Eremophila alpestris were reported from several Fennoscandian breeding grounds in the 1960s and 1970s. Counts from the species’ high alpine breeding grounds at Hardangervidda, southern Norway in the early 1980s and the first couple of decades in the 2000s, and from its arctic breeding grounds in the Varanger region, northern Norway in the period 1996-2021, show a reversal of the trend. The increase in numbers is suggested to have resulted primarily from recovery of nonbreeding habitat after cessation of extensive building of embankments to prevent flooding in the German Wadden Sea area, which is the main wintering area of Fennoscandian Horned Larks.
Cover photo: Common Moorhen. Photo: Arild Breistøl. The Common Moorhen Gallinula chloropus is listed as vulnerable (VU) in Norway due to a small population size (estimated at 110–215 pairs in 2015). The population size is considered stable. More than one quarter of the population (30–70 pairs) is thought to occur in the region of Oslo and Akershus, SE Norway. In 2018, I conducted a comprehensive survey of known and potential breeding sites to assess current population size in Oslo and Akershus. I recorded 74 pairs in 58 sites. To analyse the population trend, I collected all known records of Common Moorhen during the breeding season for the period 1995–2018. Analyses indicated that population size was stable overall. However, compared to data from 1982, sites with the largest number of pairs in 1982 have had declining population size, and these sites also had high nutrient levels. On the other hand, several new breeding sites in recently created ponds in parks, on golf courses and wastewater treatment plants have been established. Dammed ponds were occupied more often than natural waterbodies, and occupied sites were in general at nutrient-rich sites at low elevation close to the coast. Occupancy rate (proportion of years surveyed with Common Moorhen presence) during 1995–2018 was higher for dammed ponds than for natural waterbodies, and higher for smaller wetlands. Thus, analyses suggested that the most suitable sites for Common Moorhen were nutrient-rich small ponds at low elevation close to the coast, and in such sites the Common Moorhen appears to have a stable, but small population size.
Cover photo: A male Two-barred Crossbill (Loxia leucoptera). Photo: Frode Falkenberg. Two-barred Crossbills (Loxia leucoptera) have cyclic irruptions to Norway, but are generally uncommon and breeding is rare. Here I analyse data on a large irruption occurring in 2019–20 to assess the magnitude of the irruption and the ecological niche of the species. The irruption lasted one year, starting in July 2019 and ending in June 2020. Total numbers reported by birdwatchers to the website of the National Biodiversity Information Centre in Norway were ca. 7,000 individuals. Breeding indications were reported from nearly 100 sites. Analyses of elevation of records indicated that birds were often seen at low elevations before the breeding season in February–June, but moved to higher elevations during the breeding season. In a focal study area in SE Norway, breeding season surveys along elevational gradients indicated that Two-barred Crossbills occurred at higher elevations, and often close to summits of hills, perhaps representing preferences for more open forest habitats. Two-barred Crossbills often co-occurred with other seed-eating bird species, but presence was more closely related to numbers of Common Redpoll (Acanthis flammea), than to Eurasian Siskin (Spinus spinus) or cogeneric Common Crossbill (L. curvirostra). Similarly, the Common Redpoll also increased strongly in abundance with elevation, whereas the other two species did so to a lesser degree. These data suggest that the Two-barred Crossbill favors montane forests during the breeding season, and thereby has a different niche than the Common Crossbill which is distributed more widely across all elevations.
