No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Do migrating birds avoid offshore wind turbines? A method to investigate and analyze reactions of diurnally migrating birds to offshore wind farms
Abstract
When addressing potential threats of offshore wind farms on migrating birds, avoidance behavior in response to wind farms is among those commonly mentioned, meaning that wind farms can act as barriers for migrants. Substantial - but otherwise sparsely - proof for this exits from Denmark and The Netherlands. However, monitoring potential threats in the German Bight failed in providing evidence of an avoidance response of migrating birds to offshore wind farms. Minor adaptations of the current method of investigation and analysis provided here, however, have led to substantiated results. In addition, these adaptations can easily be incorporated into current standard protocols of environmental impact assessment studies. Demonstrating this, we here present an example of avoidance behavior of gannets Sula bassana in particular to a wind farm and of birds in general.
... Many migrating birds avoid entering or crossing wind farms (Desholm & Kahlert 2005;Masden et al. 2009;Plonczkier & Simms 2012;Aumüller et al. 2013;Dierschke et al. 2016). For example, Environmental Impact Assessment studies in the context of wind-turbine construction in the German Bight revealed a significant reduction of species numbers in the direction of a wind farm (Aumüller et al. 2013;Hill et al. 2014b). ...
... Many migrating birds avoid entering or crossing wind farms (Desholm & Kahlert 2005;Masden et al. 2009;Plonczkier & Simms 2012;Aumüller et al. 2013;Dierschke et al. 2016). For example, Environmental Impact Assessment studies in the context of wind-turbine construction in the German Bight revealed a significant reduction of species numbers in the direction of a wind farm (Aumüller et al. 2013;Hill et al. 2014b). In divers Gavia spp. ...
... In divers Gavia spp. and Northern Gannets Morus bassanus, common migrating seabirds in the German Bight, the observed migration event rate reduced to one-third in the direction of a wind farm (Aumüller et al. 2013). On the other hand, Great Cormorant Phalacrocorax carbo and European Shag Phalacrocorax aristotelis often show strong attraction to OWFs Vanermen & Stienen, Chapter 8), whereas that of several gull species (Hill et al. 2014b;Schulz et al. 2014) and Red-breasted Merganser Mergus serrator is weaker, although still classed as attraction. ...
The proportion of terrestrial bird species and bats migrating over the sea is much higher than one might assume. Especially during autumn migration, remarkable numbers of birds and bats can be recorded offshore. Consequently, the rapid, worldwide advance of offshore wind power facilities may pose a significant threat to migrating birds and bats in terms of increased energy expenditure and higher collision risk. The extent and the behaviour of birds and bats at offshore wind farms (OWFs) are, however, dependent on a variety of intrinsic, environmental, site- and species-specific conditions. During daytime and under good visibility as well as during clear nights, many bird species avoid entering OWFs, fly well above rotor height or fly between the turbine rows. Under these conditions, effects on flight energetics are mainly negligible and the risk of collision is generally low. In deteriorating weather situations, flight altitudes of birds at sea normally decrease and artificially lit structures may yield particular attraction. As a consequence, energy expenditure as well as collision risk may increase. Bats are observed to fly low over the sea but may also migrate at higher altitudes. However, some bats change their altitude rapidly when they approach tall vertical obstacles and, onshore, bats have been observed to feed near the turbine blades or to roost at the nacelles. Technical and logistical constraints associated with assessing actual numbers of bird and bat collisions with offshore wind turbines remain challenging. Consequently, there are only very few studies in this context highlighting which species or species groups may be particularly vulnerable, especially under adverse circumstances.
Offshore windfarms intrude upon an environment already heavily affected by human activities such as shipping and fishing. As they are large and complex installations and given the large numbers planned, offshore windfarms can be expected to have significant impacts on marine ecosystems with long-lasting effects from both construction and operation. Environmental impacts of offshore windfarms include destruction of the sea bottom and benthic communities, disruption of migrating species such as birds via barrier effects, and disturbance of sound-sensitive marine species through increased underwater noise. The various impacts affect species both concurrently and sequentially at different life stages and should therefore be assessed from a cumulative perspective.
Wind energy development contributes substantially to achieve climate protection goals. Unintended side effects, especially on wildlife, have long been discussed and substantial research has evolved over the last decade. At this stage, it is important to identify what we have learnt so far, as well as which predominant uncertainties and gaps remain. This review article aims to consolidate the state of knowledge, providing a qualitative analysis of the main effects of wind energy development on- and offshore, focusing on frequently studied species groups (bats, breeding and resting birds, raptors, migratory birds, marine mammals). We reviewed over 220 publications from which we identified predominant hypotheses that were summarized and displayed in tables. Journal publications, conference contributions, and further studies have been considered. We found that research focusing on offshore wind energy within the last couple of years has increased significantly as well, catching up with the vast amount of onshore studies. Some hypotheses have been verified by numerous publications and a consensus has been reached (e.g., correlation between bat activity and weather factors), while others are still being debated more (e.g., determination of migratory corridors) or remain unknown (e.g., effect on population level). Factors influencing potential effects were mainly related to species characteristics (morphology, phenology, abundance, behavior, and response to turbines) or site characteristics (landscape features, weather, and habitat quality). Consolidating the state of research provides the groundwork for the identification of mitigation measures and advanced planning approaches. However, the quantification of effects remains challenging and uncertainties will always persist.
Hüppop O 2010: Phenology of the "visible bird migration" across the German Bight. Vogelwarte 48: 181-267. Within a project supported by the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety dealing with possible consequences of offshore wind farms on bird migration observations of migrating birds were carried out on three islands in the German Bight, Sylt, Helgoland and Wangerooge, from autumn 2003 to the end of 2006. With "seawatching" the migration of mostly larger species (waterbirds in the broadest sense) over the sea was recorded and "islandwatching" concen-trated on the migration of smaller species (mostly passerines) over land (islands in this case). The particular goal of this study is the synoptic observation at three locations at least during the migration periods. Apart from some exceptions, at all three sites seawatching showed the highest migration intensity in the morning hours, much less migration occurred at midday and in the evening. Varying proportions of species are mainly caused by the different breeding and staging/wintering areas, whereby the three sites are touched by the birds to a greater or lesser extent. This phe-nomenon is most obvious in geese. With seawatching in the first three hours after sunrise a total of 185 species was recorded (154 near Sylt, 137 near Helgoland and 148 near Wangerooge). For 23 species, which were abundant or are regarded to be critical concerning effects of offshore wind turbines, the seasonal and daily patterns of migration intensity are described and shown in graphs, diurnal variation of migration intensity for 15 species and flock size for 11 species. In many species, migration was more intense near Sylt in autumn and near Wangerooge in spring, whereas a more balanced relation of the two migration periods was typical for Helgoland. During both seasons the daily migration intensity of the three sites was highly significantly correlated. That holds true for the overall picture of all species as well as for the migration intensities of many particular species. Due to the geographical locations of the breeding and wintering areas of most species, a general direction of migration along a SW-NE-axis can be expected. However, the results of seawatching could prove this only for Helgoland. Near Sylt and Wangerooge, most birds followed the coastline, i.e. they migrated along a S-N-axis and W-E-axis, respectively. With islandwatching in the first three hours after sunrise a total of 189 species was observed (165 above Sylt, 133 above Helgoland and 161 above Wangerooge). Phenology are described and presented graphically for 23 relatively abundant species, flock size for 10 species. As with seawatching, migration intensity was lower at Helgoland than at the two coastal islands and showed roughly the same amount of birds during spring and autumn migration. As a consequence of the preference of most passerines to migrate along a leading line, migration was stronger for many species in autumn at Sylt and more pronounced in spring at Wangerooge: While relatively few birds headed towards the sea at Sylt (autumn) and Wangerooge (spring), the great majority of birds followed the coastline southward (Sylt in autumn) and eastward (Wangerooge in spring), respectively. Obviously, passerines avoided to fly towards the open sea during daytime and followed the coastline instead. Hence, the few birds arriving from sea produced low migration intensities at Sylt in spring and at Wangerooge in autumn. The SW-NE-direc-tion predominating in bird migration in Central Europe was only approved at Helgoland. But even there, jetties of the harbour acted as leading lines, because in autumn many passerines left the island towards SE and S. Because of the leading line effects at Wangerooge (spring) and Sylt (autumn) the connection was strongest between the sites representing migration over sea, i.e. between Helgoland and arrivals above Sylt in spring, but between Helgoland and arrivals above Wangerooge in autumn. This held true for all species together as well as for the single species.
Within a project supported by the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety dealing with possible consequences of offshore wind farms on bird migration observations of migrating birds were carried out on three islands in the German Bight, Sylt, Helgoland and Wangerooge, from autumn 2003 to the end of 2006. With “seawatching” the migration of mostly larger species (waterbirds in the broadest sense) over the sea was recorded and “islandwatching” concentrated on the migration of smaller species (mostly passerines) over land (islands in this case). The particular goal of this study is the synoptic observation at three locations at least during the migration periods. Apart from some exceptions, at all three sites seawatching showed the highest migration intensity in the morning hours, much less migration occurred at midday and in the evening. Varying proportions of species are mainly caused by the different breeding and staging/wintering areas, whereby the three sites are touched by the birds to a greater or lesser extent. This phenomenon is most obvious in geese. With seawatching in the first three hours after sunrise a total of 185 species was recorded (154 near Sylt, 137 near Helgoland and 148 near Wangerooge). For 23 species, which were abundant or are regarded to be critical concerning effects of offshore wind turbines, the seasonal and daily patterns of migration intensity are described and shown in graphs, diurnal variation of migration intensity for 15 species and flock size for 11 species. In many species, migration was more intense near Sylt in autumn and near Wangerooge in spring, whereas a more balanced relation of the two migration periods was typical for Helgoland. During both seasons the daily migration intensity of the three sites was highly significantly correlated. That holds true for the overall picture of all species as well as for the migration intensities of many particular species. Due to the geographical locations of the breeding and wintering areas of most species, a general direction of migration along a SW-NE-axis can be expected. However, the results of seawatching could prove this only for Helgoland. Near Sylt and Wangerooge, most birds followed the coastline, i.e. they migrated along a S-N-axis and W-E-axis, respectively. With islandwatching in the first three hours after sunrise a total of 189 species was observed (165 above Sylt, 133 above Helgoland and 161 above Wangerooge). Phenology are described and presented graphically for 23 relatively abundant species, flock size for 10 species. As with seawatching, migration intensity was lower at Helgoland than at the two coastal islands and showed roughly the same amount of birds during spring and autumn migration. As a consequence of the preference of most
passerines to migrate along a leading line, migration was stronger for many species in autumn at Sylt and more pronounced in spring at Wangerooge: While relatively few birds headed towards the sea at Sylt (autumn) and Wangerooge (spring), the great majority of birds followed the coastline southward (Sylt in autumn) and eastward (Wangerooge in spring), respectively. Obviously, passerines avoided to fly towards the open sea during daytime and followed the coastline instead. Hence, the few birds arriving from sea produced low migration intensities at Sylt in spring and at Wangerooge in autumn. The SW-NE-direction predominating in bird migration in Central Europe was only approved at Helgoland. But even there, jetties of the harbour acted as leading lines, because in autumn many passerines left the island towards SE and S. Because of the leading line effects at Wangerooge (spring) and Sylt (autumn) the connection was strongest between the sites representing migration over sea, i.e. between Helgoland and arrivals above Sylt in spring, but between Helgoland and arrivals above Wangerooge in autumn. This held true for all species together as well as for the single species.
Prey availability is one of the factors determining the distribution of seabirds at sea. Northern fulmars Fulmarus glacialis and black-legged kittiwakes Rissa tridactyla were the most regular and frequent ship-followers across the central and northern North Sea during 2 surveys with a fishery research vessel in May-June and July-August 1992. Sixteen other species occurred less often and/or in lower numbers. Birds consumed 84% of experimentally discarded roundfish and 8% of discarded flatfish. On average, northern gannets Morus bassanus took the largest individuals of most fish species, black-legged kittiwakes the smallest. The average size choices of herring gulls Larus argentatus, lesser black-backed gulls Larus fuscus and northern fulmars lay between these 2 extremes. The choice of fish lengths by birds varied with different fish species. Northern gannet was the most successful species in consuming discards. Northern fulmars' success rates decreased with the presence of larger ship-followers but were never high. Black-headed gull Larus ridibundus and common gull Larus canus were less successful than the more frequent, typical ship-following species.
With regard to potential sites for the construction of offshore wind farms and to their possible threats for birds it is essential to enlarge the current knowledge on bird migration above the sea – especially during the night. Within a comprehensive study for the evaluation of offshore wind farms bird calls were registered automatically on a research platform in the south-eastern North Sea. The species identification of nocturnally migrating birds is almost exclusively possible only by means of their calls. Here, we present species-specific bird occurrence near an anthropogenic offshore structure in the total daily and yearly course on the basis of automatically registered calls.
From 2004 to 2007, a total of 100 species was identified. Calls from 95,318 individuals (excluding the large gulls) were used for analyses. Three quarters were passerines (predominantly thrushes), furthermore mainly waders, terns and smaller gulls were detected. 79.4% of all individuals were registered during the night. High numbers of individuals, mostly of several species occurring together, were concentrated in only a few days/nights or even hours. Bird occurrence was much higher during autumn migration than during spring migration. A maximum of 5,236 birds of different species (corresponding to 392 Ind./h) was identified in the night from 28th to 29th October 2005. The migration periods of the short-/medium distance migrants were clearly distinguishable, otherwise not those of the long-distance passerine migrants, presumably due to their much minor ambition to call. In July mainly smaller gulls and terns, in August above all terns and waders (especially Redshank) and in winter some late smaller gulls and thrushes were registered. Generally, numbers increased continually with the beginning of the night and reached a maximum before sunrise. The fewest birds were detected in the late afternoon.
Despite methodological constraints, the shown species-specific phenologies broadly match the migration times in the offshore area of the German Bight as recovered by trapping and/or by scheduled or coincidental visual observations of bird migration. Like these methods the acoustic recording cannot cover the whole occurrence of birds. Presumably, the number of birds is underestimated during fine and overestimated during adverse weather when birds reduce flight altitude. However, we assume that the birds registered acoustically on the platform reflect at least the low flying proportion of the calling species in the course of the year and in their daily variability.
The opportunity to estimate numbers of low and thereby close to an anthropogenic obstruction flying birds using calls is – with regard to the evaluation of its collision risk and the introduction of mitigation and avoidance measures (site, short-term shutdown of the construction and optimization of illumination) – not exiguous.
The occurrence of selected seabirds and coastal birds off Wangerooge in autumn: the influence of wind direction and wind force.Between 1995 and 1999 a study was made of the autumn migration of seabirds and coastal birds on the seaward side of Wangerooge Island (SE German Bight, East Frisian Islands; 53°47′N 07°54′E). Analyses are based on a total of 418 h on 118 days from 1 September to 15 November. Migration patterns in relation to wind direction and wind force are presented for 19 species. The patterns differed significantly from a hypothetical distribution. It proved possible to allocate the observed species to one of two groups, based on their occurrence patterns: 1. Those which migrated regularly and were wont to occur whatever the wind direction and wind force: divers, grebes, Great Cormorant, Common Shelduck, Barnacle Goose, Brent Goose, Great Scaup, Black Scoter, Common Eider, Sandwich Tern, Common/Arctic Tern, Little Gull, Common Guillemot and Razorbill. In general, their migration intensity is strongest during weak tailwinds (easterly winds) and during strong onshore winds from W/NW. Plainly, the latter case is not due to actual increase in migration intensity but is rather the result of birds being pushed closer to the coast while migrating farther out at sea. 2. Seabirds such as Northern Fulmar, Leach's Petrel, Sooty Shearwater, Northern Gannet and skuas occur chiefly or exclusively during gale-force winds from W or NW (weather system after passage of cyclones). The reasons for the observed patterns are discussed.ZusammenfassungIn den Jahren 1995 – 1999 wurde jeweils während der Wegzugperiode von der Insel Wangerooge aus (SE-Deutsche Bucht, Ostfriesische Inseln) der seewärtige Durchzug von See- und Küstenvögeln untersucht. Der Bearbeitung liegen aus den Wegzugperioden der Jahre 1995 – 1999 (Spanne: 01.09. – 15.11.) Beobachtungsprotokolle von insgesamt 118 Tagen über insgesamt 418 h zu Grunde. Die Vorkommensmuster von 19 Arten in Bezug zu Windrichtung und -stärke werden aufgezeigt. Sie unterscheiden sich von einer hypothetischen Gleichverteilung sehr hoch signifikant. Hinsichtlich des Vorkommens lassen sich die Arten in zwei Gruppen ordnen. 1. Arten, die regelmäßig durchziehen und bei allen Windrichtungen und -stärken auftreten können: See- und Lappentaucher, Kormoran, Brandgans, Weißwangen- und Ringelgans, Berg-, Trauer- und Eiderente, Brand- und Fluß/ Küstenseeschwalbe, Zwergmöwe, Trottellumme und Tordalk. Allgemein ist ihr Zug bei schwächeren Rückenwinden (östliche Winde) am stärksten, daneben kommt es bei stärkeren anlandigen Winden (West/Nordwest) zu Maxima. Letzteres ist offensichtlich nicht auf eine tatsächlich erhöhte Zugaktivität zurückzuführen; die ansonsten weiter entfernt ziehenden Vögel werden lediglich näher vor die Küste gedrückt. 2. Hochseevögel: Eissturmvogel, Wellenläufer, Dunkler Sturmtaucher, Baßtölpel und Raubmöwen erscheinen ausschließlich oder überwiegend bei stürmischen Winden aus westlicher und nordwestlicher Richtung (Rückseitenwetter nach Durchzug von Zyklonen). Die Ursachen für die Ausprägung der Muster werden diskutiert .
We have been the first to investigate whether long-lived geese and ducks can detect and avoid a large offshore wind farm by tracking their diurnal migration patterns with radar. We found that the percentage of flocks entering the wind farm area decreased significantly (by a factor 4.5) from pre-construction to initial operation. At night, migrating flocks were more prone to enter the wind farm but counteracted the higher risk of collision in the dark by increasing their distance from individual turbines and flying in the corridors between turbines. Overall, less than 1% of the ducks and geese migrated close enough to the turbines to be at any risk of collision.
Migratory birds are predicted to adapt their departure to wind, changing their threshold of departure and selectivity of the most favourable winds in relation to the mean, scatter and skewness of the wind regime. The optimal departure behaviour depends also on the importance of time and energy minimization during migration and on the ratio of cost of flight to cost of resting and waiting for more favourable winds. We compared departure and flight activity of shorebirds migrating in contrasting wind regimes during autumn (high probability of wind resistance) and spring (high probability of wind assistance) in southern Scandinavia, using data obtained by radiotelemetry, radar tracking and visual observations. The shorebirds changed their threshold for departure in relation to wind between the two seasons, flying almost exclusively with wind assistance in spring but regularly with wind resistance during autumn. The degree of wind selectivity in relation to the distributions of available wind effects was similar during autumn and spring indicating that reducing time and energy costs for migration was important during both seasons. These results demonstrate that migratory birds change departure behaviour in relation to the prevailing wind regime. It remains unknown whether they change behaviour not only seasonally but also in different zones along the migration route and whether they respond to differences not only in mean wind conditions but also in scatter and skewness between wind regimes. Our study indicates the possible existence of an adaptive flexibility in responses to wind regimes among migratory birds. (c) 2012 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
This is an R package (a piece of Software) to fit and do inference on mixed-effects models.
The package is Free Software (hence open-source) and the package and much documentation about it is freely available from CRAN at
https://cran.r-project.org/package=lme4
Bird use was measured on six salt marshes in New Jersey from 18 April to 18 July 1977 (2 impoundments, 2 ditched marshes and 2 natural salt marshes) in terms of species diversity, numbers of individuals and biomass. Seventy-eight species of birds were recorded in all six marshes although not all species occurred on each marsh. Species diversity was highest on the impoundments, intermediate on the ditched marshes, and lowest in the natural marshes. Species diversity and the number of individuals directly related to the amount of open surface area. The traditional species typical of salt marshes on the East Coast of North America (clapper rails Rallus longirostris, seaside and sharp-tailed sparrows Ammospiza spp.) occurred primarily in the natural salt marshes and were absent from the impoundments. Considerations of species diversity suggest that diversity in salt marsh types is essential to maintaining high species diversity in salt marsh ecosystems. Red-winged blackbirds Agelaius phoeniceus and swallows were the most numerous species, followed by gulls and terns. The impoundments had over five times as many individuals as the natural marshes. Waterfowl, gulls, terns and waders accounted for over 90% of the cumulative biomass in the six marshes, with waterfowl contributing over 50%. This study suggests that conservationists should encourage the maintenance of natural salt marshes because they are necessary habitats for some species even though the diversity and avian biomass is less on natural salt marsh areas than it is on managed areas.
Herbivore damage is generally detrimental to plant fitness, and the evolu- tionary response of plant populations to damage can involve either increased resistance or increased tolerance. While characters that contribute to resistance, such as secondary chem- icals and trichomes, are relatively well understood, characters that contribute to a plant's ability to tolerate damage have received much less attention. Using Helianthus annuus (wild sunflower) and simulated damage of Haplorhynchites aeneus (head-clipping weevil) as a model system, we examined morphological characters and developmental processes that contribute to compensatory ability. We performed a factorial experiment that included three levels of damage (none, the first two, or the first four inflorescences were clipped with scissors) and eight sires each mated to four dams. We found that plants compensated fully for simulated head-clipper damage and that there was no variation among plant families in compensatory ability: seed production and mean seed mass did not vary among treat- ments, and sire X treatment interactions were not significant. Plants used four mechanisms to compensate for damage: (1) Clipped plants produced significantly more inflorescences than unclipped plants. Plants produced these additional inflorescences on higher order branches at the end of the flowering season. (2) Clipped plants filled significantly more seeds in their remaining heads than did unclipped plants. (3) Clipped plants, because they effectively flowered later than unclipped plants, were less susceptible to damage by seed- feeding herbivores other than Haplorhynchites. (4) In later heads, seed size was greater on clipped plants, which allowed mean seed size to be maintained in clipped plants. Although there was genetic variation among the families used in this experiment for most of the characters associated with compensation for damage (seed number, mean seed size, mean flowering date, length of the flowering period, and branching morphology), in analyses of these characters, no sire X treatment interactions were significant indicating that all of the families relied on similar mechanisms to compensate for damage.
Ein Index zur Beurteilung von Beobachtungsintensität und avifaunistischer Dokumentation auf Helgoland
- V Dierschke
- J Dierschke
- F Stühmer
Dierschke V, Dierschke J & Stühmer F 2004: Ein Index zur
Beurteilung von Beobachtungsintensität und avifaunistischer
Dokumentation auf Helgoland. Ornithol. Jber. Helgoland 14:
90-99.
alpha ventus " zeigt, dass Basstölpel und weitere Vogelarten in den windparkzugewandten Raumsektoren in geringerer Häufigkeit auftreten
- Im Nahbereich Von
im Nahbereich von " alpha ventus " zeigt, dass Basstölpel
und weitere Vogelarten in den windparkzugewandten Raumsektoren in geringerer Häufigkeit auftreten. Dies lässt auf eine
Meidereaktion schließen.
Quantitative Erfassung des Vogelzugs während der Hellphase bei Helgoland
- V Dierschke
Dierschke V 2003: Quantitative Erfassung des Vogelzugs während der Hellphase bei Helgoland. Corax 19, Sonderh. 2:
27-34.
Effect studies Offshore Wind Farm Egmond aan Zee. Final report on fluxes, flight altitude and behaviour of flying birds
- Kl Krijgsveld
- Rc Fijn
- C Heunks
- Pw Van Horssen
- J De Fouw
- M Collier
- Mjm Poot
- D Beuker
- Dirksen
Krijgsveld KL, Fijn RC, Heunks C, van Horssen PW, de Fouw
J, Collier M, Poot MJM, Beuker D. & Dirksen S 2011: Effect
studies Offshore Wind Farm Egmond aan Zee. Final report
on fluxes, flight altitude and behaviour of flying birds.
Noordzeewind report nr OWEZ_R_231_T1_20111114_
flux&flight.
http://www.noordzeewind.nl/wp-content/
uploads/2012/03/OWEZ_R_231_T1_20111114_2_fluxf-
light.pdf. (letzter Zugriff: 10.01.2013)
Efterårstraekket af vadefugle (Charadrii) ved Blåvandshuk 1963-1971
- H Meltofte
- S Pihl
- B Møller Sørensen
Meltofte H, Pihl S & Møller Sørensen B 1972: Efterårstraekket
af vadefugle (Charadrii) ved Blåvandshuk 1963-1971. Dansk
Ornithol. Foren. Tidsskr 66: 63-69.
The effect of wave height on bird counts at sea
- D C Duffy
Duffy DC 1983: The effect of wave height on bird counts at sea.
Cormorant 11:21-23.
Counting birds at sea
- R S Bailey
- Wrp Bourne
Bailey RS & Bourne WRP 1972: Counting birds at sea. Ardea
60: 124-127.
lme4: Linear mixed-effects models using S4 classes. R package version 0
- D Bates
- M Maechler
- B Bolker
Bates D, Maechler M & Bolker B 2011: lme4: Linear mixed-effects models using S4 classes. R package version 0.999375-42. http://CRAN.R-project.org/package=lme4
- H Meltofte
- S Pihl
- B Møller Sørensen
Meltofte H, Pihl S & Møller Sørensen B 1972: Efterårstraekket
af vadefugle (Charadrii) ved Blåvandshuk 1963-1971. Dansk
Ornithol. Foren. Tidsskr 66: 63-69.