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Die Alpen, ein Hindernis im nächtlichen Breitfrontzug — eine großräumige Übersicht nach Mondbeobachtungen (1996)

Liechti, Felix ; Peter, Dieter ; Lardelli, Roberto ; [et al.]

Springer

Journal of ornithology 137 (1996), S. 337-356

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ISSN: 1439-0361

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract With a new standardized moon-watching method nocturnal bird migration was studied over southern Germany, the area of the Alps and northern Italy in autumn 1994 and spring 1995. Simultaneous observations from more than 300 sites showed that in autumn broad front migration was deviated and concentrated along the northern border of the Alps. Migration was concentrated in the Swiss lowlands by a factor 2 to 3 compared to southern Germany. Notable concentrations occurred also along the upper Rhine valley. Even under clear sky only about 20 to 30 % of the migrants continued their flight over the mountain ridges towards Italy. South of the Alps an important part of migration consisted of birds flying westwards, parallel to the border of the mountain ranges. Similar migratory intensity in autumn and in spring over northern Italy suggest concentrated spring migration south of the Alps. This idea is based on the fact that intensity of observed migration is lower to the north of the Alps and in general the expected density of migration is lower in spring (radar data and few moonwatching data). In principle, results showed that confronted with a mountain range (Vosges, Jura, Alps), most migrants prefer to deviate slightly from their innate migratory direction, instead of climbing up above the ridges, where they might encounter unfavourable winds.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01651074

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2

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Methodische Aspekte zur Untersuchung der Zugaktivität im Emlen-Trichter (2000)

Nievergelt, Fränzi ; Liechti, Felix

Springer

Journal of ornithology 141 (2000), S. 180-190

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ISSN: 1439-0361

Keywords: passerines ; Emlen-funnel ; migratory direction ; activity ; method

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Description / Table of Contents: Zusammenfassung Die Auswertung der in Emlen-Trichtern mittels Tipp-Ex©-Papier registrierten Aktivität von Zugvögeln zeigte zusätzlich zu den am Leuchtpult sichtbaren Kratzern, schwache Glanzspuren. Vor allem kleine, leichte Vögel (TeichrohrsängerAcrocephalus scircapeus, FitisPhylloscopus trochilus) verursachten fast ausschließlich solche. Das Verhältnis der starken zu schwachen Kratzern nahm mit der Luftfeuchtigkeit zu. Die Nahtstelle im Tipp-Ex©-Papierbogen übte einen schwachen, aber signifikanten Effekt auf den getesteten Vogel aus. Für die mittlere Richtung und die Richtungsstreuung einer Gruppe von 55 Teichrohrsängern spielte es keine Rolle, ob als individuelle Vorzugsrichtung eine geschätzte Richtung, die Modalrichtung oder die berechnete mittlere Richtung der Kratzer verwendet wurde. Wiederholtes Auszählen derselben Versuchsbogen ergab einen Meßfehler der berechneten individuellen Mittelvektoren von ± 12° (90%-Konfidenzintervall).

Notes: Summary A widely applied method of experimentally determining migratory activities and directions is the so called Emlen-funnel cage, using typewriter correcting paper (Tipp-Ex©) for the registration. We investigated methodical biases, with respect to its construction, environmental condition and the determination of activity and mean direction. The experimental birds were slightly attracted by the joint of the Tipp-Ex© paper. Small songbirds left two different kinds of claw marks: clearly visible ones (cover of the typewriter correcting paper scratched off), and vague ones, which only can be detected in appropriate light conditions (cover not scratched off but pressed). Small songbirds (e.g. Reed WarblersAcrocephalus scircapeus, Willow WarblersPhylloscopus trochilus) produced almost exclusively weak scratches, and therefore would often be classified mistakenly as inactive, if only the clearly visible scratches were counted. The relative number of well visible scratches was positively correlated with increasing atmospheric humidity, since the cover of the typewriter correcting paper is more likely to be scratched off when humidity is high. Consequently, the bird's activity is underestimated in dry air conditions. In a sample of 55 experiments no difference was found in mean direction and concentration, when preferred individual directions were (1) estimated visually, (2) assumed to be the angles with most scratches, and (3) calculated by vector addition of the single scratches. Repetitive counts of the scratches in single experiments resulted in an error for the individual mean vector of ± 12° (90%-confidence intervall).

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01651909

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3

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The Use of Low-Level Jets by Migrating Birds (1999)

Liechti, Felix ; Schaller, Esther

Springer

Naturwissenschaften 86 (1999), S. 549-551

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ISSN: 1432-1904

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General

Notes: Abstract Birds flying at high altitudes have occasionally been observed above mountain areas and the open sea. For the first time the regular occurrence of migrating birds flying within a low-level jet at heights of 5000 to almost 9000 m asl. have now been verified by radar above the Negev desert in southern Israel. Tracks of rather large birds with wing-beat frequencies of 5–6 Hz were measured to have horizontal flight speeds up to 50 m/s. Visual observations, seasonal occurrence, and wing-beat frequencies allowed to associate them with small species of the order Ciconiiformes (mainly Ardeidae) and possibly with members of the Laro-Limicolae group. These wading birds seem prone to continuing nocturnal migration into daytime under favorable conditions and to make use of high wind speeds at sometimes extreme altitudes.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s001140050673

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Nächtlicher Vogelzug im Herbst über Süddeutschland: Winddrift und Kompensation (1993)

Liechti, Felix

Springer

Journal of ornithology 134 (1993), S. 373-404

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ISSN: 1439-0361

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Description / Table of Contents: Summary This study analyses the influence of wind on the directional behaviour of nocturnal migrants. Flight paths of more than 10 000 birds were recorded at a site near Nuremberg (southern Germany) with a tracking radar (3 cm wavelength) during the migration season of autumn 1987 (30 July to 30 October). Wind measurements were taken every 4h up to 4000 m above ground level (AGL). A model is introduced to describe the relation between the directional behaviour and wind. An increasing proportion of southerly flight directions with increasing height is mainly caused by the wind and to a lesser extent by more southerly headings of birds above 1000 m AGL. Favourable winds (north-easterly tailwinds) were very rare during the observation period (Fig. 4). Nocturnal migrants compensate wind drift in relation to wind direction and not according to wind speed. The amount of compensation corresponds to an average wind speed of 2–3 m/s (7.2 to 10.8 km/h; Fig. 8). If wind speed is higher, the birds are drifted off their preferred direction (SW 230°). High flying birds (〉1000 m AGL) maintain a heading compensating for the wind below 1000 m AGL. Moreover later in the night the headings are related to the winds at low levels 4h previously (Fig. 9). No compensatory reactions to winds in preceding nights could be found. Differences in compensation for wind from the left (SE-wind compared to NW-winds) could be explained by the instability of SE-winds which usually occur in connection with inversion layers. Under strong headwind conditions (SW 〉10 m/s) many birds show more southerly headings which result in tracks towards SE or even E. This seems not to be a result of pseudodrift. The small amount of SE-migration over southern Germany showed no correlation with north-westerly winds. A classification of the migrating birds according to wing-beat pattern (echo signatures) reveals only small differences in the directional behaviour of five classes. Large and small songbirds as well as swifts show similar behaviour relative to the wind. The directional behaviour of waders and waterfowl differs by being less correlated with the model. This could be a consequence of the heterogeneity of this sample (small sample size compared to the number of species). Compared to other studies we found a large influence of the wind on the flight directions. It is suggested that the weak influence of the wind in several studies based on surveillance radar is caused by two effects: a) the detection capacity of such radars being better when the migration is at higher levels; b) high bird migration occurring mainly with tailwinds.

Notes: Zusammenfassung Die Arbeit untersucht den Einfluß des Windes auf das Richtungsverhalten nächtlich ziehender Vögel. Das Datenmaterial umfaßt Aufzeichnungen mit Zielfolgeradar von ca. 10 000 Flugwegen freifliegender Nachtzieher aus dem Herbstzug über Süddeutschland (Raum Nürnberg/Bayern). Die Abhängigkeit des Richtungsverhaltens vom Wind wird anhand eines Modells zur Kompensation von Winddrift beschrieben. Die mit zunehmender Flughöhe verbundene Abnahme der Streuung und südliche Ausrichtung der Flugrichtungen wird in erster Linie durch den Wind und in zweiter Linie durch veränderte Eigenrichtungen hervorgerufen. Für den Herbstzug günstige NE-Winde wehten in dieser Untersuchungsperiode nur selten. Bei der Kompensation von Seitenwind richten sich die Vögel in erster Linie nach der Windrichtung. Dabei wird im Mittel ein Wind mit einer Stärke von 2–3 m/s vollständig kompensiert; bei größeren Windgeschwindigkeiten werden die Vögel zunehmend verdriftet. Hochfliegende Vögel (〉1000 m ü. G.) richten ihr Kompensationsverhalten nach dem Wind unterhalb 1000 m ü. G., dabei sind mit fortdauernder Nacht die Eigenrichtungen nach dem Wind im vorangegangenen Zeitabschnitt ausgerichtet (Abb. 9). Eine Abhängigkeit des Kompensationsverhaltens von der Verdriftung aus vorherigen Nächten konnte nicht nachgewiesen werden. Vermeintlich abweichendes Richtungsverhalten bei Seitenwind von links (SE-Wind gegenüber NW-Wind) wird durch Wechselhaftigkeit dieser Winde erklärt. Bei starken Gegenwinden (SW-Wind 〉10m/s) drehen die Eigenrichtungen nach Süden. Dies ist keine Folge von Pseudodrift. Für den schwachen aber in einzelnen Nächten deutlichen SE-Zug über Süddeutschland konnte kein Zusammenhang mit Winden aus NW festgestellt werden. Die Aufteilung des Zuges in fünf verschiedene Vogelgruppen (Flügelschlagklassen) hat gezeigt, daß sich deren Verhaltensweisen in bezug auf die Eigenrichtung grundsätzlich wenig unterscheiden. Die großen und kleinen Singvögel sowie die Mauersegler zeigen praktisch keine Unterschiede in ihrem Richtungsverhalten gegenüber dem Wind. Die Klassen der Wat-/Wasservögel zeigen zwar meist schlechtere Übereinstimmungen mit dem Modell, doch dürfte dies — im Vergleich zu den anderen Klassen — durch die größere Heterogenität der Stichproben begründet sein. Im Unterschied zu zahlreichen Arbeiten mit Überwachungsradardaten konnte hier ein bedeutender Einfluß des Windes auf die Flugrichtungen nachgewiesen werden. Dies bestätigt, daß Aufzeichnungen mit Überwachungsradar vor allem hohen Zug registrieren, der bevorzugt bei günstigen Rückenwinden auftritt.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01639830

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