Ommo Hüppop

North Atlantic Oscillation and timing of spring migration in birds.

Migrant birds have been trapped on the island of Helgoland (southeastern North Sea) since 1909, with methods and sampling effort remaining unchanged throughout the last four decades. In 12 short/medium–distance migrants and 12 long–distance migrants (23 passerines plus the European woodcock) sample sizes were sufficient to calculate mean spring passage (msp) times and to relate these to climate change. All but one species, passing Helgoland en route to their breeding areas (mainly in Scandinavia), show a trend towards earlier msp–time, which is significant in 7 short/medium–distance migrants and 10 long–distance migrants. The msp–times advanced by 0.05–0.28 days per year, short/medium–distance migrants not differing from long–distance migrants. In 23 out of the 24 species, earlier msp–times coincide with local warmer msp–temperatures (significantly in 11 and 7 species of the two groups, respectively). Even more striking is the relation to a large–scale phenomenon, the North Atlantic Oscillation (NAO), during the last four decades. Again, in 23 out of the 24 species, an earlier msp-time coincides with higher NAO indices (significantly in 9 and 12 species, respectively). The NAO index can also explain differences and similarities in spring migration strategies, as well as migration routes within Europe.

Climate warming, ecological mismatch at arrival and population decline in migratory birds

Climate is changing at a fast pace, causing widespread, profound consequences for living organisms. Failure to adjust the timing of life-cycle events to climate may jeopardize populations by causing ecological mismatches to the life cycle of other species and abiotic factors. Population declines of some migratory birds breeding in Europe have been suggested to depend on their inability to adjust migration phenology so as to keep track of advancement of spring events at their breeding grounds. In fact, several migrants have advanced their spring arrival date, but whether such advancement has been sufficient to compensate for temporal shift in spring phenophases or, conversely, birds have become ecologically mismatched, is still an unanswered question, with very few exceptions. We used a novel approach based on accumulated winter and spring temperatures (degree-days) as a proxy for timing of spring biological events to test if the progress of spring at arrival to the breeding areas by 117 European migratory bird species has changed over the past five decades. Migrants, and particularly those wintering in sub-Saharan Africa, now arrive at higher degree-days and may have therefore accumulated a ‘thermal delay’, thus possibly becoming increasingly mismatched to spring phenology. Species with greater ‘thermal delay’ have shown larger population decline, and this evidence was not confounded by concomitant ecological factors or by phylogenetic effects. These findings provide general support to the largely untested hypotheses that migratory birds are becoming ecologically mismatched and that failure to respond to climate change can have severe negative impacts on their populations. The novel approach we adopted can be extended to the analysis of ecological consequences of phenological response to climate change by other taxa.

Climate change and timing of spring migration in the long-distance migrant Ficedula hypoleuca in central Europe: the role of spatially different temperature changes along migration routes

Coinciding with increasing spring temperatures in Europe, many migrants have advanced their arrival or passage times over the last decades. However, some species, namely long-distance migrants, could be constrained in their arrival dates due to their largely inherited migratory behaviour and thus a likely inflexibility in their response to exogenous factors. To examine this hypothesis for pied flycatchers (Ficedula hypoleuca), we tested the effects of the temperature regimes along their migration routes north of the Sahara on their arrival times in central Europe. To do so, we developed a site-independent large-scale approach based on temperature data available on the Internet. Temperature regimes along the migration routes of pied flycatchers within Europe convincingly correlate with their first arrival times. It can be concluded that the progression of spring migration in this species is strongly influenced by temperature en route. Because of the recent inconsistent climatic changes in various parts of Europe, we hypothesize that individuals migrating along different routes will be unequally affected by further climatic changes.

Foraging success, kleptoparasitism and feeding techniques in scavenging seabirds: does crime pay?

Scavenging seabirds in the North Sea exploit discards with different success and by different feeding techniques. Northern gannet (Sula bassana) had the highest foraging success index, followed by lesser black-backed gull (Larus fuscus) and black-legged kittiwake (Rissa tridactyla). Northern fulmar (Fulmarus glacialis), mew gull (Larus canus) and black-headed gull (Larus ridibundus) were the least successful species. Ranking species according to the ratio of fish stolen from vs. lost to other species (=robbery index), northern gannet, great black-backed gull (Larus marinus) and great skua (Catharacta skua) were at the top, northern fulmar and black-legged kittiwake at the bottom. Varying compositions of the feeding flocks influenced the foraging success of the species significantly. Both body length and body mass of the birds can well explain species order in the robbery index but not in the foraging success index. Our hypothesis that the most successful species employ particular feeding techniques and/or exhibit the strongest kleptoparasitic abilities could be confirmed to a large extent but not totally. During reduced overall feeding rates, some less successful species and/or species with weaker kleptoparasitic capabilities fared better than during intense feeding rates as predicted, some others did not.

Auswirkungen von Fluglärm auf Wildtiere: ein kommentierter Überblick

The discussion of noise effects involves physical, physiological, and psychological aspects making an evaluation quite difficult. In humans the effects of noise range from discomfort to severe, irreversible damage. In laboratory animals only strong and long lasting noise causes physiological changes that can affect health. These findings are only partly applicable to wild animals. Field studies have to deal carefully with (1) methodological difficulties in measuring sound pressure levels, (2) interspecific differences of auditory sensitivity, and (3) problems in interpreting behavioural reactions in the field. Non-standardized methods of observations and analysis make a comparison of the results found in the literature almost impossible. Especially the noise of aircraft can scarcely be assessed separately from its optical appearance. Optical or acoustical stimuli taken separately have only minor effects with the optical stimulus evoking the stronger reaction; even soundless paragliders can cause panic flights. In general, noise plays a minor role as a disturbance factor, but in combination with optical stimuli can trigger a reaction. Sonic booms and jet aircraft noise sometimes cause startle responses, which mostly do not result in severe consequences. Apparently, animals can adapt to high noise exposures. When animals react to aircraft noise, it is often due to previous experience associating the noise with an aircraft. Aside from a few accidents caused by panic flights, negative consequences of aircraft noise per se on individuals and populations are not proven. In contrast aircraft traffic in general can cause a variety of damages. Concerning the effects of noise on wildlife, many questions remain. Die Bewertung von Lärm erfordert physikalische, physiologische und psychologische Aspekte und ist dementsprechend schwierig. Die Folgen von Lärm reichen beim Menschen von Unbehagen bis hin zu gravierenden, irreversiblen Schäden. Bei Labortieren erzeugen im allgemeinen nur hohe und andauernde Lärmbelastungen gesundheitliche Veränderungen. Hiervon auf Wildtiere zu schließen, ist kaum möglich. Feldstudien müssen sich sorgfältig mit (1.) methodischen Problemen der Schalldruckmessung, (2.) artspezifischen Unterschieden der Gehörempfindlichkeit und (3.) Schwierigkeiten der Reaktionsbewertung im Freiland auseinandersetzen. Wenig standardisierte Untersuchungsmethoden und individuelle Auswertungsverfahren machen einen Vergleich der Ergebnisse aus der Literatur weitgehend unmöglich. Gerade Fluglärm kann kaum getrennt von der optischen Erscheinung eines Flugzeugs bewertet werden. Optischer und akustischer Reiz haben beide für sich meist eine geringere Wirkung. Die optische Erscheinung eines Flugobjekts hat meistens stärkere Effekte als sein Fluglärm. So können auch lautlose Gleitflieger panische Flucht verursachen. Die Störwirkung des Lärms spielt insgesamt eine eher untergeordnete Rolle, kann aber in Ergänzung zu einem optischen Reiz doch eine Reaktion auslösen. Überschall-Knalle und Düsenlärm bewirken teilweise Schreckreaktionen, haben aber nur in seltenen Fällen ernstere Folgen. Anscheinend können sich Tiere auch an starke Lärmimmissionen gewöhnen. Wenn Tiere auf Flugzeuggeräusche reagieren, so vor allem, weil sie das Geräusch früheren Erlebnissen mit Flugzeugen zuordnen. Von wenigen Unglücksfällen bei Panikfluchten abgesehen, sind negative Auswirkungen von Fluglärm als solchem auf Individuen und Populationen nicht nachgewiesen, während Flugverkehr als ganzes vielfältige Schäden hervorrufen kann. Hinsichtlich der Lärmeffekte auf Wildtiere sind noch viele Fragen offen.

Bird collisions at an offshore platform in the North Sea

Capsule Collisions with offshore structures in the North Sea could account for the mortality of hundreds of thousands of nocturnally migrating birds. Aims To assess, for the first time, the circumstances of mass fatalities at an offshore structure, including the species involved, their numbers, ages, body conditions and injuries. Methods At an unmanned tall offshore research platform in the southeastern North Sea, bird corpses were collected on 160 visiting days from October 2003 to December 2007. Corpses were identified to species and kinds of injury, ages, and fat and muscle scores were determined. Nocturnal bird calls were recorded, identified to species and quantified. Local and large-scale weather parameters were also considered. Results A total of 767 birds of 34 species, mainly thrushes, European Starlings and other passerines, were found at 45 visits. Most carcasses were in good body condition and young birds were not more affected than adults. Three quarters of 563 examined individuals had collision induced injuries. Birds in poor body condition were less likely to be collision victims than those in good condition. Mass collision events at the illuminated offshore structure coincided with increasingly adverse weather conditions and an increasing call intensity of nocturnal birds. Conclusions Assuming an average of 150 dead birds per year at this single offshore structure and additionally assuming that a considerable proportion of the corpses were not found, we estimate that mortality at the 1000 + human structures in the North Sea could reach hundreds of thousands of birds. Since offshore industrialization will progress and collision numbers at offshore turbines will consequently increase considerably, we recommend reinforced measures to reduce bird strikes at offshore structures, especially in the light of substantial declines in some migrant species.

Unchanging diet in a stable colony: contemporary and past diet composition of black-legged kittiwakes Rissa tridactyla at Helgoland, south-eastern North Sea

In contrast to the situation at the west coast of the North Sea, the breeding colony of black-legged kittiwakes Rissa tridactyla at Helgoland in the south-eastern North Sea did not exhibit severe declines since 1990 but instead numbers increased and only lately stabilised. Declines at the west coast of the North Sea were attributed to a lower abundance and lower quality of the key prey, sandeels. We hypothesised that kittiwakes at Helgoland do not rely as heavily on sandeels as their conspecifics. We analysed stomach contents of nestlings and adults of 2001, 2002, 2004 and 2006. In concordance with earlier studies of the 1980s and 1990s, young whiting Merlangius merlangus was the most important prey species in 2001, 2002 and 2004. Clupeids and sandeels were consumed in lower proportions. While earlier studies suggested whiting to originate from fisheries discards, evidence now supports that kittiwakes prey upon whiting in areas of hydrographic fronts. No whiting was recovered in samples of 2006 and the proportion of fish prey was low. Main prey items were polychaete worms (Nereidae), which were presumably consumed as swarming Heteronereis stages. An observed strong rise in water temperature in summer 2006 might have influenced food availability of kittiwakes by inducing swarming of Nereidae. Overall, kittiwakes breeding on Helgoland showed a positive population trend for several decades while mainly feeding on whiting.

Die Verbreitung und Häufigkeit ausgewählter See- und Küstenvogelarten während der Brutzeit in der südöstlichen Nordsee

Seabirds were counted from ships on 300 m wide transects in the southeastern North Sea between April and July 1993. For some species the numbers off the coast and off the Waddensea area could be estimated. Gannet (Morus bassanus, 800 individuals), Fulmar (Fulmarus glacialis, 8000 ind.), Kittiwake (Rissa tridactyla, 4200 ind.) and Common Guillemot (Uria aalge, 3100 ind.) occurred with few exceptions only in the vicinity of the breeding site on Helgoland and further towards the open sea. Lesser Black-backed Gull (Larus fuscus, 25000 ind.) and Herring Gull (Larus argentatus, 2100 ind.) were widely distributed: Lesser Black-backed Gulls concentrated in larger distances from the coast than Herring Gulls did. They were found in high densities above all near trawlers. Great Black-backed Gulls (Larus marinus, 1200 ind.) were seen regularly but always in low numbers in the southeastern part of the study area. Common Gull (Larus canus) and Black-headed Gull (Larus ridibundus) were observed almost exclusively in the Wadden Sea but in sometimes remarkably high densities. Common Terns (Sterna hirundo) were more or less confined to the area of their breeding colonies whereas Sandwich Terns (Sterna sandvicensis) were also found further out to the sea. Von April bis Juli 1993 wurden in der südöstlichen Nordsee von Schiffen aus auf 300 m breiten Transekten Seevögel kartiert. Dabei konnte für einige Arten der Bestand abseits des Wattenmeeres und der Küste hinlänglich genau geschätzt werden. Baßtölpel (800 Ind.), Eissturmvogel (8000 Ind.), Dreizehenmöwe (4200 Ind.) und Trottellumme (3100 Ind.) kamen fast ausschließlich in der Nähe des Brutplatzes Helgoland und weiter seewärts vor. Herings- (25 000 Ind.) und Silbermöwe (2100 Ind.) waren weit verbreitet; die Heringsmöwe konzentrierte sich weiter entfernt von der Küste als die Silbermöwe und trat in hohen Dichten vor allem in der Nähe von Fischkuttern auf. Mantelmöwen (1200 Ind.) wurden vor allem im Südosten des Untersuchungsgebietes regelmäßig, aber in stets geringer Anzahl festgestellt. Sturm- und Lachmöwe wurden fast nur im Wattenmeer in allerdings oftmals hoher Dichte registriert. Die Flußseeschwalbe war stark an die Kolonien nahe der Küste gebunden, während die Brandseeschwalbe auch weiter auf See beobachtet wurde.

Bestandsentwicklung, Durchzug und Herkunft des KormoransPhalacrocorax carbo an einem Winterrastplatz auf Helgoland

The numbers of Cormorants resting on the island of Helgoland (54° 11′ N, 7° 53′ E) have increased considerably since the 1970s. Annual totals of the maxima per five-day period rose by 47 % per year from 1984 to 1989. Although the observation effort decreased, annual maxima further increased to 661 birds in 1996 (Fig. 1). Up to the late seventies, annual maxima of resting birds were occurred during the migration periods, whereas since about 1980 Helgoland is increasingly used as a wintering site. Resting numbers grew mainly in September/October, reached their maxima from December to March and fell again from the end of March to May (Fig. 2). Today arrival takes place more than 100 days earlier and departure 43 days earlier than in 1979 (Fig. 3). Migrating Cormorants were mainly observed in March and April (median: 12. April) and from the end of July to October (median: 16. September, Fig. 4). They prefer eastern and north-eastern directions in spring, and western and southwestern directions in autumn (Fig. 5). 67 % of the individuals were observed to migrate in flocks of 11 to 40 individuals (median 27, Fig. 6), and 69 % of migrating individuals were counted before midday (median: 10:05 hours, Fig. 7). Six ringed birds were found or observed at Helgoland. They were ringed in The Netherlands (1), Denmark (4) and Norway (1). According to their body measurements, 19 out of a total of 36 Cormorants found dead at Helgoland are assumed to belong to the subspeciescarbo, whereas only 9 are presumablyP. c. sinensis. Hence, we believe that most birds wintering at Helgoland belong toP. c. carbo. This subspecies winters less far south thansinensis and prefers marine habitats and rocky shores. Winter maxima ofsinensis are only known from wintering sites further south but not from the North Sea and the Wadden Sea, where maxima occur during spring and autumn migration. Breeding numbers ofP. c. sinensis have increased considerably in Denmark and south Sweden since 1980/81, whereas thoseP. c. carbo numbers have increased at a lesser rate. Coinciding with the increase of winteringsinensis in the Skagerrak and Kattegat area (a formerly typical wintering site ofcarbo), there were at least 9 recoveries of birds ringed in Norway in central and south Europe from 1983–85 and 6 in northeastern Germany from 1976–89. Probably, the establishment and growth of the winter population at Helgoland is a result of increasing competition in the Skagerrak and Kattegat. Similar developments betweencarbo andsinensis have been observed in northwest France. Die Rastbestände des Kormorans auf Helgoland sind seit den 1970er Jahren stark angestiegen. Die Summe der Pentadenmaxima nahm von 1984 bis 1989 um jährlich 47 % zu. Obwohl sich die Beobachtungsintensität für Rastbestände seit 1991 stark verringerte, stieg die Maximalzahl bis 1996 auf 661 Kormorane. Bis Ende der siebziger Jahre wurden die Maxima in den Zugzeiten erreicht, seit etwa 1980 wird Helgoland dagegen zunehmend als Winterrastplatz genutzt. Die Rastbestände stiegen vor allem im September/Oktober an, erreichten Maxima von Dezember bis März und sanken von Ende März bis Mai. Der Winterbestand baute sich von 1979 bis 1996 im Herbst zunehmend schneller auf (um mehr als 100 Tage) und nahm im Frühjahr zeitiger ab (um 43 Tage). Ziehende Kormorane wurden hingegen vor allem im März/April (Median: 12. April) und von Ende Juli bis Oktober (Median: 16. September) beobachtet. Im Frühjahr ziehen Kormorane überwiegend in ost-/nordöstliche, im Herbst in west/südwestliche Richtung. 67 % flogen in Trupps mit 11–40 Individuen (Median: 27). Zugbeobachtungen fielen mit 69 % der Individuen in die Zeit bis 12 Uhr (Median: 10:05 Uhr). Von 6 Ringfunden stammen je 1 aus den Niederlanden und Norwegen sowie 4 aus Dänemark. Von 36 Totfunden auf Helgoland seit 1984 gehörten 19 nach Maßen sicher zur UnterartPhalacrocorax c. carbo, nur 9 zuP. c. sinensis. Das Gros der auf Helgoland überwinternden Kormorane stellt demnach vermutlichP. c. carbo. Vögel dieser Subspezies überwintern zudem weniger weit im Süden alssinensis und bevorzugen marine Habitate und felsige Küsten. Ein Wintermaximum vonP. c. sinensis ist daher zwar für Überwinterungsgebiete in Mittel- und Südeuropa bekannt, nicht aber aus dem Bereich der übrigen Nordsee und dem Wattenmeer. Die Brutbestände vonsinensis haben in Dänemark und Südschweden seit 1980/81 stark zugenommen, weniger diejenigen voncarbo in Norwegen. Parallel zur Zunahme der Winterbestände vonsinensis im Skagerrak und Kattegat, einem bisher typischen Überwinterungsraum voncarbo, kam es 1983–1985 zu mindestens 9 Ringfunden norwegischer Vögel in Mittel- und Südeuropa sowie 1976–1989 zu 6 Ringfunden in Nordost-Deutschland. Möglicherweise trug eine zunehmende Konkurrenz im Skagerrak und Kattegat zu dem Aufbau und der starken Zunahme der Winterbestände auf Helgoland bei. Parallelen einer Konkurrenz zwischencarbo undsinensis sind in Westfrankreich zu finden.