S4. Alone or in groups: different strategies of juvenile migrants

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1 EOU2015 Symposia S4. Alone or in groups: different strategies of juvenile migrants Organisers Andrea Kölzsch & Andrea Flack Max Planck Institute for Ornithology, Radolfzell, Germany Mikkel Willemoes University of Copenhagen, Copenhagen, Denmark Summary Recent advances and miniaturization of tracking technology has led to a remarkable increase in movement studies. One fascinating, still largely unknown aspect of a migrant s life is the behaviour of immature birds. During the first years, young birds often have higher mortality and lower site fidelity compelling scientists to focus their tracking efforts on adults. Only recently, first attempts of following the movements of first year migrants have been made in a number of large migratory species. The results reveal that juveniles have less efficient migration routes and lower foraging efficiencies than adults, leaving them more vulnerable to predation and drastic changes in habitat and climate. Certain migratory strategies, such as flying in groups, can give rise to social learning opportunities, reduced risks due to safety in numbers or aerodynamic advantages. Yet, how do juveniles of solitary migrants handle their apparent disadvantages? This symposium is meant to summarise recent advances in juvenile tracking. Our goal is to unite researchers that have experience in following immature birds to enhance our understanding of the different migration strategies. A direct comparison between social and solitary migrants will help us to disentangle the relative contributions of innate and learned components on the migratory behaviour.

2 Keynote address #1 S4.1 Andrea Kölzsch Max Planck Institut für Ornithologie, Am Obstberg 1, Radolfzell, Germany Juvenile migrants travelling in groups white storks and white-fronted geese Contrary to most small song birds, many large, long-distance migrants travel in big flocks between their wintering and breeding sites. Depending on the species, these groups can vary greatly in size, structure and composition. Group flights may decrease predation risk due to safety in numbers, increase the detection of favourable flight conditions or provide social learning opportunities. Here we will present two studies examining the mechanisms behind and implications of collective migration. First, we examine high-resolution GPS tracks of juvenile white storks (Ciconia ciconia) during their first autumn migration. We reveal the interaction rules that keep the flock together and explore how these rules vary during the different flight phases (i.e. thermalling vs. gliding). Second, we present the migratory behaviour of complete family groups of white-fronted geese (Anser albifrons) during their migration cycle. We examine how individual geese movements relate to each other, whether and how their behaviours synchronise and how the stability of family units influences migratory success. The outcomes of our studies improve our understanding of drivers of group behaviour and social migration. Andrea Flack, Max Planck Institut für Ornithologie, Am Obstberg 1, Radolfzell, Germany Wolfgang Fiedler, Max Planck Institut für Ornithologie, Am Obstberg 1, Radolfzell, Germany Gerhard Müskens, Alterra-WUR, Droevendaalsesteeg 3a, 6708PB Wageningen, Netherlands Peter Glazov, Russian Academy of Sciences, Staromonetniy pereulok 29, Moscow, Russia Martin Wikelski, Max Planck Institut für Ornithologie, Am Obstberg 1, Radolfzell, Germany

3 Keynote address #2 S4.2 Wouter M G Vansteelant IBED (CGE), University of Amsterdam, P.O. Box 94248, 1090 GE Amsterdam, the Netherlands w.m.g.vansteelant@uva.nl There and back again: factors driving ontogeny of individual migration routes in Honey Buzzards Pernis apivorus Mechanisms that drive the ontogeny of individual migration routes can have important implications for migratory connectivity between populations. However, it is currently not known to what extent environmental factors influence route choice and establishment of wintering and breeding sites in unexperienced migrants. Here, we present satellite tracking data of six juvenile Honey Buzzards Pernis apivorus from southern Finland. All birds survived the first outbound migration and established wintering sites over a broad longitudinal range in Africa. Wind drift accumulated during the outbound migration determined the longitudinal position of wintering sites. Two birds which spent their first two years in western Africa were tracked well into adulthood. Both birds returned to their natal sites via migration bottlenecks that are heavily used by adult Honey Buzzards in spring (Gibraltar and Italy), indicating these unexperienced individuals encountered adult birds from western European populations on the wintering grounds, and followed those during return migration. In subsequent years, both birds repeated the same seasonal routes which they learned as a juveniles, indicating that individuality of migration is determined by early life experiences. However, natal dispersal was not mediated by migration, indicating endogenous orientation strategies constrain breeding site selection and migratory connectivity for Honey Buzzards. Willem Bouten, IBED (CGE), University of Amsterdam, P.O. Box 94248, 1090 GE Amsterdam, the Netherlands Judy Shamoun-Baranes, IBED (CGE), University of Amsterdam, P.O. Box 94248, 1090 GE Amsterdam, the Netherlands Patrik Byholm, Natural Resource Management, Novia University of Applied Sciences /Yrkeshögskolan Novia, FI Ekenäs, FINLAND. patrik.byholm@novia.fi

4 S4.3 Marta L Vega University of Copenhagen Universitetsparken 15, 2100 Denmark marta.l.vega@snm.ku.dk Unraveling the migration program in young and adult Common Cuckoos Cuculus canorus The mechanism of avian migration and the factors that influence it have been studied under different angles but several fundamental questions on migratory behaviour remains to be answered. We studied the migration program in inexperienced and adult birds to separate the internal and external factors influencing migratory behaviour in a model species, the common cuckoo Cuculus canorus. The cuckoo is a nocturnal long-distance migrant that carries out its first solo-migration without any learning experience or guidance by other birds. Satellite-tracking of young and adult cuckoos during fall migration enabled us to compare their migration programs for the first time. We also studied how some individuals track the seasonality in food resources. We find that the migration programs in young and adults differ and propose that the young use an inherited migration program whereas the adults respond also to other factors as seasonal changes in vegetation greenness. Surprisingly the inherited migration program seems to be sensitive to environmental factors as compensation of crosswinds. We recommend the integration of the different approaches used for a better understanding of bird migration. Kasper Thorup, Head of Copenhagen Bird Ringing Centre Address: Center for Macroecology, Evolution and Climate, Zoological Museum, Natural History Museum of Denmark, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark kthorup@snm.ku.dk

5 S4.4 Cecilia Nilsson Department of Biology, Lund university, , Lund, Sweden Juvenile passerines more likely to perform reverse migration That birds migrate in the reverse direction of the expected is a phenomenon of regular occurrence which has been observed at many sites. We have used three different methods; tracking radar, radiotelemetry and ringing, to characterize the flights of these reverse migrants and investigate possible causes of reverse migration of nocturnally migrating passerines during autumn migration at Falsterbo peninsula, Sweden. Using these different methods we investigated both internal factors, such as age and fuel load, and external factors such as weather variables, competition and predation risk. Juveniles and lean birds were more likely to fly reverse directions. Juvenile birds have been shown to be less efficient foragers, and less able to cope with competition, possibly making them more likely to perform reverse movements. They could also be more likely to hesitate at the sea crossing, not having passed it before. Reverse migration on the whole was also more common with overcast skies and winds with north and east components. We did not find any effect of temperature, visibility, number of migrating sparrowhawks, or the total number of ringed birds at the site on the day of departure. We found that reverse migration is characterized by slower flight speeds (airspeed) at high altitudes and that it takes place later in the night than forward migration. Joint author Sissel Sjöberg, Department of Biology, Lund University, Sweden. Sissel.sjoberg@biol.lu.se

6 S4.5 Charles André Bost CEBC-CNRS Chizé, Villiers en Bois, France At-sea distribution and diving activity of juveniles Aptenodytes penguins in the South Indian Ocean During the first year of their life, fledged penguins at-sea disperse during several months to one year without any return at their colony. Information on their at-sea activity and survival during this period of their life cycle is essential because their mortality controls recruitment to reproductive stages and thus the future of populations. In addition, it is young individuals that disperse most and have the potential to emigrate and colonize new environments. During the last years we instrumented with data archiving tags transmitting to the Argos system a total of 20 and 21 juveniles of the 2 Aptenodytes penguins, the king penguin Aptenodytes patagonicus (from Crozet islands) and the emperor penguin Aptenodytes forsteri (from Adélie Land). First analysis indicate juveniles emperors disperse away from Antarctica toward the north of the pack-ice edge, in the polar frontal zone. The number of daily dives they performed strongly increased as well as dive depth and duration. Their diving efficiency was lower than those of adults. During austral fall and winter the individuals generally moved south-westward, precisely close to the extending pack-ice. Preliminary analysis confirm that the northward exodus exclude them of potential area of overlap with the adults. Juveniles king penguins performed very distant trips, up to 4000 km far off their colony. In autumn they gradually travelled toward the south, off the polar frontal zone. Some juveniles travelled as south as -62 8, i.e. right across dense sea ice. Juveniles behave in a very distinct way of the breeding adults, exhibiting much more exploratory looping trips. The juvenile behaviour of the 2 species is discussed in relation to the life history strategies of the Aptenodytes genus according to the marine habitat used (Antarctic vs Sub-Antarctic). Henri Weimerskirch, CEBC-CNRS, Villiers en Bois, France. Henri.weimerskirch@cebc.cnrs.fr Pierre Blevin, CEBC-CNRS, Villiers en Bois, France Caroline Bost, CEBC-CNRS, Villiers en Bois, France Caroline Bost caroline.bost@gmail.com Florian Orgeret, CEBC-CNRS, Villiers en Bois, France. florianorgeret@gmail.com