SYMPOSIUM Understanding the Migratory Orientation Program of Birds: Extending Laboratory Studies to Study Free-Flying Migrants in a Natural Setting Kasper Thorup, 1, * Richard A. Holland, † Anders P. Tøttrup ‡ and Martin Wikelski † Ã Center for Macroecology, Evolution and Climate, Natural History Museum of Denmark, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen, Denmark; † Max Planck Institute for Ornithology, Department for Migration and Immuno-ecology, Schlossallee 2, Radolfzell 78315, Germany; ‡ Center for Macroecology, Evolution and Climate, Department of Biology, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen, Denmark From the symposium ‘‘Integrative Migration Biology’’ presented at the annual meeting of the Society for Integrative and Comparative Biology, January 3–7, 2010, at Seattle, Washington. 1 E-mail: kthorup@snm.ku.dk Synopsis For many years, orientation in migratory birds has primarily been studied in the laboratory. Although a laboratory-based setting enables greater control over environmental cues, the laboratory-based findings must be con- firmed in the wild in free-flying birds to be able to fully understand how birds orient during migration. Despite the difficulties associated with following free-flying birds over long distances, a number of possibilities currently exist for tracking the long distance, sometimes even globe-spanning, journeys undertaken by migrating birds. Birds fitted with radio transmitters can either be located from the ground or from aircraft (conventional tracking), or from space. Alternatively, positional information obtained by onboard equipment (e.g., GPS units) can be transmitted to receivers in space. Use of these tracking methods has provided a wealth of information on migratory behaviors that are otherwise very difficult to study. Here, we focus on the progress in understanding certain components of the migration-orientation system. Comparably exciting results can be expected in the future from tracking free-flying migrants in the wild. Use of orientation cues has been studied in migrating raptors (satellite telemetry) and thrushes (conventional telemetry), high- lighting that findings in the natural setting may not always be as expected on the basis of cage-experiments. Furthermore, field tracking methods combined with experimental approaches have finally allowed for an extension of the paradigmatic displacement experiments performed by Perdeck in 1958 on the short-distance, social migrant, the starling, to long-distance migrating storks and long-distance, non-socially migrating passerines. Results from these studies provide fundamental insights into the nature of the migratory orientation system that enables experienced birds to navigate and guide inexperienced, young birds to their species-specific winter grounds. Introduction The migration routes of birds span the entire globe with the typical movement, at least for terrestrial species, from higher to lower latitudes and avoiding hostile areas such as deserts or seas, but several al- ternative migration patterns exist. Nevertheless, the ability to orient is a central part of the migratory strategy and the migratory orientation program is considered to be very important for the survival of individual birds and to have a strong impact on the evolution of migration routes (Alerstam and Hedenstro ¨m 1998; Alerstam et al. 2003). The easiest way to perform migration is probably to learn from experienced conspecifics. Such a strat- egy is well documented for several species, e.g., geese (Sterbetz and Szijj 1968; Essen 1982) and storks (Schu ¨z 1951). However, in many species both long and short distances are presumably travelled alone at night (Larkin 1982; Zuur 1984), and if true, these birds cannot follow conspecifics easily. The most Integrative and Comparative Biology, volume 50, number 3, pp. 315–322 doi:10.1093/icb/icq065 Advanced Access publication June 4, 2010 ß The Author 2010. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology. All rights reserved. For permissions please email: journals.permissions@oxfordjournals.org. by guest on March 8, 2016 http://icb.oxfordjournals.org/ Downloaded from