The aim

Migratory birds are able to use stellar, sunset and geomagnetic information for orientation (Able 1980, Wiltschko and Wiltschko 1995). Young migratory songbirds are thought to inherit a genetic program that enables them to find both the direction and distance necessary to reach their populationspecific wintering areas (for review see Berthold, 1986, cf. Rabøl, 1978), while adult birds to a large extent seem to navigate to reach known sites (Perdeck ,1958). At high geographic and geomagnetic latitudes, orientation by both celestial and geomagnetic cues is problematic, since the midnight sun makes star navigation impossible during much of the polar summer and the geomagnetic field lines are very steep (Skiles, 1985). In addition, the declination (the angular difference between magnetic and geographic North) shows large variation between nearby sites, the position of the magnetic North Pole is gradually shifting due to secular variation and diurnal variation of the geomagnetic field parmeters can sometimes be substantial during so-called magnetic storms (Skiles 1985). How migratory birds use their compasses and navigate in these High Arctic regions is the focus of this research project. During the Beringia 2005 expedition we have studied a number of related projects on avian orientation and optical phenomena:

Project 1 – Displacement experiments with migratory wheatears, Oenanthe oenanthe (Leg 2A, 2B, 3)
Project 2 – Optical phenomena and animal navigation in the High Arctic (Leg 3)
Project 3 – Orientation and migration in dunlins, Calidris alpina, and sharp-tailed sandpipers, Calidris acuminata (Leg 2D)
Project 4 – Migratory orientation in adult and juvenile white-crowned sparrows, Zonotrichia leucophrys gambelli (Leg 2D)
Project 5 – Compass calibration in Savannah sparrows, Passerculus sandwichensis (Leg 2D)

The experiments and measurements were performed at different sites in High Arctic Russia and North America, including sites on ice close to the magnetic North Pole and at the geographic North Pole.

The fieldwork

We used circular cages, so-called Emlen funnels (Emlen and Emlen 1966; photo 2 and 3) to record the migratory activity and orientation of the experimental birds. Numbers of individuals and numbers of tests are given in table 1. These cage experiments were performed under the natural migration period of the species under study and were mainly performed outdoors, or after exposure to outdoor orientation cues indoors in a tent. In project 1, where the orientation of displaced wheatears was studied on the tundra at Wrangel Island, and at locations on the ice, the birds were transported by helicopter to the study sites and exposed to the natural geomagnetic and celestial conditions for approximately 1h prior to the experiments being initiated. The birds were thereafter transported back to the icebreaker Oden, where they were kept in separate cages in an isolated container during the study period. We recorded the birds’ mass (g) using a Pesola spring-balance and estimated the fat content by a 10-degree visual scale for fat classification (Pettersson and Hasselquist 1985) at capture and prior to experiments, to see how the birds prepared for migration flights by putting on fat. The birds’ activity in the cages onboard the icebreaker were recorded on a computer to keep track of their diurnal activity rhythm and how that varied during the transport across time zones. We also sampled the hormones in the faeces, to look at hormone variation during the day and night and how that changed over the study period. At the beginning, middle and end of the cage experiments (leg 3, site 2 and onwards) in the field we measured the degree of polarization and the direction of the skylight polarization pattern (G. Horváth; photo 1).

In an opportunistic way we measured the different optical phenomena visible from the icebreaker Oden during leg 3. These polarimetric measurements were performed by Gabor Horváth with a portable full-sky (180° field of view) imagining polarimeter (fixed on a tripod with the optical axis pointed to the zenith), which could register the patterns of the radiance, degree and angle of linear polarization of the whole sky (from the zenith to the horizon) in the red (650 nm), green (550 nm) and blue (450 nm) parts of the spectrum. Evaluation of the measurements will take place in the Biooptics Laboratory in Budapest headed by Gabor Horváth. The imagining polarimetric technique is described in detail by Gál et al. (2001), and Horváth and Varjú (2003). The measurements taken onboard Oden on leg 3 covered wellknown optical phenomena which have not been documented previously in the field, exemplified by halos, foggy skies above Polynyas, fogbows and clear, overcast and sunlit foggy skies. Some of these optical phenomena might be important to and used by animals navigating the high Arctic, or they may simply demonstrate the physical limitations with which the animals have to cope (for example navigation in fog).

Preliminary results

In total we performed 1 613 orientation cage experiments with 204 individuals of three species of passerines and two species of waders during the Beringia 2005 expedition (table 1). These birds were captured in Provideniya (64°26’N, 173°11’W) in Russia (wheatears), in Bethel (60°47,350’N, 161°46,822’W; white-crowned sparrows), Tutakoke in the Yukon Delta (61°14,793’N,  165°36,160’W; dunlins and sharp-tailed sandpipers) and at Kanaryarmiut Field Station (61°21,691’N, 165°07,706’W; Savannah sparrows) in the Yukon Delta in Alaska. The results are currently being analyzed, and they will be presented in a number of scientific papers as well as in two undergraduate projects at the Department of Animal Ecology, Lund University. In the summer and autumn of 2005 the southwest Alaska region was struck by bad weather, which had severe effects on the possibility to perform cage experiments with birds. Despite this we were able to record the migratory orientation of an impressive number of birds (table 1). Many of these experiments showed very high and concentrated migratory activity.

The results will be used to answer questions related to:

• expected differences in migratory directions between different populations of birds (dunlins, and sharp-tailed sandpipers)

• expected differences in migratory directions between age groups (white-crowned sparrow), and

• whether the birds use a magnetic compass during migration or not.

Furthermore, cue-conflict experiments were performed to investigate the interrelationship and compass calibrations between sunset and magnetic compasses in the Savannah sparrow and other species (for a review on the topic, see Muheim et al. in press, Åkesson et al., 2002). The experiments performed with displaced juvenile wheatears, close to the magnetic and at the geographic North Poles (figure), will be used to evaluate the birds’ ability to navigate in High Arctic regions on the basis of natural celestial skylight and steep geomagnetic field lines. Previous displacement experiments with white-crowned sparrows to nearby regions in North Canada have suggested that displaced adult and young sparrows are able to detect longitudinal displacements (Åkesson et al., 2005, Åkesson et al., 1995), and that they are also able to use their magnetic compass in steep geomagnetic fields (Åkesson et al., 2001, Sandberg et al., 1998). The wheatears’ orientation will be analyzed relative to the availability of visual (sunset) orientation cues, as measured by the polarimetric method described above.

Acknowledgements

We are grateful to the Swedish Polar Research Secretariat, Oden Crew, Kallax Flyg, FIBE AB Överkalix and Brian J. McCaffery and co-workers at the U.S. Fish & Wildlife Service, Yukon Delta National Wildlife Refuge for logistics support.