Orientation and navigation strategies of migratory birds at high northern latitudes

The opportunity to spend time in subarctic areas has led to my interest in how migratory birds orient at high northern latitudes in a "magnetically extreme environment".

At high northern latitudes, the magnetic field lines cross the surface of the Earth at very steep angles of inclination. The steeper the field lines are the more difficult it is for birds to decide on the correct magnetic north-south axis and transform this information into a migratory direction. Still, orientation cage experiments at high northern latitudes have shown that migrating birds can detect magnetic compass information at very steep angles of inclination.

White-crowned sparrow

In 1999, the Swedish Polar Secretary organised a large expedition called Tundra Northwest, where mostly Swedish and Canadian scientists spent a total of 3 months, divided into two legs, on a Canadian Ice breaker, starting from Sweden over Greenland and crossing the Northwest passage to about the border to Alaska and then returning on a more northerly route back to Greenland. Along the route, stops of 2-3 days allowed the scientists to go on land and collect data and perform experiments. In the main orientation project led by Susanne Åkesson, white-crowned sparrows were displaced from Inuvik, NW Territories, Canada, to the North Magnetic Pole, at that time located at Ringnes Ellef Island, and on across the Northwest passage to Iqaluit. While Susanne and Ulf Ottosson displaced the white-crowned sparrows across the Arctic, Jens Morin and I stayed in Inuvik and carried out the control experiments and additional experiments with white-crowned and Savannah sparrows.

Displacement route from Inuvik, Northwestern Territories, Canada (single point) to the North Magnetic Pole and on to Iqaluit.

Our team: Ulf Ottosson, Susanne Åkesson, Jens Morin, Rachel Muheim

Our research focused on the following questions:

Importance of magnetic compass orientation at high northern latitudes

Orientation experiments that we carried out in Inuvik show that both white-crowned and Savannah sparrows can orient towards the seasonally expected migratory directions from high Arctic latitudes when tested with access to magnetic compass cues only (simulated overcast experiments; Muheim and Åkesson 2002). In cue-conflict experiments, white-crowned sparrows shifted their preferred direction according to an artificial deflection of the magnetic field and recalibrated their celestial compasses, thus prioritized magnetic compass information in favour of celestial cues (Åkesson et al. 2002).

Sensitivity of the magnetic compass to steep angles of inclination

During the displacement from Inuvik to the North Magnetic Pole at Ellef Ringnes Island we could study the birds' orientation at locations with angles of inclination increasing from 81.8° at Inuvik to 90° at the magnetic pole. This allowed us to study how sensitive their magnetic compass is, i.e. while displaced to places with angles of inclination approaching 90° at the magnetic pole. To our surprise, the sparrows could select a magnetic compass course in geomagnetic fields with an inclination deviating as little as 1.4° from the vertical, but were disoriented at the magnetic North Pole itself, suggesting a highly sensitive and precise magnetic compass (Åkesson et al. 2001).

The picture shows 5 compasses at Ellef Ringnes Island (location of the North Magnetic Pole in 1999). Each compass is pointing into a different direction, since the vertical magnetic field does not provide any directional information. Picture by Susanne Åkesson.

Response to longitudinal displacement - navigation in the high Arctic?

After the displacement to the East of the North Magnetic Pole and across the 0° declination line, both juvenile and adult birds abruptly shifted their orientation from the migratory direction to a direction that would lead back to the breeding area or to the normal migratory route (Åkesson et al. 2005). Possible explanations may be that the birds compensated for the displacement. The vertical magnetic field at the North Magnetic Pole could have acted as a signpost, i.e. indicated to the birds that they had migrated too far to the east, thus had to compensate by flying back, or they reacted to the sudden change from positive to negative declinations after the crossing of the magnetic pole. The change in orientation as a reaction to changing declination along the eastward displacement shown by both juvenile and adult white-crowned sparrows tested under clear sky and simulated overcast conditions shows that these birds took regular readings of both magnetic and celestial orientation cues.

Map with magnetic declinations in the area of the North Pole. Each change in blue color indicates a 20° change in magnetic declination, which is the difference between magnetic and geographic North.

Feasibility of the use of a magnetic compass at high northern latitudes

During longitudinal flights at high latitudes, birds will be exposed to rapid and large changes in declination. These changes become more extreme the closer a birds is to a magnetic pole. Studies extrapolating migration routes illustrate that constant magnetic courses north of 270° and 90° will eventually lead birds towards the magnetic North Pole (Muheim, Alerstam and Åkesson 2003). Birds thus should preferentially rely on alternative information when selecting their migratory direction at high latitudes. The only other cues available during the light polar summers are the sun compass and the associated polarized skylight patterns during sunset and sunrise. Stars do not become visible until just before the migratory season, thus birds born in areas with midnight sun have only limited time to learn to use their star compass before the onset of migration. The use of a sun compass in combination with keeping the inner clock on the time of the departure site when traveling along longitudes (staying time-lagged), as was suggested for migrating waders at high northern latitudes, is a very interesting alternative. Such a time-lagged sun compass leads the birds along orthodromic sun compass routes, that are similar to great circle routes, and leaves the possibility open that birds can identify longitudinal displacements by comparing the mismatch between their inner clock (e.g. expected time of sunset and sunrise) and the natural day-and-night scheme. For migrants traveling at high latitudes on the American continent, such sun compass routes are shorter and more direct than constant magnetic courses. However, see page on Compass calibrations for the latest theory on this...

Last updated: 11/11/2007

The simulations in Muheim, Alerstam and Åkesson (2003) show that none of the compass courses alone can fully explain the migration routes followed by night-migrating passerines from their high Nearctic breeding areas to the wintering sites further to the South. Thus, the birds' orientation along the migration routes must be a more complex process than assumed in the analysis, provided that the results of the orientation experiments reflect the departure orientation of the arctic passerine migrants in a reliable way. It is therefore reasonable to suspect that successful long-distance orientation requires (1) that the birds use different compass mechanisms depending on environmental conditions and (2) that they change their preferred orientation (changes possibly triggered by endogenous program or external cues) during the course of migration. The arctic species in our analysis seem to require a level of complexity in their migratory orientation, with regard to both compass mechanisms and course changes, that clearly exceeds what has been suggested for e.g. passerines migrating from Europe to Africa.