Do Nearctic Northern Wheatears (Oenanthe Oenanthe Leucorhoa) Migrate Nonstop to Africa?

Abstract

We present data suggesting that Northern Wheatears (Oenanthe oenanthe leucorhoa) breeding in West Greenland and Canada may be able to accomplish migration to their wintering grounds in West Africa in one direct, transatlantic crossing of more than 4000 km (great circle distance). This conclusion is based on analyses of wing lengths, body weights, and timing of departure from West Greenland and arrival on an island 350 km off the coast of Morocco. Previously, it has been suggested that Nearctic wheatears migrate to Africa by a two-step journey, the first leg comprising a shorter transatlantic crossing to western Europe. A long, direct flight has previously been considered unfeasible as the predicted flight costs were considered to be too high. However, recent insights in aerodynamic theory make these long ocean crossings appear more feasible, especially when taking the use of tailwinds into account.

Gauge-and-compass migration: inherited magnetic headings and signposts can adapt to changing geomagnetic landscapes

“…Locations were chosen with no more than 15% barren habitat and at least 10% low vegetation. This produced very similar range to that found in the literature (51,65). Migrants were considered successful if they arrived in Africa between 20°W -5°E and 5°-15°N (48,49,65).…”

“…Juvenile leucorhoa wheatears migrate independently from high-latitude natal areas in North-East Canada, Greenland and Iceland (between 13°-80° W and 55°-84°N) to sub-Sahelian West Africa, often detouring via Europe (50)(51)(52). Initial departure locations were randomly-selected from within the natal region, based on interpolated landcover data within a 1° by 1° latitude (64).…”

“…54°N) for the Iqaluit individual tracked using geolocation (48). However, given extreme pre-migratory fattening by leucoroha wheatears in the Nearctic (50), a direct crossing to Africa from the Southern end of their range is feasible and possibly used, involving upwards of 72 hours non-stop flight (49,51). We assessed model-evolved individuals from SW Greenland (60°-70°N, 45°-55°W) and S Iqaluit (62.5°-66°N, 60°-72.5°W) according to arrival success (in 2015) and by comparing discrepancies between mean arrival latitudes of free-flying migrants to Europe, to latitudes where signposts were encountered among successful modelled migrants, or to the latitude of first arrival to Europe (excluding Iceland) among non-signposted modelled migrants.…”

“…Leucorhoa wheatears face a single overriding energetic bottleneck, the Atlantic Ocean (47)(48)(49), while negotiating a large-scale region with strong geomagnetic gradients (33) in a rapidly shifting geomagnetic landscape (30). We compared the model's predictions with real migratory data of wild, free-flying leuorhoa wheatears (48,(50)(51)(52).…”

“…Leucorhoa wheatears can potentially reach Spain or even Africa in several days of non-stop flight (51,52) but are known to detour ( Zugknick ) via North-West Europe, with tracked migrations (Fig. 1a) from Baffin Island via Britain or Ireland (44) and from Southwest Greenland via France and Spain (52,53). Long-distance bird migrants typically intersperse periods of daily or nightly flight-steps with extended periods of stopover, particularly where energy reserves are readily acquired and most needed (64,65).…”