SPECIES

Northern Wheatear Oenanthe oenanthe Scientific name definitions

Erica H. Dunn, David J. T. Hussell, Josef Kren, and Amelia C. Zoerb
Version: 2.1 — Published October 25, 2022

Movements and Migration

Dispersal and Site Fidelity

Natal Philopatry and Dispersal

Juveniles do not disperse widely until the end of Preformative Molt (see Appearance: Molts). During fourth and fifth weeks of age, 68% of young on Skokholm Island (n = 549) were still within 300 m of their nest site (maximum 800 m); during the sixth week, 75% were within 500 m (maximum 1,250 m) (4). Young began to leave the island by ~8 weeks after fledge.

Some proportion of birds show natal philopatry. In Sweden, 18% of young returned to breed within 6 km of the study site, with a median natal dispersal distance of 1,308 m (10% and 90% quantiles = 470 and 3,388 m; n = 203) (87). Estimates of first-year survival from isolated populations provide additional estimates of natal philopatry: 29–32% in the Netherlands (88); 21 ± 0.05% in France (89) and 18% in Scotland (90); see Demography and Populations: Life Span and Survivorship. Where study sites are embedded in continuous suitable habitat the opportunities for dispersal are much greater, and estimates of natal philopatry are correspondingly low. At Iqaluit, Baffin Island, 56.7% of breeding males captured were yearlings (n = 104 over 8 years; DJTH), but none of either sex had been banded as a nestling (n = 131) (91).

For birds returning to natal area to breed, median distance between natal nest and first breeding site is often greater for males than for females; in Germany: 1,012 m for males (n = 26) vs. 628 m for females (n = 22) (92); in France: 583 ± 321 m for males (n = 13) and 436 ± 249 m for females (n = 17) (89); but no difference between the sexes in Shropshire, United Kingdom: 1,041 m for males (n = 41) and 1,013 m for females (n = 41) (93). Birds that bred a second time in their natal area reduced the distance between natal and breeding sites, by 41% in males (n = 8) and 22% in females (n = 7) (92).

Adult Fidelity to Breeding Site and Dispersal

For unbiased estimates of breeding site fidelity see Demography and Populations: Life Span and Survivorship.

Of 157 adult breeders in a small isolated French population, 46% returned to breed again; moving between years a median of 70 m for males and 150 m for females (89). Distance between successive nests in Shropshire, United Kingdom also averaged smaller for males: 250 m (n = 84) vs. 341 m for females (n = 87; 93). For leucorhoa returning to Iqaluit, Baffin Island, distance between successive nests was 1.1 km ± 1.1 SD (range 0–2.8; DJTH). Distance between successive nests of oenanthe in Sweden did not differ between sexes; males moved 308 m (n = 135) and females moved 352 m (n = 116), with a wide range for both sexes (75–4,700 m) (26).

As with natal philopatry, degree of adult philopatry may be influenced by the expanse of suitable breeding area surrounding the study site. Of 204 breeding leucorhoa banded in Iqaluit, Baffin Island over 7 years, only 4.9% were detected breeding within the study area in a subsequent season. However, based on analysis of feather isotopes, at least 38% of breeders were estimated to be immigrants, with no difference among age or sex classes; indicating substantial dispersal by experienced breeders (91).

Fidelity to Overwintering Home Range

There may be large scale movements within the overwintering range related to change in local habitat conditions (44). Geolocator tracking has shown most individuals move among overwintering areas once or twice a season that are separated by several hundred to 1,000 km (63, n = 12; H. Schmaljohann, personal communication, n = 8).

Defense of territories in overwintering areas can persist for at least 53 d (94; see Behavior: Agonistic Behavior), but it is unknown whether individuals use the same sites in different years.

Migration Overview

Complete, long-distance, primarily nocturnal migrant, with the distinction of being one of the few avian species that breeds in the Americas, but overwinters in the Eastern Hemisphere (95). Essentially the entire global population overwinters in sub-Saharan Africa, requiring long-distance travel for most individuals, including trans-Atlantic flights for leucorhoa (Figure 5).

From European portions of its range, subspecies oenanthe takes a southerly route to overwintering areas in sub-Saharan Africa. From eastern Eurasia they move southwest to Africa, with individuals from the farthest eastern range in Alaska crossing Siberia, central Asia and the Middle East in a journey of up to 14,500 km (96, 68). O. o. libanotica follow similar southwesterly routes from their more southern Eurasian breeding areas. Spring and fall routes are similar for oenanthe (though with individual variation), and spring passage is more rapid (Timing and Routes of Migration).

Migration of leucorhoa is very different. Fall migrants depart southeasterly from Greenland and northeast Canada, then cross the North Atlantic nonstop—a distance up to 3,500 km (67). Some birds may fly directly to west Africa, but many (possibly most, but proportion unknown) make landfall in western Europe before continuing overland up to another 4,000 km southward across the Sahara to overwintering areas. Spring routes differ from those in fall, likely because of seasonal differences in favorable winds. Spring migrants travel to the North Sea region before shifting direction towards Iceland, where breeders bound for Greenland and Canada stop over before continuing. In contrast to oenanthe, subspecies leucorhoa migrates more slowly in spring than in fall (67), presumably a consequence of the more roundabout route.

Timing and Routes of Migration

Post-breeding

Departure from breeding areas takes place in August across most of the breeding range (2, 63, 68), although September for north-central and central Russia, Altai, and Tien Shan (earlier from high elevation, 2), as well as for southern Kazakhstan and Turkmenistan. Geolocator data indicate that disappearance from the breeding grounds in August does not reliably indicate start of active migration, which may only begin several weeks later (67; C. M. Meier, personal communication).

Dates of passage through particular locations are notably protracted, especially where routes are shared by migrants from widely separated portions of the breeding range. Passage of European breeders across the Mediterranean and coast of North Africa is concentrated within September and early October, but ranges from mid-August to November; in Israel, migration continues from late August to early October, and in the Gulf States from late August to November (2).

Arrival at most overwintering areas is from mid to late September into early October, but can extend into early December (2, 44). Later arrivals are evidently from more distant breeding grounds: 12 breeders in Sweden tracked by geolocator arrived from early to late October (63), and 8 individuals from Alaska arrived throughout November (68). Prolonged arrival of migrants may be the explanation for a doubling of density at study sites in Nigeria between late autumn and mid-winter (65), although within-season movements related to rainfall and seasonal changes in habitat quality (44) may also contribute.

All but a few late nesting leucorhoa leave Iqaluit, Baffin Island by mid-August (DJTH, 97), by which time there is steady coastal movement southeastward. Other than a few late-nestling local birds, no adults were captured between 8 August and 8 September (n = 55; DJTH). Nonetheless, a few do linger. One late departure was an adult seen 25 August that evidently was molting (short tail, hop-skipping rather than flying; DJTH), and an adult with a geolocator did not leave from the latitude of Baffin Island until 25 September (67).

Departure of breeders from Greenland occurs mainly from August to late September, with a few birds remaining as late as early November (98). Most observations of migration from ships in the North Atlantic and in Iceland are in September (99, 2). Arrival at Helgoland Island (Germany) is in the latter half of September, on average 10 d later than southbound oenoanthe that breed in western Europe (100). O. o. leucorhoa reach Algeria mainly from November–December, though some reach Sahel by October; and arrive in Mali from October–November (44). The bird tracked by geolocator from Baffin Island reached its overwintering area in West Africa the third week of October (67).

Pre-breeding

Spring departure from the African overwintering area is similar for all subspecies: February through May but with peak passage in most places in March and April (see 44 for country-specific dates). Eight individuals tracked with geolocators from east Africa left between 23 March and 22 April (68).

Most of the broad-front passage across the Mediterranean also takes place in March–April, overlapping peak arrival dates at European breeding areas. Some birds reach the United Kingdom as early as February, though most arrive mid-March through early April (4, 101, 102, 64). Median passage on the continent appears to be a bit later: second half of April in Belgium and Italy; late April in the Swiss Alps (C. M. Meier, personal communication), early May at Helgoland (Germany), southern Norway and Sweden, and eastern Baltic (64); and mid-May for breeders in arctic regions of Norway (2).

Geolocator data show that male oenanthe breeding in Europe leave wintering areas about 11 d before females (64) and the earlier onset of migratory restlessness in male leucorhoa (103) suggests they also depart before females. At stopover sites in western Europe, males precede females by 2.3 d in oenanthe and 6 d in leucorhoa (64, 104). O. o. leucorhoa males also move through Africa and Europe at a faster pace than females, increasing the gap between the sexes as they move northward. Male oenanthe tend to arrive in Sweden 3 days before females (105), and first year birds of both sexes lag 6 days behind older birds of the same sex (106).

Dates of passage and presumed arrival of local breeders for North Asian oenanthe are as follows (2). Red Sea coast of Saudi Arabia: early March; Persian Gulf states: late February–May (peak in May); Middle East: late February to mid-May; southern coast of Turkey: early March–early May; Black Sea coast: early April; Transbaikalia, Russia: mid-April; Yakutsk region, Russia: early May; far north of Russia: late May–early June. Two birds tracked from Africa with geolocators arrived on Alaskan breeding grounds in the last week of May (107), but there is a very early record (end April) in Canada’s Yukon Territory (60).

O. o. leucorhoa leave Africa in the same period as oenanthe: February to May but mainly March–April (2, 44); a geolocator-tracked individual began spring migration in mid-March (67). O. o. leucorhoa move rapidly across Europe, with median passage through the United Kingdom, Belgium, Helgoland and southern Norway in late April to early May (64). Although leucorhoa arrive in the United Kingdom about a week behind oenanthe (where the latter is a relatively early migrant), they migrate more rapidly and reach Helgoland about a week before oenanthe (64).

Most leucorhoa arrive in Iceland in May, though some by mid-April (2). The sole recovery of a leucorhoa banded in Canada was a recently dead bird found in Iceland in the second week of May (108). Birds arrive in Greenland mainly between late April and late May (98); some as late as June (2). Most probably reach Baffin Island in late May into early June (DJTH, 97), although a male tracked by geolocator arrived at the longitude of Iqaluit, Baffin Island on 8 May, and the earliest arrival reported to DJTH by a local resident was 11 May.

Routes

O. o. oenanthe migrate from Europe on a broad front, more or less north-south; libanotica breeding in southern areas presumably join the flow. Observation at oases indicate stopovers are a regular part of trans-Saharan flight (109, 110, 111, 6). Band recoveries indicate that breeders in the United Kingdom migrate primarily through western France and Spain, crossing the Mediterranean at its western end (112). Breeders from Scandinavia move through Germany, southeastern France and eastern Spain; evidence is lacking as to whether the Alps are avoided (63). Central Europe is likely the source of the numerous migrants on Malta, Cyprus, and Crete (112). Despite these general patterns there is considerable variation; ringing recoveries from Morocco, Algeria and Tunisia each include individuals ringed at breeding sites all across Europe (44), and European populations mix broadly in overwintering areas (64). Geolocator studies show lengthy stopover in the Mediterranean region both in spring and (especially) fall, but are unable to determine whether sites are primarily on the north or south side (63).

Subspecies oenanthe and libanotica that breed in northern Asia, also migrate on a broad front; see Cramp (2) for further details on timing and relative densities during migration. Birds from western Canada and Alaska cross into Asia primarily via the Seward Peninsula of Alaska; only scattered individuals are recorded in the Aleutians (113). Eight oenanthe individuals tracked by geolocator illustrate individual routes across the full journey to Africa (68; H. Schmaljohann, personal communication). In fall, most birds made short stopovers in Sakha Republic (central Siberian Plateau), but thereafter there was considerable individual variation. Most individuals moved through the area where borders of Mongolia, Xinjiang, Altai Republic, and Kyrgystan converge, but one took a more northern route to the Ural Mountains. Stopovers of up to 2 weeks were frequent during this part of the journey. Thereafter all routes converged on the Caspian Sea area. Stopover periods of 17–27 d were scattered across northern Iran and Iraq, after which birds moved rapidly across Saudi Arabia to overwintering areas in Ethiopia and South Sudan.

Spring routes of the same 8 individuals were more uniform, and more direct (68). All 8 birds passed between the Caspian Sea and the Persian Gulf, most after directly crossing Saudi Arabia (one bypassing it to the north). Stopovers of 6–9 d were recorded in Saudi Arabia (2 birds), Iran and Turkmenistan in the Caspian Sea region (4 birds), and central Kyrgystan (2 birds), with shorter stops scattered across the same three regions (H. Schmaljohann, personal communication). Spring equinox precluded tracking over much of the remaining route, but at least 2 birds stopped over for 5 d in Irkutsk, northwest of Lake Baikal.

Within East Africa, oenanthe move through Egypt both along the Nile Valley and through open desert (44). Further south the main route is through the Rift Valley and east of Lake Victoria. Fall passage appears heavier than in spring in Algeria, Kenya, and Uganda (44), and there is evidence of East–West fall movement through Sudan.

Fall migrant leucorhoa move southeast along the coasts of Baffin Island and western Greenland prior to embarking on nonstop transatlantic flights (114; DJTH). Landfall in western Europe is relatively southern for birds banded in Greenland; fall recoveries are from southwest France, Spain and Portugal (98). The geographic position of Iceland suggests that birds breeding there may typically arrive further north in Europe, but evidence of origins is lacking. Models of weather and flight capabilities indicate that fall conditions frequently are sufficient to support nonstop transatlantic flight from Greenland to Europe (115), and a Northern Wheatear tracked with a geolocator flew 3,400 km non-stop from the longitude of Baffin Island to western Europe in about 3 d (67). There is no evidence to date that Canadian breeders stop over in Greenland during migration, but it seems likely that it would occur at least occasionally. There is considerable circumstantial evidence, but none direct, that at least some leucorhoa from Canada and Greenland may bypass Europe entirely in fall and make first landfall in Africa (116).

Recovery of banded leucorhoa indicate the primary migratory route between Europe and Africa is between Spain and Morocco (44), though some spring migrants have been recorded in the eastern half of Algeria (117).

O. o. leucorhoa is common farther north in western Europe during spring as compared to fall, and spring recoveries of Northern Wheatear banded in Greenland occur in northern France, Belgium, and the United Kingdom (98). Spring migrants reaching Helgoland shift direction from North to Northwest in preparation for transatlantic flight to Iceland (118). Many migrants are assumed to make that shift west of Helgoland, although some birds continue further north and shift to northwest only in southern Norway. Few leucorhoa are captured east of Helgoland; long-winged individuals captured at Rybachy (eastern Baltic) are likely oenanthe from Siberia (119).

Migratory Behavior

Migration is primarily at night (120), though continuous for 3–4 days during trans-Atlantic flights in autumn (67). Overland migration may continue into daylight when conditions are favorable (e.g., 121, 122). Diurnal, ground-level movement along shorelines in migratory directions is commonly observed in the early stages of departure from Baffin Island and western Greenland (DJTH, 114), and similar behavior has been noted on islands in the North Sea (123, 124).

Models suggest the most favorable winds for nonstop trans-Atlantic flights from southeast Canada to Europe occur at about 3,000 m; within the range of known migration altitudes for passerines (115). Fall departure of local breeders from Iceland is correlated with tailwind components at 100 and 1,500 m above sea-level (125), similar to the altitude of favorable winds for trans-Sahara flight (126). In the absence of barriers to be crossed, the importance of wind assistance in decision to initiate a flight may be reduced (68).

Individuals migrate independently rather than in cohesive flocks but groups are commonly observed during heavy migration, especially at geographic concentration points (e.g., groups of 20–300 birds collect in coastal Alaska during second half of August; 62), prior to crossing the Bering Strait. Weather-related autumn fallouts of Northern Wheatear numbering in the thousands occur from time to time in Britain (127), and on Helgoland Island in Germany (128), perhaps involving leucorhoa ending trans-Atlantic flights.

Fidelity to Migratory Routes

Geolocator data for 12 birds from Sweden showed modest variation in the routes among individuals, and between seasons by the same individuals, particularly in whether they crossed the Mediterranean through Italy or at the western end, but estimates for total distances traveled did not vary greatly (5,162 km ± 139 SD in autumn, 5,247 km ± 255 SD in spring) (63). Fall routes taken by 8 geolocator-tracked oenanthe that bred in Alaska were also broadly similar but individually variable, although most individuals had significant differences in some portion of their spring and fall routes, and the total distances traveled varied more widely (14,800 km ± 1,800 SD) (68). No information on fidelity to routes between years.

Fidelity to Stopover Sites

Thousands of Northern Wheatears ringed on Helgoland over many years provide no evidence that individuals stop at the same sites in subsequent years (H. Schmaljohann, personal communication). At a population level, there is good evidence that most birds make lengthy stopovers in the same general regions (see Timing and Routes of Migration), but even with low tracking resolution, it is evident that birds from the same breeding area do not stop over in the same locations (63, 68).

Movement Behavior During Stopover

Individuals with access to favored foraging sites on beaches of Helgoland Island often set up a temporary territory and stopped over for more than a day (see Behavior: Agonistic Behavior), while those using grassland habitats were much more mobile, and usually departed on the day of arrival (124).

Duration of Stopover Period

Overall time spent in stopover during fall migration of 8 geolocator-tracked Alaska-breeding birds was 44 d ± 8.7 SD (range 33–60) (68). Median duration of fall stopovers was 2.7 d per 1,000 km, compared to spring values of 2.3 d.

Twelve geolocator-tracked birds from Sweden spent an average of 84% of their 61-day fall migration in stopover. Stopovers included 5–6 stops during the 17–45 days spent traveling south to the Mediterranean region, where birds rested 18–44 d before crossing the Sahara. Similarly, 76% of the 33-day spring migration was spent in stopover, with longest periods in the Mediterranean region (9–33 d), followed by short stops during the remaining 4–16 days of travel across Europe to the breeding grounds (63).

Of 101 spring migrant oenanthe at Helgoland Island, with only a short flight to Scandinavia ahead, only 16% stayed for at least one night after capture; mean stay was 1.6 d ± 0.8 SD (n = 16). By contrast, 53% of 80 leucorhoa facing lengthy over-ocean flight lingered on the island for an average 3.8 d ± 2.4 SD (n = 42; 129).

Duration of Migratory Period

Eight Alaska-breeding oenanthe tracked with geolocators completed fall migration in 92.9 d ± 7.3 SD (range 82–104). Variation in total stopover duration was the main factor affecting total speed of migration. Excluding stopover time, mean speed (seasons combined) averaged 185 km/d ± 54 SD (range 136–424; calculated from 68).

For 12 Swedish birds with geolocators, fall migration lasted 49–72 d, about twice that of spring migration (20–48 d). Average overall migration rate was estimated at 86 km/d ± 12 SD in fall and 167 km/d ± 39 SD in spring. Excluding days of stopover, average travel speeds were 492 km/d ± 132 SD in fall and 711 km/d ± 192 SD km/d in spring (63). In both seasons, the 1,500–2,000 km Sahara crossing was completed in a mean of 3.8 nights, or roughly 400–500 km/night.

Fall migration for a single leucorhoa tracked from Baffin lsland by geolocator lasted 26 d, with an average speed (including stopover time) of 290 km/d. The non-stop trans-Atlantic portion of the flight lasted no more than 4 days and was completed at a rate of about 850 km/d (67). Spring migration of the same bird was completed at an average speed of about 130 km/d and took longer (55 d vs. 26 d), presumably a result of the more circuitous spring route and a probable stopover in Iceland.

Control and Physiology of Migration

Energetics

Comparative studies of oenanthe and leucorhoa in experimental and field settings demonstrate important differences in the complex interaction of factors that control migration, including distance of impending flight, endogenous condition, fuel stores, and weather conditions (130).

Cross-breeding among subspecies has shown migratory refueling strategies to be genetically controlled and inherited (131). Onset of migratory restlessness (an accurate proxy for probability of departure from a stopover site) and increase in body mass occur at appropriate times of year in the absence of environmental cues, indicating endogenous control and an internal clock (132). Protandry is a result of earlier onset of spring restlessness in males than in females (103; see Timing and Routes of Migration). Nocturnal restlessness increases with date in the season without regard to refueling rates, indicating an endogenous timing factor that speeds departure of late migrating individuals (133).

Subspecies leucorhoa both eat more and have a higher mass-specific fuel deposition rate than do oenanthe, indicating higher food assimilation efficiency in this subspecies (32). In addition, adult male leucorhoa have higher refueling rate than do young birds. However, within these subspecies fuel deposition rate does not differ between spring and fall, indicating that endogenous refueling rates are not the cause of more rapid migration in one season than the other (134).

Endogenous pre-migratory mass increase in captive oenanthe is a result of fat accumulation, with no increase in flight muscle mass (135). Fat accumulation explained 83% of fall variation in body mass; reaching 42% of total body mass at peak fattening. There was a 1.5 g reduction in water content through the run-up to migration, possibly contributing to lower cost of flight. Feather mass was 1.6–2.1 g, about 9.5% of body mass, and total non-water tissue mass was estimated at 3.7 g (135).

Daily mass gain at Helgoland Island during fall is typically 0–3.5% of lean body mass, but can be as high as 6% (100). In oenanthe, mass gain in spring is similar to that in fall, but leucorhoa gain more quickly in spring: typically 2–7% of lean body mass per day and sometimes over 10%. Subspecies leucorhoa preparing for trans-Atlantic spring flights can gain 1.7 g/d and up to 20 g over a 2-week stay (136, 100).

Most mass gain in captive birds prior to fall migration occurs in September, both in oenanthe (135) and leucorhoa from western Greenland (137). Mass of all birds captured on Baffin Island from 21 August–18 September was 31.7 g ± 2.8 SD (n = 44). Based on mean mass of birds with fat scores of 0 that were caught earlier in the season (27.7 g ± 1.54 SD; n = 46), the early September fuel load (fat as proportion of lean mass) was roughly 0.14 (DJTH). Fuel loads required for over-ocean flights in still air are 0.6 for the distance from Europe to Iceland (about 1800 km), and 0.9 for a 3,000 km directly flight from the southern tip of Greenland to western Spain (125). Fuel loads of 0.9 in leucorhoa translate to a body mass > 50 g, which has very rarely been reported, but flights occur with wind-assistance and thus require lower fuel loads (125). Nonetheless, the fuel load of the fattest bird captured on Baffin Island (17 September) was only about 0.36, indicating that most fuel accumulation for trans-Atlantic flight must occur closer to departure time (25 September for a single adult tracked by geolocator from the longitude of Baffin Island [67]). Three birds shot in the Tanzerouft Desert of Algeria and Mali during March and April had fuel loads of 0.54, 0.71, and 1.1 (109), indicating that substantial fuel loads are also the norm for desert crossings.

Average total energetic cost of migratory flights for 3 geolocator-tracked oenanthe covering 14,500 km during fall travel from Alaska to African overwintering area was estimated at 2,630 kJ ± 500 SE (96); the energy equivalent of about 70 g of fat.

Experiments designed to mimic repeated stopover refueling showed that oxidative damage during repeated bouts of hyperphagia was prevented by apparent retention of uric acid, an anti-oxidant produced during protein metabolism (138). Oxidative damage is reduced considerably during stopovers as short as 2 days, regardless of food intake or fuel accumulation, indicating that the need for physiological recovery alone is likely an important factor in the temporal partitioning of migratory flights (139). Migrants captured at stopover sites and fed ad libitum show rapid increase in multiple parameters of constitutive immune function (140), but levels appear not to affect departure decisions (7).

Decisions to leave a stopover site to continue migration involve energy stores on arrival as well as quality of the site for refueling (141, 142). Nocturnal restlessness increases with total distance to final destination, whether over land or ocean (132, 143); fall restlessness is higher in oenanthe departing from Alaska than in it is in leucorhoa leaving Iceland.

Endogenous accumulation of fuel differs among subspecies, and is also related to the nature of the impending flight. Fuel moderate in oenanthe (regardless of total overland migration distance, but see 144) and higher in leucorhoa facing trans-oceanic flight (132, 143).

Corticosterone level in birds at stopover sites increases both with advancing season and with greater wind assistance towards destination. High levels within individuals predict greater departure probability and earlier departure in the night (145). Levels rise within several hours of flight initiation, indicating that decisions to depart are made towards the end of the day (139); the rise possibly functions to mobilize stored energy to fuel the flight.

The probability of oenanthe departing from Alaska in fall was higher as fuel load increased and temperature decreased. Though fuel loads were lower than in leucorhoa facing over-ocean flights, they were always greater than needed simply to cross the Bering Strait; a strategy that allows birds leeway to skip unsuitable stopover sites or withstand adverse weather conditions (146). All departures from Alaska were within 0.5–2 h after sunset, in line with data for other species showing earlier departure when length of night is short (146, 147). Departure from fall stopover sites spread across the route to Africa were affected by temperature and wind speed at ground level, but in a complex manner that changed with migration distance remaining and with season (68).

Most birds initiate flights from Helgoland Island 2–5 h after civil twilight, regardless of subspecies (148) and without respect to age, though first-year birds departed later in fall (100). Fuel load affects hour of flight initiation (118, 149, 150), and birds with high loads are more oriented toward their ultimate destinations (148, 118, 147). About half of radio-tracked spring migrants make exploratory flights on a few nights before complete departure; each lasting 1–9 min and covering up to 1 km, possibly serving to test wind conditions (148).

Orientation

Alaska-breeding oenanthe tracked on migration clearly did not follow a great circle route. No compass course dominated in directing migration path (96). The authors suggested that overall migration direction is endogenously controlled, with shifts along the route triggered by a combination of internal and external clues.

Experimental shift of light polarization pattern at sunset did not cause free-flying Northern Wheatear to alter departure direction in fall (151), but individuals did appear to use cues from magnetic fields to navigate. Compared to control birds, naïve hand-reared oenanthe reduce migratory restlessness in fall as the magnetic field is experimentally shifted southward towards the overwintering area (152), and alteration of magnetic fields to simulate greater distance to destination stimulates greater fuel deposition (144).

Brain activation studies indicate that the Northern Wheatear can detect cues from magnetic fields (153), but there is no proof as yet that birds can detect angle of magnetic inclination (96). Some work has suggested Northern Wheatear may use a magnetoclinic compass as the primary means of navigation, but the most thorough analysis of 3 geolocator-tracked oenanthe from Alaska concluded that use of a fixed sunset compass is more likely (154).

Recommended Citation

Dunn, E. H., D. J. T. Hussell, J. Kren, and A. C. Zoerb (2022). Northern Wheatear (Oenanthe oenanthe), version 2.1. In Birds of the World (P. G. Rodewald and B. K. Keeney, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.norwhe.02.1