Wind - Habitat Dynamics

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Several species of shorebird that nest in the Arctic make remarkable non-stop trans-oceanic migrations to non-breeding areas in the southern hemisphere. Scientists at the USGS Alaska Science Center have discovered many fascinating and previously unknown details about these long-distance migrations by instrumenting individual birds with Argos satellite transmitters (see ASC Shorebird Research web site). Results of analyses that examined the role of winds (highlighted below) have documented the perceptive ability of bar-tailed godwits to time their migration departures with weather conditions that provided tailwinds. And, while most godwits completed their migrations with net wind profit, a few individuals were forced to negotiate inclement weather systems en route that imposed severe, life-threatening headwinds.

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Bar-tailed godwit "Z0" instrumented with an implanted Argos satellite transmitter (note dorsally exposed antenna) to facilitate aerodynamics during the species non-stop flights across the Pacific Ocean. The map inset shows Z0's track from her non-breeding area in New Zealand to a spring staging area in the Yellow Sea (10,000 km in 8.8 days, non-stop), then to a breeding area in Alaska (4,200 km in 5.5 days, non-stop), and finally a trans-Pacific return flight to Australasia (9,800 km in 7.6 days, non-stop). 

Graphic shows relative strength of headwinds or tailwinds during approx. 9-day, 10,000 km, non-stop, trans-Pacific migrations

In the role of wind in Bar-tailed Godwit migrations, this graphic shows each line as one godwit as it flew from Alaska to Australasia in 6 hour increments. The plotted values (y-axis) are ratios derived by dividing the distance the godwit flew through the air (air distance) by the distance the godwit traveled over the earth (ground distance). Strategically, almost all godwits chose a time to depart Alaska that capitalized on markedly favorable tailwinds. Thereafter, most godwits experienced favorable or near-neutral wind conditions throughout their flight south (i.e., most lines are near or below 1.0). However, three satellite-tracked godwits encountered challenging headwinds as they crossed the North Pacific.(Credit: Lee Tibbitts, USGS. Public domain.)

In the role of wind in Bar-tailed Godwit northward migrations, this graphic shows tailwinds are often favorable due to the preva

In the role of wind in Bar-tailed Godwit northward migrations, this graphic shows tailwinds are often favorable due to the prevailing eastward direction of the jet stream and the Aleutian Low pressure system to develop near the Yellow Sea and propagate eastward.(Credit: Lee Tibbitts, USGS. Public domain.)

The role of wind in these long-distance migrations can be examined using data sets that describe weather conditions worldwide every 6 hours. In this figure, each colored line represents one godwit as it flew from Alaska (on the left) to Australasia (on the right) in 6 hour increments. The plotted values (y-axis) are ratios derived by dividing the distance the godwit flew through the air (air distance) by the distance the godwit traveled over the earth (ground distance). The ratio is < 1.0 in tailwind conditions, and > 1.0 in headwinds. Strategically, almost all godwits chose a time to depart Alaska that capitalized on markedly favorable tailwinds. Thereafter, most godwits experienced favorable or near-neutral wind conditions throughout their flight south (i.e., most lines are near or below 1.0). However, three satellite-tracked godwits encountered challenging headwinds as they crossed the North Pacific.

Godwit H4 departed Alaska on 10 September 2006 on the west side of a moderately deep depression in the Gulf of Alaska that afforded 39–46 km/hr tail winds. The bird’s initial track speed was 85 km/hr. Over the next 24 hours the bird flew beyond influence of the depression and entered a region of very weak (18–28 km/hr) quartering westerly headwinds. At this juncture H4 was 30 hours into its flight and had flown 2200 km at an average ground speed of 73 km/hr. During the next 30 hours, H4 became entrained in a long fetch of direct 65–74 km/hr headwinds that formed between a rapidly deepening depression to the west and a building ridge of high pressure to the east. In contrast to the strong wind assistance during the previous 30-h period, the strong opposing winds caused H4 to travel less than half the distance (960 km) at an average ground speed of 32 km/hr. Once south of the Hawaiian Archipelago (~20°N), H4 again encountered tailwinds and flew south for another 6.5 days, landing on the island of Ouvea, New Caledonia, 1500 km short of the core nonbreeding area­, where the temperature sensor in the transmitter indicated that H4 died 2–7 days later.

Bar-tailed godwits migrating from their spring staging areas in the Yellow Sea to breeding areas in western Alaska typically depart with tailwinds and benefit from tailwinds throughout most of their flights. Tailwinds are often very favorable owing to the prevailing eastward direction of the jet stream, and a propensity for the Aleutian Low pressure system to develop near the Yellow Sea and propagate eastward. Godwits often migrate to Alaska in tandem with the westerly winds along the Aleutian Low’s southern edge. One satellite-tracked godwit (E8), however, became entrained in headwinds on the Aleutian Low’s northern edge; details of E8’s flight are annotated and animated below.

Godwit E8 departed the Korean Peninsula on 24 May 2007 with strong westerly tailwinds (ca. 36–54 km/hr) associated with the remnants of a super typhoon and a rapidly developing and eastward-moving depression over eastern China. On 26 May, E8 had moved east-northeast in tandem with the leading eastward edge of the system. During these first 42 hours of flight, E8 had covered a minimum ground distance of 2800 km at an average ground speed of 66 km/hr, and had realized considerable wind assistance. The bird continued east but became entrained in the depression where it encountered southerly crosswinds winds of 28–55 km/hr. Shortly thereafter the depression merged with another and deepened further, and E8 became ‘trapped’ on the back (north) side of the depression where it experienced strong (46–74 km/hr) easterly headwinds as E8 and the depression moved northward in tandem over the next 48 hours, eventually entering the Bering Sea. During this period the bird’s ground speed dropped to 30 km/hr. When within 110 km of the nearest land and 450 km of the nearest Alaska breeding area, but while still flying into 46–55 km/hr headwinds, E8 abruptly turned 180º and, assisted now by tailwinds, flew due west 1200 km to the coast of the Kamchatka Peninsula, Russia. Nine days later on 9 June, E8 flew east 1500 km back to Alaska but did not nest.

Key Findings

Advances in satellite telemetry, and global data sets of daily weather conditions, have fostered pioneering empirical studies of avian migration.

Gill, R. E., Jr., D. C. Douglas, C. M. Handel, T. L. Tibbitts, G. Hufford, and T. Piersma. 2014. Hemispheric-scale wind selection facilitates bar-tailed godwit circum-migration of the Pacific. Animal Behaviour 90:117-130. doi:10.1016/j.anbehav.2014.01.020

Dodge, S., G. Bohrer, R. Weinzierl, S. C. Davidson, R. Kays, D. C. Douglas, S. Cruz, J. Han, D. Brandes, and M. Wikelski. 2013. The Environmental-Data Automated Track Annotation (Env-DATA) System: Linking animal tracks with environmental data. Movement Ecology 1:3. doi:10.1186/2051-3933-1-3

Battley, P. F., N. Warnock, T. L. Tibbitts, R. E. Gill, Jr., T. Piersma, C. J. Hassell, D. C. Douglas, D. M. Mulcahy, B. D. Gartrell, R. Schuckard, D. S. Melville, and A. C. Riegen. 2012. Contrasting extreme long-distance migration patterns in Bar-tailed Godwits Limosa lapponica. Journal of Avian Biology 43(1):21-32. doi:10.1111/j.1600-048X.2011.05473.x

Gill, R. E., Jr., T. L. Tibbitts, D. C. Douglas, C. M. Handel, D. M. Mulcahy, J. C. Gottschalck, N. Warnock, B. J. McCaffery, P. F. Battley, and T. Piersma. 2009. Extreme endurance flights by landbirds crossing the Pacific Ocean: Ecological corridor rather than barrier? Proceedings of the Royal Society B 276(1656):447-457. doi:10.1098/rspb.2008.1142