Radar Observations of Arctic Bird Migration at the Northwest Passage, Canada

Abstract

ABSTRACT. Bird migration was recorded by tracking radar and visual observation at 23 sites in the region of the Northwest Passage, between Baffin Island and Herschel Island in the Beaufort Sea. The studies took place during a ship-based expedition from 29 June to 3 September 1999. A total of 692 tracks (average duration 160 s) of bird flocks on postbreeding migration were recorded. Eastward migration was widespread, with the highest intensities at three sites in the southeastern Beaufort Sea. Mainly shorebirds were responsible for these movements, migrating along routes similar to great circles towards Nova Scotia and other parts of the Atlantic coast of North America (whence they depart on transoceanic flights towards South America). Some of the birds in this migration system probably originated from Siberia, as indicated by high-altitude eastward migration at a site 100 km north of the coast in the Beaufort Sea. Another category of eastward migrants consisted of jaegers, terns, and red phalaropes traveling towards the Davis Strait region and into the Atlantic Ocean. Southward migration was recorded at Baffin Island. A westward migration was pronounced at King William Island (with simultaneous eastward migration) and Amundsen Gulf, while northward movements were important at Banks Island and Melville Island. Apart from westward molt migration of common eiders at Amundsen Gulf, the westward and northward tracks reflected mainly jaegers, terns, gulls, and red phalaropes. These birds were probably making northward flights to exploit pelagic food resources in waters where the ice had recently broken up before their westward migratory exodus from the Arctic region towards the Pacific Ocean. The mean altitude of migration was 793 m, with 27% of all tracks above 1000 m and a maximum height of 3.95 km. The altitude distribution was clearly lower than those of the corresponding migration in Siberia and the shorebird migration at Nova Scotia. The average ground speed (14.9 m/s) was only slightly faster than the mean air speed (13.8 m/s), and migrants gained in speed from the winds (ground speed exceeding air speed) in only 55% of all cases. This means that wind assistance in the study area was much less pronounced than that documented for the migrants in Siberia and Nova Scotia. Bird migration at the Northwest Passage may be characterized by, on average, lower altitudes, less favorable winds, shorter flight steps, and a more widespread accessibility to stopover sites than migration at the Northeast Passage.Key words: Arctic birds, bird flight, bird migration, Canadian Arctic, Northwest Passage, Nunavut, orientation, radar RÉSUMÉ. On a enregistré la migration aviaire par observations effectuées à l'oeil nu et au radar de poursuite sur 23 sites localisés dans la zone du passage du Nord-Ouest, entre l'île de Baffin et l'île Herschel dans la mer de Beaufort. L'étude s'est déroulée du 29 juin au 3 septembre 1999, durant une expédition navale. On a enregistré un total de 692 poursuites (durée moyenne 160 s) de bandes d'oiseaux...

A polar system of intercontinental bird migration

“…The birds' flight directions suggested that these movements formed part of a major postbreeding migration system that was not restricted to flights across the Arctic Ocean between central and eastern Siberia, but probably also involved long flights between Siberia and North America (Alerstam & Gudmundsson 1999b). Our studies in the Beaufort Sea (at longitudes 130-1408 W) revealed similarly intensive eastbound movements of birds arriving from northern Alaska and possibly also directly from Siberia across the Arctic Ocean (Gudmundsson et al 2002). The flight directions north of Siberia as well as in the Beaufort Sea suggested that the birds were not maintaining constant geographical courses but changed their directions in approximate accordance with great circle orientation, possibly through sun compass orientation without correction for the longitude-dependent shift in local time (Alerstam et al 2001).…”

“…We have earlier used tracking radar onboard ice-breaking ships to chart bird migration patterns in the Arctic Ocean along both the Northeast and Northwest Passages (Alerstam & Gudmundsson 1999a;Gudmundsson et al 2002). During these studies, we discovered intensive highaltitude eastbound migration by mainly shorebirds, skuas and terns in July and August over the Arctic Ocean north of the Siberian tundra coast in a wide sector including the Laptev and East Siberian Seas between longitudes 110 and 1708 E (Alerstam & Gudmundsson 1999a).…”

Birds: blowin’ by the wind?

“…Studies from the arctic region have revealed that flight altitude may also depend on the length of the actual flight stage. Birds heading for a long-distance flight across the pack ice or the North Atlantic ocean (Richardson 1979; Alerstam and Gudmundsson 1999) chose considerably higher flight altitudes than birds crossing the Northwest passage in Canada, these latter having countless occasions for a stopover (Gudmundsson et al 2002). As the high-flying birds had much more wind support than those at lower levels (<1000 m.a.g.l.…”

Algorithmic System for Identifying Bird Radio-Echo and Plotting Radar Ornithological Charts

“…Houghton 1964, Chernikov and Shupjatsky 1967, Eastwood 1967, Hardy and Katz 1969, Bruderer and Joss 1969, Kropfli 1970, Skolnik 1970, Zavirucha et al 1977, Chernikov 1979, Ganja et al 1991, Bruderer 1992, Miller et al 1998, Russell and Gauthreaux 1998, Buurma 1999, Venema and Russchenberg 2000, Gudmundsson et al 2002, Komenda-Zehnder et al 2002, Larkin et al 2002, Gauthreaux and Belser 2003 * table presents only a small part of the numerous studies of bird echo characteristics ** ESA (s) scattering cross-section…”