The magnitude and timing of migration by soaring raptors, pelicans and storks over Israel

Abstract

The magnitude and timing of the autumn and spring migrations of 35 species of medium‐and large‐sized raptors, White Pelicans Pelicanus onocrotalus and White Storks Ciconia ciconia were studied in Israel. Observations were carried out from the ground by a line of observers covering most of the width of Israel across the line of migration and by radar. There was a high correlation between the counts obtained by ground observers and by radar. On average, about half a million raptors (mainly Lesser Spotted Eagles Aquila po‐marina, Honey Buzzards Pernis apivorus and Levant Sparrowhawks Accipiter brevipes), 250,000 White Storks and 70,000 White Pelicans passed during autumn, and about a million raptors (mainly Honey Buzzards, Steppe Buzzards Buteo vulpinus, Steppe Eagles Aquila nipalensis and Black Kites Milvus migrans) and 450,000 White Storks passed during spring. Peak numbers were higher–over a million raptors and half a million White Storks. There was high interyear variation in the number of migrants recorded during the study, probably caused by weather and counting efforts. For some species, the whole world (Lesser Spotted Eagle and Levant Sparrowhawk) or Palaearctic (White Pelican) population passes over Israel during migration, allowing an estimate of the world populations of these species. Mean dates of arrival of most raptors are highly predictable, with confidence limits ranging between 1.5 and 5.5 days. The migration periods of White Storks and White Pelicans are longer and their mean day of appearance is less predictable (confidence limits range from 4.2 to 13.8 days). During autumn, 90% of the migrating populations of nocking species, such as Levant Sparrowhawk, Lesser Spotted Eagle, Honey Buzzard and Red‐footed Falcon Falco vespertinus, pass within 13, 15, 16 and 18 days, respectively, while nonflocking species, such as Egyptian Vulture Neophron percnopterus, Marsh Harrier Circus aeruginosus and Short‐toed Eagle Circaetus gallicus, generally take twice as long to pass. Similar passage periods were recorded in spring. For most species, the autumn migration period was longer than the spring migration period, probably because in autumn adults move before the young birds. Three factors affected the timing and spread of the migration wave: age at first breeding, diet and size of the breeding area.

Understanding soaring bird migration through interactions and decisions at the individual level

“…These decision rules (5 and 10) use orientation towards the destination and are further based on complete randomness. This mechanism is supported by evidence from field observations on soaring bird migration (Leshem and YomTov, 1996a;Pennycuick, 1972;Pennycuick, 1998) as well as foraging scavengers, which follow other birds when searching for food within a similar detection distance as the birds in Simsoar (Jackson et al, 2008).…”

“…The mean annual migratory population that passes through northern Israel in autumn exceeds 180,000 individuals (Alon et al, 2004;Leshem and YomTov, 1996a), with 90% of the population passing in approximately 3 weeks along the Jordan Valley over a narrow front approximately 20 km wide (Leshem and Yom-Tov, 1998). An illustration of this migration pattern is shown via an interpreted radar image in Figure 1.…”

“…This leads to migratory bottlenecks where birds from distant breeding or wintering areas converge in space and time. Two main areas of convergence for western Palearctic soaring migrants are on the western and eastern borders of the Mediterranean sea at Gibraltar and Israel respectively (Bildstein and Zalles, 2005;Leshem and YomTov, 1996a). Convergence may also occur due to natural leading lines such as mountain ranges and coastlines (e.g.…”

Попередні Результати Радарних Спостережень Нічной Міграції Птахів В Ізраїлі

“…Numerous studies have been devoted to soaring bird migration over Israel (Yom-Tov, 1988, Leshem & Yom-Tov, 1996, Shirihai et al, 2000. Due to technical constraints, nocturnal migration is not studied as intensely.…”

The associations between weather and topography on golden eagle flight behaviour at a wind farm in the Canadian rockies.

“…For this reason, golden eagle migration in North America is often concentrated in locations where conditions are favourable for providing these updrafts, such as mountain ranges lying perpendicular to the main axes of prevailing winds (Alerstam 2001, Bildstein 2006. Raptors are known to initiate migration within a narrow date range each year Likely triggered by the change in day-length, the consistency of annual migration events are believed to be genetically driven (Alerstam 1990) Findings in migration reseaich indicate that daily passage rates exhibit more within-year variation, likely due to weather and count efforts, than total numbers counted between-years (Leshem andYom-Tov 1996, Bildstein 2006a) For example, the arrival of migiant raptor species at a watch-station in Israel over a four-year period was highly predictable by date, with only ± 1-5.5 days variation observed between years (Leshem and Yom-Tov 1996). Hence, the passage of migrant raptors in both space and time can be predicted fairly accurately.…”