Author's personal copy Journal of Arid Environments 73 (2009) 139–141 Contents lists available at ScienceDirect Journal of Arid Environments journal homepage: www.elsevier.com/locate/jaridenv Short communication Highways as flyways: Time and energy optimization in migratory Levant Sparrowhawk R. Yosef* International Birding & Research Centre in Eilat, P. O. Box 774, Eilat 88000, Israel article info abstract Article history: A successful migratory strategy is the result of optimizing three important factors – time, energy and Received 7 March 2008 safety. Raptors mainly use soaring-and-gliding flight that results in time and energy minimization. Received in revised form 4 July 2008 I observed migratory flocks of Levant Sparrowhawk as they took off from nocturnal roost, to understand Accepted 21 August 2008 the environmental and anthropogenic factors affecting their early-morning flight behavior. The earliest Available online 16 October 2008 flocks converged in a straight line from the roosts to the highway and flew above it for 40–70 min after sunrise. The flocks stayed ca. 40–100 m in above the highway which suggested that the Levant Spar- Keywords: rowhawk utilized the heat released by the highway surface to improve flight conditions. Twenty-five Accipiter brevipes Eilat Levant Sparrowhawk that took off from the roost and headed across open areas had to flap an average of Levant Sparrowhawk 16.8 Æ 1.9 wing beats per minute, which was significantly greater (paired t ¼16.8, P ¼ 0.0001) than the Migration 8.8 Æ 1.8 wing beats per minute for the same individuals when flying over the highway. The data indicate Tar roads that Levant Sparrowhawk, that have behaviorally modified and adapted to flying along highways, are able to migrate an hour earlier in the day and to conserve almost 50% of the energy they would otherwise have had to invest in covering the same distance in flapping flight. The result of this strategy maximizes timing of migration while minimizing energy expenditure. Ó 2008 Elsevier Ltd. All rights reserved. Alerstam and Lindstrom (1990) found that a successful In Israel, the Levant Sparrowhawk is an abundant migrant in migratory strategy is the result of optimizing three important both spring and autumn. It is estimated that ca. 90% of the world factors – time, energy and safety. The time and energy expended population of the species passes through Israel within a short on migration is dependent on the fat load, flight speed and costs. period of a fortnight, i.e., the last two weeks of April, during spring Unlike many Passerines, waders and waterfowl that fly exclusively migration (Shirihai et al., 2000). Interestingly this is also the only by flapping flight, raptors mainly use soaring-and-gliding flight. raptor known to migrate at night in the region (Stark and Liechti, This flight strategy results in time and energy minimization. For 1993; Yosef, 2003). Additional raptor species have also been example, Pennycuick (1972) showed that in a White Stork (Ciconia observed to migrate at night in North America and Western Europe, ciconia), the energy consumption in flapping flight was 12 times including Turkey Vulture (Cathartes aura), Northern Harrier (Circus higher than in soaring-gliding flight. cyaneus), Osprey (Pandion haliaetus) and Peregrine Falcon (Falco The Levant Sparrowhawk (Accipiter brevipes) is a medium- peregrinus)(Tabor and McAllister, 1988; Russell, 1991; DeCandido distance migrant that breeds in the western Palearctic region and Allen, 2006). and winters in the east Sahel of sub-Saharan Africa (Snow and Stark and Liechti (1993) argued that Levant Sparrowhawk Perrins, 1998). Levant Sparrowhawks are considered rare; shifted from soaring-gliding flight at the beginning of the season information on their distribution, populations and status is to extended flapping flight towards the end, which could be limited (Cramp and Simmons 1980). Their principal migration explained by the raptors switching from energy- to time-mini- routes lie entirely within the Middle East with especially large mizing migration. Spaar et al. (1998) found that soaring-gliding concentrations found at the Eilat migratory bottleneck during Levant Sparrowhawk maximized cross-country airspeed accord- spring (Shirihai and Christie, 1992; Frumkin et al., 1995; Shirihai ing to optimal flight theory and minimized time needed per et al., 2000). distance. In flapping-gliding flight they adjusted their airspeed with respect to the wind in order to fly at the maximum range speed, suggesting that they minimized energy consumption per * Tel.: þ972 7 633 5339; fax: þ972 7 637 6922. distance. Their calculations on aerodynamic flight theory showed E-mail address: [email protected] that the optimal migratory strategy of the Levant Sparrowhawk 0140-1963/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jaridenv.2008.08.005 Author's personal copy 140 R. Yosef / Journal of Arid Environments 73 (2009) 139–141 with respect to time and energy depended on feeding conditions take off time of other raptors resorting to flapping-gliding as en route. They suggested that in poor conditions both time and a migration strategy. energy are minimized by a pure soaring-gliding flight strategy. Later in the morning, ca. 60–90 min after sunrise when However, if food is available soaring-gliding flight is combined surrounding areas heat up, other raptor species were observed to with flapping flight when no thermals are available. The last will take off from the areas surrounding the highway. These flocks minimize time spent on migration. comprised mostly Black Kite (Milvus migrans) and Steppe Buzzard Here I report observations of migratory flocks of Levant Spar- (Buteo buteo vulpinus). With the appearance of other raptors in rowhawk as they took off from nocturnal roost and to try to the region, the stream of Levant Sparrowhawk dispersed from the understand the environmental and anthropogenic factors affecting immediate region of the highway and proceeded north along the their flight behavior. Rift Valley using the thermals in which the other raptors were In previous studies and during the IBRCE ringing program (eg., observed. This also suggests that Levant Sparrowhawk are able to Yosef et al., 2003; Yosef and Fornasari, 2004) in Eilat (2933N, migrate an hour earlier in the day and to conserve almost 50% of 3457E) we have observed that the Levant Sparrowhawk is an the energy they would otherwise have had to invest in covering early-morning migrating species and takes off is usually initiated the same distance in flapping flight during the cool hours of the within 30 min of sunrise. At this time of the morning in late April, it morning. is cool (13–18C), there is no thermal activity, and most other raptor On three (3) of the eight days I observed an Egyptian Vulture species (Steppe Buzzard Buteo buteo, Yosef et al., 2002) are still at (Neophron percnopterus) and a Brown-necked Raven (Corvus rufi- roost. All individuals and flocks were observed to converge in collis) apparently patrolling the highway in order to scavenge for a direct line over the major highway, no. 90 that leads out of Eilat to road kills. The Levant Sparrowhawk flocks ignored these the rest of Israel to the north, located along the western side of the individuals. Arava (Rift) Valley, and that is between 1 and 3 km from the roost The large majority of Levant Sparrowhawk are seen migrating sites. in large flocks by soaring-gliding flight (Shirihai et al., 2000). In order to understand the advantages of their modified Further, Spaar et al. (1998) believed that a considerable propor- behavior of flight along the tar-surfaced highway, during spring tion of the population, between 10 and 20%, migrated by flapping 2005, on 8 different mornings I followed the flocks in a car flight. But little is known about the flocking behavior and its logic. immediately upon their take off and convergence over the highway. Spaar et al. (1998) speculated that there is a balance between I followed the flocks from the northern exit of Eilat until they a soaring-gliding strategy in a large flock, and a mixed flight dispersed later that morning. strategy of single migrants. They suggested that the strategy In order to evaluate the relative energetic savings as a function adopted was controlled by food availability – in years with high of this behavioral modification, I counted the number of wing beats food abundance they can speed up their migration by resorting to per minute of 25 Levant Sparrowhawk while they traversed the flapping flight and in poor years switch to a pure soaring-gliding open areas, and then when the same individuals were flying along strategy. My observations suggest that irrespective of whether the highway. Data of those I was able to follow in only one of the they travel singly or in flocks, Levant Sparrowhawk appear to be two habitats was not included in the analyses. I reasoned that this able to modify their behavior and take advantage of anthropo- would allow me to understand the relative energy saved by flying genic changes by flying earlier in the day with minimal energy over the highway. expenditure. In this case it appears that the day’s migration is I also observed and noted when other raptor species became initiated earlier irrespective of food availability, and is governed active in order to see how they influenced the migratory behavior by man-made environmental benefits acting on the Levant Spar- of the Levant Sparrowhawk. rowhawk in their attempt to minimize time and energy spent on All means are expressed x Æ SD. I undertook two-tailed paired migration. It also appears that the Levant Sparrowhawk is able to t-tests to check for statistical significance, and chose P ¼ 0.05 as the incorporate anthropogenic features, such as highways, in their minimum acceptable level of significance.