The daily pattern of autumn bird migration in the northern Sahara

Abstract

The temporal pattern of migration by passerine birds during the night, and their arrival during the day at the Egyptian coast and in the northern Sahara Desert was investigated. The mean direction of nocturnal migration at the coast was south-southeast, while at all desert sites it was south-southwest.Birds arrived at the Egyptian coast only during the second half of the night which is explained by the fact that n o birds could have taken off from the Mediterranean Sea. At least some of the birds landed at the coast where they spent the day before taking off shortly after sunset. These birds passed the desert sites at the expected time of day assuming a ground speed of 18 m per second. However, the origin of the birds passing the desert sites early a t night is unclear. They must either have spent the day in the desert north of the study sites or they had overflown the Egyptian coast in the afternoon without landing.The landing of birds during the day a t the desert sites was bimodal. This pattern of arrival is explained either by some birds having landed a t the Egyptian coast in the early morning before continuing, or by deteriorating conditions later in the day during flight or when resting in the desert, that obliged them to seek shelter at the desert sites.A correlation between the number of migrants observed during the night and the number of resting birds in the desert on the following day suggests that an unknown proportion of birds might regularly use an intermittent migratory strategy that includes rest periods by day when crossing the desert, whereas others might adapt a non-stop migratory strategy.In Europe, many migrating bird species, especially longdistance migrants, are known to migrate exclusively during the night (Dorka 1966). A number of ultimate factors have been proposed to explain this behaviour, most prominently the possibility of feeding during daylight and the avoidance of predators during the day (Palmgren 1936). better temperature regulation and water balance (Dorka 1966) and the calm atmospheric conditions that prevail at night (Kerlinger & Moore 1989). Knowledge of the temporal pattern of migratory behaviour under extreme conditions, such as a desert crossing, might give further insight into the adaptive significance of the general phenomenon of nocturnal migration. In addition it might suggest physiological constraints that limit migration.Two strategies for crossing deserts have been proposed: a non-stop migratory strategy with flight during day and night (Moreau 1961) and an intermittent migratory strategy with flight during the night and rest during the day (Biebach

Migration of Passerines through some Protected Areas in the Eastern Part of Egypt

“…Moving further south and east in the eastern desert and across the Nile Valley, the density of migration at the northern part of the western Red Sea coast in Hurghada is higher than in Sharm El Shiekh and along the Nile Valley and western desert in Fayoum, which confirms the results of Kiepenheuer and Linsenmair (1965), Biebach et al (1991) and Bruderer (2001).…”

“…However, the migration intensity at the western Mediterranean coast in Egypt is little known, there is an obvious decrease in migration intensity from north to south along the Nile Valley and the Red Sea Coast and the higher intensity of migration in the eastern Egypt than in the western part. This is also confirmed by Biebach et al (1991), Bruderer and Liechti (1995) and Bruderer (2001).…”

Spring passerine migrants stopping over in the Sahara are not fall-outs

“…Furthermore, numbers of birds found in the desert during daytime were regarded as being comparatively low compared to the total number of migrants estimated by Moreau (Wood 1989). This non-stop hypothesis was challenged by Bairlein (1985Bairlein ( , 1992 and Biebach et al (1986Biebach et al ( , 1991 who proposed an alternative intermittent strategy that involves regular stopovers in the desert and in oases. The main argument for an intermittent migration strategy was that an unexpectedly high proportion of passerines grounded in oases were in good physical condition with sufficient fuel stores to continue migration (Bairlein et al 1983;Bairlein 1992;Biebach 1995).…”

An Overview of Bird Migration Studies in Egypt

“…This means that under good weather condition (tail wind at high altitudes) all species make a non-stop flight, whereas under bad weather condition (head winds at high altitudes) some species make the intermittent and others non-stop flight. Biebach et al (1991) studied the daily pattern of autumn bird migration in the northern Sahara, where the temporal pattern of migration by passerine birds during the night and their arrival during the day at the Egyptian coast and in the northern Sahara Desert was investigated. A correlation between the number of migrants observed during the night and the number of resting birds in the desert on the following day suggested that an unknown proportion of birds might have regularly used the intermittent migratory strategy that included stopover periods during day when crossing the desert, whereas others might have adapted the non-stop migratory strategy.…”

“…During four migratory seasons from 1980 to 1985, H. Biebach and his colleagues of the Max-Planck Institute fr Verhalternsphysiologie studied bird migration in Bahariya oases. This work was particularly useful in illustrating the species composition and behavioural strategies of birds crossing the Egyptian portion of Sahara (Biebach 1985(Biebach , 1988(Biebach , 1990(Biebach , 1992(Biebach , 1996Biebach et al 1986;Biebach et al 1991;Biebach et al 2000).…”