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OSTRICH 2011, 82(1): 49–56 Printed in South Africa — All rights reserved
OSTRICH ISSN 0030–6525 EISSN 1727–947X doi: 10.2989/00306525.2010.541502
Autumn and spring migration of the Reed Warbler Acrocephalus scirpaceus in Egypt – some interesting aspects and questions Agnieszka Ożarowska1*, Katarzyna Stępniewska1 and Wed Abdel Latif Ibrahim2
2
1 Bird Migration Research Station, University of Gdańsk, Al. Marszałka Józefa Piłsudskiego 46, 81-378 Gdynia, Poland Nature Conservation Sector, Egyptian Environmental Affairs Agency, 30 Misr Helwan El-Zyrae Road, Maadi, Cairo, Egypt * Corresponding author, e-mail:
[email protected]
Four ringing stations of the SE European Bird Migration Network in Egypt (at the coasts of the Mediterranean and Red seas, in the Nile Valley, and at the northern edge of the Sahara) provided data on birds resting in adequate habitats. At three stations more birds per day were caught in spring than in autumn. Deviating geographical conditions induced high capturing numbers at the Red Sea coast, particularly in autumn. Differences between spring and autumn may indicate loop migration and/or seasonally differing flight or resting strategies. Wing-length distribution may indicate passage of different populations through Egypt. In autumn, birds with low fat scores were caught in high proportion after the crossing of the Mediterranean Sea, while average fat scores increased in birds approaching the edge of the Sahara.
Introduction Despite huge numbers of Palaearctic migrants passing Egypt from their breeding grounds in Eurasia towards wintering areas in Africa every year (Alerstam 1990, Berthold 1993, Newton 2008), our knowledge of bird migration systems in this region is still quite limited. So far studies have mainly covered the passage of raptors and water birds (Goodman and Meininger 1989), while during the last decade papers on passerine migration in this region of Africa have also been published (Biebach et al. 2000, Bruderer 2001, Hasseb et al. 2004, Hilgerloh and Raddatz 2009, Yohannes et al. 2009). In this paper we focus on Reed Warbler Acrocephalus scirpaceus migration in this region. The Reed Warbler (Acrocephalidae; Fregin et al. 2009) is a typical habitat specialist preferring wetlands, though on wintering grounds it has also been recorded in grassland, crops, in garden hedges and acacias by water (Moreau 1972, Cramp 1992). It is a long-distance migrant wintering in sub-Saharan Africa; it leaves breeding grounds as early as July–August (Cramp 1992, Hagemeijer and Blair 1997). Birds from northern and western Europe migrate in a south-western direction towards western Africa, while those from central and eastern Europe migrate in a south-eastern direction to eastern and southern Africa (Zink 1973–1985, Cramp 1992, Busse 1987, Busse 2001, Fransson and Stolt 2005). In Egypt, two subspecies of the Reed Warbler, i.e. S. scirpaceus and S. fuscus, can be observed (Goodman and Meininger 1989, Cramp 1992, Svensson 1992, Hagemeijer and Blair 1997). They are very similar in morphology (Svensson 1992) and hence difficult to separate (Merom et al. 1999, Morgan and Shirihai 1997). Consequently, subspecies identification of many individuals captured in the Middle East could be impossible.
During autumn migration the Reed Warbler is a common migrant in Egypt and is recorded there from the beginning of August until late November, while during spring migration it is present from mid-February until late May; it sporadically over-winters in Egypt. It also breeds in Egypt, though the population is sparse (Goodman and Meininger 1989). Egypt contains mostly desert habitats and the areas allowing migrants, particularly such habitat-specialised species as Sedge Warblers Acrocephalus schoenobaenus or Reed Warblers, to rest and refuel are limited. In this study, we analyse capturing data of Reed Warblers from four ringing stations between the Egyptian coast of the Mediterranean and the northern edge of the Sahara. Data collection took place between 2001 and 2007, with only partial temporal overlap among the stations, but covering the main parts of the species’ spring and autumn migration. The aim was to compare the seasonal passage as well as the wing length and fat score of the birds resting at the four sites, and from this to get information on the resting behaviour of a habitat specialist crossing an area between two large ecological barriers. Materials and methods Study sites Data on Reed Warblers were collected at six Egyptian ringing stations of the SE European Bird Migration Network (SEEN) (Table 1) during various autumn and spring seasons (2001–2007). The stations were located in different regions of Egypt between the Egyptian coast of the Mediterranean and the northern edge of the Sahara (Figure 1). Egyptian SEEN ringing stations are situated mainly in reedbed habitats, which are the most extensive at Burullus
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Ożarowska, Stępniewska and Ibrahim
Table 1: Number of Reed Warblers Acrocephalus scirpaceus (retraps excluded) captured at six Egyptian stations; the years, seasons and period of work are given for each station Station Burullus
Season Autumn
Year 2005 2006 2007 2006 2007 2001 2002 2003 2001 2002 2007 2007 2003
Spring Wadi El Rayan
Autumn
Spring Hurghada
Autumn Spring Autumn
Saluga-Ghazal (Aswan)
2004 2005 2004 2005 2005 2005 2003
Spring Wadi Gemal
Autumn Spring Autumn
Sharm El Sheikh
Mediterranean Sea Burullus
Ringing stations
Cairo
30°N
Wadi El Rayan Sharm El Sheikh 0
200
400 km
Hurghada
EGYPT
AFRICA
Saluga-Ghazal
Wadi Gemal
ea dS Re
EGYPT
Lake Nasser
30°E
Figure 1: Localisation of SEEN ringing stations in Egypt
(31°31′ N, 30°55′ E) in the Nile delta. Wadi El Rayan (29°12′ N, 30°19′ E) and Hurghada (27°14′ N, 33°45′ E) ringing stations, surrounded by several kilometres of desert, are the only areas with dense vegetation appropriate as the stop-over places for passerine migrants, while Saluga Ghazal (Aswan) ringing station (24°04′ N, 32°52′ E) covers an area of rocky islands on the Nile River within the First Cataract Protected Area (0.5 km2). Migrants were also captured at Sharm El Sheikh (27°51′ N, 34°17′ E) and Wadi Gemal (24°38′ N, 35°04′ E) ringing stations, though in very low numbers; these two sites were therefore excluded from
Period of work 1 September – 2 November 28 August – 6 November 2 September – 3 November 12 March – 8 May 5 March – 2 May 3 September – 28 October 3 September – 2 November 6 October – 29 October 2 March – 28 April 3 March – 28 April 24 September – 18 October 9 March – 15 May 28 August – 11 September, 2 October – 27 October 15 August – 15 October 1 September – 20 October 19 March – 16 May 1 March – 29 April 1 September – 23 October 16 March – 29 April 27 August – 25 September
Number of captured birds 121 196 111 221 618 204 228 16 541 830 314 828 92 76 50 335 207 7 125 1
any further analyses. Birds were captured there mainly in non-reed habitats, i.e. in bushes or fruit trees, casuarine and eucalyptus trees. Data collection We applied the standard SEEN methodology including constant mist-netting, standard set of biometric measurements (fully-grown individuals: wing and tail length, wing formula; weight – accuracy 0.1 g; fat score) and orientation tests on directional preferences of migrants (Busse 1995, 2000). Number of nets at each station was 30–40 and was stable throughout the respective capturing periods. In case of difficult-to-identify species several specific measurements were taken, e.g. for Reed and Marsh Warblers Acrocephalus palustris it was the length and location of the notch on the 2nd primary (Svensson 1992). The subspecies of captured Reed Warblers could not be distinguished so the data could include both A. s. scirpaceus and A. s. fuscus. Ageing of Reed Warblers was based on plumage characters and the following age-classes were distinguished: juvenile, immature (after summer partial moult) and adult birds (after first winter complete moult and onwards). Data analysis Seasonal capturing dynamics, wing length and fat score distributions of captured Reed Warblers (retraps excluded) were analysed to characterise passage of this species in the studied region. In order to obtain a general pattern of seasonal capturing dynamics we applied a five-day running average according to the formula: Cw = (a + 2b + 3c + 2d + e) / 9
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where Cw = running average of number of birds captured in day c; and a, b, c, d and e = numbers of birds captured in five consecutive days. To compare wing length and fat score histograms we applied Bayesian statistics.
§ Prob NE EvidNE 2log10 ¨ ¨ Prob EQ ©
Mediterranean Sea Burullus 2
Cairo
In total, 1 416 Reed Warblers were captured at six ringing stations during autumn, while 3 705 were captured during spring migration (Table 1). Despite long periods of netting in autumn at Wadi Gemal and Sharm El Sheikh stations, only few Reed Warblers were captured there (Table 1). Spring migration at the four analysed stations was more intense than autumn, except Hurghada, where the migration intensity was equally high in both seasons (Figure 2). It is worth noting that in autumn the highest number of birds was captured there, although the studied period was short and most probably missed the main passage at the beginning of the season. Seasonal capturing dynamics of the Reed Warbler at Burullus and Hurghada stations, where the highest numbers of migrants were captured, are given in Figure 3. Autumn migration at Burullus ringing station was already intensive at the beginning of the study (early September), whereas from mid-October the numbers of captured birds declined. At Hurghada ringing station the study started later, still capturing dynamics during the corresponding period resembled that observed at Burullus (Figure 3b). Throughout the spring migration season (March–May) the number of captured birds was quite stable at both stations (Figure 3c). Data on the wing length of captured Reed Warblers are given in Table 2. The analysis of wing length distribution of Reed Warblers captured in autumn and particularly in spring (Table 3) showed a significant difference between individuals captured at Burullus and all the other stations:
13 12 Hurghada
EGYPT ea dS Re
Results
30°N
3 12 Wadi El Rayan
· ¸ ¸ ¹
where Prob EQ = probability of a hypothesis that both histograms have a common set of multinomial parameters, ProbNE = probability of a hypothesis that each histogram has its own set of multinomial parameters, and EvidNE values were classified in the following classes: ≤0, bad (none of the analyzed models was favoured); >0 and
